Preamp with - American Radio History

Preamp with - American Radio History
Preamp with "Presence" -
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www.americanradiohistory.com
AmericanRadioHistory.Com
See page 23
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BALANCED PERFORMANCE
Now Available on this
NEW
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more area for labeling
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rugged, non -warping construction
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another EXTRA -VALUE feature
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preserves full orchestral balance
throughout the entire audible frequency range
there's nothing that's quite as important
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end result, in terms of listening enjoyment.
Suppose you're recording a symphony orchestra. Every note
and overtone of every instrument must come through with the
same relative value as in the live performance. And Audiotape's
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to the fullest possible extent.
This means faithful, well -balanced reproduction of all musical
instruments, from the lowest rumble of the bass tuba to the
highest overtones of the piccolo. It's a factor to which the
trained ear is particularly sensitive an Audiotape advantage
that appeals strongly to the most critical professional recordists.
Audiotape's output, frequency response, noise level and distortion are correctly proportioned for the most satisfactory end
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I
NSOUND RECORDING
-
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AUDIO DEVICES, Inc.
444 MADISON AVE., NEW YORK 22, N.
Offices in Hollywood
Export Dept.,
13 East
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40th St., New York 16, N.Y., Cables "ARIAB"
www.americanradiohistory.com
AmericanRadioHistory.Com
Successor to ..17,%.)(e) -Established 1917
TO THE
E. E.
INCLUDING
OR
PHYSICS
GRADUATE
WITH EXPERIENCE IN
RADAR
C. G. McProud, Editor and Publisher
Henry A. Schober, Business Manager
Harrie K. Richardson, Associate Editor Edgar M. Villchur, Contributing Editor
Florence Rowland, Production Manager S. L. Cahn, Advertising Director
H. N. Reizes, Advertising Manager
Edgar E. Newman, Circulation Director
OR
ELECTRONICS
HUGHES RESEARCH AND
DEVELOPMENT LABORATORIES ARE ENGAGED IN
A CONTINUING PROGRAM
FOR DESIGN AND MANUFACTURE OF ADVANCED
RADAR AND FIRE CONTROL
Representatives
H. Thorp Covington, Special Representative
7530 North Sheridan Road, Chicago 26, III.
Sanford R. Cowan, Mid -West Representative
67 W. 44th St., New York 18, N. Y.
West Coast
J. W, Harbison
James C. Galloway
816 W. 5th St.. Los Angeles 17, Calif.
CONTENTS
JANUARY, 1954
SYSTEMS IN MILITARY
Vol. 38, No.
Audio Patents- Richard H. Dorf
London Letter Richard Arbib
Letters
Audiology -W. R. Ayres
Editor's Report
Ioseph Marshall
The New Golden-Ear Amplifier -In Two Parts -Part
Stereophonic Nomenclature -N. M. Haynes
Design of a Professional Tape Recorder-William F. Boylan and
William E. Goldstandt
Preamp with "Presence "-C. G. McProud
Adventures with a Bass Reflex-Milton S. Snitzer
Handbook of Sound Reproduction -Chap. 15, Part 1 -Edgar M. Villchur
1
2
-
1-
-
6
8
10
14
17
19
20
23
26
27
30
Audio ETC Edward Tatnall Canby
Record Revue-Edward Tatnall Canby
32
43
New Literature
44
New Products
Yuk
58
Cho
-Leung
Philosophy
Reproducer
:
A
New
The Perfect Loudspeaker
59
'
Review
Book
63
Industry Notes and People
64
Advertising Index
COVER
The piano that sounds like an orchestra, yet needs only one man to operate. Thus
reads the headline of a flyer released by the manufacturer of the instrument,
Trio -Art Piano Company, of Philadelphia. The device incorporates
a record changer, an FM tuner, and a disc recorder, any or all
of which may be used with the piano for a variety of
purposes. The instrument was developed by
Louis Luberoff, president of the company, and the photo features pro sional pianist Milton Bugay.
RADIO MAGAZINES, INC., P. 0. BOX 629, MINEOLA, N. Y.
(title regLstered U. S. Pat. Off.) is published monthly at 10 McGovern Avenue, Lancaster, Pa. by
Magazines, Inc.. Henry A. Schober, President; C. 0. McProud, Secretary. Executive and Editorial Offices:
204 Front St., Mineola, N. Y. Subscription rates-United States, U. S. Possessions and Canada, $3.00 for I year.
45.00 for 2 years; elsewhere $4.00 per year. Single copies 35c. Printed in U. S. A. All rights reserved. Entire contenta
copyright 1952 by Radio Vagazines. Inc. Entered na Second Class Matter February 9, 1950, at the Post Office, Lancaster, Pa. under the Act of March 3. 1879.
AUDIO ENGINEERLNO
Radio
AUDIO ENGINEERING
ALL -WEATHER FIGHTERS
AND INTERCEPTORS.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
YOU WILL' serve as technical advisor in the field to companies and
government agencies using Hughes
equipment.
TO BROADEN yourfield of experience in radar and electronics you
will receive additional training at
full pay in the Laboratories to become
thoroughly familiar with Hughes
radar andfire control equipment.
AFTER TRAINING you will be
the Hughes representative at a company where our equipment is installed; or you will direct operation
of Hughes equipment at a military
base.
THE GREATEST advancements in
electronics are being made in this
sphere because of military emphasis.
Men now under 33 years of age will
find this activity can fit them for
future application of highly advanced
electronic equipment.
HUGHES
RESEARCH AND DEVELOPMENT
LABORATORIES
SCIENTIFIC AND
ENGINEERING STAFF
Culver City, Loa Angeles County, Calif
Assurance is required that relocation of
the applicant will not cause
disruption of an urgent military project.
I
AZ II)
dnua+ors
ttIL.Ott'0
for high quallly audio
Richard H. Dorf*
the prerorations of such male
feminists as anthropologist Ashley
Montagu (we discount the female
feminists since they are prejudiced) to the
effect that the ladies are superior to the
gentlemen, very few of the men interested
in high -quality sound will dispute the assertion that the members of the supposedly
gentler sex are less than adept at adjusting
electronic apparatus for best results. A
simple example is the tuning of a radio
receiver or tuner. It does not really seem
to much to ask that the signal be tuned to
the center of the i.f. pass band so that we
have no more distortion than necessary.
Yet, the lady either gives the dial a careless flick, achieving a kind of hanging onto- the -station's-coattails effect as we
catch just a glimmer of the lower sideband,
or if cautioned to the take -heed point she
may spend several minutes tuning over the
signal so slowly and carefully that lack of
audio memory makes it impossible to recognize the right point when it comes.
Tuning "eyes" and meters don't seem to
help. And if we supply a.f.c. she may continue to complain about the noise between
stations -the loud rush on FM or the miscellaneous noises and whistles on AM.
Having begun this way, to give the male
ego a boost, we must add in the interests
of truth that many males (fortunately not
those technically trained) suffer from the
same disease and that many women do not.
Nevertheless, a rather simple invention by
B. S. Vilkomerson provides very nearly
the same kind of bandswitch tuning for
high-quality AM and FM receivers that
we find on TV sets, eliminating all noise
between stations and forcing the user either
to tune to the center of the signal or hear
nothing whatever. The patent number is
2,639,375 and it is assigned to RCA.
The scheme is quite simple and useful.
When the receiver is tuned between stations or anywhere but at the almost exact
center of a signal the audio system in the
receiver is inoperative. It operates only
when the receiver is tuned exactly right.
If Fig. 2 represents the bandpass characteristic of a wideband i.f. system, the r.f.
stages and local oscillator must be so adjusted that the i.f. center or carrier frequency fall within the shaded area before
the audio will come through.
Figure 1 illustrates schematically how
the system works, using as illustration an
AM detector circuit. It will be obvious that
it can be used on FM as well, with some
small alterations. IFT is the last i.f. transformer and the 6AT6 is the combined diode
detector and first audio amplifier. The detector diode is D,. In conjunction with the
ordinarily filter components and potentiometer, it works in the usual way. The tube
is cathode- biased by R,, which is bypassed
for audio by Cr.
The 6C4 is a bias control tube which
works as part of the tuning -aid system.
Its cathode is in shunt with that of the
6AT6, and its grid is connected through
R, and R, to the combined cathodes. Normally, (ignoring diode D. for the moment)
it is conducting heavily. This conduction
current passes through R, in addition to the
current drawn by the 6AT6; the combined
currents cause a high enough voltage across
R, to cut off the 6AT6.
The i.f. signal is connected to diode D.
through a crystal whose series resonance
frequency is equal to the center frequency
of the i.f. pass band. It does not conduct
unless a signal whose carrier is in the
center of the pass band -that is, a signal
which is accurately tuned-appears. When
this happens and D. does conduct, its load
is R,, through which the rectified current
passes in such direction as to make the
diode end of the resistor negative. R.-C, is
a filter which eliminates audio-frequency
variations from this rectified signal and
passes to the grid of the 6C4 a practically
pure d.c. voltage which is negative with
respect to the cathodes.
Until this signal was properly tuned, the
6AT6, as we have said, was cut off by its
DESPITE
PRECISION AND GENERAL
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use Cinema's best...
Instantaneous control,
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Use the
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Write for catalogue 18A8
for more information.
255 W. 84th St., New York 24, N. Y.
CINEMA ENGINEERING CO.
DIVISION AEROVOX CORPORATION
1100 CHESTNUT STREET
BURBANK. CALIF.
FACTORY REPRESENTATIVES
THROUGHOUT THE NATION
EXPORT AGENTS. Fraser & Hansen. Ltd
301 Clay St. Son Froncisco. Calif. Li S A
Fig.
2
1
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
PARTIAL SPECIFICATIONS
POWER OUTPUT: 10 watts at
less than 1% total harmonic distortion. Frequency response 20
to 20,000 cps. ±1 db.
HUM LEVEL:
70
db below full
rated output. There is a hum
balance control on the chassis.
REGULATION: Less than 2 db
from no load to full load with a
damping factor of 10:1.
PANEL CONTROLS: Treble
Control and Power Switch: 12
No. AR-410 amplifiPr.
db boost, 20 db droop at 10,000
cps. Bass Control: 15 db boost.
20 db droop at 30 cycles. Loudness Control: three section control to boost bass and treble as
volume is decreased to follow
the Fletcher -Munson curves.
INPUT SELECTOR SWITCH:
5 position: Microphone, Foreign
Records, American Records,
Radio, Auxiliary (television,
tape recorder or crystal phono).
o
Stromherg- Carlson pioneered the idea
of perfectly matched units for the
Audiophile who wants top quality
hut can't huy everything at once.
FOR INSTANCE ... You can start with the
amplifier and bring your equipment
entirely up -to -date for only $79.95.
If medium power (10 watts) will suit your listening needs.
here's how to do the best possible job at the least investment.
Assuming that your present pick -up, speaker and speaker
housing are Ldequate, the Stromberg- Carlson "Custom 400"
10 -watt amplifier will do more to improve performance than any single unit you can buy. And its low
price makes this a practical way to mart bringing
your installation to true Hi -Fi quality.
e
STROMBERG- CARLSON
Sound Equipment Division
SEND COUPON
FOR
COMPLETE
ENGINEERING DATA
STROMBERG-CARLSON Sound Equipment Division
1219 Clifford Ave., Rochester 21, N. Y.
I'd like to know all about your AR -410 Amplifier. Please send a copy of your Bulletin SED 40.62.
Name
Address
L
AUDIO ENGINEERING
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
3
Fig. 2
high positive cathode voltage. In addition,
both diodes were biased in the nonconducting direction by this same positive cathode
voltage.
The small negative 6C4 grid voltage
when D, first conducts begins to reduce the
positive cathode voltage. That reduction
reduces the diode bias, which in turn allows
additional conduction of D, (and, of course,
of signal diode D,). The additional conduction of D, makes the 6C4 grid still more
negative. There is, in other words, a sort of
snowballing quasi- trigger action, so that
as soon as the frequency is right and D,
begins to conduct, the entire circuit very
quickly reverts to a state where the 6C4
is almost cut off and the cathode voltage
is reduced to the proper point for normal
amplifier operation.
Never before has there been a range of Hi -Fi
speakers to match the new DUOTONE units manufactured by Philips. These loudspeakers, which
replace the Alnico V, feature the introduction of
TICONAL', the most powerful of the modern
magnet steels. TICONAL gives a high flux density
making possible an air gap of twice the normal
depth which results in the most natural tone reproduction yet achieved. Here is a complete line of
speakers that give the same tone quality whether
operating at a whisper or under full power.
*
Improved cone design gives extended
fat
frequency response
When Not to Patent
In these days of accelerated electronic
development there are very few individual
inventors-those not employed profession-
-
ally at inventing or at least engineering
compared to 20 years ago and the earlier
years when almost all inventions were
made by individuals under their own
steam. Still, the individual-often not an
engineer or even a professional technician
-very frequently does invent a new device
or circuit, for the conception of an invention requires first an idea and only later,
if at all, a facility with the slide rule. And
all too often, the individual inventor's first
thought is, "I'll get a patent!"
So he goes to a patent attorney. The
attorney has a search made, singles out
those aspects of the invention which are
not precluded by "prior art," and prepares
an application and drawings for the Patent
Office. The Patent Office receives the application and after acknowledging and
numbering it, goes on with its prior work
until the examiner gets to the application
of our inventor -which may take months
because of the backlog. After looking over
the application in detail, the examiner
probably returns it to the attorney with
comments indicating that all or nearly all
the claims will be disallowed for this and
that reason. If the inventor wants to proceed-and his attorney assures him, rightly,
that things aren't as bad as they seem
the attorney rewords claims and specification and sends them back to the Patent
Office. Again there is a wait, after which
the examiner goes to work again, accepts
certain claims, and disallows others. This
ball-tossing can go on several times over
quite a period. But after a time-almost
never less than two years, often much
more -things are settled and a patent is
issued. This is so, provided no other parties
have entered an interference in the Patent
...
absence of peaks and dips resulting in better reproduction
*
Various cones for small speaker types
*
Rectilinear response curves guide
selection of larger types
*
External centering prevents cone
stresses
*
Sealed air gap prevents
*
Optimum bass reproduction
*
Favorably priced competitively
boom',
-
Write DUOTONE today
for folder on the
complete line of sneakers and microphones
0%0WAN..
EYPORT, NE7V
RSEY
Office.
By this time the inventor has spent $300
or more on search, filing, draftsmen's and
attorney's fees. If he has not succeeded in
selling, leasing, or otherwise assigning
rights to his invention, he is that much out
of pocket ; he has succeeded in cluttering
up the Patent files with another specification and possibly in bolstering his ego
Canadian Representative. CHARLES W. PO:NION, TORONTO, CANADA
Export Division: A0. AURIEMA, INC NEW YORK CITY, N. Y.
'A patented invention of Philips laboratories
-
(Continued on page 38)
4
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
3-PHAsE
4,<PWCA-go/VS
E-CORES
ve/made
from SILECTRON strip
(grain- oriented silicon steel)
The use of "E" cores, wound from grain -oriented silicon steel, results in
weight and size reduction as well as higher efficiency and possible cost
savings. "E" cores can be supplied in a variety of window sizes and core
areas from 1, 2, 4 or 12 -mil Silectron strip, for high or low frequency
All Arnold cores are made by precision methods,
3 -phase applications.
and carefully tested under closely controlled conditions to assure highest
quality and reliability. We'll welcome your inquiries.
WRITE FOR BULLETIN TC
C -Cores
-105
to meet any requirement
For your single -phase applicat ions,
Arnold "C" -Cores are available in
any shape and quantity, and in any
size from fractions of an ounce to
hundreds of pounds
. wound
from Silectron strip in a wide
range of ultra -thin and heavier
gauges. (Sizes up to 10 lbs. in
12 -mil strip; to any weight in
thinner gauges.)
AUDIO ENGINEERING
AIAD
ARNOLD ENGINEERING COMPANY
T
(
SUBSIDIARY OF ALLEGHENY LUDLU+1
STEEL
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General Office & Plant: Marengo,
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DISTRICT SALES OFFICES
Los
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JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
New
fork:
350
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iinois
Fifh Ave.
Boston: 20C Berkeley St.
5
RIDER'S
3Í:titiinjn
"BEST SELLERS"
forSOUND from AtoZ
RICHARD ARBIB:
enthusiasts in the U.S.A.
who build up a library of tapes from
programmes recorded over the air,
would be envious of the wealth of transmissions of serious music which are available to
the British listener.
In England, there is no commercial
broadcasting. All the radio programmes are
devised and transmitted by the Government
controlled British Broadcasting Corporation. There are three main B.B.C. programmes which, during the daytime, can be received virtually free of interference in 90
per cent of the area of the British Isles. The
Home Service is transmitted from 6:30
a.m. to 11 p.m., the Light Programme from
9 a.m. to midnight and the Third Programme from 6 p.m. to 11: 30 p.m. Of these
three programmes, it is the Third Programme which is specially devised to capture the interest of the lover of chamber
music, operas, symphonies and all types of
classical music.
TAPE RECORDING
GUIDE TO
AUDIO
EPRODUCTION
by David Fidelman
Mere's an a to z explanation of the reproduction of sound
from the fundamentals to
all phases of audio reproduction systems.
Design, construction and assembly of these
systems and their components. Comprehensive methods for testing individual units.
Explanation of Circuitry of preamplifiers and
amplifiers. Complete discussion of pick -up
devices (phono cartridges, tuners and microphones), loudspeakers and enclosures.
Charts, tables and graphs keep mathematics
to minimum. Engineers will value the book
for design charts and testing methods. Practical circuits for home or custom construction enable building of systems tailor -made
to individual needs.
...
ONLY $3.50
50 Per Cent Serious Music
HIGH FIDELITY
SIMPLIFIED
h" 1) k
by H. D. Weiler
LIFE magazine's lune 15, 1953 issue reported
enthusiastically how "High Fidelity Simplified" the only book quoted expains the
complete Hi -Fi story. RADIO- Television News
-
-
stated: "Those planning high fidelity music
systems for their homes will save themselves
time, money and trouble by reading this first,
then making purchases.
Typical Chapters: Sound!; Acoustics, Electronics and Music; The Simple Loudspeaker;
The High -Fidelity Loudspeaker; Loudspeaker
Enclosures; The Basic Amplifier; The Ampli.
fier -Part 2; The Record Player; The Tuner;
Use of the Music System; Tape Recorders.
ONLY $2.50
OBTAINING
AND
I
INTERPRETING
TEST SCOPE
TRACES
by John
F.
Analysis of the programmes recently
issued by the B.B.C. shows that the Third
Programme transmits 1,149 hours of serious music in a year out of a total transmission time of 2,167 hours. The Home
Service had a serious music content of 18.2
per cent of its transmission hours. During
the course of a year, the recording enthusiast who kept his receiver tuned to the
Third Programme could transfer to tape
practically any symphony, concerto, and
chamber music written by any of the leading classical composers, and complete
operas performed by many of Europe's
greatest artistes. This is apart from the
many programmes of instrumental music
which are used to fill up at odd half hours.
Many of the operas are either relays of
performances from the great opera houses
of the Continent, including those transmitted direct from the Bayreuth Festival
at Salzburg, Austria, or high quality recordings made by European broadcasting
organizations and loaned to the B.B.C.
Forty Different Programmes
If the recording enthusiast is not satisfied with the programmes transmitted
e
Multitore Solders Ltd., Hemd Hemp-
for Checking Test Equipment; Checking
Audio Systems With the Scope; the Scope's
use in Checking Components, and four other
ONLY $2.40
Buy these books now
from your Jobber, local bookstore or, It
unavailable from these sources, write to:
Complete Operas without Breaks
Owing to the tact that an entirely interference -free signal can be obtained during
the Summer, the serious music- minded
tape recording enthusiast has got into the
habit of recording his programmes in the
Summer and listening to them in the Winter. It is, however, infuriating when one
is undertaking a recording of a complete
opera from Glyndebourne (the opera house
built in a garden in Sussex, a Southern
County of England) to obtain the first two
acts with very high quality and the third
act accompanied by a slight whistle. This
all comes about because the performances
during the six -weeks season in the Summer,
commence at 5:30 in the afternoon and
after an hour- and-a -half dinner interval,
finish at 10 :00 p.m. which is often half an
stead, Hertfordshire.
(Continued on page 37)
4116x1r+a1EVIIIMMffinon
Reproduction of the
original painting of
"His Master's Voice"
trade mark, by FranBarraud.
cis
This
painting is now kept
in the Directors' dining room of Electric
& Musical Industries
Ltd. at Hayes, Middlesex.
jOJ+YN F /Jafh'
PUBLISHER, INC.
oa=111111,
480 Canal Street, New York 13, N. Y.
6
from England, he can, in the evening, by
twisting a dial on his tuner unit, put on to
tape 30 or 40 different programmes from
Continental stations.
However, there is one great snag for
the hi -fi enthusiast. Owing to the hundreds
of transmitters located in the Continent of
Europe, there is, after dark, considerable
interference from one with another. It is
practically impossible in England, to obtain an entirely interference -free signal
from the main B.B.C. transmitters. Once
night has fallen the tape recordist often
has to reduce top to tape a signal free from
whistle.
There is only one B.B.C. transmitter
operating on FM and this is an experimental one having a limited range. Music
lovers heard with satisfaction the recent
statement in the House of Commons by the
Postmaster General that the B.B.C. were
authorised to build a chain of FM stations
but it may be a year or so before they provide the signals which are so eagerly
awaited.
Recording enthusiasts in many of the
leading cities overcome their difficulties by
not taking the programme off the air at
all. They join one of the many relay companies who pipe the B.B.C. programmes
over wires to apartments or houses in the
same way as the Electricity Companies
distribute the current which lights and
heats their homes.
Rider
People interested in audio will welcome this
book which shows over 500 actual photographs of test scope traces. Complete explanation of how to use scopes and what test
scope traces mean. Valuable for audio systems and test equipment and also for TV
receivers, and FM and AM receivers. Specific
test equipment set -ups are shown with each
application. There is no other book like it!
Typical Chapters: What's in a Scope; Getting
Familiar with the Scope; Auxiliary Test
Equipment for the Scope; Using the Scope
chapters.
ittrr
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
IT
4;
BE DONE !
Yet many have attempted to try it.
The round hole needs a round peg
-
custom -fit to meet the need. In the
Radial type projectors and
paging speokers with
36')' dispersion for maxi mun coverage at lowest
cost and ease
ins- allatian.
\1
of
lI
-_'
-
So why waste
cation
'7
loudspeaker capacity
and amplifier power using the wrong
speaker for the ¡ob? University makes
available over 50 different models of
speakers, each designed to meet a
particular requirement most efficiently.
University loudspeakers are appli-
,` uvn
Wide angle and bi- directional types for covering
broad areas with a mini
mum of speakers under normal ambient noise levels.
choice of a speaker, just as in the
choice of the peg, the point of application should be the governing factor.
engineered
to provide
performance with maximum economy- technically and cost optimum
04:15
wise.
is for music or
voice, or both
either indoor or
outdoor use; whether in a fixed position in a factory or for mobile use on
a vehicle, boat, train or airplane ...
there's a University speaker that can
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CHECK
Whether the need
-for
s
Ref ex trumpets in various
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...
UNIVERSITY FIRST!
tECMNILOG
FREE -new 1953 copy of the
University Tecinilog
Complete unto -date manual of sound theory,
application and installation requirements
SEND for your copy today.
AUDIO ENGINEERING
UNIVERSITY LOUDSPEAKERS
BO
INC.
SOUTH KENSICO AVENUE WHITE PLAINS, N. Y.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
7
LETTERS
Our European Correspondent
SIR
:
The articles written by Edward Tatnall Canby, record critic,
suP
reallY
fiant
tube for
a
amateur economist, and third -rate world traveler, have dismayed me. I have taken a shower in many a European hotel and
never had the maid follow me into the bathroom.
If things in Europe don't conform to what Mr. Canby is used
to it is mostly because Europeans look for sound engineering
and not a lot of chromium-plated gadgets. I believe European
radios of good manufacturers can hold their own against anything produced in the U. S. Remember that the Ferranti pickup,
the Telefunken microphone, and the Williamson amplifier are
all products of old and doddering Europe.
G. VISSER,
c/o M. M. C.
performance
your
Curacao, N. A.
Williamson or
ultra.linearhlampIifier?
SIR:
I wish to say that I especially appreciated Canby's fine write -up
on his European trip, the one from Rome particularly. His fine
understanding of what is truly real and important in life was
refreshing!
HARVEY
Check these ratings
Lo Jolla, Calif.
SIR
CONNECTION .El =6.3 Volt*
........
..........
ii.
=..
Ems
w.. ....
a...
.
MMMMM
V1I!1I -_61?
AIRM::::
e
VIELPTAsi.:
00
200
300
PUTE
e00
VOLTS
CLASS ABI PUSH -PULL AMPLIFIER- TRIODE CONNECTION
Grid
connected to Ilote Volves are for two tubes
2
Healer Voltage
Heater Current
Plate Voltage
Grid Voltage
Peak AF Grid to Grid Voltage
Z.roSignal Plate Current
Maximum Signal Plot. Current
Load Resistonce
Total Harmonic Distortion
Power Output
6.3
0.9
400
-45
90
65
130
4000
4.4
13.3
Vous
Amp.
Volts
Volts
Volts
Ma.
Ma.
Ohms
Percent
Watts
RATINGS (Interpreted According to IMA Standard M8 -210)
Volts
Heater Voltage
6.3
Volts
Maximum HeaterCathode Voltage
200
Volts
400
Maximum Plate Voltage
Maximum Grid s2 Voltage
400
Volts
Volts
Maximum Plate Voltage (Triode Connection)
400
Maximum Plate Dissipotion
23
Watts
Watts
Maximum Grid
3
Dissipation
Watts
Maximum Plat. Dissipation (Triode Connection)
26
Megohm
Maximum Grid Resistance (Fixed lias)
0.1
Maximum Grid Resistant. (Self lias)
Megohm
0.5
2
In creating the 5881, Tung -Sol engineers have made fullest use
of design and production techniques which have proved themselves over the past 15 years. Pure barium getter to effectively
absorb gas for the life of the tube-gold-plated wire to minimize
grid emission -are among the major design improvements in the
5881. This tube is directly interchangeable with the 6L6.
Tung -Sol produces the 5881 under laboratory conditions to insure peak efficiency and maximum uniformity. Order it from
your regular supplier.
TUNG -SOL ELECTRIC INC., Newark 4, N. J.
Sales Offices: Atlanta, Chicago, Culver
City (Los Angeles), Dallas,
Denver, Detroit, Newark, Seattle
TUNG -SOL makes: All -Glass Sealed Beam Lamps, Miniature Lamps,
Signal -Hashers, Picture Tubes, Radio, TV and Special Purpose Electron
Tubes and Semiconductor Products.
8
JESPERSON,
When Is Equipment "Commercial "?
of the Tung -Sol 5881
Satt. TRIODE
H.
8012 Girard Ave.,
:
Mr. Canby's analysis (November issue, page 34) of the conflict between craft -produced and mass-produced equipment was
astute. I feel it was unfortunate, however, that he chose the
word "commercial" to describe the mass -produced assemblies.
Webster defines commercial as "executed for commercial purposes or pertaining to commerce or trade." And the patent
license clause which was for so many years affixed to millions of
mass -produced home radios stated that they were not sold for
commercial purposes. Furthermore, some manufacturers who
produce both "craft" and what Mr. Canby calls "commercial"
gear also make a third line of equipment used in broadcast stations and for other definitely commercial purposes.
All of this suggests that some terminology other than "commercial" is needed to describe mass-produced equipment designed to bring better than average audio into the home. In
fact, new terminology would be very useful to describe all three
classes clearly.
Mr. Canby need not apologize for his promotion -mindedness.
Those of us who are craft minded about this audio thing are
going to need his word -mongering -and soon!
G. I. JONES,
Mgr., Electronic Sales,
Graybar Electric Co., Inc.,
420 Lexington Ave.,
New York 17, N. Y.
Crossover Networks
SIR:
It is stated in Mr. Crowhurst's article on constant -resistance
crossover networks in the October issue of Æ that the total
energy delivered to the speaker assembly must be constant. But
this does not necessarily imply that the total acoustic energy
remains constant. When the two cones move in anti -phase the
sound pressures tend to cancel out, especially at the crossover
frequency with the double-element filters. Both
signals being
equal and opposite, the resulting sound pressure will be zero.
When one of the speakers is reversed in phase the result is
a 3-db rise in the crossover region. This is unconsciously done
in the phasing of the system, the rise remaining unobserved,
like the gradual phase change of 180 deg. from zero to infinite
frequency.
Only the one -element system exhibits the correct feature of
keeping the pressure- response curve straight even when one
speaker is reversed. In the latter case there is also a phase shift
of 180 deg. between zero and infinite frequency. Presumably
this is not observable either, because transients undergo a deviation which decreases rapidly with time, the time constant being
the reciprocal of the angular velocity of the crossover point.
Experiments proving this point are quite easy to make. The
behavior of the total pressure is to be derived from the sum of
the voltages across the speakers. The Nyquist plots of the filter
systems will immediately show what has been stated above.
E. DE BOER,
Physical Lab., Univ. of Amsterdam,
Pl. Muidergracht 6,
Amsterdam, Holland
(Continued on page 42)
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
Regardless
of model
(.4
...
Presto has only
one quality
Ii2)1
Take,
for instance,
the finely
engineered ...
w
PRESTO RC -7 TAPE RECORDER
E
Q U
I
P
M
E
N T
The completely portable PRESTO RC -7 is a precision recorder in every detail. Yet it's
rugged and durable for heavy-duty field recording, and equipped with every feature
this service demands. Built around a sturdy 3 -motor drive, the RC -7 contains the same
high -quality components found in Presto's fine studio equipment.
SPECIFICATIONS
Dynamic range better than 50 db at
3% distortion.
Three -motor drive system.
No friction clutch or friction brakes.
Heavy -duty construction throughout.
Separate erase -recording- playback
The RC -7 has separate recording and reproducing heads. Monitoring from tape is
instantaneous. Mechanical friction devices, which always require constant adjusting,
are totally eliminated from the RC -7, and virtually no adjustment is needed through.
out the life of the machine. Note the RC -7's other features in the column at the left.
heads.
Twin speed: 71" /sec. or 15" /sec.
Frequency response SO to 15,000 cps.
Reel size: 7" standard, 101/2" with
RA -1 adopter.
engineering experience as the world's foremost producer of precision recording equipment has been devoted to making the RC-7 the outstanding
leader in fine tape recorders, in flawless performance, simplicity of operation, and
-at
All of
f
Flutter: at 71/2" /sec., 0.25
15" /sec., 0.20.
Available in 110 or 220 volts and 60
or 50 cycles.
Weight:
41
lbs.
n.-nr,.=
NEW RA -1
REEL ADAPTER
enables owners of the
RC -7 and 900 -R1
recorders to use 101/2"
reels. Carries out all
normal functions,
such as fast forward
PRESTO'S
long and thoroughly satisfactory service.
Write for complete engineering data and price
I
RECORDING CORPORATION
PARAMUS, NEW JERSEY
and rewind speeds.
Easily attached.
Export Division:
Canadian Division:
WORLD'S
LARGEST
MANUFACTURER
OF
PRECISION
25 Warren Street, New York 7, N.Y.
Walter
P.
Downs, Ltd., Dominion Square Bldg., Montreal
RECORDING
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AmericanRadioHistory.Com
EQUIPMENT
AND
DISCS
20 -20
PLUS!
S -226 -Q
Output
Transformer
±1 db 10- 100,000 cycles
watts
20
5
10
30- 40,000
watts at
watts at
cycles
10
cycles
15
cycles
Insertion loss
0.5 db
Primary impedances
6,600 CT & 1,650 CT
Cpnnected between halved
inpedances, frequency
response is extended at
each end: between doubled
impedances,
1 db 15-45,000 cycles.
Write
today
for the
Peerless
Catalog
Feedback from Output
Transformer Tertiary
SiNce introduction in practical form in
the late thirties, the popularity of nega-
tive feedback has spread to being included in practically all commercial power amplifier designs of high specification performance. As with most complex problems,
there is no unique solution to that of applying controlled degeneration, and many variations upon several basic schemes have
been applied.
Whether the sample of voltage fed back
should be taken from the output transformer primary or secondary, or from a
tertiary winding, depends upon the characteristics wanted, and upon the required
stability and permissible cost. Tertiary
feedback has been a useful compromise
offering much of the advantage sought with
secondary feedback, with greater freedom
from parasitic oscillation. While stability
requirements may necessitate use of a primary feedback plan, the lower hum, distortion and output impedance possible with
tertiary feedback often warrant its serious
consideration.
Assuming solution of the oscillation problem, secondary feedback could presumably
out-perform a tertiary feedback plan on all
counts. But in applying extensive feedback
by the secondary method, maintenance of
unconditional stability, if possible at all,
tends to be more a laboratory curiosity than
a production reality. Influence of the form
of feedback upon potential amplifier stability
has been described earlier in this series.1
The more important advantages of tertiary over primary feedback are the relative
convenience of feeding back to a single ended input stage from a push -pull output
s RCA Victor, Camden, N. J.
1 AUDIOLOGY,
"Feedback from output
transformer secondary," AUDIO ENGINEESING, July 1953. Also AUDIOLOGY, "Stability
testing of feedback amplifiers," Sept. 1953.
Dimensions:
4','s x 31fé' 3'6"
X
stage, and reduction of hum due to plate supply ripple. To account for the latter,
consider Fig. 1 in which an output transformer is shown with primary, tertiary and
secondary windings, each available for
feedback. With primary feedback (only),
plate -supply ripple is divided across the
load and tube in series. Since the plate (to
ground) impedance is made very low by
the feedback, practically the full plate supply ripple appears across the load. Secondary or tertiary feedback makes the impedance looking into the transformer primary very low compared with the tube
impedance, so only a small fraction of the
plate- supply ripple appears across the load.
Through study of the situation depicted
in Fig. 2, it may be seen how high -frequency amplifier stability can be made
almost as good with tertiary feedback as
with the primary feedback plan. Shown
single -ended for simplicity, the high -frequency transformer coupling network of
Fig. 2 is represented as three leakage inductances and three shunt capacitances. All
quantities including the load impedance are
shown referred to the primary side of the
transformer. Subscripts p, s, and t refer to
primary, secondary, and tertiary, respectively. Lpr is the leakage inductance between primary and tertiary, etc. The load
impedance, if a cable and loudspeaker, is
principally capacitive in the high- frequency
range where oscillation troubles customarily
arise.
Oscillation due to feedback connection is
the result of a basically degenerative circuit actually being regenerative at some
frequency (usually above the desired pass band). It naturally follows that the feedback loop would preferably be devoid of
phase- shifting elements effective in the
pass -band, and that the transition to a regenerative circuit outside the pass -band
would occur at such extreme frequencies
PEERLESS
Electrical Products
A
DIVISION
OF
TEC
9353 Santa Monica Blvd., Beverly Hills, Calif.
161 Sixth Avenue, New York 13, New York
Fig.
10
Fig. 2
1
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
Illustrated: R -5 portable unit
also available for rack mounting
VARI -TROL
knob...
the sensational one knob editing control to
L--
/5 051E
eititle THE OW
WIM
wind or re -wind tape at continuous or vari-
able speeds... moves the tape in either
direction at full or playing speeds, or stops
tape instantly.
PIANO KEY
The most advanced professional tape recorder ever
engineered ... designed and developed for the
Armed Forces by Stancil -Hoffman ... now used the
world over ... tested and proven superior to any
other tape recorder, regardless of cost! Now
available for commercial use.
Write for prices and complete specifications
-5.
controls...
the new electrically interlocked, centralized
keys for quick, one hand editing. An exclusive feature found only in the Stancil -Hoffman
R
Geist 8 Associates
60 East 42nd Street
New York 17, N.Y.
Canada: S. W. Caldwell, Ltd.
150 Simcoe Street
Toronto 1, Canada
H. J.
Chicago: W. Cozzens
220 Kedzie Street
Evanston, Ill.
Hawaii: S.O.S. Recording
1545 South Beretania
Honolulu, Hawaii
HOFFMAN
921 North Highland Avenue
Cable Address: STANHOFF
Hollywood 38, California
Phone: H011ywood 4 -7461
-5.
OTHER FEATURES
Automatic tape lift protects heads from
wear ... insures tape position for recording.
Three motor units ... two reel torque -sensitive motors and one drive system ... direct drive capstan gives positive timing.
Two speed motor control for 71/2 and 15
ips ... automatic "pre" and "post" equalization.
Ideal for instrumentation too.
REPRESENTATIVES:
AUDIO ENGINEERING
R
control panel with forward, rewind and stop
Stancil- Hoffman R -5 recorder is
greatest functional and technical achievement
in years!
New York:
An exclusive feature found
only in the Stancil- Hoffman
SPECIFICATIONS
Operates vertically on racks, horizontally,
in consoles and in motion ... for both
fixed and portable operation.
Complete recording and play back system
in two convenient carrying cases, only
20" wide, 14" tall. Three wide range,
low noise microphone inputs, monitor amplifier and speaker output.
Designed for full remote control.
Maximum total distortion less than 1.5 %.
Flutter less than 0.1% RMS at 15 ips.
Signal -to -noise exceeds 60 db.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
11
that the amplifier gain would not permit
oscillation. Particularly when the feedback
loop encompasses several stages, the output
transformer is not the only circuit element
contributing phase- shift, although it is
perhaps the greatest single offender.
When the voltage sample for feedback is
taken directly at the load (secondary feedback), phase -shift from generator to output
depends upon the load (over which the designer usually has no control), and can exceed 180 deg. in this part of the loop alone.
This of course can occur even with the load
disconnected; however, then the frequency
for 180 -deg. phase -shift may be high
enough that the amplifier gain is insufficient
for oscillation. For this reason, secondary
feedback amplifiers may be stable at no
load and yet oscillate with a certain range
of capacitive loads connected.
When the feedback signal is sampled at
the primary winding (primary feedback),
the phase -shift from generator to feedback
Precision
Prints
YOUR PRODUCTIONS
BEST REPRESENTATIVE
sampling point cannot possibly exceed 90
deg. regardless of transformer or load resonances, so the stability obtainable would
appear to be maximized through use of the
primary feedback connection.
At high frequencies the tertiary winding
(provided for feedback purposes only) is
separated from the primary by a leakage
inductance Lpt, and from the secondary
by leakage inductance Lt.. Additionally,
the tertiary winding has a distributed and
terminating capacitance Ct, but this is small
and independent of the amplifier load.
Similarly the effect of an associated tertiary
feedback network is usually negligible.
Clearly then, if the leakage inductance between primary and tertiary is much smaller
than that between secondary and tertiary,
the phase difference between primary and
tertiary voltages can be small and practically independent of the load. An output
transformer of this characteristic permits
application of tertiary feedback in practically the same quantity as the amount of
primary feedback usable with the same
tr
CLOSE CHECK.
PROCESSING
Picture anti sound results are held
to the closest limits by automatic
temperature regulation, spray development, electronically filtered and
humidity controlled air in the
ing cabinets, circulating filtered
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requirements of sound track development are met in PRECISION'S
special developing machinery.
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Our Advanced Methods and our constant checking and adoption of up-tothe-minute techniques, plus new engineering principles and special machinery
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Newest Facilities in the 16mm field are available to customers of Precision,
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_AM
Precision Film Laboratories -a division of I. A. Maurer, Inc., has 16
years of specialization in the 16mm
field,consistently meets the latest demands for higher quality and speed.
and capacitance connected from plate to B +
(ground). Employment of this device to an
extent materially effective in improving stability usually has the undesirable side -effect
of severely limiting power output at high
audio frequencies.
A more powerful method is that of using
a minor loop within the major feedback
loop. One simple way is that of including
(in addition to tertiary feedback) a minor
primary- feedback loop from power amplifier plate to (say) the cathode of the preceding stage. The primary- feedback circuit itself is readily made stable, and it provides
a low transformer source impedance within
the tertiary feedback loop. An important
(Continued on page 54)
PRECISION
FILM LABORATORIES, INC.
ui
21 West 46th St.,
New York 36, N.Y.
JU 2 -3970
11
12
transformer and associated amplifier circuit.
With either primary, secondary, or tertiary feedback, the phase-shift from output
generator to the feedback sampling point
can be reduced through employment of a
tube with low plate resistance rp. Feedback
to an earlier stage does have the external
effect of producing a low output impedance
as measured at the load terminals or at a
power amplifier plate, but in so far as a
single feedback loop gain-phase characteristic is concerned, the source impedance for
the transformer primary winding is simply
rp of the output stage. A point favoring
primary feedback is that this consideration
is rarely significant, adequate stability being
obtainable even with very high plate resistance in the output stage.
For improvement of high -frequency stability, one may in effect lower the transformer source impedance at high frequencies through use of a "parasitic suppressor,"
consisting preferably of a series resistance
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
If you want professional sound quality
Sound engineers know that the selection of a fine
amplifier, pickup and speaker system is only part
of the story; that unless the turntable is of equal
quality, music reproduction must suffer. That is
why they insist upon such high standards for turn-
table performance.
do as the professionals do...
Rek -O -Kut precision turntables are made to conform to the highest standards in the professional
field, and they certainly represent the finest you
can use in the home. A Rek -O -Kut turntable will
make all the difference in the world. The finer your
present system, the more apparent the improvement will be. Whether you select the deluxe T -12H
or the standard LP -743, the entire performance of
your sound system will become a new and thrilling
experience.
use a
precision turntable
Rek -O -Kut Precision Turntables are priced from
$59.50. Write for specifications and descriptive
literature to Dept. KA -1.
The REK -O -KUT COMPANY
Manufacturers of Professional Disc Recorders and Specialized Sound Systems
31 -01 Q
Bulvard, Lng Island City 1. Nw Yrk
-
Export Division, 458 Broadway, New York 13, U.S.A. Cables Morhanex
In Canada: Atlas Radio Corp., Ltd., 560 King Street, W., Toronto 2B
AUDIO ENGINEERING
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
13
EDITOR'S REPORT
1953 IN RETROSPECT
for magazine
IT
editors, news commentators, radio stations, and
other organs of communication to look back over the
past year every time the last number on the calendar
changes. And since we number ourselves in one of those
categories, we feel constrained to do likewise.
It is this observer's opinion that 1953 will be remembered as the year that the public found out about
hi -fi
least in the advertisements in consumer media.
We have been beating our drums -and sometimes our
gums, chest, and even at times the air waves-on behalf
of good audio in the home since 1947. Since we have
enjoyed good Music reproduction equipment ourselves
for years, we have felt that everyone should be able
to have the same pleasure, and we have done our best
to "sell" the idea throughout the world. So, after six
years of carrying the Word, we find that everyone is
getting into the act-many just translating the already available technical material into language the layman
can understand, while others just extol the idea without
actually telling how to achieve such a Nirvana.
When Æ was first launched, there were so many
who were unfamiliar with the word "audio" as to cause
doubt that a magazine would ever attract the public
the strange
particularly the non-technical reader
word appeared as a title. Yet in the first year that Æ
was on the public newstands, its paid circulation increased approximately 48 per cent, which proves something. Another bit of evidence of the interest in this
subject lies in the fact that Æ now has just under 200
life subscribers-readers who believe in audio as well as
in Æ. To date no wag has yet thought to inquire if
"life" meant his or Æ's, but this may be the result of
the wording on the life subscription card, which states
plainly that the holder will receive 1E for "the rest of
his natural life." (Italics ours.) One of the most flattering compliments lE has ever received was a check in
the amount of $185 from a company in the business of
making tape recorders and other audio equipment-the
$185 was for seven life subscriptions and two 2 -year
subscriptions. DuKane Corporation may not have got
the first life subscription card, but they are certainly
responsible for the greatest individual number of them.
We thank DuKane, and we appreciate the compliment.
Perhaps we blow our own horn too much, but we
have never forgotten the second issue of Radio News,
which appeared sometime before 1920. Its then editor,
Hugo Gernsback, mentioned the reception accorded the
first issue and concluded with a phrase essentially like
this :
yet we believe that one must blow loudly
and lustily upon his own horn for fear it may not be
blown upon." History has proved that Radio News
now developed into Radio and Television News -had
reason to cite its own merits, for it too was a pioneer
in the field. Remember that radio broadcasting and the
tremendous business associated with it had not started
by then, although it had been described by Nicola Tesla
as early as 1894.
IS AN ALMOST UNIVERSAL CUSTOM
-at
-if
"...
14
-
-
So it was with 2E -in 1947 only a few of us aficionados knew what high -quality sound reproduction was.
We like to number ourselves among the first in the
hi -fi field, yet every so often we mention the date of
our own initial interest, only to find that the person to
whom we are speaking was interested in hi fi two years
before we were. Someday we are going to trap someon4
into claiming he had a push -pull audio amplifier -a.c.
operated, of course -in 1905.
1954 IN PROSPECT
What is there to look forward to in 1954?
We believe that the major trend in the next year will
be toward simplification. As we have long pointed out,
it is not necessary to have an exact equalization curve
for every possible record characteristic
is better to
provide adequate flexibility and then to set the controls
to make the music sound right. With the influx of new
families into the hi -fi fold, more and more record libraries will be built on LP's and 45's, both of which
are fairly well standardized as to recording characteristics. Thus the amplifier of the future will have one
position for phonograph, one for radio, and possibly
several more for TV, tape recorder, spare, auxiliary,
and what not. But
spite of the article on page 23it will not be necessary to provide so many equalization
curves because most records will play correctly with
the same position. Suitable tone controls will provide
the required flexibility. Already the newer ceramic
pickups are designed to fit the presumed average characteristics, and they play well into a "flat" amplifier.
While big loudspeaker enclosures will continue to be
popular with those who can afford both the cost and
space for optimum performance, there is certain to be
a continued trend toward the smaller housings with
performance more closely approaching the Big Berthas.
Record changers and transcription players with only
two speeds are almost sure to be introduced -the speeds
being 33 1/3 and 45, of course-and with less complication there is certain to be improved performance with
respect to flutter and rumble. Tuner sensitivity will
move rapidly toward the 1 -µv point to ensure quieting
which is entirely adequate for high-quality reception
even in the fringe districts. The power amplifier is fairly
well stabilized -10 watts being the minimum acceptable,
and 30 to 40 watts being standard for the larger installations.
That, anyhow, is our guess, and like the panelists in
one of our favorite TV shows "What's My Line?"
we should be entitled to one free guess before the
questioning starts. What's yours?
-it
-in
-
-
VILLCHUR AGAIN LECTURER
The spring session of Mr. Villchur's course on sound
reproduction begins at New York University on February 3; classes meet every Wednesday from 7:00 to
9:45 p.m., and continue until May 19. Registration may
be effected at N.Y.U. Division of General Education,
Washington Square, New York beginning January 18.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
m glad 'J
Here's how I solved a problem that bothered me
uaiieI...
... and may be bothering you.
Many of my favorite recordings happen to be 78's. They mean as much to me as any of my
newer LP's or 45's. Changing pickups was often a real nuisance -and yet I wasn't willing to
give up the superior quality of my two Pickering cartridges.
Last fall my dealer offered a suggestion. "Wait a little longer." he said. "You'll be glad you did."
He was right. I now have Pickering's new turn -over cartridge. A simple flip of the handy
lever and I'm ready to play any favorite that fits my mood --whether it's standard or microgroove.
More than that, I'd swear my recordings sound better than ever.
c.hr glad
g
awaited
... tut you
wont have to.
Ask your dealer to show you this convenient new turn -over cartridge. Have him demonstrate it.
See if you, too, don't hear the difference!
PICKERING and company incorporated
Oceanside, L. I., New York
PICKERING PROFESSIONAL AUDIO COMPONENTS
CJ0Z
ZU/GO'
Cll/?
...Demonstrated and sold by Leading Radio Parts Distributors everywhere.
For the one nearest you and for detailed literature, write Dept. A -3
AUDIO ENGINEERING
»
ezeyzee
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
11111111! 11111.1,
15
Germanium crystal grown at Bell Telephone Laboratories (life size). It is sliced into hundreds of minute pieces to make
Transistors. Transistor action depends on the flow of positive current -carriers as well as electrons, which are negative. Arsenic
-a few parts per 100,000,000-added to germanium produces prescribed excess of electrons. With gallium added, positive
carriers predominate. Latest junction type Transistor uses both kinds of germanium in the form of a sandwich.
THEY GREW IT FOR TRANSISTORS
-
Heart of a Transistor Bell Telephone Laboratories'
new pea-size amplifier -is a tiny piece of germanium. If
Transistors are to do their many jobs well, this germanium must be of virtually perfect crystalline structure and uniform chemical composition. But it doesn't
come that way in nature.
So -Bell scientists devised a new way to grow the kind
of crystals they need, from a melt made of the natural
product. By adding tiny amounts of special alloying substances to the melt, they produce germanium that is precisely tailored for specific uses in the telephone system.
This original technique is another example of the way
Bell Laboratories makes basic discoveries -in this case
the Transistor itself -and then follows up with practical
ways to make them work for better telephone service.
Section of natural germanium, left, shows varying crystal structure.
At right is sectioned single crystal grown at Bell Laboratories.
IMPROVING
TELEPHONE SERVICE
CREATIVE
MEN
FOR.
IN
AMERICA PROVIDES CAREERS FOR
SCIENTIFIC
AND TECHNICAL
BELL TELEPHONE LABORATORIES
www.americanradiohistory.com
AmericanRadioHistory.Com
FIELDS
5
The New Golden -Ear Amplifier
JOSEPH MARSHALL
In Two Parts -Part
1
Combining virtual direct coupling, neutralization, two feedback loops, and a high
degree of balancing, this unit is reasonably free of distortion at normal volume
levels. The companion preamplifier offers several unusual features worthy of study.
DESIGN and components have made tremendous
strides in the past few years and
there are several commercial amplifiers
available today capable of reproduction
which, for all practical purposes, is as
good as it has to be for even the more
critical ears and beyond the various
program sources, broadcast or recorded,
in over -all fidelity. The Williamson circuit, for instance, though simple, produces results which are very hard to
quibble with. And yet the Golden -Ear
Complex, frustrated in the absence
of sheer perfection, continues to drive
many of us into expending much brain
energy, money and time, trying to reduce the remaining short distance to be
traversed to achieve perfect reproduction. The amplifier described herein
represents still another effort at producing an amplifier with the least possible
distortion of all forms, and the maxiAUDIO AMPLIFIER
*
The Bleachers, Ozone, Tenn.
-a
10ME&
9002
12Ax7
12 AU?
mum possible width of frequency response. Its band -width is limited principally by the output transformer and
with the best available today runs nearly
flat from 2 or 3 cps to over 10J,000 cps;
amplitude distortion is nearly non- existant except in the top 3 db of the power
output where it is just measurable; intermodulation is a fraction of one per
cent except again in the very top 3 db of
the output; the transient response is
almost completely flat throughout the
entire audio range of 20 to 20,000 cps ;
the amplifier is so stable that nearly 100
per cent feedback has to be applied to
drive it into oscillation and the period
of oscillation when it occurs is between
20 and 40 cycles per minute. The power
output depends on the output tubes used
pair of 6AR6's will produce 20 watts
of nearly distortion -free output, while
807's, 5881's, KT66's and the like will
deliver 15 watts; with an appropriate
power supply and output transformer,
1.5.1
Ultra- Linear tetrode or Extended Class
A operation may be employed to double
the output.
Design Principles
The cardinal principles of hi -fi design can be summarized in the followwk. rules:
1) Operate the various stages under par-
ameters producing as little distortion
as possible.
2) Cancel as much as possible of what
distortion is produced by balanced
configuration or feedback or both.
3)Make the amplifier and indeed the
whole reproducing chain as nonresonant as possible by keeping the
response curve as flat as possible not
only over the audio range but for
three or four octaves above and below
the audible range.
4) Eliminate, neutralize, or minimize all
positive feedback loops which might
cause oscillation, regeneration, hangover, or other transients.
Now let us see how these principles
6A96 (OR 607 OR x766)
6C4
1000
1000
1000
470
0.5
604
6AR6
(OR 607 OR
TO
6766)
GARS
FILS.
666
so
n xFMR?
r1111:4LV
r
+ T50V
-125V
099
so
T
Tso
400V
(
FUS
0
10
117V
AC
35-40V
TO
12AU7,12Ax7, 9002 9 604 FILAMENTS
Fig. 1. Schematic of the power amplifier section of the New Golden -Ear amplifier.
AUDIO ENGINEERING
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
17
are expressed in the practical amplifier
diagrammed in Fig. 1.
At first glance the circuit resembles
that of the Childs amplifier which employs the cross -coupled inverter and
which contributed the excellent cathode
follower driver used here; but there are
several very significant differences. The
design is eclectic, using elements derived
from others, but in an original combination. The distinctive features are, first
the means of broadening both the high and low- frequency response; second, the
high degree of balance and of distortion cancellation; third, the low degree
of phase shift which permits huge
amounts of inverse feedback; and finally,
the minimization of positive feedback
and consequent flatness of tratrsient re-
Fig
the
Top view of
power amplifier
2.
chassis.
sponse.
The Practical Circuit
The author has been much intrigued
by the cross -coupled inverter ever since
it was described by van Scoyoc five
years ago, and called attention to it in
an earlier article.' We have used it now
in several forms not only in audio amplifiers, but in 'scope amplifiers, volt-
meters, and distortion meters, and 'the
more extensive the usage the greater the
admiration for it. As far as we can see
it has no faults as a phase inverter and
many virtues not possessed by any other.
It can be balanced both in amplitude and
frequency response at least as well as
the best transformer; if the output voltage is held below 50 volts or less, it is
distortion -free; on the low side, its
response is down to direct current, and
on the high side to more than 50,000
cps ; it has inherent voltage and current
inverse feedback; and finally, since the
input tube is a cathode follower, it
presents a very light load to any input
and provides a good low- frequency response with a reasonable input capacitor.
With such an excellent phase inverter
at hand, and with new output transformers also available flat for an additional octave or more at each end than
the best ones, the problem was to keep
the response of the amplifier between
inverter and output transformer comparably flat.
The direct coupling of the phase inJoseph Marshall, "For golden ears
only," AUDIO ENGINEERING, April 1950.
verter immediately suggested that the
direct coupling be maintained throughout the entire amplifier, for a really flat
low frequency response. Those who tried
direct-coupling in its heyday, 15 years
ago, will remember the headaches involved. Many of these can today be
eased. The cross -coupled inverter, for
instance, makes a stable push -pull d.c.
amplifier of 3 or 4 stages quite practical.
Unfortunately, there were two serious
deterrents. One was the fact that for
the highest output with lowest distortion
we wanted to use big triodes with fixed
bias. This is not impossible to achieve
with direct coupling but it is difficult.
Another was that we would require a
power supply (or two in series) delivering 800 volts or more.
Actually, the very difficulty : self suggested the solution. Unless a driving
transformer is used, the only practical
high- fidelity method of coupling fixedbias power triodes to an R -C coupled
amplifier is through a cathode follower
which may be direct coupled to the
power tubes. But a cathode follower has
a very high input resistance. Therefore,
a moderate sized coupling capacitor
would produce a time constant which
would extend the frequency response
down to 1 or 2 cps, or even lower. If
then, the amplifier were designed in the
form of two direct -coupled sections, one
containing the phase inverter and volt-
Underside of
the power amplifier
Fig. 3.
chassis.
age amplifiers, and the other the cathode
follower directly coupled to the output
tubes, and if we then joined these two
sections with a capacitor at the cathode
follower input, we would have an amplifier which, for all practical audio purposes, is as good in low- frequency response as a direct -coupled amplifier but,
being isolated so far as direct current
is concerned into two sections, would
require only a single 400 -volt power
supply and would permit the use of fixed
bias on the output tubes; it would, moreover, be much moire stable than a d.c.
amplifier.
The practical amplifier fully realized
the expectations and produced no construction or adjustment headaches whatever ; indeed, it was, if anything, easier
to adjust and keep in adjustment than
any other amplifier we had ever used.
It is, to be sure, somewhat extravagant
in the use of tubes, but the direct coupling holds down the number of component parts to a number no greater
than that in much simpler amplifiers, and
the performance is quite superior.
The Amplifier Circuit
The 12AÚ7 and 12AX7 comprise the
cross -coupled inverter. This is direct
coupled to a pair of 9002's, as driver
amplifiers. Miniature tubes were used up
to the power stage to hold down tube
capacitance. Either a 12AU7 or a
12AX7 could be used instead of the
9002's. The former would yield a somewhat higher output and be more suitable for use with 6B4's in the output
stage; the latter would yield more gain
and permit more feedback or obviate the
need for additional voltage amplification.
The 9002's, however, are excellent tubes
for the purpose and provide a gain of
about 17-as against 12 for the 12AU7
-and a practically undistorted output
of 60 volts per side.
The 9002's are coupled to the 6C4
cathode followers (one 12AU7 would
serve identically) through a 0.1 fsf ca -.
pacitor. Since the effective input resistance of the cathode follower is ten
times the grid resistor, or in this case,
5 megohms, the time constant is 0.5
(Continued
Iñ
AUDIO ENGINEERING
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on
lit
JANUARY. 1954
Stereophonic Nomenclature
N. M. HAYNES
A complete lexicon of terms is proposed to end the present
confusion of jargon on stereophonic and binaural sound.
INTERESTED ill the art of
stereophonic reproduction cannot
help but recognize the state of confusion which exists in the terminology
generally used.
Such terms as binaural, trinaural,
point source, diffused source, source
free, multichannel, true binaural, panoramic, spatial reproduction, bistereonauralphonic have already seen the light of
day. Descriptions, too, of "in the round,"
"auditory perspective," "focus," plus a
host of explanatory and translatory errors have piled up a linguistic hodgepodge in a field where such confusion
need not exist.
Along with the flush of a new (or rebirth of an old) art will be heard the cry
of the hucksters, salesmen, advertisers,
and pseudo -technicians who use and
embrace terms which serve their blaring
needs but are nevertheless confusing
and meaningless in character. To systematize stereopohonic terminology and
attempt to bring intellectual order out
of a chaotic scramble of expressions is
the hopeful intent of the writer.
Stereophony is analogically rooted in
the history of stereoscopy, a phenomenon
which was first correctly explained by
John Kepler in 1611. During the past
three hundred and forty years, a series
of optical terms describing equipment,
techniques, and effects have become well
established. This time proven heritage
should be carefully examined for help in
clearing the rubble of stereophonic semantics.
A,ONE
Philosophy of Modern Nomenclature
ideally, from the semantic viewpoint,
words should convey maximum information with minimum effort. This implies
avoidance of specialized nomenclature
which is clear only to those skilled in a
specific art. Special meanings given to
common terms understood py a select
few contradict the modern concepts of
free exchange of information. It would
be ironical and contradictory for a scientist skilled in optics, or a physician in
physiology, or a psychologist expert in
visual illusions to be baffled by monstrous
stereophonic nomenclature. That such
monstrosities have appeared is regrettable; their perpetuation is inexcusable.
A 75 per cent redundancy in the English language' is caution enough to avoid
* Engineering Vice-President, Amplifier
Corp. of America, 398 Broadway, New
York 13, N. Y.
1 Shannon, C. E., "Preduction and entropy of printed English,' Bell Syst. Tech
J., Vol. 30. No. 1 (Jan., 1951), pp. 50-64.
AUDIO ENGINEERING
the addition of useless words. No one
can deny that new effects, techniques,
and equipment require new descriptive
terminology, but a haphazard conglomeration of unrooted, confusing, and
philologically meaningless terms is contrary to the basic concepts of language.
By analogy, root, or classification new
words should at least imply if not express their meanings.
If we sort the rubble of contemporary
stereophonic terminology through a
three -compartment sieve labelled "Technique," "Effect," and "Analogy," we can
quickly separate and classify useful
terms and recognize the need for additional systematized nomenclature.
The Greeks Had a Word for it
is a combining form from
Stereo
the Greek stereos, meaning hard, firm,
solid. It is used in scientific terms to express hardness, firmness, and solidity.
By leaning heavily upon optically aceepted terms which have withstood the
test of time, we can readily begin from
the term stereoscopic, which implies the
effect of localizing matter in space
visually. Stereoophonic, by physiological
...
apd neurological analogy would then
refer to the effect of localizing sound
sources in space.
Translatory problems are well recognized and it is no surprise to find amusing explanations for stereophonic reproduction. One example is, "Stereos in
Greek .. means volume. Stereophonic
would indicate that you can hear volume,
which seems contradictory. Yet, we are
able to 'focus' our ears on part of a
sound source; for instance, we can distinguish one conversation from a confusion of voices and assign it therefore
some sort of volume."
This queer definition stems from the
translator's failure to recognize an idiom
of our space -time continuum. The volume he means to describe is not one of
sound intensity but the goemetric measure-a volume of space. A more acceptable and meaningful explanation would
be, "Stereo in Greek means solid or the
volume occupied by solids in space.
Stereophonic would indicate that you
can localize sound in space."
In the analogous field of microscopy,
there are three general types of instruments. The common or standard microscope is equipped with one eye-piece and
one or more objectives (nose-pieces) ;
the binocular microscope has with two
eyepieces (for simultaneous viewing
with both eyes) and the usual set of
objectives; and the stereo microscope
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
has two eyepieces and a jointly used set
of objectives. The stereoscopic microscope produces a stereoscopic effect. It
is not called a binocular microscope because not all binocular microscopes are
stereoscopic Though prism binoculars
provide stereoscopic vision as a by -product of their construction, they are not
specifically designed for stereoscopy. In
fact, the stereoscopic effect is artificially
exaggerated because of the increased
spacing of the objective lenses (which
are usually approximately twice as far
apart as the eyepiece lenses). This
stereoscopic exaggeration is not a byproduct of Galilean field glasses.
The term binaural means of or pertaining to, or used by or with, both ears.
Two earphones or earmuffs are binaural.
The use of this "equipment" term in
place of the "effect "term stereophonic is
a pure and unadulterated barbarism ! In
just the manner that "binocular" does
not imply or express "stereoscopic" so
"binaural" does not imply or express
"stereophonic." Similarly, the term "true
binaural" is a premeditated barbarism,
for it also mixes techniques and equipment. Monstrous terms like bistereonauralphonic result from abortive terminology applied to combinations of faulty
techniques and corrupt effects. Such
gobbledegook should be looked upon as
premeditated nonsense, as it undoubtedly
was by its originator.
If we group our suggested nomenclature into four logical divisions and use
self -explanatory or analogical terms
where they exist, much of our present
confusion will vanish. Furthermore,
nomenclature will at least have meaning to nearly all in acoustics and be
understandable to many in other scientific fields.
!
Terminology For Stereophonic Effects
Stereophonics, n.: The science which
treats of the recording, reinforcement, or
reproduction of sound in such a manner as
to provide a sensation of spatial distribution
of the original sound sources.
Stereophonist, n.: One versed in the
use or manufacture of stereophonic equip-
ment.
Stereophony, n.: The art of using, designing, or
equipment.
manufacturing
stereophonic
Stereophonically, adv.: In a stereophonic
manner ; by means of stereophonic equipment.
Stereophonism, n.: The state of being
stereophonic.
Stereophonous, a.: Same as stereophonic.
(Continued on page 54)
19
Design Of A
Professional Tape Recorder
WILLIAM
F.
BOYLAN
and
WILLIAM
Design and operational features of
THE PRESENT STATE of the magnetic
recording art has made possible the
design of recording equipment with
extremely high performance standards
excellent frequency response, low distortion and flutter-and so on. While performance standards are of the greatest
importance, a survey of individuals and
requirements in the professional recording field made it plain that certain purely
operational features were very much in
demand as well, such as ease of tape
handling, precise and instant control of
tape motion, good editing facilities, accurate timing, portability, and 'other
similar points.
These factors were taken into prime
consideration in the design of the new
tape recorder pictured in Fig. 1. In addition to fulfilling the high performance
standards required in quality professional work, the machine provides extremely quick and easy operation. It
consists of two major units, the tape
transport and the record-reproduce amplifier unit which includes the high -frequency oscillator. Both major assemblies
may be mounted in the console as shown,
in a portable carrying case which is
furnished, or in a standard 19 -inch relay
rack.
-
a
E.
GOLDSTANDT
new high -quality machine.
record, and reproduce heads, compliance
arms, and an inertia-stabilizing roller to
filter out tape speed irregularities produced as the tape leaves the pay-off reel.
The layout of these components not only
governs the performance of the unit to
a great extent, but also affects the simplicity of operation. In the machine being
described the tape path is straightforward and free of loops and curves
around guiderollers.
A 3- position function control lever is
included. Its positions are marked OPERATE, LOAD, and EDIT. When the lever is
placed in the LOAD position the compliance arms, tape guide, and head covers
are put in such a position that "straight line" or "slot" loading of the tape is permitted. This feature eliminates most of
the inconvenience normally encountered
in tape threading. The head covers are
open wide in the LOAD position for ease of
head inspection and marking of tape.
After the machine has been loaded
with tape, the control lever is placed in
the OPERATE position. This brings the
compliance arms and head cover back
into their normal positions. In the OPERATE position, the tape does not come
into contact with the heads except dur-
ing normal forward operation. This
allows the tape to be run at high speed
forward or rewind without excessive
wear on the heads. When the tape is
moving in the normal forward direction,
as for playback or record, the tape guide
and head cover are solenoid- actuated to
cause the tape to engage the heads.
When the control knob is placed in
the EDIT position the pushbutton switches
are locked out of the circuit, and the
tape is held against the heads. If one
Tape Transport Unit
The complete tape transport, shown in
Fig. 2, is constructed on a standard 19inch rack -mounting panel. The panel is
12/ inches high and the mechanism
extends 8 inches behind the panel.
One of the principal design objectives
for this project was to produce a mechanism which would afford easy operation
and tape handling. In order to accomplish this, considerable effort was directed to the problem of panel layout.
Among the people interviewed, the general trend of opinion indicated that the
normal tape direction should be from
left to right in both relay rack and console mounted machines. This arrangement dictated a front panel 19 inches
wide with the height of the panel kept to
a minimum to preserve portability.
In any professional recorder certain
minimum components should be included
in the panel layout. These are a constantspeed capstan and pressure roller assembly, a tape tensioning or hold -back
device, a take -up system to spool the
tape after it passes the capstan, erase,
1.
The new
Magnecord M -80 recorder in its console
cabinet. A portable
case is also provided.
Fig.
*
Assistant Chief Engineer and
Mechanical Engineer, Magnecord, Inc., 225
West Ohio Street, Chicago 10, III.
20
AUDIO ENGINEERING
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JANUARY, 1954
ing, compliance arm guide, and tapebreak switch. It filters out effects of tape
sticking as well as high -frequency flutter
components caused by the pay -off reel.
Head Assembly
Fig.
the
Top view of
tape transport
2.
unit.
"Drop -intoslot" tape threading
makes
reel hub is then grasped in each hand
the tape may be moved back and forth
across the heads, permitting easy and
rapid cueing.
In addition to the function control
lever, other controls located on the front
panel include four pushbutton switches
labeled REWIND, STOP, FORWARD, and HI
FWD (high speed forward). Two rotary
switches are located on the lower right hand side of the panel, one of which controls the tape speed, 7.5 or 15 inches per
second. The other rotary switch turns
the recorder mechanism on and off.
A record warning indicator light is
provided on the transport unit panel
which tells the operator when the unit
is ready to record. This indicator light is
lit when the record- playback switch
(located on the front panel of the amplifier) is in RECORD position. When the
tape is not in motion the indicator is lit
by d.c. from the amplifier, and when the
tape is in motion it is excited by the
high- frequency bias supply, which operates only when the tape is moving forward at recording speed.
The complete transport unit consists
of eight unitized assemblies. These are
two reel motor and brake assemblies,
capstan -drive assembly, stabilizer roller
assembly, head assembly, front -panel assembly, pushbutton control box housing
the control relays, and the high-fre-
for easy
eration.
op-
quency bias -erase oscillator which also
includes the power supply for the solenoids.
Each of the two reel assemblies consist of a torque motor mounted directly
on the front panel, as illustrated in Fig.
3, with a brakg assembly mounted on the
rear end bell of each motor. Solenoid
actuated band brakes provide for the
necessary differential braking to keep
the tape at constant tension during
braking so that it does not throw loops
when 't is stopped after high-speed running. During normal forward operation
a reverse torque is applied to the pay -off
motor, which maintains a relativery constant tape tension while the tape is being
unwound from the pay -off reel. Slightly
greater torque is applied to the take -up
motor to provide sufficient torque to
spool the tape.
The tape is pulled by a direct -drive
assmbly consisting of a 600 /1200- r.p.m.
hysteresis synchronous motor with an
integral ground capstan. A flywheel is
mounted on the rear shaft extension of
the motor. The capstan drive operates
with the same characteristics in the
horizontal as in the vertical position.
Timing accuracy in the neighborhóod
of 3 seconds in 30 minutes can be expected.
The stabilizer assembly consists of a
flywheel, tape roller and bearing hous-
Fig. 3. Underside of
the transport unit.
AUDIO ENGINEERING
JANUARY, 1954
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The high performance characteristics
of the M -80 recorder are dependent to a
large extent on the precision record and
playback heads as well as the head
mounting assemblies and tape guides.
There are three heads in this assembly,
illustrated in Fig. 4.
The erase head is a low -impedance
device requiring approximately 1 ampere
of ultrasonic current. It is of the double gap variety, which assures complete
erasure.
The record head is a new unit developed specificially for this recorder. Its
impedance is approximately 50 ohms at
1,000 cps. Precision lapping such as that
used in optical work has been employed
to assure a very straight and uniform
gap. Since recording is done with the
trailing edge of the gap, the straightness
of the gap edges is more important than
the gap width itself. The record head gap
length is in the order of .0007 to .001
inch. The reason for this large gap is to
Fig.
4.
The three heads are mounted
complete subassembly.
in
a
reduce the noise recorded on the tape
due to residual localized d.c. magnetizations of very small magnitude.
The reproducer head is similar to the
record head in construction except that
the gap length is of the order of .00025
inch. The reproduce head is even more
critical than the record head and greater
care is taken in manufacture to assure
uniform gap length as well as gap edges.
The impedance of the playback head is
approximately 6,500 ohms at 1,000 cps.
There are two determining factors which
dictate the impedance of the head. As the
impedance is increased, greater output
voltages are obtained, lowering the requirements of the playback amplifier
equivalent input noise. However, as the
impedance is increased, lower resonant
frequencies of the head and connecting
cable are encountered. The resonant frequency of the head and cable should be
higher than the highest frequency to be
reproduced.
The heads are mounted in triple shielded Mu -metal cans to reduce hum
pick -up. Glass tape guides are employed.
The front panel assembly contains
mountings for the control box and oscillator unit, plus the pressure roller assembly, compliance arms, tape guide
linkages, and the power on -off switch
and tape speed selector switch. Figure 3
is a rear view of the unit showing all the
assemblies in place.
21
itt
Control Box Assembly
The control box assembly contains the
relays and relay power supply as well as the
Fig. 5
control buttons.
5lxPL
The control box assembly, shown in
Fig. 5, is contained in a special mounting
shell. All relays, pushbutton switches,
and the relay power supply are mounted
on a single chassis and are readily accessible for servicing during operation
by simply removing the chassis from the
mounting assembly. Four relays are
located on this chassis, three for normal
forward, rewind, and high forward.
These three relays have interlock circuits to prevent any two operations from
occurring at the same time. To prevent
tape breakage, the normal forward relay
is locked out of the circuit until the machine is stopped.
ERASE
050
I
TB1
I
--
LO_
0
5
6
0
0
B
9
0
0
10
1DG
DC-
A-----1-
12
11
13
- tro
-------.--224E.------i
0
I
11
I
9
I
16
ITB-2
°
-0 \
3
AMP
00/10
30
501.0
30
30
TTT
50 at
BIAS LEVEL
ADJ
2500
004
P1
B-
B
1
2
GOPO
5
°ç1(
6
A
3v 5
0 6
HEAD
.+11
mn11
Fig.
Schematic of the bias oscillator and
6.
relay
power
An additional time -delay relay -the
time delay being acomplished by an R -C
network
included to supply a voltage
surge to the take -up motor when the
machine is initially started in a normal
forward mode. This feature prevents the
occurrence of a loop of tape between
the capstan and the take -up- motor when
the machine is started, resulting in
smoother starting.
Terminals are provided on the control
box assembly for remote control connections.
The oscillator assembly contains the
high-frequency erase and bias oscillator
circuits, as well as a 115 -volt L-C -filtered d.c. power supply used to energize
the solenoids. The oscillator is a push pull Hartley as shown in the schematic
of Fig. 6, using a 12BH7. This tube has
a higher plate dissipation rating than the
previously used 12AU7 and should give
longer service without replacement. A
special, improved, high -Q oscillator coil
has been employed, to result in lower
even -order harmonic content.
The oscillator coil secondary feeds the
erase head in series with an 0.5 -uf coupling capacitor. This capacitor has the
funtion of resonating the erase head
inductance at the operating frequency
of the oscillator, which is approximately
70 kc. Approximately one ampere of
high- frequency current is supplied to the
erase head. The voltage drop caused by
the reactance of the 0.5 -µf capacitor is
used as the supply voltage for the record head bias. Lower harmonic content is
achieved by feeding the record head
from a voltage source developed across a
capacitive reactance, which results in
lower noise being recorded on the tape.
The bias current is fed through a rheostat which is used for bias adjustment.
-is
supply
Record And Reproduce Amplifiers
The amplifiers are mounted on the
standard
x 19 -inch rack mounting
panel shown in Fig. 7. Fig. 8 shows the
chassis mounting the tubes and major
components in a horizontal position. The
front panel contains the controls. An
input selector switch provides for operation from a high -impedance balanced or
unbalanced bridge input or a 50 -ohm
microphone. The VU meter function
switch has three positions, record level,
playback level, and bias measurement.
The record -playback switch includes a
REMOTE position allowing the record or
playback function to be controlled from
a remote location. A monitor jack is
provided on the front panel to provide
monitoring directly from the program
source or from the tape. The monitoring
voltage is switched simultaneously with
the VU meter. An equalizer switch suits
equalization to 7%- or 15- inch -per -second tape speed.
The record amplifier consists of three
stages of voltage amplification V3, V2,
followed by an output stage V. which
supplies current to the record head and
contains the pre- equalization.
The input stage is a newly developed
form of the cascode circuit described by
5/
Fig
7
The amplifier unit
is
mounted on
a
19
-inch rack panel.
Fig. 8. Side
view of
unit
with side panels removed shows "dish
mounting" with tubes
the
amplifier
horizontal.
Compo-
nents are board
mounted
for easy
replacement.
(Continued on page 60)
22
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JANUARY. 1954
Preamp with "Presence"
C. G. McPROUD
Introducing
circuit which departs from "flat" to pro-
a
vide the elusive quality called presence, and which incorporates most of the features desired by the critical listener.
amplifier and equipment construction
has usually been in the direction
of completely "flat" response curves, it
is well established that certain types of
correction are useful to compensate for
microphone placement, for deficiencies in
equipment, and for personal preference.
However, the use of a separate control
for increasing "presence" has not been
introduced in home equipment to date,
although it has been used in professional
equipment for many years-although not
necessarily by that name.
In the early 30's, certain types of loudspeaker systems in theatres were in need
of some form of correction in the midrange to increase the illusion of realism.
It is probable that the deficiency was due
to the speakers themselves, but in any
case a correction in the form of a small
boost somewhere between 2000 and 3000
cps. was introduced to improve presence.
The boost was of the order of 4 db, and
was usually located at 2700 cps.
Following some experimentatjon along
these lines, it was found that the addition of a boost ranging from 4 to 6 db at
2700 cps gave the illusion of moving a
solo violinist out in front of the loudspeaker, or of causing the singer with a
popular band to step out in front. Admittedly the effect is slight, but it is sufficiently noticeable to warrant its inclusion in the amplifier to be described.
WRILE THE GENERAL TREND in
The Complete Circuit
-
Every so often, a confirmed experimenter feels the urge to make a change
usually having in mind the desire to add
one or more operating features which
appear to be desirable. Reviewing the
real or fancied faults in existing circuitry, the writer planned a preamplifier
and tone-control amplifier which would
incorporate all of the desired features.
Taking the steps one by one, they add
up about as follows:
Some preamplifiers do not operate as
quietly as would be desired -having a
hiss or hum level too high for complete
satisfaction. Furthermore, it was felt that
the low- frequency boost required for
magnetic pickups began to flatten off too
soon, resulting in insufficient bass in the
lowest range -that is, below 50 cps.
Some amplifiers have insufficient compensation characteristics for the most
critical listener, and while the trend for
the newcomers to hi -fi seems to be to
reduce the number of available curvesAUDIO ENGINEERING
largely because those who are entering
the hi -fi field "fresh" will generally build
their libraries exclusively from the LP
and 45 catalogs-there is some advantage to having complete flexibility.
The tone -control circuit first described
by Baxendall' and more recently for use
with American tubes by Barbers offers
some interesting possibilities. Principal
among these is the variation in the inflection point as the amount of boost or
cut is changed. The advantages of this
show up when using a wide -range loudspeaker system with usual source material-both records and radio programs.
In addition to the presence control, it
also seemed desirable to incorporate a
low -pass filter system into the amplifier,
and the L-C network described by Mar kow3 was investigated for the purpose.
Fig. 1. (Left), Centralab Couplate for the
tone -control circuit. (Right), the Couplate assembled on a dual -concentric control.
And as this writer has long been a proponent of the loudness control, this too
had to be included -but with some form
of decompensation which could easily be
an uncompensated volume control.
Adding these up, one arrives at the
astonishing figure of eight as the required number of controls, nearly as bad
as the early TV sets before the trend
toward simplification resulted in sets
with only two knobs. Follownig the same
procedure, the amplifier was planned to
use only four "apparent" knobs -each
being a dual concentric control. Thus
the phonograph preamplifier becomes a
dual switch each with five positions ; the
tone control becomes a dual- concentric
Wireless World, October 1952.
Basil T. Barber, "Flexible tone control
circuit," AUDIO ENGINEERING, September
I
2
1953.
3 Elliott W. Markow, "Record improvement with h. f. cutoff filters," AUDIO ENGINEERING, November 1952.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
assembly of two potentiometers ; the
presence control and the low -pass filter
switch are combined into a third unit;
and the fourth consists of another dualconcentric control-one section being
the loudness control and the other being
a volume control.
Obviously, few of these units are
readily available from jobber stocks, so
they were described to Centralab, and
the four complete units were soon forthcoming. Centralab engineers had already
designed the Senior Compentrol, which
combines the loudness control with a volume control, and which employs a
printed circuit " Couplate" with all the
compensating elements. A study of the
Baxendall circuit indicated that another
Couplate could be built with three capacitors and four resistors in a single
unit, as shown at the left in Fig. 1, and
assembled onto the dual potentiometer at
the right. Thus the construction of the
entire tone-control circuit is considerably simplified. A standard line of Centralab units-available primarily to
manufacturers -included dual concentric
switches and dual units with a switch
and a potentiometer. These were kept in
mind during the layout of the amplifier
circuit, and when the requirements were
settled, the problem of making the controls was left to Centralab. All four units
are available for anyone who wishes to
duplicate the amplifier.
One of the features of the construction
is the use of "custom- built" mounting
boards for many of the components.
While resistor -board construction is not
uncommon in factory -built equipment,
it is less often encountered in handcrafted units because of the difficulty of
obtaining these strips with terminals located ideally for the particular circuit
being built. However, with the Alden
terminal cards, any desired number of
terminals may be installed exactly where
the user wishes. Figure 2 shows the main
terminal board with the four sockets attached to it and with most of the terminals in place. Detailed information
about the terminal boards and the method
of using them is included with the constructional data.
Preamplifier Details
The amount of low -frequency boost
available from the conventional equalized
feedback circuit depends upon the gain
available from the two tubes. Consider,
for example, the use of two sections of
a 12AX7 with gain of around 40 for each
23
-
been made for switching inputs. The preamplifier has input and output jacks
the input coming directly from the
pickup and the output being fed to a
selector switch on the tuner. The output
of the tuner switch if fed back to the
input of the tone -control section, and its
output is fed in turn to the power amplifier. There is no reason why the switching should not be incorporated in this
chassis if it is desired, but for the writer's application the tuner switch was
most convenient. Furthermore, this
method provides complete flexibility and
permits easy interconnection of other
Fig. 2. Resistor mounting card assembled in small chassis with four sockets attached. Terminal lugs may be stoked into any desired holes in the board, and thus fit any circuit. Grid
and input circuit components are on the top side; plate and decoupling components are
located on the bottom.
section, or a total gain of 1600. This
corresponds to approximately 64 db. For
an output of 1 volt and an input of 10 mv
at 1000 cps, a gain of 100 is required,
which is 40 db. This gain must be available at 1000 cps. However, to provide
the low -frequency boost required for
proper equalization of magnetic pickups,
it is necessary that an additional gain of
20 db be available at 50 cps (for a 503cps turnover). Since the maximum gain
available from the tube is around 64 db
and 40 is required at 1000 cps, the remaining 24 is all that is available for
boost of the low frequencies. Now the
frequency- response curve does not consist of two straight lines, but is composed
of the flat portion above turnover, plus
a portion which increases with lowering
frequency at the rate of 6 db per octave,
plus a portion which is again flat. but
which represents the total gain of the
two sections of the tube without feedback. These three straight lines are
joined with curving sections, as shown
in Fig. 3.
From this, it is seen that there is
hardly sufficient low-frequency boost
available from a 12AX7 to provide full
equalization for the AES curve nor for
the 800 -cps turnover, if the compensation is to extend fully to the lowest frequencies to be passed. This discussion
does not apply to the New Orthophonic
curves, since they roll off with a maximum required boost of 18.6 db at 30 cps.
The LP and NARTB curves are similar
in the low-frequency range.
When tubes with less gain than the
12AX7 are employed, the difference is
even more noticeable, which may account
for a deficiency in low- frequency boost
when a 12AY7 is used in a circuit designed for the 12AX7.
To correct fully for the necessary low frequency boost, it is apparent that more
gain is required from each of the tubes
(or tube sections). The logical answer
is to use two pentodes. Some pentodes
are too noisy for this service, considering that the input signal is in the range
of 30 mv. The circuit was first built up
with 5879's, but these tubes-while of
excellent low -noise characteristics-have
hardly sufficient gain to give the desired
low-frequency boost. The Genelex Z729,
recently introduced in this country, is
24
-a
Tone -Control Section
claimed to have even lower noise and
hum than the 5879, but it has an available gain about equal to that of a 6AU6.
The latter tube is likely to be somewhat
noisy in low -level applications, particularly if a.c. is used on the heater. With
the Z729, however, suitable performance
with respect both to gain and noise has
been achieved.
The circuit is relati'ely conventional.
A feedback circuit from the plate of the
second tube returns to the cathode of the
first, and frequency corrective circuits
are introduced in the feedback loop.
Series capacitors control fhe turnover
frequency, with the New Orthophonic
rolloff being obtained by connecting a
shunting resistor across one of the capacitors. The turnover frequencies available are 800, 500LP (for New Orthophonic), 500, 400 (AES), and 300.
The high -frequency rolloff is provided
by connecting suitable capacitors and resistors across the feedback resistor to
give rnlloff of 4. R. 12. and 16 db in addi-
_
MIN
m
preamplifiers or tone-control amplifiers
for comparative tests
condition which
is often required in this particular installation.
50
wo
500
1000
FREQUENCY N CYCLES PEA SECCtC
Fig. 3. Construction of the curve obtained from
feedback network around two tubes. Curve
asymptotic to two straight lines.
is
tion to a flat position. All of the switching is accomplished by a Centralab
Series 30 switch -the panel section consisting of a single deck with two 5 -position switches and the rear section consisting of another single deck with one
5- position switch. All of the resistors
and capacitors are mounted on the resistor board, with flexible leads connecting to the switch. The schematic of the
preamplifier is shown in the left portion
of the over -all schematic, Fig. 4. The
response curves of the preamplifier section are shown in Fig. 5. It will be noted
from the schematic that no provision has
The remainder of the circuit comes
under this heading, although there are
several other functions incorporated in
this section of the amplifier. The first
step consists of the "presence" circuit,
which includes R,,, R,,, Rn, Cn, C,,, and
L. This is a simple loss network with a
tuned circuit in the shunt leg. The tuned
circuit is shunted by a 50,003 -ohm linear
pot which varies the amount of boost
from 0 to 6 db. The boost is approximately linear with respect to the amount
of rotation of the pot. The L-C circuit
is tuned to 2700 cps, and listening tests
have shown that the L-C ratio prescribed
gives about the best effect. A smaller inductance and larger capacitor could he
tuned to the same frequency, but the
"bump" in the response curve is narrow,
and the subjective effect is not as desirable.
The Baxendall circuit provides no
gain from the first tube section since it
is used as a cathode follower. Furthermore, there is rather more high -frequency equalization in the tone -control
circuit than is considered desirable.
Since additional gain was necessary, the
first section is used as an amplifier with
improved performance throughout. In
the final form the control section requires
an input -of .08 volts for an output of 1.0
volts which gives some leeway for operadon of the volume and loudness controls.
With the Couplate and the dual pot, it
is only necessary to connect four wires
between the tube chassis and the control
to have a complete low- and high -frequency tone-control circuit. The response curves obtained are plotted in
Fig. 6 for the center or flat position and
for two degrees of both boost and cut.
The second section of V, feeds the volume control and the first section of V, is
located between the volume control and
the loudness control, giving complete
isolation between the two controls and
eliminating any interaction. The final
tube section, Via, is a cathode follower
which feeds the low -pass filter circuit.
The filter circuit is an adaptation of
the network described by Markow,3 and
is connected at the output of the cathode
follower. This circuit requires the use of
another inductance, but the performance
meets the specification laid down before
the construction was begun. The control
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
S
o
R29
IÌTVVr
R9 0111E11
1200
1
;
CQ'1000,r1
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ISSDONd
RN
R12
TONES
12000
R30 11,000
D-W
SNL.
o
NOTE
1
R215
IS
SECTION
OF
E-o
CONTROL
LOUDNESS
CENTRAL AO
33¡!00
NOTE 2
RIS
ANO
SR3
,
s.s
ARE
C29
ONE UNIT
0056
0
12V
SW1A
0
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VS
VI
12V
V2
Fig. 4. Overall schematic of the
is a Centralab 30a unit, and consists of
four 5- position switches mounted on two
decks and operated by the outer shaft,
-a
together with the presence control
50,000 -ohm linear pot operated by the
inner shaft. Three of the switch sections
are used in the filter circuit, while the
terminals of the fourth serve as tie
points for, the matching resistors, R,,
R., Rs', and Rs. The eight capacitors
and the four terminating resistors are
mounted on another Alden terminal card,
as shown in Fig. 7. The frequency -response curves for the filter section are
shown in Fig. 8.
It may be argued that the presence of
the filter network after the output of the
cathode follower detracts from the advantage of the follower as an output
source -usually considered desirable in
case the power amplifier is to be located
at some distance from the control section. However, for this particular application the two units are to be located
close enough that a three -foot cable will
be used for making the connection, and
the impedance of the output under the
worst condition-that is, at "flat "-is of
the order of 11.000 ohms, and a shunt
capacitance of 300 µµf could be tolerated
with a droop of only 3 db at 50,000 cps.
Under these conditions, therefore, it was
considered preferable to locate the filter
at the output of the control -unit rather
than at some earlier section of the cir-
1300
500
00
300
SOOLP
.15
10
tion.
cuit.
Volume and Loudness Controls
In order to provide loudness -control
action in the amplifier, and yet to be able
to use as much or as little compensation
as might be desired, both types of controls are provided. A 0.25 -meg volume
AUDIO ENGINEERING
preamplifier and control sections.
control is located between Vas and Va,
and the compensated control is located
between Va and 17410. The Senior Compentrol employed here consists of two
controls with concentric shafts-the volume control being operated by the outer
shaft and the loudness control being
operated by the inner shaft. Any degree
of compensation can be obtained quite
readily. The response curves of the loudness- control section, Fig. 9, are shown
for the maximum- volume condition, and
for conditions where the 1000 -cps level
is 10, 20, and 30 db below maximum,
respectively.
Circuit values have been adjusted for
minimum IM distortion at normal output, resulting in a figure of 0.7 per cent
at 2 volts. There is adequate gain from
any tuner with which the amplifier has
been used, and the output from. typical
LP records is within 6 -db of that from
the AM and FM tuners being used.
Measured
Fig.
5
curves obtained from
the preamplifier sec-
o
J
s
Considered from the standpoint of the
number of controls in the amplifier, this
unit seems to have overstepped the
boundaries of the current trend toward
simplification. However, viewed from the
front panel, there are only four knobsapparently-and these are arranged in a
convenient fashion. There is sufficient
flexibility for the most critical listener,
yet for the other members of the user's
family-those who would normally be
confused by eight controls-the preamplifier switch may simply be left in the
position, and the tone,
500LP and
presence, and filter controls can be left
in the "flat" position. Either of the level controlling knobs may be used to set volume. The choice of knobs and switch
position arrangement on the preamplifier
control is such that the 500LP and the
12 position are coincident, and could
easily be arranged to be "straight up" in
(Continued on page 55)
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FREQUENCY IN CYCLES PER SECOND
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
25
Adventures With
MILTON
S.
Reflex
a Bass
SNITZER'
This clear, straightforward story outlines the only satisfactory
a useful bass -reflex enclosure.
way to design, build, and adjust
the writer's
audio setup has been improving in
all directions except perhaps the
most important-that of the loudspeaker
and its enclosure. It is true that about a
year and a half ago I did obtain a high quality 10-inch loudspeaker, but this
loudspeaker went right into my "temporary" speaker enclosure. This enclosure which had been temporary for
the previous 9 or 10 years, consisted of
a rather nondescript bass -reflex enclosure which had been built into the lower
section of an old corner bookcase. Its
outstanding characteristics were a
muddy bass and plenty of hangover. The
volume, as nearly as I could figure it
because of the irregular shape, was too
small for the speaker, being less than 3
cubic feet. The port, all of 28 square
inches, was less than one -half the area
of the speaker cone so that it produced
practically no low- frequency radiation.
As a matter of fact, there was no discernable difference in sound quality with
the port closed up. I think now that the
port was put into the enclosure for appearance's sake only. Later, an impedance curve taken with the speaker in
this enclosure showed a pronounced peak
at the resonant frequency of the speaker,
at which frequency the top and rear
panels of the enclosure buzzed wildly,
and there were several small peaks between 90 and 130 cps as well. Finally, I
FOR A GOOD MANY YEARS,
* Managing Editor, John F. Rider Publisher, Inc., 480 Canal St., New York, N. Y.
resolved to replace my temporary enclosure.
Limits Set
Sometimes the design of a bass -reflex
enclosure can be very difficult in that the
designer doesn't know quite where to
start because of all the variables. In this
case, however, certain definite limitations existed at the start. The enclosure
was also going to serve as a table for a
TV receiver ; therefore, it had to have a
top surface that could accommodate the
set comfortably and a height that would
not raise the TV receiver above a comfortable viewing level. A 2 by 2 -foot top
surface would allow enough overhang
for the TV set and a 2 -foot height would
put it at a comfortable viewing level. So
2 feet was established as the basic dimension. It was also decided to put casters
on the enclosure so that could be moved
easily in case the rear of the TV set had
to be gotten into. The casters could
easily be hidden inside a 2 -inch recessed
toe base. The result appears in Fig. 1.
The next consideration was the proper
size of port to be used. This is easily
determined from the basic formula for a
Helmholtz resonator or from design
charts based on this formula.' In order
to use the formula or the charts, it is
first necessary to know the enclosure
volume and the resonant frequency of
the unmounted speaker. With a 2 -foot
cube constructed of fl -inch stock and
with the front recessed by
inch (to
allow for grill cloth mounting), the inside dimensions are 22 x 22/ x 22/
inches. This produces an inside volume
of just under
cubic feet. Deducting
the volume to be occupied by the speaker
itself, a rear panel brace, a horizontal
partition (to be discussed later), and
the volume to be occupied by the padding
when it is tightly compressed, yields a
net internal volume of 6.2 cubic feet.
Next, it is necessary to know the
resonant frequency of the 10 -inch
speaker to be used. This was measured
with an accurately calibrated audio
oscillator, an a -c volt meter (set to its
2.5 -volt range), and a resistor. The resistor used was a 90 -ohm, 10 -watt, non inductive unit which happened to be
available. The resistance and power
rating are not critical. With the output
of the oscillator connected through the
resistor to the unmounted loudspeaker,
and with the meter connected across the
/
6/
Fig.
26
1.
The enclosure during experimentation.
' AUDIO
ENGINEERING, Dec., 1950, p. 22,
and July, 1951, p. 14.
70
FREQUENCY
Fig.
IN
100
CYCLES
200
PER
700
SECOND
2. Impedance curve of the unmounted
speaker shows its 58 -cps resonance.
speaker voice coil, it is possible to measure the required resonant frequency.
With this set -up, as the oscillator frequency is varied, the voltage across the
speaker changes in direct proportion to
its impedance. Hence, at the frequency at
which the impedance rises to maximum
(this is at cone resonance), a voltage
peak also occurs. The results of this
procedure are shown in Fig. 2 where the
actual voltage across the speaker is
plotted for frequencies from 30 to 300
cps. Note that the unmounted speaker
resonates at about 58 cps and that the
amplitude of the resonant peak is over
five times the amplitude at 30 cps.
Now that we know that the volume of
the enclosure is 6.2 cubic feet and that
the resonant frequency required is 58
cps, reference to the design formula or
charts shows that the port area should
be close to 60 square inches. This area
is practically the same as the cone area
of the speaker ; hence, it appeared to be
a good choice. The port was actually
made 16 x
inches, or 72 square
inches, to allow for tuning.
Another problem had to be considered
before actually starting construction;
this had to do with the cubical shape of
the enclosure. Since experimenters in
the field have found that resonant frequency of a cubical enclosure of certain
volume and port area is somewhat higher
than that of a rectangular enclosure with
the same volume and port area, it was
decided to compensate in advance for this
effect. This took the form of a horizontal
partition, mounted midway between the
bottom of the speaker and the top of the
port as shown in Fig. 3. This partition
extends across the entire width of the
enclosure and back a distance of 15
inches. Such a partition has the effect
of reducing the resonant frequency of
the enclosure.
(Continued on page 49)
4/
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
70
JANUARY, 1954
Handbook of
Sound Reproduction
EDGAR M. VILLCHUR
The Power Supply, Hum and Noise. Chapter 15, Part II.
Hum Pick -up from Alternating Fields
POWER
i
into the output stage
of an amplifier by pick -up from a.c.
fields requires efficient coupling to the
source, such as that provided by close
proximity of the input and a power
transformer. In low -level stages the
coupling need only be slight to cause
trouble. A bad case of hum induction,
for example, can result from locating a
record changer in such a position that
the magnetic cartridge is allowed to
swing into the field of a nearby power
supply.
High- impedance circuits are especially
susceptible to hum pick -up. The impedance between ground and the "hot" lead
receiving the hum voltage forms the
lower arm of a voltage divider, as illustrated in Fig. 15-7, and the value of
upper arm determines how much of the
hum will be introduced. When there is
a likelihood of hum and noise pick -up
in long high -impedance cables, therefore,
it is advantageous to use an impedance
stepdown device such as a transformer
or cathode follower at the beginning of
the cable, and to match the line to the
input circuit at the other end of the
cable, if necessary.
Hum is picked up from both electromagnetic and electrostatic fields -from
the former by inductive coupling and
from the latter by capacitive coupling.
There are two basic methods of avoiding
such pick-up; careful placement of parts
and leads, and shielding. The specific
precautions for decreasing pick -up by
parts, leads, or by the tube itself include:
I. Careful placement, relative to a.c.
fields, of conductors carrying low -level
signals. Power -supply components and
HUM INTRODUCED
* Contributing
Editor,
AUDIO
ENGI-
NEERING.
CAPACITIVE COUPLING
TO SIGNAL CHANNEL
SOURDE
OF
NUM
NOT
LEAD
4
o
-7.
Voltage divider formed by coupling
path between the grid and hum source as
upper arm, and grid -to- ground impedance us
lower arm. The lower the relative value of R,
the less the hum.
Fig. 15
AUDIO ENGINEERING
os.
RANSFORMER
WWWIAWIWA
CRASSIS GROUND
// I:E= ////////
.
15-8.
Hum pick -up from the line due to
grid -to -earth capacitance. Cr = capacitance between transformer primary and case, Ccu =
capacitance between chassis and earth, Caa =
capacitance between grid and earth. For relief,
CCE must be shorted out by earthing the chassis,
or the grid must be shielded from earth.
Fig.
low -level stages must be kept far apart,
if possible on separate chassis.
2. The use of shielded power components.
3. The use of shielded audio trans-
formers.
4. Mounting inductive components in
a particular physical position, which
makes for an angle between the signal
carrying conductor and the hum field
providing minimum coupling.
5. Use of metal tubes and grid -cap
shields. (It should be noted that aluminum shields placed over glass tubes will
deflect electrostatic fields only. )
6. The use of tubes with top grid connections, to remove the grid socket pin
from an adjacent heater pin or other
danger point.
7. Twisting a.c.-carrying pairs for
field cancellation.
8. Shielding of critical leads. (Again
it must be noted that the braid of
shielded wire is non -magnetic, and that
such shielding will only be effective
against capacitive pick -up.)
9. Connecting the chassis to earth
(actual ground). This is for the purpose
of eliminating capacitive hum pick -up
from the a.c. power line through the
somewhat obscure path shown in Fig.
15-8. An amplifier grid is coupled to
the earthed side of the line through the
grid's capacitance to earth Cos, and the
amplifier ground is coupled to the other
side of the line through the chassis -toline capacitance Cr in the power transformer. A voltage divider is formed by
the grid resistor and the grid -to -earth
impedance Cc,. A good cold water or
waste pipe ground connected to the
chassis shorts out Ces and anchors the
JANUARY, '1954
www.americanradiohistory.com
AmericanRadioHistory.Com
chassis at earth potential. It is necessary
to test for the best power plug polarity
because of the unbalanced grounding of
one side of the power line. An indication
of hum due to earth- capacitance effects
is the tendency of the hum amplitude to
change when one's hand is brought into
contact with the chassis.
A useful procedure for determining
whether hum is being coupled between
two points is to introduce a grounded
sheet of iron as a test shield between the
point of entry and suspected malefactor.
For capacitive coupling a non -ferrous
shield will work. If the result of such a
test is doubtful the unit in question can
be temporarily removed physically, with
extension leads providing the electrical
connections.
Hum from Tube Heaters
All of the elements of a vacuum tube
are immersed in the field of the heater.
Both electrostatic and electromagnetic
coupling takes place, and the electron
stream itself is directly influenced by the
heater field. In addition, there are two
high -resistance paths of direct connection between the tube elements and
heater. Leakage in the insulating mounting supports of the tube or in the tube
socket material provides one, and
thermionic emission from the heater to
the cathode provides the other.
There is considerable variation among
different tube types and between different tubes of the same type as to their
susceptibility to heater hum. Certain
tubes have been designed especially for
use in low -level circuits where hum and
noise must be kept to a minimum. AntiTABLE 15-1
LOW -NOISE TUBES
Tub* Type
12AY7
RCA 5879
Characteristics
Dual triode is (each section)
40. Heater center -tapped.
Pentode. In triode connection, is= 21. Average hum
value as triode under opti=
mum conditions, referred to
grid, listed as less than 4 µv.
Two interwound heater coils
have
opposing
magnetic
fields.
Pentode l low -noise 6J7)
RCA 1620
W.E. 347 -A Glass triode, top cap, p,= 16
Genelex Z729 Pentode (British). Mfr. lists
(provisional maximum hum voltage, re-
designation)
ferred to grid of 1.5 µv at
voltage gain of 180.
27
RESISTOR
CORRECT
OR
D
TO PROVIDE
C
CHOKE
OF
RESISTANCE
6V. ACROSS
HEATERS
C1
(A)
(s)
-9. A -Low
voltage d.c. heater supply.
B-Low current d.c. heater supply. R provides
the correct voltage drop for the tube section
and is preferably of the negative- temperaturecoefficient type to protect the heaters from
initial current surges.
Fig. 15
hum design precautions include the use
of structures which provide minimum
capacitance between the heater and the
other tube elements,. the use of double wound or center-tapped heaters with
opposing magnetic fields for each half,
and special care in the manufacture and
processing of heater insulation material.
A list of low -noise voltage amplifier
tubes appears in Table 15-1.
There are several ways of reducing or
eliminating hum due to heaters. The
most effective method, of course, is to
use d.c. or an a.c. of supersonic frequency' as the "A" supply. Two types
of d.c. supply are illustrated in A and B
of Fig. 15-9. A third method of securing d.c. appears in Fig. 15-10. The
heaters of the most critical stages are
connected in series with the cathodes of
the output stage, forming part of the
bias resistance, and a.c. signal variations
are kept out of the heater circuit by a
high value of cathode bypass capacitor.
1 R.
W. Smith, "Heater supplies for
amplifier hum reduction," Aunro ExcENeERING, August, 1948, p. 26.
Fig. 15-10. Method for providing the heaters
of low-level stages with d.c. R, must be of such
value as to keep total bias voltage at correct
value; R, keeps heater current at 150 ma.
28
This circuit involves no extra parts and
should be used whenever applicable.
Construction of a fairly elaborate d.c.
supply ought not to be necessary except
where unusually low levels of signal are
to be amplified or where an especially
low hum level is required.
The hum resulting from a.c. heater
operation may be reduced considerably
by the circuits appearing in A and B of
Fig. 15-11. When the adjustable tap
of the potentiometer bridging the heater
circuit is grounded, the voltage on one
side of the heater, relative to ground, is
always opposite in phase to the voltage
on the other side of the heater, and cancellation occurs between the opposing
electrostatic fields. The application of
positive d.c. voltage to the heater circuit, as illustrated in B of Fig. 15-11,
makes the heater positive with respect
to the cathode and prevents emission
from heater to cathode, but keeps the
potentiometer center -tap at a.c. ground
potential.
Heater -to- cathode coupling is most
troublesome when the cathode is not at
or close to a.c. ground potential -when
the cathode resistor is unbypassed, and
especially when the unbypassed resistor
is of high value. The use of cathode load
resistors or of unbypassed cathode bias
resistors in the design of low -level
stages, therefore, must be accompanied
by care with regard to hum.
It is quite easy to determine whether
or not the heater of a stage is a source
of significant hum. The heater supply is
disconnected from the stage, a six -volt
battery is substituted temporarily, and
the new hum output is compared to the
old by ear or oscilloscope. Determination
of whether the heater is acting as a
source of hum can often be made even
without the battery, by noting whether
the hum disappears instantaneously when
heater voltage is removed, or merely
fades gradually with cooling of an indirectly heated cathode. If the heater
has been at fault the hum will cease immediately upon removal of the voltage.
Chassis Currents as a Source of Hum
(A)
10-15 V.D.0
200 - 300V.
O.
FILTERED
1111111:11
25K1
25
C1
V
Ie)
A-
Fig. 15-11.
Effective circuit for reducing
hum resulting from a.c.- operated heaters.
Elaboration of method shown in A, including
positive bias on heater to prevent heater-to-
B-
cathode emission.
In some cases, particularly in low gain amplifiers, the circuit designs of
Fig. 15-11 may be simplified and sufficient hum reduction still achieved. The
potentiometer may be replaced by a
center -tapped resistor, or a center -tapped transformer heater winding may be
used, and occasionally simply grounding
one side of the heater line is adequate.
The heater circuit must never be left
floating with respect to ground, however,
because the heater winding, normally
part of the main power transformer, is
coupled capacitively to the high-voltage
winding. When the heater winding is
grounded the coupling path to the h.v.
winding acts as the high -impedance
upper arm of a voltage divider in a
closed circuit, with the relative impedance of the lower arm, formed by the
heaters themselves, insignificantly small.
Other measures helpful in combatting
heater hum are bypassing one or both
ends of the heater to ground, reducing
the heater voltage to 10 or 15 per oent
below its rated value, and using tube
sockets of low-leakage material.
A metallic chassis or other ground
return has minute a.c. voltage drops appearing across parts of it. These voltages
are created by the considerable flow of
alternating current in heater or highvoltage return circuits. Voltage drops
may also be created by current induced
in a section of a chassis or ground return
wire (effectively forming a 1 -turn coil
called a "ground loop ") by the alternating field of some inductive component.
Figure 15-12 illustrates how voltage
created by chassis current may inadvertently be introduced into the signal channel by wiring which places the difference in chassis potential between the
ground returns of the grid and cathode
resistors. The return path from the
heaters to the transformer winding
passes between points A and B of the
chassis. It might seem that the resistance
between these points must be so small
as to be of no significance. But a simple
application of Ohm's law will reveal the
fact that with the heavy heater current
flowing, let us say 3 amperes, a resistance of only .00033 ohm will create an
IR drop of 1 millivolt. This voltage is
1 /10th that of the
signal output of a
G.E. variable -reluctance cartridge, or
only 20 db down from the cartridge
signal level.
The relief required in the circuit of
Fig. 15-12, that of connecting the cathode and grid resistor ground returns at
,4R
RESISTANCEY
Fig. 15-12. Introduction of hum voltage between grid and cathode due to flow of a.c.
return current through chassis.
AUDIO ENGINEERING
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OF
CHASSIS
JANUARY, 1954
the same point, is obvious. In order to
avoid hum from chassis currents entirely,
the physical sequence of ground -return
connections is often planned so that the
situation illustrated cannot occur. An
effective method is to ground all returns
to a tinned copper bus bar, beginning
with the heater and filter capacitor returns and the center tap of the high voltage winding, continuing with returns
of the output stage and each voltage
amplifier in order, and ending with the
lowest-level stage on the chassis. The
bus bar is connected to the chassis at one
point only, the signal input jack of the
amplifier.
Other devices for avoiding chassis
current hum are:
1. Connection of ground returns in
the same physical sequence as described
above, but to the chassis itself.
2. Grounding grid and cathode returns
from the same stage at the same point,
with special care to make a low- resistance joint.
3. Use of non -magnetic chassis to
avoid concentration of electromagnetic
fields. (This involves a sacrifice of the
electromagnetic shielding effect of the
chassis.)
4. Use of low -resistance copper or
copper- plated chassis.
A.c. currents may also flow in the
ground cable between interconnected
chassis or between the record player and
chassis. The chassis ground of one unit
may be at a different potential from that
of the other chassis relative to the a.c.
supply, due to line bypass capacitors, reverse plug polarity, different heater ground circuits, and so on. This potential is difference is sometimes measurable
when each unit is plugged in but not
connected to the other. Efforts must be
directed at eliminating the source of the
voltage difference and at arranging circuit layout and cable ground points in
such a way that the undesired current
flow cannot introduce hum into the amplifying channel. The IR drop of the
inter-chassis current may also be decreased by connecting the two chassis
together with heavy copper braid, making contact over a large area of metal.
Hum caused by chassis currents is the
most difficult to trace ; critical analysis
of the circuit and of the physical layout
is required. Suspected sections of the
circuit may be checked by experimental
changing of the physical locations of
ground- return connections. Another useful test is to short out temporarily two
chassis points between which hum voltage is presumed to exist by heavy pressure of a screw driver or by the connection of copper braid.
Modulation Hum
Hum may be picked up in r.f. circuits,
but not in the ordinary way. The inter stage networks or transformers coupling
r.f. stages cannot possibly pass hum frequencies directly; hum can only get
through such networks as the sideband
of a radio- frequency signal. In order for
line -frequency components to appear in
the signal, therefore, they must not only
be introduced into the signal channel but
they must modulate an r.f. carrier. When
AUDIO ENGINEERING
the hum-modulated carrier has passed an
r.f. coupling device the existence of hum
is attested to only by the presence of two
new radio frequencies equal to the carrier plus the hum frequency and the
carrier minus the hum frequency. It is
for this reason that hum whose source
has been in r.f. stages is called modulation hum and only appears when an r.f.
signal is also present.
We have already seen that two mixed
signals will be subject to intermodulation
and produce sum and difference frequencies only when they are passed through
a nonlinear device. Hum introduced into
the converter stage of a superheterodyne receiver (which is purposely made
nonlinear to mix the local -oscillator and
incoming-signal frequencies) will therefore be most readily incorporated into
the r.f.. signal as an additional set of
sidebands. It is commonly picked up by
heater-to- cathode leakage, and the stage
must be treated in the same way as a
low -level audio amplifier.
EMTN
i+ANTENNA
COIL
1
B- Or RADIO RECEIVER
NON
-LKM
WIRING
-
ELEMENTS IN
HOUSE
OXIDIZED JOINTS, ETC
Fig. 15 -13. Introduction of modulation hum
in antenna circuit.
Modulation hum is also introduced in
the antenna circuit. Figure 15-13 shows
how the a.c. line is in series with the r.f.
input terminals of an a.c. -d.c: type radio
receiver, for one plug polarity. The 60cps voltage is completely blocked by the
r.f. antenna transformer, but oxidized
joints and other nonlinear elements in
the power line create 60 -cps modulation
of the r.f. The common preventive measure, other than testing of plug polarity,
is to install a bypass capacitor across the
line, establishing a short path for the r.f.
signal across the a.c. power generator.
The type of circuit illustrated in Fig.
15-13 ties
directly to one side of
the line. A similar analysis applies to
receivers with transformer power supplies, where the path from the line to
is completed by the capacitance between
the power transformer primary and
chassis. Connection of an external
ground to such a receiver shorts out the
modulating voltage.
B
B
against tenacious elements of hum which
are due to conditions that cannot readily
be corrected.
Negative feedback reduces all hum
generated within the feedback loop (although if the feedback voltage is secured
from an unbypassed cathode resistor
there will be more hum generated). The
signal-to -hum ratio is reduced in the
same proportion as harmonic distortion,
provided the signal amplitude is boosted
back to its former value. Gain within
the feedback loop is, of course, sacrificed.
The outputs of push -pull tubes are
combined out of phase, and much
of the hum originating in the stage
will be cancelled. The degree of cancellation will depend upon how similar the hum voltage generated in each
tube is to that of the other, and how well
balanced the tubes are. It may be necessary, in the case of filamentary- cathode
tubes such as the 6B4, to try several corn binations of individual tubes before a
quiet pair is found. Devices to improve
the balance of push -pull tubes are hum
reducing devices ; in the absence of
better facilities minimum hum output,
with the phase splitter tube removed
from its socket, may be used as a rough
indication of balance. Circuits which are
designed to balance the input signals to
each push -pull grid have no effect on
hum except indirectly, in that unbalanced input signals will influence the
setting of any potentiometer controlling
the balance of the tubes themselves.
Bass -boost networks must be inserted
in as low-level a stage as possible so as
not to accentuate hum introduced before
them. This is the reason preamplifiers
for magnetic pickups do not provide the
required bass equalization in their output circuits.
Occasionally it is found that reducing
hum from a particular source raises the
total hum level. This occurs because the
eliminated hum had been out of phase
with, and was partially cancelling, hum
from other sources. Such cancellation
may be used in a controlled manner. The
"hum-bucking" coil, linked inductively
to the field coil of electrodynamic
speakers and placed in series with the
speaker voice coil is an example of purposeful cancellation. Circuits allowing
more sensitive balance bf the injected
out -of -phase voltage have been designed.
(Continued on page 39)
General Methods of Hum Reduction
The best type of hum reduction is the
discovery and elimination of the causes.
There are situations, however, where
reduction below a given point is not
practical, or where one is already committed to somewhat undesirable conditions. In addition to the design principles
discussed above there are general techniques of hum reduction that work on
hum due to any source. These techniques
should not be applied as a substitute for
good workmanship, but alongside it.
They may also be used as a weapon
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
Fig. 15 -14.
Circuit for cancelling plate -supply
ripple and
regeneration
due
to
inadequate
filtering and decoupling. The value of C, in
relation to the cathode -to- ground impedance
determines the value of the cancelling voltage.
(After Wen -Yuan Pan)
29
Ere
Edward Tatnall Canby
Craft and Commercial
Since writing in the November issue
about the new commercial mass -produced
"hi -fi" phonographs and their craft -style
competition (that was written back in midSeptember) I've had a good chance to
study vast reams of advertising, attend
press parties -and read correspondence.
Nobody, but nobody, has written in as
interestingly on the subject as Mr. Leon
Ferguson, who operates a record shop in
Memphis.
Mr. F. has just added a hi -fi department to his store, and refutes me clearly
and explicitly on one point: he sells both
commercial phonographs and net -price
craft -style components, all in the same
show room, and he invites listening via
full -page newspaper ads. On the one hand,
he offers several brands of "factory assembled high fidelity phonographs ", as he
puts it, and on the other, the component
parts to "build your own high fidelity home
music system"-both types illustrated in
parallel columns in the same ad. Small company components, at regular net.
This is an interesting experiment, still
only a few weeks old when I got the information. In that short time, one of the
two types had already sold 9 to 1, roughly,
over the other
leave you to guess which,
since the information was confidential!
But the important thing is that here, at
last, a wide -awake record store man has
realized that not only do records and machines naturally go together, but that
records and good equipment, up -to -date
equipment, are decidedly of equal interest,
to the record collector. Why shouldn't any
small record shop do the same? A lot will
be trying soon-though few, I fear, will
be enterprising enough to offer both types
of playing equipment as does Mr. Ferguson, the craft and the commercial. A trend?
I certainly hope so.
-I
Parallel
Which brings up a point I've had in mind
ever since one large manufacturer showed
both his "commercial" and his "component"
lines in one press demonstration. I think
it's clear to most of us that net-price hi -fi
30
Parallel and Stepwise
of the craft type gives more audio for the
money than the ready -made commercial
hi -fi (so named) at prevailing list prices.
It does, at least, on levels above the very
lowest where, as suggested in November,
mass production has a big edge.
Convenience -big selling point of the
commercial machine -is, however, another
and very legitimate attribute. People do buy
commercial machines by the millions just
because they are, in fact easy to buy and
install, simple to operate, good looking
but most of all, easy to buy and simple to
operate. That's a true balancing factor for
lots of folks.
Mr. Ferguson has neatly laid out his
"line" of thought in these very terms. His
ads offer EITHER the simplicity and
convenience of the new "factory-assembled"
phonograph OR the greater sound value
of the component -type system. Note well
that the economies of the latter are stressed
-"it saves you plenty !" -but that its less
great convenience is admitted. (Not in so
many words, for etiquette in ads allows
for nothing derogatory except in glittering
dangling comparatives -"the better soap"
or "more chocolat -y than ever ". In ad
language, he says "it takes little technical
ability to assemble these parts
all you
do is plug together and install anywhere in
your own home. ") A well struck balance,
putting the situation into simple alternatives that can be directly demonstrated via
the equipment he offers.
This approach is what I can best call
the Parallel Comparison, offering equal,
but different alternative values- emphasizing the economics of craft -type hi -fi
components.
-
...
Not
So
Simple
Of course it really isn't quite that simple.
Mr. Ferguson has rightly tailored the situation to fit his own judiciously limited
offerings. A few basic items of each type
for sale, an uncluttered, uncomplicated shop
and a simple, easily grasped sales policy.
Good. Yet if we look beyond his shop to
the larger scene, we know that the Parallel Comparison isn't that way any more.
What about the readily -assembled machines, put together from craft -type components and sold at net -price economy?
What of the semi-component models, with
perhaps anonymous amplifiers and speakers
but still essentially component-type in construction, which are now hitting the big
department stores? And what of the sort
of thorough installation service that even
Mr. Ferguson is likely to have to provide
-giving his customers, on demand, what
amounts to a ready -to -play machine cornpletely installed? Though most newcomers
to hi -fi still think you must do your own
soldering, and are thereby enormously disturbed, we know ourselves that if any
progress has been made in component distribution, it has been, these last years, in
the greater and greater degree of pre assembly made available
meet this very
need, more and more adequately. An old
story in these columns.
Thus, it's not necessarily true that
EITHER we buy convenience, one -piece
and mass produced, OR we buy good audio
-and do our own laborious putting -together. It's only partly true.
Not enough people know that cabinets
now come with holes bored in them and
many a dealer will put a speaker or a
changer right into them for you, and wire
the whole up as well. Not enough people
know that most component equipment comes
with the plugs already on and the dealer
will plug in the plugs for you, if you don't
dare. Not nearly enough people know how
convenient a flexible home system can be,
and how good looking, for a reasonable
price and no effort except kibitzing. You
don't really have to move a finger if you
don't want to. Right, dealers? (Groans
from the dealers, who would dearly love
to get out of the installation part -but
they can't.)
-to
Stepwise
So much for the argument that EITHER
we buy commercial, for convenience and
laziness and what- have -you, OR we buy
craft, for audio value, and inconvenience,
combined. Now, look closely and hard at
(Continued on page 52)
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EDWARD TATNALL CANBY
costing $25.50. I never could afford more than
a few excerpts from it. This modern version,
ever so much better and clearer and more authentic, weighs exactly 1 pound 10 ounces and
costs about $8. All hail the LP !
OLD MAN BACH'
tBach: Mass in
B Minor. Chorus, Orch.
Radio Berlin, Lehmann. Soloists.
Urania UR -RS 2 -1 (2)
This two-pocket album, in Urania's lower
priced "Request" series without notes or
booklet, contains, as I found to my aurpriae,
the best B Minor Mass I have yet to hear on
records -and that includes some of the more
celebrated versions? This one. first, is straightforward, without fancy conductor's showings
of temperament the tempi are reasonable and
good, instead of exaggeratedly slow or fast,
the dynamics are as common sense would
dictate, the diction of the chorus is good, the
words spoken Intelligibly and sensibly. What
a relief-after so many freakish versions of
this sort of music!
More than this, the performance, while not
sensational in any dramatic way, is thoroughly
musical in every aspect, the soloists
miraele-are all good and well balanced among
themselves and every one of them sings Bach
naturally and like Bach, not like Verdi or
Wagner! The chorus is a bit bouncy at times,
but seldom. and the prevailing feeling is one
of thoughtfulness and concern with the meaning of music and text. Best of all, the physical
set -up of forces is wholly in the new manner
-that of Bach himself more or less -with a
reasonably small chorus, a small orchestra of
the right instruments rightly balanced, a
discreet harpsichord (not exaggerated) ; the
solo arias are done with a perfect understanding that they are essentially chamber music
for vocal solo, with often only a single instrumental solo as assisting obbligato and a single
cello and the discreet harpsichord as accompaniment. The old grandiose style of doing
Bach (which led merely to general fuzziness
on discs) "orchestrated" these lovely in -between numbers to symphony orchestra size and
so spoiled the contrast between them and the
big chorus-orchestra numbers -not to mention the more delicate balance between solo
Instrument and voice.
What else? That's not the end of the virtues here. The recording, doubtless another
radio tape, Is good, adequately wide in tonal
range and without unpleasant distortion, the
mike arrangement gives the chorus billing, in
the foreground and very much alive with the
orchestra beautifully balanced against it. The
solo singers are neither too !lose nor too loud
common complaint in many a new Bach
record. The somewhat studio-like acoustics are
not dead enough to kill the music; rather, the
good details are brought out. And, with a few
watts extra power, the loud parts can sound
just as big and impressive as if there were
400 -odd performers. Congrats to the Request
Series.
Mind you, in 1936 (and for many a year
after) there was only one huge version of the
B Minor Mass on records, running to a fabulous 34 sides, weighing perhaps 50 pounds,
.
-a
-a
*780 Greenwich St., New York 14, N. Y.
'Vox's PL -6074 (4) lists the same per-
formers, may be from same original.
32
erBach: St. Matthew Passion. ( ) Anon.
Chorus and Orch., Scherchen. Soloists.
Westminster WAL 401 (4)
(2) Amsterdam Toonkunstchoir,
1
Concertgebouw
Orchestra,
Mengelberg.
Soloists. (1939)
Columbia SL -179 (3)
Here is another of the super-Bach works in
two versions -the Westminster is unabridged.
accounting for the 4 discs, while the Mengelberg version was recorded at a performance
in 1939.
These big works -the St. Matthew, and St.
John Passions, the B Minor Mass-from
Mendelssohn's time in the 1830's on for a
century were performed in huge and inspiring
mass productions, using orchestras of super symphonic size and choral groups in the
hundreds. In late years we have finally gone
back to an approximation of the original Bach
intentions, with a very
h smaller group,
the original instrumentation (as noted above)
-and a net gain in clarity and sense that
more than makes up for any loss of grandeur.
The Mengelberg version comes from an annual tradition that went back for decades
and decades of that ancient conductor's incredibly long stay with the great Dutch orchestra ; it represents, in effect, a performance
of about 1895, in the grand manner exaggerated. Romantic, temperamental in ways
that are almost unbelievable today. Great,
gusty crescendos, ominously slow and majestic
tempi, weird swoopings and gaspings in the
chorales and the solos, all were part of the
old Mengelberg style, which might be compared to a dramatic reading by Sarah Bernhardt, or Shakespeare by Sothern and Marlowe Crazy, eccentric, of another time -and
yet interesting too, for old Mengelberg in his
eighties was still a great musician. The grand
dramatic moments of the story of the passion
of Christ are musically capitalized to the full
and with effect, if in bizarre ways.
The Scherchen version, done by a middle -old
conductor who is a mere youth beside Mengelberg, is an odd contrast. Physically it is far
more modern, more authentic and better recorded. It uses the now standard smaller
!
group, the proper instruments, achieves the
right chamber music balance In the solo parts.
The solo voices are good. notably the superb
bass Jesus of Heinz Rehfuss. (The tenor
evangelist, Hugues Cuenod, has a voice that
is too tight and nervous in spite of floe musicianship.) The recorded sound is hi -fi and
ultra- clear. (Mengelberg's solos are, to put it
mildly, atrocious, the recitative a travesty of
the true style.) All of which would seem to
give Scherchen and Westminster the palm with
no further ado -yet. .
There's a dogmatic, hard quality in Scher chen's Bach that is not good. His interpretations of many passages are as inexplicablesoft when loud would seem called for, rough
when mildness is seemingly implied, and so
on-as
Mengelberg's are eccentric, and as
Fritz Lehmann's in the Mass, above, are
eminently reasonable. This St. Matthew does
not rise to eloquent heights of inspiration
and Mengelberg's does, style or no style.
-
More specifically, as an old choral singer
and long -time lover of choral music I feel
strongly that Scherchen ignores the text, both
the over -all meaning and the specific textual
expression of the musical phrases ; he plays
the music like a symphony, and he forces the
chorus -and the soloists -to be symphonic
instruments, whose words are merely mumbled
conveniences towards tone production. His
crescendi and his climaxes are purely of an
instrumental kind, not tied to the flow of the
living German ; his chorale hymn melodies are
as though harmonizations for vocal background, wordless. This is extremely disturbing
to anyone who has felt the power of Bach to
express words, to cry out in living word phrases. It is a hurt that no choral singer
can forgive.
Scherchen treats his soloists to the same
they are hauled unrelentingly with the most
rigidly mathematical time-beating straight
through their ornamental phrases, as though
they were of the most secondary importance
and their words quite meaningless, which is
anything but the case.
Therefore, I do not like this St. Matthew,
and in spite of many lovely moments (that
superb Jesus, again, is worth the whole album) if it came to a choice between the two,
I would turn to Mengelberg. His Is the greater,
if crazier, performance.
-
Bach: The 48 Preludes and Fugues of the
"Well- Tempered Clavier."
t (1 ) Rosalyn Tureck, piano.
Vol. 1: Dacca DX -127 131
Vol. 2: Decca DX 128 (3 )
°12) Isolde Ahlgrimm, pedal
harpsichord. Vol. 1: Columbia SL -191 (31
(vol. 2 to come)
°Bach: The Six French Suites. Isolde Ahlgrimm, pedal harpsichord.
Columbia ML 4746.
-
Never rains but it pours. Here again
think back to the 30 -odd years during which
record collectors waited and waited for a
complete version of the monumental "48"
preludes and fugues that would be generally
available! These all came in one mail delivery.
The "48," two sets of preludes and fugues,
two pairs for each key on the piano octave
keyboard, did a lot more than prove that
tempered pitch would work. For n century or
so they were almost the only known works
of Bach and they have influenced every great
composer and a couple of billion mere listeners
and would -be keyboard artists during some two
centuries. They are not meant for piano -there
was no piano worth hearing at the time. It's
a question whether some weren't better suited
for the clavichord, which uses delicate struck
strings, but many most certainly were played
on the big harpsichord, with its two keyboards,
Its numerous ranks of tone color, its massed
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JANUARY, 1954
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doubling -up of octaves for big climaxes. (The
harpsichord plucks the strings mechanically.)
Bach on the piano is always a compromise,
adding more expression in the loud- and-soft
aspects, adding the nice blurrings of the
sustaining pedal which the harpsichord does
not have, losing heavily in clarity because of
its relative lack of sharp overtone color. A
thick mass on the piano is mud, where on the
harpsichord Its details stand out clearly. Yet
thousands of pianists have made good adaptations for the piano's own expression, and
Rosalyn Tureck, above, is one of the best
available choices for a good job of Bach on
this relatively monotonous instrument. Monotone, that is, when used for Bach.
Tureck's Bach "48" is beautifully done on
the whole, with a due sense of the original
intention, a good feeling for the best way to
bring the music out in this different medium,
and a minimum of "pianism"-the playing of
Bach as though it were half -baked Rachman'.
not!. She gets a finer clarity in the complicated parts than any pianist I've heard recently except Gieseking and her phrasing and
rhythm are impeccable. Nevertheless, enough
is enough. These works, after an hour or so,
become more and more obviously non-planistic,
the piano itself has a more and more monotonous sound. Occasionally, Tureck tries too
hard for variety by using staccato harpsichord
imitations and the like. Taken individually,
these are top performances- and most people
will want to hear them that way, especially
piano students, who can learn much.
But piano students may learn even more
from the Ahlgrimm harpsichord records now
launched by Columbia to cover the entire
Bach keyboard literature aside from the
organ music. Here is a good match to the great
Landowska in her RCA Victor recordings!
Ahlgrimm is far less of a virtuoso dramatist, more the objective and careful musician,
than the incomparable Landowska, who will
remain forever in her own special category.
This younger woman is a fine "normal" musician who plays Bach with the utmost authority and clarity and musicianship, with
complete ease and considerable technique, If
without the Landowska fervor (and eccentricity). Pianists will find almost as much
to interest them in Ahlgrimm's detail work
with fingers and rhythms and tone colors as
in the Landowska discs-and these are very
much better recorded for harpsichord sonority.
Indeed, I don't think I've heard a better
harpsichord sound.
But the special feature here, aside from top
recorded sound, is the pedal harpsichord.
This is a copy of a device that Bach is known
to have used, a keyboard machine with a
special section at floor level operated like an
organ by a pedal board for the feet -thus
allowing for the organist's triple -play technique, using both hands, plus the feet, heel
and toe. (A pedal piano is impracticable because piano tone is influenced by pressure,
which cannot be well controlled in the feet;
but the harpsichord and organ tones are
almost independent of pressure -one is a
valve mechanism, the other a "click"-type
pluck of a string.)
You might guess that on records a pedal
harpsichord would sound like any other, since
we can't see the pedals in action and we don't
know which limbs are playing what music.
But, Interestingly enough, it turns out that the
pedals make a vast difference in the musical
effect. The reason is simple, as any organist
will know.
Organ technique, with pedals, puts the bass
line of the music frequently down in the feet,
leaving the left hand with only inner parts
and no bass. Pianists, however, learn quickly
to feel that the bottom notes are always under
their left hand fingers. There is no odder
feeling for a pianist than his first try at an
organ, with the bottom of the music detached
and shifted to his feet Like eating chicken
with the toes.
Bach, you see, was an organist -that's why
he liked the pedal harpsichord. His playing
was organ -conscious, on any instrument; he
would write big, solid bass passages, for any
instrument or orchestra, or chorus, at the
drop of a pencil and, as an organ technician,
would instantly transfer these to any pedal
board that found itself beneath his feet
organ or otherwise. Pianists, lacking this
pedal- sense, sometimes do not hear the pedal
element in Bach's keyboard music, nor are
ordinary harpsichordists too aware of
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though the big 16 -foot harpsichord can mechanically double the bass notes in hefty
octaves to give a pedal effect.
On the Ahlgrimm pedal harpsichord, then,
you will hear a remarkable number of big,
sonorously detached passages that come, manifestly, from the lady's feet. And, in these
familiar Bach works played thus with an
unfamiliar technique, some surprising and
wholly legitimate effects (if we know Bach)
come out. Interesting, and listening organists
will get itching toes.
Volume Two is due soon. Meanwhile the
single LP of the six French Suites, the short
and tuneful works often heard and played,
is a supplement, or a beginning if you don't
want to tackle a whole album at once Not
as good as the "48" job.
t
*Bach: Complete Works for Solo Violin.
Rolph Schroeder, using the curved bow.
Notes and supervision by Albert Schweitzer.
Columbia SL -189 (3)
Here's an extraordinary novelty -for those
who have got far enough in Bach and /or
violin (playing or listening) to get its full
import.
The violins we use today, the best of them,
were made centuries ago in Italy; the rest
are imitations of the old ones. The instrument
itself has scarcely changed at all. The bow,
on the other hand, is a different story the
present backwards -curved "straight" bow with
its hairs tightly stretched by a screw mechanism dates from a mere century ago, well
after Bach's time.
The straight bow plays loudly and lightly,
thanks to its great tension. But, over the
curved bridge, it cannot play more than three
of the four strings and that only with a
;
heavy and loud dig. (The curved bridge keeps
the fiddler from accidentally scraping more
than one string at a time when he's playing
single tones.) In Bach's day the much older
curved bow was still used. The arch of this
bow allowed the hairs to be slackened until
they could curve over all four of the strings
to play a solid chord
strange and very
pleasant string effect. More, the player controlled tension of the hairs with his thumb
for faster single notes he tightened them up.
Not enough tension for today's loud tones,
but for that disadvantage, there were the
-a
;
other advantages.
Not since Ole Bull, the eccentric Scandinavian violin genius of the late 19th century, has a big violinist used the old bow.
Too limited, of course, for concert use -and
one might ruin one's technique for Tchai-
kowsky and Vleuxtemps and Lalo and Paganint But this man, Rolph Schroeder, became
interested many long years ago. worked to
design a modern equivalent (and improvement) to get Bach's arched bow effects,
introduced it-and lost everything in the war.
He started again afterwards, and here he is,
with the enthusiastic blessing of the great
Albert Schweitzer.
The unaccompanied sonatas and partitasincluding the great Chaconne so often played
in transcriptions for piano, orchestra, guitar
and what have you -are, even here, not
exactly easy fare for the uninitiate. A solo
violin, even with complete chords, must still
suggest, sketch, imply a lot for the inner ear.
However, if you know the works a bit and
have listened to the great fiddlers do their
level best to play "chords" that are no more
than scratchy arpeggios across the strings,
you'll really be amazed at the quiet, smooth
way in which the complete harmonies of all
four strings roll out of this violin from the
Bach-style bow. In spite of Heifetz, Szigeti,
Schneider and a host of others who play with
the modern bow-this Is the way the music
was written to be played.
How is Mr. Schroeder musically? Not
unlike Schweitzer himself ; slow, careful,
deeply thoughtful, highly musical and with
a deep understanding of these works, a German -style thoroughness that in some sections
may seem to lack "zip." But that, of course,
is merely according to our somewhat hysterical American taste. Superb violin recording In a big liveness, good for both music
and instrument and superior to the deadened
sound of the recent Ileifetz (straight bow)
recording.
!
AUDIO ENGINEERING
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1
JANUARY, 1954
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Outstanding recorded sound for the
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Noticeably good performance
tt Outstanding or especially interesting performance
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ESTRA-WAGN ER
(Wagner: Siegfr. Rhine J.; Funeral March;
Fire Music. Wurttemberg, Leitner,
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Wagner: Tannhauser, ((Faust Overtures.
Wurttemberg, Leitner; Munich Phil., F.
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'° Decca DL 4061
War-horses, except the Faust overture, unusual enough in this good performance to
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Vocal solos) close -up, loud.
Wagner: Flying Dutchman, Tannhauser Ov.,
Ride of Valkyries.... Vienna Philh. Knappertsbusch.
London LL 800
'Wagner: Lohengrin Preludes, Tannhauser
Ov., Meistersinger Prelude, Ride of V.
Detroit S., Paray.
Mercury MG-50021
The Vienna disc is full -bottomed, solidly
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Not as "stringy" as many earlier ffrr records
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the lighter parts are sheer Mercury ! Interesting and amusing, if not good Wagner.
worth a dozen of the routine sort.
SIBELIUS
"'Sibelius: Symphonies #5, #6. Stockholm
S., Ehrling.
Mercury MG 10142
It Sibelius Symphony #1. Royal Philh.,
Beecham.
Columbia ML 4653
°Sibelius: Symphony #2. London S., Collins.
London LL 822
(*Sibelius: Four Legends. (Lemminkainen
Legends./ Danish State Radio Symph.,
Jensen.
London LL 843
Here's part of the current Sibelius comeback, via LP. The Mercury Swedish series
is technically so -so, the sound rather distant
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pulls out the stops and turns on the juice to
the limit. (Probably what Sibelius had in
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.) Good recorded Bound, with the
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The London Second Symphony is superbly
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LEADER IN SOUND
HIGH RUSSIAN
"Rimsky- Korsakov: Scheherezade. Vienna
State Opera Orch., Quadri.
Westminster WL 5234
Same Radio Berlin Symph., Rucht.
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with- quickly." I'd swear Westminster has
added a few pots and pans to Rimaky's score,
Just for the fi of it. As to Urania's "Request"
series (low priced) version, it's neither tired
nor too-hasty, but a very adequate and alive
performance that will never hurt the music minded. Not as hl as Westminster's, but
plenty good on its own, with pots and pans
In reasonable balance, A faintly radio-tape
sound, the highs not entirely clean, though
hardly bad enough to bother most people.
tt,Rimsky- Korsakov: Skaska; Snow Maiden
Suite. (Snegourotchka), Philharmonia, Fistoulari.
M -G -M E3017
tt.Rimsky- Korsakov Program. Philh., Fistoulari; Susskind; London Symph., Weldon.
M -G -M E3045
The Snow Maiden is full of good humored
and nicely orchestrated marches interspersed
with bird songs and other intriguing sounds
very well played, beautifully miked the early
Skazka is a pompously colorful work about a
legendary tomcat. Both enjoy really superb
recording from the acoustical standpoint, as
do the companion sections (which vary somewhat) in the Rimeky collection. The latter
includes the one-movement piano concerto
(Jacquinot) on Russian themes, and a number
of interesting odds and ends from the R!msky
catalogue, all excitingly played as well as
beautifully miked. M-G-M continues to amaze
in records like these which, one might think,
would tend towards the superficially popular
under such a label! Only some surface noise
and the extreme high pre-emphasis (with a
bit of distortion) keep these from the absolutely top category.
tDMoussorgsky: Pictures at an Exhibition.
Stravinsky: Fire Bird. Phila. Orch. Ormandy.
Columbia ML 4700
Irn (Same two works) Radio Leipsig Symph.,
Abendroth; Borsamsky. Urania UR -RS 7 -18
Contrast ! The Philadelphia recordings are
of a common Ormandy sort where war- horses
are involved- meticulous, beautifully accurate,
a bit heavy, intense, yet somehow on a high
level of utter routine. Fire Bird conies off
better than Pictures in this respect. Superb
big bass and sharp highs, in the usual big
resonance. The Urania radio tape ( "Request"
again) is much inferior as to quality, with
unimpressive highs and a narrow, distant
sound ; level is low and the Pictures break
uncomfortably two numbers from the end
thanks to non-variable grooving. Performances
are fast, nervous, probably due to (radio)
time deadlines. Not so hot, and no bargain.
ORDERING DIRECTLY FROM FACTORY
° Prokofieff:
Classical
(#1).
Glinka, Russian and Ludmilla Ov. Borodin:
Steppes of Cen. Asia. Moussorgsky: Night
on Bald Mt. Suisse Romande, Ansermet.
London LL 864
A mouth -filling pot -pourri, with some lovely
and very accurate string playing, careful,
musical performance, an unusually slow tempo
for the first movement of the Classical, which
is as sharp as pins and needles even so.
Good high -level job for this type of disc.
rdTchaikowsky: Symphony #6 ( "Pathétique "). Amsterdam Concertgebouw, Van
Epic LC 3003
Kempen.
Tchaikowsky: Romeo and Juliet; Ov.
"1812 "; Capriccio Italien. Amst. Con certg., Van Kempen.
Epic LC 3008
These Tchaikowsky performances on the
new label are good to my ear- clean, accurate,
avoiding the excess of schmaltz that too many
of our own home orchestras favor, yet keeping the spirits high (or low as the case may
be) and the interest keen. Some will prefer
the juicier type of interpretation. New labels
often run into technical trouble at first : the
Pathetique disc has a tinny unpleasant sound
in the highs that suggests an unclean upper
middle and no top; the Romeo and Juliet
disc, same outfit, is much better, with only
a trace of the same sound. Both are basically
well done as to acoustics and the Romeo, with
the other two items played with verve and
-'-en humor, rates very nearly excellent. Just
hat slight disorder of the upper regions.
(Two more Romeos are waiting -sorry, I've
_..ached
capacity!)
AUDIO ENGINEERING
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Symphony
-
JANUARY, 1954
{
1
To simplify microphone placement in
even the most difficult acoustic appli-
cations for Recording ... Broadcasting
LONDON LETTER
... P.A.- install the
l)ruan paye o)
UNIDYNES 55s, 556s
hour after dark. Practically every opera
performed during this short season is transmitted in full by the B.B.C. on at least two
occasions, so generally, your enthusiast has
the opportunity of avoiding breaks when
changing reels, by picking up the missing
portions during the second performance.
Although no figures are published, it is
generally thought that the sales of LP
records are less per head of population in
England than in the U.S.A. Perhaps the
fact that so much good music is available
daily on the air in England is the explanation.
Readers who would like these letters to
deal with any specific subject, are invited
to write me at : Richard Arbib, Multicore Solders Ltd., Hemel Hempstead,
England.
I wonder how many record enthusiasts
realize that the famous "His Master's
Voice" trademark, which appears on the
millions of R.C.A. Victor discs, was devised to publicise cylindrical records?
If you were a very privileged visitor to
the vast E.M.I. factories at Hayes, Middlesex, England, you might be fortunate
enough to be invited to lunch in the directors' dining room. On the wall you would
see the original painting of "His Master's
Voice." If you examined it carefully, you
would see quite clearly the outline of an
old fashioned phonograph under the gramo-
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The history as to how all this came
about was recently revealed by the British
H.M.V. Company.
The idea of the picture was conceived
and executed by Francis Barraud, whose
paintings were exhibited at the Royal
Academy. He was the fourth son of Henry
Barraud, the celebrated animal painter.
Towards the end of the last century, when
his brother died, his dog Nipper became
attached to Francis. They became such fast
friends that he eventually took Nipper to
his own home and there he remained
throughout his little life.
Barraud had inherited from his brother
a small phonograph of the type that employed wax cylinder records, as well as a
number of records. When he played these
records he noticed the peculiar interest
which Nipper took in the sound of the
voices (which perhaps resembled that of
his late master), that came from the
trumpet. Watching him one day, Barraud
conceived the idea of putting Nipper and the
phonograph on canvas and giving it the
title "His Master's Voice".
When the picture was finished, it showed
Nipper listening to an old- fashioned cylinder phonograph, and it occurred to the
artist that it would be an excellent trade
mark for a manufacturer of these instruments. He took it to the most prominent
cylinder phonograph manufacturing corn pany, and was sadly disappointed when
they did not seem at all impressed by the
originality and beauty of the picture. He
mentioned his failure to an artist friend,
who suggested that the picture might be
brightened up by painting a brass horn in
place of the black one which was used on
the phonographs of that period. Mr. Bar raud had never seen a brass horn, and upon
enquiry learned that one could probably be
borrowed from a small company in Maiden
Lane, off the Strand, called The Gramophone Company.
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37
On a very memorable day in September,
Barraud came into the little office of
the then infant Gramophone Company,
and asked for the loan of a brass horn.
This somewhat unusual request brought
forth explanations, which resulted in the
Manager, William Barry Owen, immediately requesting to see the painting itself.
The painting, which was then still in the
hands of the hesitating phonograph company, was eventually refused and returned
to Mr. Barraud, who at once brought it
to Mr. Owen, with a suggestion that he
could easily paint out the phonograph and
paint in a gramophone. It took only a short
time to do this and the picture then entered
into the possession of The Gramophone
Company.
After the picture had been adopted as a
trademark by the British Company, it was
eventually used by most of their Overseas
Associates with the exception of certain
Eastern Countries, where a dog is an unclean animal.
Some of you may be interested to know
what happened to Nipper. He died in the
earlier years of this century, and was buried
in the garden of the studio which Barraud
occupied in St. John's Wood, London,
which is only a few hundred yards from the
vast E.M.I. St. John's Wood Recording
Studios, where the majority of the English
H.M.V. records have been recorded during
the last 20 years.
1899,
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at high cost. The invention is now at least
two years behind the times, so any chances
he may have had are diminished. The question is- should he have done it?
The answer depends on a few points.
First, not every invention has commercial
possibilities. Before even seeing an attorney,
the inventor should have enough familiarity
with the field of the invention or people
in it to determine roughly whether it is the
sort of thing someone might want to manufacture for profit. Does it do a new job?
An old job better or cheaper? Is it a job
worthwhile doing? Can it be made on a
production basis without too many skilled
hand operations ? And so on.
If possible the inventor should try to
interest a prospective assignee or two before applying for a patent. While many
companies will not even look at an unprotected invention for fear of later being
accused of stealing it, some will-and almost always they will be scrupulously
honest. In addition, the inventor can protect himself to a good degree by detailing
the invention in writing and mailing it to
himself or a friend or attorney by registered post. If the envelope is retained unopened the date of registry is presumptive
evidence of the date of conception.
If a buyer or assignee is found, let him
pay the patenting costs and by all means
consult a patent or general attorney before
concluding any agreements. But if no commercial interest seems to exist, take a deep
breath and try to evaluate the idea from
a purely nonenthusiastic, impersonal standpoint. You can save a lot of money by not
applying for a patent on an invention you
won't be able to sell. And at the very least
you can earn an encouraging fee by writing
an article about it for this or some other
magazine. Many fine inventions are uncommercial in character but of interest to
many people who would like to read about
them.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
JANUARY, 1954
1
1
SOUND HANDBOOK
(from page 29)
Figure 15-14 illustrates a methods for
cancelling out ripple from the plate
supply of a stage, which at the same
time opposes motorboating. The voltage
divider formed by C and the cathodecircuit impedance, across which the B +
ripple appears, injects a portion of this
ripple at the cathode of the tube, out of
phase with the ripple normally appearing
on the following grid. The value of C is
adjusted so that the injected voltage is of
the correct amplitude.
A method for cancelling line- frequency
hum is shown in Fig. 15-15. The source
of cancelling voltage is the heater winding, which must be grounded at some
point, and the point of injection is a
voltage -amplifier cathode. The rheostat
R1 allows adjustment for best cancellation and the ability to compensate for
changed hum conditions, while the fixed
resistor R, prevents the injected hum
from being increased to such a point that
the resultant total hum is equal to or
greater than the original amount. A
certain amount of corrective phase shift
may be inserted by using a capacitor in
series with R,.
The first time the circuit of Fig.
15-15 was used by the writer it produced a 20 -db reduction in 60 -cps hum
and the effect was fairly stable, although
the control had to be readjusted every
few months. On another occasion the
hum -balancing circuit had very little effect except to change the waveform of
the hum. If the phase of the cancelling
hum is hopelessly distant from a 0- or
180-deg. relationship with the original
disturbance, no adjustment of the potentiometer will do any good.
The introduction of out-of -phase hum
voltages must not be attempted without
observing certain precautions. The neutralizing hum must always be injected
at a point on the same side of a volume
control, tone control, or selector switch
as the source of hum being cancelled. If
this is not the case a change in the setting of the control will destroy the
counterbalance and cause the hum to reappear, perhaps more strongly. It is also
necessary to guard against the reaps
your ears audition this revolutionary sound component. Check its smoothness ... range of response...
sensitivity and every factor vital to quality performance.
You'll agree with the high-fidelity experts who report:
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AI -406
Wen -Yuan Pan, "Circuit for neutral-
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15 -15. Circuit for cancelling line -frequency hum. A capacitor in series with R, can
be used for corrective phase shift to bring the
phase of the cancelling voltage opposite to that
of the voltage being cancelled.
Fig.
AUDIO ENGINEERING
JANUARY, 1954
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AmericanRadioHistory.Com
39
pearance of hum due to changes in the
characteristics of the hum being neutralized, and periodic readjustments of hum
balance may be necessary.
The
OVERWHELMING CHOICE
of tonie -quality conscious
visitors to the New York
Audio Fair were the
Bozak. Loudspeakers.
Countless audiophiles and
music lovers at the Audiorama
heard the Bozak Speakers,
went away, and returned
time and again to
enjoy their discovery.
From the Monaural
two- and three -way systems,
including the fabulous B-310
with its "On- the- Stage"
realism, to the astounding
Binaural demonstrations of
Cook Laboratories reproducing
16 -cycle organ tones,
the Bozaks were once again
the sensation of the Audio Fair.
Tracing Hum Sources
The technique of tracing the source
or sources of hum appearing in the output of an amplifier is, of course, based
upon a knowledge of the ways in which
hum gets into the signal channel. Testing must not be done haphazardly or
the work may degenerate into inefficient
puttering, confused by a complex hum
which has several sources. The stages
should be cleaned up in order, beginning
with the output stage and working back.
The usual method is to remove the tubes
of all the stages of amplification preceding the stage being investigated, and to
work on the amplifier in that condition
until the hum level is satisfactory. If
the hum has been created by currents
which flow only when the tubes of earlier stages are working, the lower -level
tubes must be allowed to remain in their
sockets, but their signal output should be
grounded out by an alligator -clip lead.
Determining the predominant frequency of hum being traced, by oscilloscope or even by ear, often furnishes a
clue as to the source. Thus B- supply
hum from a fullwave power supply has
a fundamental frequency of twice the
line frequency, while the fundamental
frequency of heater -induced hum is the
same as that of the line. There are several ways in which an oscilloscope can
be used to determine the hum frequency;
probably the simplest method is to adjust the controls for a screen pattern of
one full cycle (hum to vertical input)
with a line-frequency test signal (available on the scope) as horizontal time
base, and then to count the number of
cycles of hum that appear on the screen.
Two cycles will mean 120 -cps hum, and
one cycle, 60 -cps.
Mic,ophonics
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The elements of a tube cannot be anchored with perfect rigidity and therefore may be set into vibration. Such
vibration introduces itself into the signal
by influencing the electron stream of the
tube and microphonic noise, typically a
high pitched, pure -toned sound like that
of a tuning fork, may be produced. It is
called "microphonic" because of the
translation of mechanical vibration into
an electrical disturbance. When the
vibration is caused by sound from the
speaker an acoustical feedback system
is set up which can work the tone into
a self -sustaining howl.
Tubes in low -level circuits are most
subject to microphonics. Occasionally
other components, such as tuning capacitors, exhibit the same behavior. Certain
tubes, like the 6C4, are well known for
their microphonic tendencies, while other
tubes are especially designed to resist
microphonic vibration.
Measures taken to prevent microphonic effects include:
1. Replacement of microphonic tubes,
even though the tubes may be perfectly
normal electrically.
2. Shock -mounting the tube sockets
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JANUARY, 1954
of critical low -level stages on rubber or
similar material.
3. Physical location of critical stages
to avoid mechanical or acoustical disturbance, particularly from the loudspeaker.
4. Choice of anti- microphonic tube
types in original design (see Table
15-1).
Random Noise
Noise voltages are generated by the
random, uneven flow of electrons in a
resistor or within a vacuum tube. The
random electron motion in a resistor is
called thermal agitation and goes on
constantly without any outside source of
voltage. Random noise in the tube results from shot effect, collision ionization, and other causes, which all add up
to the fact that individual electrons do
not arrive at the plate in orderly sequence but at random, like buckshot hitting a target.
Thermal noise generated in an input
resistor determines the ideal limit of the
signal -to -noise ratio, and hence the
lowest value of signal which may be
used as input. The thermal voltage
across a conductor is directly proportional to the resistance and temperature
of the conductor, and also directly proportional to the width of the frequency
pass band. Within the determination of
these factors, thermal agitation in a
resistor is irreducible.
At 63 degrees the r.m.s. thermal
agitation voltage across a resistor may
be expressed as:
E'= 1.6x10 xR
where E= r.m.s. volts of noise, R=
resistance in ohms, and, (f, - f,) _
frequency pass band in cps.
Random noise generated within a tube
varies greatly with tube type and with
individual tubes. In general, pentodes
generate more of this kind of noise because of the random distribution of electrons between screen and plate. The
relationship to frequency bandwidth is
the same as that of thermal agitation
noise in a resistor.
The noise voltage developed within
a well designed triode with a gain of
20, not counting hum, may be expected
to be of the order of 28 microvolts at
the plate.* Since the amplification is
20 we would compare the signal at the
grid to a noise voltage of 1.4 microvolts.
Noise may be specified either in an
absolute level or as a signal -to -noise
ratio. If the noise is measured without
consideration of frequency the results
are unweigbted. When a more accurate
determination of practical nuisance value
is desired a noise reading may be
weighted by a frequency characteristic
inverse to the appropriate Fletcher -Munson frequency -vs- loudness contour.
REFERENCES
RCA Receiving Tube Manual, RCA Tube
Dept., Harrison, N. J. 1950, pp. 33-56.
F. Langford- Smith, "Rafiiotron Designer's
Handbook," 4th ed., RCA, Harrison,
N. J., 1953, Chap. 12, Sec. 10.
4 Harry F. Olson, "Elements of Acoustical Engineering." D. Van Nostrand Co.,
±0.75 db
20 to 40,000 CPS
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THE FINEST FOR LESS. This is the amplifier designed to provide optimum performance in limited- budget home music
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Hum and noise: 80 db below rated output.
Speaker out. imp.: 8 and 16 ohms. 4 inputs: 1 magnetic phono, 1 high-imp. mike.
1 tuner, 1 aux. (for crystal phono, tape,
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specially designed output transformer
with interleaved windings for virtually (Aux, Tuner, Mic, Flat, AES, and
distortionless output; input for mike; NARTB). Controls at top of chassis:
selector switch for proper loading of G.E. G.E.-Pickering input switch; also bias, outor Pickering cartridges; equalizer for put balance, hum balance controls (screwaccurate playback of all records; separate driver type). Tubes: 3- 12AX7, 2 -6L6;
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5Ú4G rect. Entire chassis is beautifully
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Specifications. Rated output: 24 watts. finished in satin -gold. Size: 8connectors,
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warm -up drift; built -in antennas- ferrite loopstick for AM, folded dipole for FM; external
antenna terminals; phono input for crystal
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Two auxiliary AC outlets. Complete with tubes
For 105- 125v., 50 -60 cy. AC. Shpg. wt., 16 lbs
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KNIGHT Model 721 FM-AM Tuner -Amplifier
Tuner and amplifier in a single chassis. Tuned
RF stages for FM and AM; temperature-compensated FM; separate bass and treble controls;
built -in preamp; 3- position equalizer; hum balance adjustment; push -pull beam -power
audio amplifier (10 watts output); built -in
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terminals. Audio response is to +0 to -3 db,
30- 15,000 cps at 2 watts. Handsome gray panel;
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JANUARY, 1954
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1954 Catalog
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KNIGHT Model 719 FM -AM Tuner -Preamp
Full -fidelity FM -AM reception. With preamp
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Tuned FM and AM RF stages; temperaturecomp. FM; hum-balance adjustment; built -in
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deep. Edge -lighted dial. With tubes. For 105125 v., 50-60 cy. Shpg. wt., 17 lbs.
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2nd ed., 1949, p. 293.
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LETTERS
Jensen Woofers
SIR:
We were very much interested to read
in the November issue of .E a description
of how to convert a Jensen Auditorium
speaker to a woofer.
However, we regret very much that we
no longer are making any 18-inch cone
housings, either for our catalog line or for
contract customers. We have received quite
a few letters as a result of the article and
have been forced to advise the writers that
we cannot supply 18-inch speakers. Of
course, if we receive a sufficient number of
letters, a special run may be justified.
I should like to suggest that there are
many old 14-inch Auditorium speakers in
the field available at bargain prices and
they make very good woofers, especially
with horn loading.
KARL KRAMER
Technical Service Manager,
Jensen Mfg. Co.,
6601 S. Laramie Ave.,
Chicago 38, Ill.
Advertising Claims
SIR:
OfU'U
I want to raise a cry of protest out of
the wilderness of current hi -fi advertising.
For many years it was possible to read ads
about new products and decide from the
data therein whether the equipment would
or would not do a certain job in a certain
way. Claims could usually be found to be
fairly accurate by making tests. Thus a
faith was built up by the manufacturers
among the technical and nontechnical
people who read the ads.
Now that hi fi for the masses is here
(in itself a very fine thing), manufacturers
are succumbing to the temptation to use
ordinary consumer -goods advertising techniques even in technical publications such
as 2E. This usually involves ads made up by
consumer agencies and written by ordinary
copywriters whose only acquaintance with
technical matters is schooling in the technique of the superlative.
The result is a hodgepodge of wild
claims and false superlatives on a precisely
equal level with soap advertising and the
whole thing does nothing but confuse the
ordinary man when he tries to select equipment. When he sees the "super-power
Hercules 6V6 amplifier with no distortipn
and infinite frequency range' selling for
only $29.50, the "specifications" of its ad
writeup look just as good as those of the
really fine amplifier selling for three to
six times the price. It is only when he pays
his $29.50 and gets the Hercules home that
he realizes it doesn't really sound as good
as his neighbor's old 6L6 (no- feedback)
amplifier.
Would it not be possible for the audio
manufacturing industry to indulge in a bit
of introspection and come up with a more
reliable and realistic approach toward consumer advertising?
ABOUT CROSSOVERS?
Several characteristics are used by recording companies
when they make records and many companies have changed
recording standards from time to time.
Altec simplifies the problem of accurate reproduction of these
various recording characteristics with the
A -433A control unit. This unit does not
require an instruction book for the playing
of every record. Its simple three crossover
selector, used in conjunction with continuously
variable tone controls, allows you to play any type of record as it
should be played, with easy and uncomplicated adjustment
to the proper setting. Prominent FM music stations have found that
the use of more than three crossover selectors
is
;
not necessary
for high quality sound reproduction.
depend on Altec for the finest in home music systems
and Altec equipment is well worth waiting for. Altec fidelity is highest
fidelity without compromise. See your Altec dealer soon,
or send for illustrated booklet.
You can
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JANUARY, 1954
NEW LITERATURE
Jensen Manufacturing Company, 6601
S. Laramie Ave., Chicago 38, Ill., is distributing a convenient proposal form for
use by dealers in recommending high
fidelity music systems for customers. The
new form provides space for listing first,
second, and third choices of all hi-fl components. Thus a dealer can give his
customer a written expression of three
recommendations of components based on
specific needs and in various cost brackets.
Aaoo Sound Corporation, 115 W. 45th
St., New York 36, N. Y., satisfies needs of
both novice and initiate in "Sound Advice," the company's new 1954 catalog.
Unique in its convenient pocket-size format, the 148 -page book contains a thorough approach to all aspects of high
fidelity written by Irving Greene, director
of the Asco Sound Studios, as well
as product listings of virtually all well known equipment manufacturers. Copy
will be mailed free on request.
Federal Telephone and Radio Company,
100 Kingsland Road, Clifton, N. J., comprehensively explains the design, application, specifications, and circuitry of selenium rectifiers in the second edition of
Federal's Selenium Rectifier Handbook.
Also covered are power supply circuits
for such applications as phonographs,
audio amplifiers, mobile radio, photocell
amplifiers, and intercommunication systems. Expanded to 80 pages, the second
edition is sectionalized for rapid reference,
with three major divisions of technical
material. Priced at fifty cents, the book
is available through any Federal distributor, or may be ordered direct from the
company.
Arrow Audio Center, 65 Cortlandt St.,
New York 7, N. Y., includes an informative section titled 'The How, What, Why,
and Where of Hi -Fi" in a new 104 -page
catalog which will be mailed free on request. Profusely illustrated, and complete
with specifications of most of the high
fidelity equipment on the market today,
the Arrow catalog is an excellent buying
guide. Write for it.
Engineering Products Department, RCA
Victor Division, Camden 2, N. J., is releasing an attractive and informative
folder titled "Custom -Built Equipment for
Television" which will be of distinct value
to holders of station CF's. Illustrated
with photographs and drawings of major
stations now on the air, the folder is an
excellent thought stimulator for anyone
expecting to build a station in the future.
Requests should specify Catalog B.30.
Carter Rotor Company, 2648 N. Maplewood Ave., Chicago 47, Ill., is now releasing its new Catalog No. 553, a complete listing of the entire line of Carter
d.c.- to -a.c. converters. In addition to product listings, the catalog contains a selector
chart showing correct Carter converters
for operating leading makes of wire and
tape recorders, sound projectors, and
phonograph mot or s. Electrical and
mechanical specifications, performance
charts, and other vital information are
arranged in convenient and attractive
form. Request for copy should be addressed to Dept. 6.
Standard Electrical Products Company,
2240 E. Third St., Dayton, Ohio, illustrates and describes the full line of
transAdjust -A -Volt variable- voltage
formers in a distinctive new 18 -page
catalog which will be sent on request.
Design and construction details, dimensions, and performance characteristics of
the various models of auto-, isolating, and
metering transformers are included.
Telex, Inc., Telex Park, St. Paul, Minn.,
manufacturer of hearing aids and electroacoustical equipment, has issued a catalog
sheet on the Telex Twinset, said to be the
lightest twin magnetic receiver ever
made. Weighing but 1.6 ounces, the unit
contains two tiny receivers which are
rested on the temples (not on the ears),
sound being piped to the ears through a
slender tubular arm.
Cal- Tronic Corporation, 11305 Hindry
Ave., Los Angeles 45, Calif., has recently
published a new 12 -page bulletin titled
"Electronic Test Equipment." In addition
to introducing the company and its services, the booklet illustrates and describes
the various types of equipment the firm
manufacturers. The devices shown are
highly specialized in nature and will be
of interest principally to advanced engineers.
AUDIO ENGINEERING
for
OUTSTAI1D111G
`
HIGH FIDELITY!
DtRECT
UY
How
TUNERS
P
and
'PR E - FAB
COLLINS
RECEIVERS
AUDIO PRODUCTS CO.
Two ALL NEW Complete Kits foe
Every M.ghFidel,ty Need
Collins Tuner Kit is complete with
punched chassis, tubes, power transformer,
power supply components, hardware, dial
assembly, tuning eye, knobs, wire, etc., as
well as the completed sub- assemblies: FM
tuning units, AM tuning units, IF amplifiers, etc., where ap pl i c a b Ia. All subassemblies wired, tested and aligned at
the factory make Collins Pre -Fob Kits easy
to assemble even without technical knowledge. The end result is a fine, high quality, high fidelity instrument at often less
than half the cost
because you helped
make it and bought it direct from the
Each
-
factory.
s
P riiprP11-9
_
available in kit form with the
Amplifier mounted in the chassis. wired and
The FM -11 tuner is
IF
-_
$1525
FMF -3 Tuning Unit
$55
FM Tuner Kit
tested by us. You mount the completed RF Tuning
Unit and power supply, then after some simple
wiring, it's all set to operate. 11 tubes: 616 RF
amp, 6AG5 converter, 6C4 oscillator, 6BA6 1st IF,
(21 6AU6 2nd and 3rd IF, 12) 6AU6 limiters, 6AL5
discriminator, 6AL7 -GT double tuning eye, 5Y3 -GT
rectifier. Sensitivity 6 to 10 microvolts, less than
42 of 1% distortion, 20 to 20,000 cycle response
with 2DB variation. Chassis dimensions: 121/2"
wide, 8" deep, 7" high. Illustrated manual supplied. Shipping weight 14 lbs.
best for FM. The most sensitive
and most selective type of "front end"
on the market. 6 to 10 microvolts sensitivity. Image ratio 500 to 1. 616
tuned RF stage, 6AG5 converter, 6C4
oscillator. Permeability tuned, stable
and drift free. Chassis plate measures
61/2 "x41 /2'. in combination with the
IF
amplifier, the highest order of
sensitivity on FM can be attained.
Tubes included os well as schematic
and instructions. Draws 30 ma. ShipThe
6
ping weight FMF -3:
able t`i1 S3.85.
21'2 lbs.
Dial avail.
PM
M
ANT, M
17
MI
:
0111
PM
wIAM
03
Amplifier
IF -6
remarkable value! 6 tubes are used
in the IF amplifier: 6BA6 1st IF, (2)
A
6AU6
2nd and
3rd
IF's,
(2)
mensions:
weight:
3
11
lbs.
*'
x 21/2 ".
AM -4 Tuning Unit
$7750
6AU6
limiters and 6AL5 discriminator. High
gain, wideband response (200 KC) for
highest fidelity. 20 to 20,000 cycles.
Distortion less than 1/2 of 1%. Draws
40 ma
220 volts. Chassis plate di-
FM /AM Tuner Kit
The original 15 tube deluxe FM /AM pre -fab kit
maller chassis. The tuner now
redesigned on
measures 14" wide by 12" deep by 71/2" high.
This attractive new front and dial assembly opens
up new applications where space is at a premium.
Kit includes everything necessary to put it into
operation -punched chassis, tubes, wired and
aligned components, power supply, hardware, etc.
Kit comprises FMF -3 tuning unit, IF -6 amplifier,
AM -4 AM tuning unit, magic
eye assembly and complete
instructions. All tubes included.
Shipping weight 19 lbs.
Shipping
$24"
t
superhel performance! A
tuning condenser gives 3 tuned
stages with high sensitivity and selectivity. Assembly is completely wired,
metested and aligned ready for
diate use.
e. Frequency coverage 540 KC
to 1650 KC at a sensitivity of 5 microvolts. Tubes 6BA6 RF amplifier; 6816
converter; 6BA6 IF amplifier and 6A16
detector. Draws 30 ma G: 220 volts.
Mounts on a chassis plate measuring
4 "x71,á ".
Shipping weight 21'2 lbs.
Dial available at $3.85.
Tops in AM
3 -gang
1.
P
ANA. Prod .a.Co. Inc.
0 S.. 3M. Westfield,
N. J.
Tel INIOAeW 2.4390
-
AE -1
IM AM Tenet Kit 0 Slid. Kul. Dial Aaemelr
Teninq Unit C 114 Amplifier O
Tuning Unit
IM Tener Kit
IMI.]
AM
ADDKESS
ICITr._
_._ .............-..............._.......STAH
!-..
..
let KI,
IAmoen,
t teiol emaee, e,Ie.ed S
See
weights, odd
Cheek
...pine ce
0
S
Stoner Orde,
_.WHEN. YOU THINK OF TUNERS. THINK OF COLLINS AUDIO PRODUCTS
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
NEW PRODUCTS
Oabinart Klipsch Enclosure Kit. Complete from hardware to pre -cut battle, the
new Kit series recently announced by G
& H Wood Products Company, 75 N. 11th
St., Brooklyn 11, N. Y. Is based on the
Klipech corner horn enclosure design by
Cabinart for 12- and 15 -in. speakers.
Known as the K -12 and K -15, the enclosures arc supplied In unfinished birch
to withstand high temperature, yet is
low- priced for application in mass -produced equipment. Built for continuous duty operation, it is equipped with self aligning oll- impregenated sleeve bearings
and dynamically balanced rotor. Shaft
diameter and length may be specified by
the ' customer. Provision for two -speed
operation is available on order. Complete
information may he obtained from Electro
Engineering Products Company, Inc., 609
W. Lake St., Chicago 6, III.
magnetic cartridges, two for tuner,
crystal cartridge, or tape recorder, and
one
for high- impedance microphone.
Three -position equalizer provides flat
playback or equalization for NARTB or
AES recording curves. Separate bass and
treble tone controls are calibrated from
-16 to +16 db. Screwdriver -type adjustments are afforded for balancing out hunt.
balancing output tubes, and for adjustment of bias.
,
Tape Identifying Label. The annoying
problem of visually Identifying program
material on sound tape reels is solved by
the Irish "Reel Tab," which is being
offered free to professional tape users.
Designed to replace the china marking
pencils and the makeshift scraps of paper
which are used so frequently for this
purpose, tite Reel -Tab fits snugly beneath
the edges of any type of 7 -in. plastic or
Extended-Range Antic Oscillator. Suitable for making measurements requiring a
sine -wave signal from 20 cps to
..
cycle, the Model 411 oscillator
sistance -capacitance -tuned unit t'
ode follower in the output of ncu t.
Frequency accuracy is nuuntained through
the use of deposited -carbon resistors in
the frequency determining network. Low level measurements are facilitated by a
panel switch which reduces output voltage,
-
-
i
which can be finished In exact style and
color desired. h:tsy-to- follow assembly
and finishing instructions arc included.
metal reel, whether the reel is full, partially full, or empty. Requests for the
heel Tab should be addressed to Nat
Welch, Orradio Industries, Inc., T -I20
Mat'vyn Road, Opelika, Alt.
Two -Rotor Two -Speed Tape Recorder.
Tape recordings approaching professional
quality can be produced with the new
Masco Model 53 recorder in which flutter
and wow content have been reduced to
less than 0.3 per cent at 7.5. Ips. Up to
two hours of recording on a single 71 -In.
spool is afforded at 3.75 ips. Inputs are
Karlson Enclosure Kit. Exaot ly the
saune size and construction as the finished
model of the Karlson Ultra -l" ilelity en-
closure, the new Type 15P147 kit consists
of 34 pieces cut -to -size parts which, when
distortion and hunt content. Additional information will be supplied on request by
The Clough- Brengle Co., Dept. AE, Chicago
40, 111.
Shaded -Pole Motor. Engineered for use
phonographs, tape recorders, and similar devices, the new Model MS -3600
shaded -pole motor has an exceptionally
high power -to -size ratio and Is designed
in
provided for microphone, radio or phonograph; outputs for external speaker, external amplifier, or telephone line. Timing
indicators under both supply and take -up
spools Indicate recording time consumed
and permit quick spotting of desired
portions of tape for editing. Full technical
specifications are available on request
from Mark Simpson Mfg. Co., 32 -23 49th
St., Long Island City 3, N. Y.
Knight 24 -Watt High- Pidelity AmpliAlthough low in price, the new
Knight amplifier recently introduced by
Allied Radio Corporation, 100 N. Western
Ave., Chicago SO, Ill., affords many of the
features usually expected only in much
more expensive equipment. Frequency response at 24 watts output is 20 to 40,000
cps within +0.75 db. Harmonic distortion
is less than one per cent and intermodulation less than two per cent at rated output. Four inputs are provided; one for
assembled, will afford the saute standard
of high -fidelity performance. The kit is
made up of rough plywood which furnishes a good surface for the application
of veneer, or it may be used as is in hid don installations such as 'walls, closets,
and the like. Constructed of 3i -in. plywood throughout, the kit is supplied with
fier.
44
cutout for 15-in. speakers with 12 -in.
adapters available on request. Karlson
Associates, Dept. IA, 1379, E. 15th St.,
Brooklyn 30, N. Y.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
1
CORONATION
30 -watt Supra- Linear AMPLIFIER
McINTOSH
An advanced version of the
Williamson with several impor-
tant
1
$92.50
Complete with tubes
THE
NEW
RCA
AUDIO SIGNAL
GENERATOR
Especially suited to the require nts of the Service Technician,
the Audio Experimenter, the Factory and the Laboratory.
Model WA-44A
-
Extremely valuable for measuring performance of
amplifiers, tone controls, equalisers, loudspeakers, and other audio
circuits and components. Has DC isolated cathode- follower outputs so
that signals can be injected into any point without loading the circuit
er reflecting any reactance. Other outstanding features include:
Frequency Range: 11 cps to 100 kc.
Response -2:1 db.
Additional
60 -cycle for Intermodulation Distortion tests.
Regulated oscillator
power supply.
Weighs only 10 lbs.
Complete with tubes, shielded cable, and instructions............ $87.50
complete front end unit providing extreme flexibility with ease of
operation. A 5-position switch permits input selection of AM, FM,
Phono, Microphone, TV, Tope, or any other sound source. A rumble
is incorporated
orporated to minimize or completely eliminate turntable
noise. Five sliding switches
switches act
controls. They are used
individually or in
thereby permitting at least 11 turnover
points from 280 to combination
1350 cycles. Another series of five sliding switches,
similarly used, allow at least 11 different roll -off characteristics to
match almost any record pre -emphasis curve. In addition to a conventional volume control there is a 5- position aural compensator which
maintains proper bass and treble loudness at low volume levels. Power
is obtained from the main amplifier or from a separate supply.
A
filter
Complete with tubes in attractively
styled cabinet
Less Cabinet
$94.50
88.550
A HI -FI SPECIAL!
RCA
STUDIO PICKUP
Model MI -11884
Consists of the famous Gray .L."103-5 arm together with GE
Professional Cartridge with
mil diamond stylus for microgroove records. ONLY
1
$34.50
MAGNECORD
VOYAGER
0
One -Case Portable TAPE RECORDER
Model PTA-VAN
A professional-quality portable unit designed for
use wherever top- quality recording and reproduction ore
STEWART WARNER
required. Oper-
ates at either 15" /second or 71/2" /second, with a frequency response
within 3 db from 50 to 15,000 cycles at 15" /second. Hos high as well
as low impedance inputs. Output is 600 ohms. Provided with earphone
monitor jock which is in the circuit for both record and playback. Di men.
sions: 756x175/ x19'/. inches. Weight: 42 lbs.
Power requirements: 110v., 60 cycles A.C.
PORTAFONE Model 73
Citizens 2 -Way Radio
A
Model C -108
PROFESSIONAL AUDIO
COMPENSATOR
modifications.
circuit
Through the use of matched,
high -quality components, and
an output transformer, specially
designed and wound for the
unit, the Coronat.on has achieved
unusually fine performance.
Frequency Response: 10 to 100,000 cycles ± db. Power Response: 20 to 20,000 cycles ±.25db.lntermodulation Distortion
is less than .15%, and Harmonic Distortion less thon .1 %, at
15 watts. Class A -1 operation. Power supply is self -contained,
with outlet for furnishing power to a preamp unit. Uses KT -66
output tubes.
May be operated from tuner, preamp, high -level pickup, tape
recorder, or other sound source. Operates any speaker system,
8 -16 ohms. Hum and noise level is 96db below full output.
Dimensions: 15 x 41/4 x 71/4 inches.
NEW
THE
ÑÉw
lightweight, self- contained radio receiver and transa transmitting and receiving r range from
$524.00
mitter. Has
miles, depending upon
system for the construction engineer, the nsurveyor, the TV service technician, and the many others in the need of inexpensive
means for short range communication. Any U.S. citizen
over 18 years of age ca easily secure a license for this
approved equipment. No technical knowledge required.
Portatone weighs only 28 ounces and fits comfortably into the hand.
Power can be obtained fromn several supplies. The Portafone Handy
Battery Pack is for portable use, and fits into the carrying case. The
Portafone Central Station Power Pack is for use where 115 volt AC
outlet is available. The Portafone Citizens Radio Power Pack is for
use with automobile storage batteries. One Battery or Power Pack is
required for each Portofon unit.
Portafone Model 73, per pair, including antennas and c rrying cases
eus
(less battery or power pock /-____.....
-$199.50
several hundred yards to several
terrain. The perfect communication
Add
Handy Battery Pack
__.............._....__..._._
Central Station Power
Citizens Radio Power Pack /specify 6 or
12
Fed. Excise To.
volts)
Visit the HARVEY AUDIOtorium
If you want to Se and Hear th
finest
the widest selection of
high fidelity equipment
be sure
to visit the HARVEY AUDIOforium.
It will thrill you.
7.00
6.45
34.65
31.00
THE
NEW
REL
Precedent
FM TUNER
Unquestionably the finest FM tuner
ever made. This successor to the famous 6468 incorporates every important advance developed in the art of FM reception. Sensitivity is 2
microvolts for better than 40db quieting. Frequency response is 30 to
40,000 cycles
ldb. Waveform distortion it less than
for 100/
modulation. Provides 2.volt output to high impedance, and .2 volts to
600 ohms. Front panel includes slide -rule dial, tuning meter, signal
strength meter, tuning control, rodio frequency and audio gain controls,
and power switch. Power supply is self -contained. Supplied complete
with tubes.
Chassis only (for custom installations)
t
.5/
$325.00
Relay Rock Model
335.00
360.00
Cabinet Model (Mahogany, Walnut or Blonde)
.
.
.
.
CDHARVEY
NOTE: Prices Net, F.O.B., N.Y.C.
Subject to change without notice.
AUDIO ENGINEERING
RADIO COMPANY. INC.
103 W. 43rd Street, New York 36, N. Y.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
JUdson
PI500
2 -1500
45
GOLDEN EAR AMPLIFIER
CROWNING
(from page 18)
ACHIEVEMENT
which brings the response down to about
before phase shift sets in. The capacitor would be made larger but this
value fits in well with the values of the
feedback loop, as we shall see.
To maintain the best possible balance,
all the resistors in the two opposite sides
are matched to about 1 per cent. It is
not necessary to use precision resistors.
Ordinary resistors can be matched on a
bridge or even an ohmmeter. Out of any
five of a given value, two can usually
be found which match to 2 per cent or
better. To insure against changes in
value, be careful not to overheat the resistors when wiring them in place. If
a large pair of pliers grips the lead between the soldering point and the resistor body, most of the excess heat will
be dissipated in the pliers. Even inexpensive carbon resistors, if not overheated, will maintain their value to 1
per cent for years. The remaining unbalance of the whole amplifier can later
be balanced to one tier cent or better by
2 cps
IN LISTE>.1I1G
PLEASURE
Th
RY
aranatian
INTFDFI F(-TR(1NIfc
adjusting R1.
The Driver and Output Stages
CLASS A -I
WILLIAMSON CIRCUITRY
SUPRA -LINEAR
30 Watt Amplifier
It's new! There's nothing like it.
It's the very finest quality ampli-
fier combining every desirable
feature: high power, versatility,
minimum distortion, and the lowest cost ever.
COMPARE:
Ultra compact,
precision crafted throughout, with
polished chromium chassis. Plug -in
electrolytic condenser, terminal
board for all circuit components,
sealed multi- section grain oriented
output transformer, KT-66 output
tubes. Frequency response 10 to
100,000 cycles +
db; intermodulotion distortion at 15 watts 0.15 %;
hum and noise level 96 db below
1
full output; preamp power.
Hear The Coronation soon at your
dealer, or write direct. Dealer
inquiries invited.
INTERELECTRONICS
C O R P O R A T I O N
2432 Grand Concourse, New York 58, N. Y.
46
The cathode follower, direct -coupled
to the power tubes, is the circuit developed by Ulric Childs and works very
well indeed. In fact, it is the only
method the author has used which is
entirely foolproof and adaptable to different types of output tubes. The cathode
and grid resistors of the follower are
matched. Bias to the power tubes is adjusted with the pot R5, and the output
tubes are balanced by the pot in the
cathode legs, R5. Any of the big triodes
(or tetrodes as triodes) except possibly
300A's and the 6AS7, can be used in
this circuit providing only that the output transformer and power supply are
suitable. The 6AR6's are the optimum
tubes delivering 20 watts with only
nominal distortion. The drivers are
driven a trifle hard to supply the 60 -plus
volts needed by 6B4's but they can
manage it. 807's, KT66's and 5881's
will provide 15 watts with very low distortion and their lower driving requirements improve the over -all gain by a
factor of between 50 and 100 per cent.
Using a set of adapter sockets, the author has tried all these tubes (except
the 6AS7 and 300A) in the circuit and
all work comparably well, although to
repeat, the 6AR6 appears to he the optimum tube.
Having achieved a more than satisfactory low- frequency response, the next
problem was to improve the high -frequency response. The cross -coupled inverter and the cathode follower driver,
offered no problems. The first section
of the inverter is a cathode follower and
the second section is fed by the very
low impedance of the cathode follower;
moreover, the second section has considerable inverse feedback of both the current and voltage type. The combination
therefore has an extremely good high frequency response. The 9002's and the
output tubes, however, were a different
matter. Ordinarily, the high- frequency
output of triodes begins to fall off at
15,000 cps or even less because of the
Miller effect. The first measure was to
neutralize these two stages. This was
done with fixed 1.5 µµf capacitors with
the 9002's, and with 3-40 µµf ceramic
trimmers in the case of the output
tubes. Neutralization corrects for the
Miller effect, all but eliminating it, and
extends the high- frequency response
considerably beyond 20,000 cps. However, it doubles the output capacitance.
This was the reason for using miniatures. The output capacitance of 9002's
is about 1 µµf, as against 3 µµf for each
section of a 6SN7. Thus even after
neutralization, the output capacitance
of the miniatures, and therefore the
high -frequency response, is better than
with the larger tubes unneutralized.
No adjustment of the neutralization
for the 9002's is necessary. The power
tubes, fed from a separate filament winding, are neutralized by opening the
filament circuit and adjusting the neutralizing capacitor for minimum output
with a steady tone applied to the amplifier input.
Neutralization brought the high -frequency response to about 50,000 cps but
this was still not as good as desired.
Therefore, an inner feedback network
was introduced from the plates of the
output tubes to the cathodes of the 9002's.
Since the cathode resistor is 0.1 megohm, it was easy to keep phase shift
down. For 10 per cent feedback, 1.0 -meg
series feedback resistors could be used.
With a 0.5 µf bathtub capacitor, the time
constant was 0.5, or the same as that of
the coupling to the cathode follower.
Thus, in effect, the two capacitors neutralize each other and extend the flat response below 2 cps. This loop provides
about 16 db of feedback which is sufficient to extend the high -frequency response to nearly 100,000 cps. The amplifier response from input to plates of the
output tubes is now flat from 2 cps to
nearly 100,000 cps.
This feedback network includes the
two stages responsible for most of the
distortion -the drivers and the output
tubes; and therefore reduces the distortion by a factor of six. Since the
feedback is balanced (the feedback resistors are matched) it also produces
dynamic and frequency balance.
With so little phase shift in the amplifier proper, it is obvious that the
feedback which can be applied from the
transfcrmer secondary to the input is
limited only by the phase shift of the
output transformer and the sacrifice in
gain which can be tolerated. Although
balanced feedback could be used, the unbalanced, single -ended type, suffices to
perform the two jobs which need to be
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
l
done -first,
to compensate for any
irregularities and slopes in output transformer response, and second, to provide
additional cancellation of distortion. We
have applied as much as 40 db of feedback, iir addition to the 16 db of the
inner loop, before instability resulted.
In practice, however, about 18 to 20 db
is more than sufficient to do the job
and still leave sufficient gain to produce
full output with an input signal of 10
volts, easily provided by the triode amplifier of a tuner. With a total feedback
factor, so far as the drivers and output
tubes are concerned, of between 30 and
50, depending on the feedback of the
main loop, it is no wonder that distortion is reduced to an insignificant minimum even at full output.
One other factor remained for solution before such stability could be
achieved. The flat frequency response
was one item on the way to a good
transient response. There remained the
minimization of feedback loops. These
loops, of course, exist in every amplifier
using a common power supply and
triode tubes. Neutralization eliminates
the feedback loops through tube capacitance. The rest was a matter of adequate
decoupling. Although the amplifier has
five stages, two of these are cathode
followers and produce no phase shift.
Therefore, the amplifier can be considered a three -stage device. Nevertheless, decoupling down to 2 cps or less
presented a problem. In this amplifier,
as in the original Golden Ear amplifier,
it was solved by the use of a VR tube
in the input stage. The VR tube is the
best of all decoupling devices. After
all an element which will smooth the
long period variations of a d.c. supply,
has a very low impedance to a.c. even
of periods as low as 1 or 2 cps. The VR
tube simultaneously performs two other
functions : as an excellent hum filter, it
delivers very pure d.c. to the amplifier
input stages; it also stabilizes this stage
by maintaining a constant voltage. Since
the whole balance of the amplifier is dependent on the stability of this first
stage, an extremely stable d.c. amplifier
is achieved.
Actually, the amplifier alone can be
driven into oscillation only by applying
something between 90 and 100 per cent
feedback -in other words, oscillation
sets it just before the input signal is
completely cancelled out. Indeed, even
when the preamplifier, with four additional stages, was fed from the same
power supply, the stability was still remarkable, although the transient response deteriorated considerably.
It will be noted that the over -all feedback network, being direct coupled, will
unbalance the input stage since the feedback resistor and voice coil appear in
parallel with the cathode resistor. Therefore, after feedback is adjusted, the
balance control should be readjusted.
D.c. balance may be measured by connecting a VTVM from plate to plate of
the 9002's and adjusting for zero voltage. Better over -all balance, however,
is obtained by using the following
method: after balancing the output tubes
with their cathode balancing potenti-
AUDIO ENGINEERING
ometer, connect the "off" grid of the
inverter to the signal grid, feed in a
constant -tone signal and adjust the balance control for a null in the output.
The cross -coupled inverter is a differential amplifier and if the same signal
is fed to both grids and the amplifier
is fully balanced, complete cancellation
occurs. (This fact makes the circuit
highly useful for distortion measurement
and phase angle measurement and indeed
with slight modifications this amplifier
could serve as a distortion measuring
amplifier.) At any rate in this way the
whole amplifier can be balanced almost
perfectly from input to output.
A few details remain. Since failure of
the output tube bias supply would apply
-
BA -12-C
USE AS
a high positive voltage to the grids of
the output tubes with almost inevitable
damage to them, a T/4 -amp fuse is placed
in series with the output cathodes and
ground. A rise of plate current such as
would occur with a bias failure, will
blow the fuse, opening the plate-supply
circuit and protecting the tubes until
repairs are made.
The cathodes of the 9002's and the
6C4's are 50 volts or more above ground.
The center -tap of the filament winding
feeding these and the cross -coupled inverter, is therefore returned to a positive
voltage of around 40 volts, provided by
a high -resistance divider across the
power supply. Actually this makes little
if any discernible difference in the hum
BA -1-F
A:
USE AS
Pre -Amplifier
Program Amplifier
Monitor Amplifier
up to 8 watt output
-
A:
Booster
Isolation Amplifier
EVERY STUDIO... EVERY STATION
needs only these basic audio amplifiers!
QUALITY- meets highest
broadcast standards!
EXCELLENT
-
these twp
units answer the problems encountered in building custom consoles or
enlarging present facilities.
CUSTOM APPLICATIONS
PLUG -IN
DESIGN -permits
simplified
maintenance plus flexibility of interchanging units!
COMPACT -the small size
of these
plug -in units permits savings of up
to 50% in space!
Here are two audio components that offer you maximum convenience for
application in AM -FM -or TV broadcasting! Why not build your system
with versatile General Electric equipment... today's best guarantee of performance and continued service.
r
Choose from a complete G -E
amplifier line to fit every broadcast audio requirement!
General Electric Company, Section 4414
Electronics Park, Syracuse, New York
Please send me complete information on G -E broadcast amplifiers.
NAMF
ADDRESS
CITY...
___ ___________
L.-GENERAL
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
_.
__._.
_ __STkII
ELECTRIC -47
level which is completely inaudible,
even with ear at the woofers and even
when 6B4's are used. However, it is
good insurance against heater- cathode
leakage and breakdown.
The bias supply should deliver 125
volts if 6AR6's or 6B4's are used. The
same value will do for other tubes, but
as little as 105 will suffice for 807's,
KT66's and the like. The author used a
150 -volt power transformer, of the type
used in TV boosters, but a filament
transformer used backward, as diagrammed, will serve.
It will be seen that all five rules of
design are faithfully followed : (1) distortion is held down by operating highpower tubes at a fraction of their maximum output, and the voltage amplifiers
well below their maximum output; (2)
nearly perfect balance and a huge
amount of feedback in two loops results
in a high degree of cancellation of what
distortion is produced; (3) by virtual
direct coupling, neutralization, and feedback the amplifier is made non-resonant
from nearly d.c. to more than 200,000
cps, and finally, by neutralization and
effective de- coupling, the amplifier is
made extremely "stiff" and resistant to
oscillation, regeneration, or the formation of various transients.
CREDIT
TO YOUR
HIGH
for
FIDELITY
SYSTEM
7, 10, and 12
/I /IFjJIf/77/'
1//,C
3 -SPEED RECORD CHANGERS
INCH RECORDS
Medal 3/532
Intermixes 10 and
inch records.
List Price
$65.00
12
Model 3/531
Nonintermix.
List Price
$54.50
_.
Medal 3/534
Single record player.
List Price -.. $33.60
W000 BASE
Mahogany Finish.
Specify Changer or
Player.
List Price
$9.50
Available at
Radio Parts Jobbers,
Distributors. and
Dealers
HI -FI
Performance
It is easy to be extravagant about
Write for complete details lo: Dept. FA -1
215 East 37th Street, New York 16, N.
ROCKBAR CORPORATION
HYCOR
Y.
TYPE 4201
PROGRAM EQUALIZER
Features
.
$19 5.00
.
LOW HUM PICKUP through the use of toroid coils.
Switch contact noises are inaudible even at microphone levels.
Low frequency equalization peaked at 40 cycles and 100 cycles in 2 db steps up
High frequency equalization peaked at 3 kc, 5 kc and 10 kc in 2 db steps up
Low frequency attenuation in 2 db steps at 100 cycles and has a maximum attenuation
High frequency attenuation in 2 db steps at 10 kc and has a maximum attenuation
General Specifications
DIMENSIONS:
CIRCUIT:
...
to 12 db.
to 12 db.
of 16 db.
of 16 db.
Standard rack panel, slotted, 3'i" high. Maximum depth 7'2".
Bridged "T" constant impedance.
IMPEDANCE:
500 /600 ohms, in -out.
INSERTION LOSS: 14 db constant.
CONTROLS:
Low and high frequency selector switches. Low and high frequency
controls in 2 db steps, in -out key.
Engraved panel, medium gray baked enamel. (Special colors and
FINISH:
finishes upon request.)
Send
HYCOR SALES COMPANY
11423
VANOWEN
STREET
NORTH HOLLYWOOD, CALIF.
48
for Bulletin
E
one's own brain child and hand work,
particularly when instrumentation bears
out subjective impressions. As .1E has
pointed out editorially, audio design is
approaching the stage where instruments of distinctive character, rather
than mere reproducers, are being produced. The new Golden Ear amplifier
has a distinctive character. It is very
clean, particularly in the bass-much
cleaner than any previous amplifier used
by the author. This is partially because
of the extended bass response but perhaps more because of the really extraordinary transient response which reduces the production of ringing and
other forms of transients to a point of
mere academic rather than practical import, and therefore greatly improves the
definition of the reproduced sound. The
measurable aberrations over the normal
operating range of 6 milliwatts to 10 or
12 watts are very small-too small for
accurate measurement on the author's
rather crude home -made instruments
and too small for discernment by ear.
No doubt time will provide circuit and
components improvements which offer
hope of further perfection ; but for the
moment, the Golden -Ear Complex is
satisfied more completely than ever before, and there is hope that this satisfaction will last long enough to channel
brains and energy into other, less well realized channels-including those of
making an adequate living.
-
Eninnnnmunuuuuuuuunmunnunnnnunnnmuuuuunuuuuuuunumm_
Representatives:
GO WEST!
BEEBE ASSOCIATES
AUDIO FAIR-L.A.
1155 Waukegan Road, Glenview, Illinois
BURLINGAME ASSOCIATES
103 Lafayette St., New York City
HARRISON I. BLIND
1616 Cord St., Indianapolis 24, Ind.
February 4, 5, 6
Alexandria Hotel
=
unuunnnuunnonuumuuuummmuuummn,:nnnnininnninnnlnnrm=
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
t
DC ON FILAMENTS
"TA B"
BUY
THATS
BASS REFLEX
(from page 36)
A must for "super hi -fi ".
No hum level with DC In
the filament supply. Bridge
Ielenlum rectifier 6000 mid
brute filter 6.3 or 12.6
volt. DC /2 amp for preanp
or amplifier.
Model 2DCF
$12.98
...
A
As above except
model 4DCF
DIAMONDS AN "LP'S"
BEST FRIEND
B
amp
$20.98
BUY RIGHT WITH "TAB"
THAT'S SOUND HI -FI ADVICE
Protect your records that's "sound" advice. Mall
your cartridge, we replace rtyll at colt at
diamond only.
A. Diamond single stall for Astable, Phil's,
Magnavox, RCA, Shure C Webster $12.00
B. Diamond (.001) LP & sapphire (.003) 78
for C.E. RPX047, 050, 051 cart. $14.00
Same except diamonds (.001) & (.003)
Headquarters leading hi-fi manufacturers. Before buying
consult "TAB" for your audio needs. Outline your problems and we will help in selecting, trading, exchanging.
or buying ht-fi equipment. Write and be convinced. We
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CABINET MODEL 4666. "TAB"
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Fig. 3. A horizontal partition was inserted to
avoid the raised resonance frequency of a
cubical enclosure.
The enclosure was constructed of flinch plywood throughout. All joints
were grooved, glued, and screwed so as
as to be rigid and airtight. A vertical
brace, about 3 inches wide was mounted
inside the back to prevent low -frequency
panel resonances. The 15 -inch partition
which was glued and screwed to the
front panel and t* the two side panels
prevented any low- frequency panel resonances at these points. A double thickness of % inch Fiberglas acoustic insulation was tacked to all inside surfaces.
As mentioned previously, the front of
the enclosure was recessed by about
inch so that the plastic grill cloth could
be attached. How this was accomplished
is shown in Fig. 4. After the operation
of the enclosure was checked (as described below), the grill cloth was stapled to the front panel. Then 34-inch
inch thick)
triangular molding trim
was tacked into place, forming a neat.
picture -frame effect.
(4
TOP, BOTTOM
OR
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10, 6 & 3 kc. Drown plastic
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LP
play best when vertical at rest. Compact, smartly
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triode amplifier. The lut word In
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distortion .05 %, 5 watts; .08%. 10 watts; 1%, 50
watts. slum: 921313 below full output. 9 tubes, 115 V
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Model SOA
5159.50
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A true high fidelity system by Fisher. Ultra hi -11 amplifier model 50A, Master audio input model 50 -CM.
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The
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Model 711C
$44.75
Model 711 less cabinet $39.95
5
tweeter 25 watt/
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5
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15" coaxial PM &
2V'
MOLDING
THAT'S
RI
A
Fig. 4. Side view
IAI
and front view (B) show
was attached to give a
how the grill cloth
professional appearance.
AUDIO ENGINEERING
\\
BUY
Dept. A -E
I
111
$97.50
50 -05t
HF & LF response. Famous HI -Fl Speaker
20 to 17,500
AUDIO INPUT CONTROL
Model 50.CM Pre -Amp. & Amp. A Cadillac In performance & look.. Simple to operate. Feature. include: 5 separate input., compensation for all type. of recording.,
16 equalization combinations bus & treble. loudneel
teompenuled & non- compensated). All control accurately
calibrated. Response: 20- 20,000 cm. + 1DB. Hum;
volt.,
90 DB below 2 volts. 3 tubes plus 2 redid-era. 115
60 eye. operation. Shpg. wt. 9 lbe. Set In beautiful
mahogany cabinet with brass panel. A. shown aber..
All 8 ohm V,C., Alnico V magnet. &
inbilt network, two wires needed for
ENCLOSURE
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Companion unit for the TM -15A old range amplifier,
er any ultra -linear anlpl. Features; 4 input channels,
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3 pos turnover & roll -o)T. Bass & Treble mauls. All com$19.95
ponents & instructions. Shpg. wt. 4 lbs.
Mfg..
The perfect addition to any audits
system. Four low frequency turnroll-off
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tone
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Drown plastic cabinet.
balance.
115 V 60 ey. Shpg. wt. 31/4 lbs.
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FISHER MODEL 50 -PR
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T
GARRARD RC -80 CHANGER
and
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78 rpm records. Jewel mounted
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$45.08
Special RC80 with G.E. RPX050 dual cart. .. $47.00
PREPAID
WITHIN
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-45
THAT'S
A
LIBERTY STREET, NEW YORK 6, N. Y.,
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
THE 48 STATES.
ORDER
CHECK WITH
DEPOSIT.
OR 255.
PH.: RECTOR 2 -6245
OF
BUY
U.S.A.
49
Checking Operation
PRECISION
FOR
EQUIPMENT
PERFORMANCE...
MODEL DR -12A OUTSIDE DRIVE TURNTABLE
Three speed, low cost, with performance features formerly found only in very expensive
machines. This new principle in turntables
meets high professional standards for broadcast or high fidelity recording reproduction.
The usual method of tuning a bassreflex enclosure is to adjust the port
until the mounted speaker has two impedance peaks of about the same amplitude about equally spaced above and
below the free -space resonance of the
speaker. To obtain the impedance curves
of the speaker-and -enclosure combination, the same set -up was used as had
been employed previously to check the
resonance of the speaker alone.
25
MAINTENANCE...
BASS REFLEX
PORT CLOSED
MODEL DM -I
PORTABLE DISTORTION METER
MODEL FL-2 PORTABLE
FLUTTER METER
Self - contained,
pocket - sized,
measuring distortion on a single frequency. Supplants larger and more expensive laboratory equipment where single
frequency measurement is adequate. Readings are obtained
quickly, completely independent
of flutter.
>
05
0
]D
50
FREQUENCY
with the
IM -3B INTERMODULATION METER
Compact, convenient and fast, measuring
with a single instrument, intermodulation distortion, power output and level, frequency
response, hum, noise and gain. A complete
instrument for sound system testing.
MODEL
AUDIO EQUIPMENT
LTD.
10
70
100
CYCLES PER
IN
200
500
SECOND
Fig. 5. This was the speaker impedance curve
RESEARCH
&
u
Handy,
low -cost
meter
allows for fast, precise
measurements of turntable
wow, RPM and turntable
and tape recorder flutter.
Permits the cbservation of
speed variations in all
types of recording media.
402 East Gutierrez Street
7,Zecodry eamuydody
DIVISIO
Santa Barbara, Californ
aeade rite
audio anthology
and
the 2nd audio anthology
The original
audio anthology is still
being ordered by people who have
worn out their first copy or who have
just learned about the book. Contains
reprints of 37 articles which appeared
in AUDIO ENGINEERING from May
1947 through December 1949. An invaluable reference work on audio in
the home.
CUT OUT
2nd audio anthology continues
from where the first left off and contains reprints of articles from January
1950 through July 1952. In both
books the articles were brought up to
date, corrected where necessary, and
assembled by subject. the 2nd a a may
still be had with board cover.
the
MAIL TODAY
port completely
blocked.
As the first step, a piece of scrap ginch stock was screwed over the port,
closing it entirely. The "infinite baffle"
so produced behaved just about as expected; its impedance curve appears in
Fig. 5. Note that a single large peak
occurs at about 64 cps; this is about 10
per cent higher than the resonant frequency of the unmounted speaker. The
amplitude of this peak is almost as great
as that of the resonant peak of the unmounted speaker. In addition, smaller
peaks occur at about 125 and 155 cps,
Next, one -third of the port was opened
by screwing a smaller piece of scrap
stock over two -thirds of the opening.
With a port area of only 24 square
inches, the impedance curve appeared
as shown in Fig. 6. The large peak has
moved up to 68 cps and its amplitude
has been reduced substantially. Also, the
amplitude of the two small higher -frequency peaks has been reduced. Note
that the curve rises at 30 cps indicating
the possibility of a definite peak at this
or a slightly lower frequency. Unfortunately, the low- frequency limit of the
audio oscillator used was 30 cps so that
it was not until later measurements were
taken that it was realized that there
existed a peak in the vicinity of 30 cps.
Next, two- thirds of the port was uncovered, with the results shown in Fig.
7. The large peak has continued to move
is now
slowly upward in frequency
at 70 cps-and downward in amplitude.
-it
Book Division, Dept. 3V,
Radio Magazines, Inc.,
P. 0. Box 629, Mineola, N. Y.
25
2.0
Sirs: Enclosed is
check
money order for $
copies of
audio anthology
copies of the 2nd audio anthology
copies of the 2nd audio anthology
.
Please send me
(paper cover)
(paper cover)
(board cover)
15
$2.00 each
$2.00 each
$3.00 each
BASS REFLE
PORT 1/5 OPEN
05
Name
(please print(
0
50
Address
50
FREQUENCY
Gty
50
Zone
State
Fig,
6.
400
CYCLES
200
300
PER SECOND
Impedance curve with port area reduced to 24 square inches.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
70
IN
JANUARY, 1954
How The Adventure Turned Out
5
2.0
1.5
S
BASS REFLEX
PORT 2/3 OPEN
10
os
o
30
Fig.
70
50
FREQUENCY
IN
200
100
PER
CYCLES
7. A 48- square -inch port
300
SECOND
produced this
curve.
If the impedance curve of the 6.2cubic -foot bass -reflex enclosure with a
port area of 72 square inches is compared
with the curve of the unmounted 10 -inch
loudspeaker as in Fig. 10, it can be seen
that the enclosure resonates at a frequency about 6 cps lower than the 58 -cps
resonant frequency of the speaker. A
somewhat smaller enclosure or a larger
port probably would have raised the low frequency peak from 36 cps to perhaps 40
cps, and the high -frequency peaks from
73 cps to perhaps 85 cps. It also would
probably have boosted the low peak by
In addition, a pronounced low- frequency
peak is now seen to exist at about 33 cps.
The port was then completely opened
with the results as shown in Fig. 8. Both
peaks have moved upward slightly in
frequency; the larger peak occurring at
about 73 cps and the smaller peak occurring at 36 cps. Note also that the amplitudes are somewhat more equalized, with
the amplitude of the larger peak having
been :reduced and the amplitude of the
smaller peak having been increased compared to the previous figure. The high-
featuring
Speakers
1
r
I
I
20
15
4
UNMOUNTED SPEAXER
s
s
jui
1
lo
iR-
0.5
30
50
FREQUENCY
70
IN
MO
100
CYCLES
......
200
PER
300
SECOND
the final bass -reflex enclosure.
1.5
BASS REFLEX
PORT ALL OPEN
ó
10
o.s
70
50
FREQUENCY
Fig.
SOUND COMBINATION
a tenth of a volt and lowered the high
peak by a tenth of a volt to make the
two amplitudes exactly equal. However,
it was decided, especially after a listening test, to leave the enclosure just as
is In the first place, at the slow rate at
to
o
3o
ciNCDOii
Fig. 10. These two curves show the results of
2.5
3
25
MAXIMUM TONAL REALISM
In Minimum Space
At Minimum Cost!
W
200
100
CYCLES PER
300
SECOND
entire port area produced
this impedance characteristic.
8. Using the
frequency minor peaks have all but
disappeared.
At this point, it was decided to try the
effect of damping the port. A % inch
thick layer of Fiberglas was stretched
over the open port, with the result, that
both peaks were lowered in frequency
somewhat. The low- frequency peak was
reduced considerably in amplitude, but
the amplitude of the higher -frequency
peak was actually increased somewhat
(see Fig. 9). As a further experiment,
the enclosure was moved from the corner
where it is to be used and where all the
curves shown were taken to another location against the longer wall in the room.
When this was done, the curve of Fig. 8
was obtained except that the 73 -cps peak
moved up to about 78 cps.
which the resonances increased with
larger port areas, it would appear that a
considerable increase in port area would
be required for perfect tuning. Since the
port now extends almost the entire width
of the front panel and almost the entire
height up to the support for the partition, it would not be practical to increase
its area very much. Secondly, we are not
using a high -quality 12- or 15 -inch
speaker here with a cone resonance of
40 to 50 cps, but we are employing a
good 10 -inch speaker having a somewhat
higher cone resonance (58 cps). In
such cases it is usually recommended
that the enclosure be tuned slightly below
the speaker resonance. When this is
done, a slight extension of low -frequency response results and no peaks
exist above 80 cps to mar reproduction.
re Is a so001 con,il.tiO- that makes music come al ve
home. Tle aco. Ytically engineered KINGDOM
CABINET Is male of Ha dwwod 54" thick. Repr duces beta
high and low Fequerc es with full tonal realism. Small it
:lee. Versatile and Dxaatve
Blends witt modern or
'eV every
.
Et, visaed completely assembled w.th
LORENZ LP-21! WOBFF91, LORENZ LP-65 TWEETER Avo
CINGOOM 111,1 NIGH PASS FILTER (Shown below). All perfectly matched and G Encei to bring you all the musicat
alarm and enc,antm.nt of tSe original perfornance .
!Natural, clear and crap up to 1E.000 cycles.
traditional inte'rors
.
csbmet w tie
C" a :6" a 19 ". Available in color&
with tae fo Icwirg finishes: Mahogany or
KINGDOM
*weaker system Size:
COMPLETE
lo harmonize
$69.50
Blonde, Net
Urr,ished $67.00
r
CINGDOM CABINETS OYL- fo
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o
COMBINATION
SeUNO
Ne
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Unfinished
$ +6.95
01AIR510E STAND
$2445,,
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Mode Expressly for KINGDOM Products
LORENZ Speakers nave been tested and found
excellent with the KINGDOM CABINETS. the Rohe
The
IV
C ABINART
and CLECTRO VOICE BARONET. Other
well.designd cab-nets should work equally well.
I/45
LORENZ
TWEETER
25
i
,"
Carries the highs- CIea16 CIW
and Crisp up to 16,000 :yycclee.
Power: 2 watts. Impedaen
m
5.5 ohms. Size: 21/2" dia.
Net
20
fÿ.90
1.5
BASS REFLEX
PORT ALL OPEN
AND DAMPED
1 10
t
Io
°30
50
FREQUENCY
70
IN
200
100
PER
300
Fig.
curves
AUDIO ENGINEERING
LP.215 LORENZ
'WOOFER' LOUDSPEAKER
masterpiece N sound engs
veering. Performs
over the Full range.
40
13,500 cycles.
watts. Impedance:
She 8W' dia.
-
smoothie
Response.
Power, S
d
ohms
SECOND
Fig. 9, Placing damping material over the port
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52
)
from increasingly this year-everywhere.
It is a comparison of the utmost importance for all those who are building and
distributing craft -type components, an argument that must be studied hard as a new
"line" which would seem directly to contradict the very basis of the above -discussed and very familiar Parallel Comparison. It is, in my improvised terminology,
the Stepwise Comparison.
The argument is, namely, that the massproduced "hi-fi" phonograph is the best
buy for the Great Middle Class of record
collectors, the modestly priced big value
for the multitude ; whereas the component
lines of hi -fi equipment are super -duper
near -professional parts for the home,
costing more, designed for the connoisseur,
the privileged few, the Man who can Afetc., etc. A very familiar arguford
ment, needless to say, in other fields,
notably autos and liquor, but what about
hi -fi? Is not this a somewhat remarkable
"line" in view of long -familiar values?
Haven't we been saying, claiming, all along
that hi -fi components are more economical
than commercial counterparts?
There is truth to be found here, contradiction or no. It is quite true -and I suggested this in November-that craft -type
manufacture is by definition specialized,
relatively small- scale, and cannot expand
its advantageous standards into real mass
production. Yes, the craft hi -fi industry
has expanded tremendously -as a whole.
But that whole is still made up of very
many separate parts and these operations
continue to be, relatively, small-scale.
Craft -type equipment, which is inherently
of good quality, is not really practicable
below a certain quality level, as we know.
It can't compete in the bottom price areas.
But the big -company argument is that
it can't compete at all in terms of true mass
production. We, say the big companies,
are the only ones who can bring aúdio
quality, in a practical forni, to the millions;
better a sensible compromise and huge production than nothing at all, for the millions
whom craft hi -fi cannot possibly reach.
A rather tough argument to answer,
though to my ear it doesn't ring entirely
right. I think this kind of persuasion savors
a wee bit of the publicity office, OR what
is sometimes called institutional advertising. One might suggest that if craft -type
hi -fi could reach the millions in terms of
its own publicity, on an equality with the
information concerning commercial machines, it might very well expand enough
to take care of a rather large number of
those very same millions, without losing
its essential quality. Somehow, I can't feel
that the said millions are unduly deprived
by craft hi -fi's inability to reach them, nor
can I quite feel that mass production is the
one great benefactor, in this case I Still
there's a lot to be said for this line. Just
look up the figures on units sold, say, of the
Columbia 360, which has a year's lead on
the other newer machines.
Component hi -fi, in the large- company
...
Enlightening...
AUDIO ENGINEERING
(front page 30
a wholly different comparison that has now
made its appearance and will be heard
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
-
JANUARY, 1954
view, is for the few, who want the best.
That implies very definitely that component
hi -fi costs more. Now if the complementary
craft lines offered by these companies
(built in part by smaller hi -fi makers) were
actually sold at levels that competed with
the already existing small- company offerings, the argument would be senseless;
money for money, these large companies
would be running themselves out of their
own market. Why try Soandso's hi -fi table
phonograph when Soandso's own hi -fi components obviously give you better sound?
Therefore it is not at all surprising to
find that large-company craft component
lines are specifically arranged to fit above
the fanciest of the mass -type machines as
to cost, thus limiting them rather pointedly
to the deluxe category. Component hi -fi,
then, is by definition deluxe hi -fi in this
arrangement, and must be necessarily, to
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support the whole argument. That's the way
you'll find it, with only a few exceptions.
This is the Stepwise Comparison, with
craft hi -fi on the top step.
Which leaves an unexpected and happy
loophole for the smaller established craft type makers-through which they will
undoubtedly wiggle with adroitness. If
according to the Stepwise Comparison
large- company component lines must be
more expensive than the best of the ready made machines -which means that an
ensemble must sell for perhaps $200 at a
minimum-then small- company craft hi -fi
has the field to itself in the area directly
competing with the "hi -fi" mass produced
phonograph! A good idea.
And that, finally, brings me around to
Mr. Ferguson again. Though he is, nominally, a professed apostle of the Parallel
Comparison, trading craft quality directly
against mass -produced simplicity and convenience, in actuality he is, price for price,
trading low -cost craft hi -fi alongside of similarly priced mass production hi -fi -and
there he has the bull by the tail! For he is
taking the Stepwise Comparison, negatively,
for what it's worth-to him. Lots.
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1954
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An interesting situation. I've noticed
that, following the developing wave of hi -fi,
many small radio and record stores are
now adding modest displays of hi -fi equipment (using the term always in its popular
and present sense) to supplement their
records, radios, TV and toaster lines. Here
an amplifier, there a changer or a hi -fi
table phono or the Columbia XD extension
speaker. In most cases these added hi -fi
attractions are large-company lines, either
commercial or craft type. (Mr. Ferguson
is one of the few record dealers I've heard
of who feature only small -company craft
hi-fi.)
Which means that most small stores are,
whether they know it or not, following the
philosophy of the Stepwise Comparison.
EITHER you buy a moderately priced
one -piece mass produced unit OR you buy,
on a higher step, the deluxe, fancy, custom.
special separate components. More expensive-of course. No suggestion at all, in
this philosophy, that for equal cash there
are economical choices in both types, that
sound for sound, craft components can
make the more economical system, not the
more expensive. That's where Opportunity
is still knocking at our doors. Open up!
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-_
53
AUDIOLOGY
(from page 12)
One of America's
Lending studio
E/i.sllribu torn
practical objection to this plan is that the
primary feedback portion of the system
may increase output hum to greater extent
than the tertiary feedback reduces it. To
avoid this difficulty, a variation has been
used in which a dividing network shifts the
sampling point from primary- feedback at
high frequencies to tertiary (or even secondary) form at low frequencies.
One of the most powerful of easily applied
systems is that of cathode- follower connection of the tube to the output transformer
primary, with major -loop feedback of tertiary form to an early point in the amplifier. While the cathode follower is simply
one form of primary feedback, it has here
the advantage of low output hum due to
plate supply ripple. The abnormal grid signal requirements of a cathode- follower
power output stage may be reduced to more
readily attainable magnitude by including
only a portion of the primary turns in the
cathode circuit, the remainder being in the
plate circuit.
With adequate attention given to transformer design and the provision of low
primary source impedance within the major
feedback loop, the tertiary feedback method
makes possible the usual desirable features
of a high -quality audio amplifier, with a
degree of stability not realizable in a secondary- feedback system.
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54
¡rom page 10
Stereophonic, a.: Pertaining to or
adapted to the stereophone (see below) ;
produced by the stereophone, as stereophonic magnetic tape recordings; stereophonic sound system, stereophonic reproduction.
Rek -O -Kut
General Electric
Tannoy
Grey Research
University
Grommes
V -M
Hallicrofter
Weathers
H. H. Scott
Wharfedale
Jensen
ETC.
Leak
for
STEREOPHONIC NOMENCLATURE
Meissner
Newcomb
Terminology For Stereophonic Equipment
Stereophone, n.: An acoustical system
plurality of microphones (or
other transducers), transmission channels,
and reproducers are arranged so as to provide a sensation of spatial distribution of
the original sound sources to the listener.
Stereophonic sound system2 (Stereophonic loudspeaker system) : A sound
system in which a plurality of microphones,
transmission channels, and loudspeakers are
arranged so as to provide a sensation of
in which a
spatial distribution of the sound sources
to the listener.
Stereophonic headphone system: A
sound system in which a plurality of microphones, transmission channels, and stereo headphones are arranged so as to produce
the sensation of spatial distribution of the
sound sources to the listener.
Stereo -headphones: A pair of headphones, each of which can receive sound
from a separate audio system.
An American Standards Association
definition of "Acoustical Terminology"
sponsored by the Acoustical Society of
America in cooperation with the Institute
of Radio Engineers proposed for trial and
study Feb. 15, 1949 and approved and
adopted by the ASA July 31, 1951 (Z24.11941). In keeping with the suggested terminology and to differentiate it clearly
from a stereo -headphones system, it should
be changed to stereophonic loudspeaker
system, as indicated in parentheses.
Stereo -loudspeaker: A loudspeaker system consisting of two or more loudspeakers
placed in two or more loocations, and which
can be energized by a stereophonic amplifier system so as to produce a stereophonic
effect.
Stereo -microphones: Two or more
microphones so spaced apart and connected
to a stereophonic amplifier as to enable
stereophonic recording or reinforcement.
Stereo -cephaloid microphone: A plurality of microphones arranged within a
structure designed to produce diffractoins
and acoustic pickup patterns simulating
normal human hearing.
Terminology For Stereophonic Techniques
Loudspeaker stereophony: The art of
producing stereophonic effects with loudspeakers.
Headphone stereophony: The art of
producing stereophonic effects with headphones.
Multi-channel stereophony3 : The art
of producing stereophonic effects with more
than two electrical transmission channels.
Terminology For Deficient
Stereophonic Effects
It is to be anticipated that improper
technique, defective equipment, or detrimental environment will result in impaired
stereophonic effects. Descriptive nomenclature for some common deficiencies follows :
Crossed stereophonism: Sources originally in the right field are heard in the left
ear and vice versa. (In headphone stereo phony crossing earphones produces this
effect.)
3 May be called 3- channel or 4- channel
stereophony, etc., to indicate the number of
transmission channels used.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
Diphonic stereophonism: Produces two ral" recorder would be completely and
localizations for a single sound source.
simply described as a two -channel
stereophonic recorder (or simply as a
Multiphonic stereophonism: Produces stereophonic recorder) which can obmultiple localization of a single sound viously be used for either headphone or
source.
loudspeaker stereophony. A recording
Dynamic diphonia: Slight movements (tape, disc, or film) made for stereo of listener's head produces abrupt shifts in headphone listening only would be
apparent sound source positions. Produced labeled "For Stereo -Headphones." The
when stereo -loudspeakers are not properly now famous Bell Telephone Laboratories
phased and the listener is positioned between stereophonic demonstration equipment
would be labeled "Three- Channel Enloudspeaker acoustic fields.
ultra -fidelity
ultra-utility
with
ultra -smart
hanced Stereophonic Loudspeaker Sys-
Diffused stereophonism: Produces the tem." A more complex system would be
effect of spreading point sources of sound, described as a "Six-Channel Stereocharacterized by loss of precise localization. phonic Loudspeaker System."
Any form of defective stereophonic
Compressed stereophonism: The condensation of a wide acoustic field into a reproduction could be clearly described,
narrow area. Occurs when a 100 -piece or- as, for example, crossed reverberatory
chestra spread across a 50 -foot stage is stereophonism, indicating that the acousplayed back to sound as though it were tic fields are crossed and that the stereophonic effect is diminished or destroyed
coming from a 10 -foot stage.
by excessive reverberation.
Expanded stereophonism: The opposite
It is the writer's hope that the sugof compressed stereophonism.
gested or similar nomenclature will soon
Reverberatory stereophonism: Occurs become standardized so that literature
when stereophonic effects are diminished describing developments, measurements,
or lost because of excessive reverberation and deficiencies in stereophonic recording, reproducing, or reinforcing equipduring pickup or reproduction.
ment will be meaningful to all who are
Reflective stereophonism: Occurs interested in the art.
when stereophonic effects are diminished
or lost because of excessive reflection durBIBLIOGRAPHY
ing pickup or reproduction.
Rudolph Flesch, "Pursuit of Translation,"
This suggested terminology now Harper & Brothers N. Y., 1951, p. 43.
makes it relatively simple to describe Edward Tatnali Canby, "Record Revue,"
AUDIO ENGINEERING, Sept., 1953, p. 47.
any kind of stereophonic system or ef- Tinkham,
R. J., "Binaural or Stereophonic,"
fect with minimum ambiguity or confuAUDIO ENGINEERING, Vol. 31 No. 1 Jan.,
sion. For example, the barbaric "binau-
HEAR the difference, SEE the difference
1826
ultra -fidelity ensemble
The proof of unprecedented
superiority of the new RAULAND
Ultra- Fidelity Ensemble is in
its unmatched performance.
That proof awaits you now at
your Hi -Fi dealer. The Master
4 Amplifier is of matchless
quality. The unique self- powered
"Libretto" Remote Control -Preamp,
with its amazing flexibility,
is an ingenious innovation. The
laboratory tests are a revelation, but the ultimate proof of
superiority is in the thrilling
listening and operating experience.
The specifications summarized
below can only hint of the quality
of this new dimension in sound.
1953, p. 22.
the master amplifier
A truly superb instrument
PREAMP WITH "PRESENCE"
(from page 25)
the normal playing position for LP records. Similarly, the two indicating points
on the tone-control are arranged to be
"straight -up" when in the flat position,
and the control tapers are designed to
have a "flat" range of at least 15 deg.
The non -indoctrinated user can be told
to leave the filter and presence control
alone
that would solve the problem.
used in the prototype. While there is no
particular need for this type of construction, it does simplify the work to
some extent.
Figure 2 shows the resistor mounting
card used in the original model. The
resistor card, together with the tube
sockets which are mounted on the card,
was attached to a channel designed for
mounting onto the chassis with rubber
Construction
grommets. With the Genelex Z729 tubes,
The construction of this unit follows however, the extra care in reducing
fairly simple lines, with the possible ex- microphonics has turned out to be unception of the resistor board which was necessary, and the sockets may just as
-if
with frequency response of
±0.3 db, 20 to 40,000 cps at rated 20
watts output. Harmonic distortion less than
0.5% at rated output, less than 0.3% at 10
watts. Intermodulation distortion less than
0.4% at 1 watt (home level), 0.7% at rated
output (measured at 60 and 7,000 cycles 4 to
ratio). Output imp., 8 and 16 ohms. 4 -posilion input selector-for magnetic pickup, crystal pickup and 2 auxiliary. Dimensions: 14'
1
x9'x8"high.
the LIBRETTO
remote control
A true remote control, completely self- powered and capa-
of operation several hundred feet from
amplifier. Uniquely fashioned in the form of
a luxuriously bound book (only 83 x 11 x 2'
thick). Backbone lifts to provide easy access
to tuning controls. Operates flexibly in either
horizontal or vertical positions.
ble
.Eo
CONTROL FUNCTIONS
A
a
faj¡land model
in the
B
--
Fig. 6. Curves showing the limits of tone
c
o
control action, together with an intermediate curve for
D
both boost and cut.
E
E
gG
-,L.___
_1g
(flat, 150, 300,
450, 700, 1000 cycles). 2. 6- position roll -off control (flat, -5, -8, -12, -16,
24 db at 10,000
cps). 3.Volume Control -instant choice of convention1. 6- position crossover control
A
-EO
-
al control or loudness control. 4. Bass Tone, +24 db
lo -20 db at 20 cps (db calibrated).5. Treble Tone,
+18 db to -30 db at 10,000 cps (db calibrated).
Custom-Engineered, Custom-Styled
For Audio Connoisseurs
Sae the RAULAND
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ro
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FREQUENCY IN CYCLES PER
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3515
AUDIO ENGINEERING
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
W.
Addison St., Dept. AD, Chicago 18,
M.
55
less expensive units may be used. But
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The Remarkable New
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FM -AM TUNER
Fig. 7. Mounting of the components for the low pass filter circuit. The input impedance -adjusting resistors Rn to R. are mounted on the
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This new superheterodyne FM -AM
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A
chassis, although the original was made
size which is
on a 3 x 6 x 14 base
rather difficult to obtain. Layout of the
terminal card is not difficult, but since
every constructor has his own ideas of
just how he wishes to do the job, specific layout is not indicated. With the
Alden terminals, however, it is possible
to arrange the terminals so that all of
the grid -circuit components -as well as
the cathode resistors and their by -pass
capacitors, and the compensating resistors and capacitors -may be placed on
one side of the board, and the plate and
screen resistors, together with the decoupling resistors and certain other
components can bet,placed on the other.
This requires that the bottom of the
chassis be cut out to provide access to
the "bottom" of the resistor board, since
changes -may be required during the
construction or-possibly-afterwards
when service becomes .necessary..
The mica capacitors used in the equalizer circuits may best be Silver Micas,
since they may be obtained with the
closest tolerance. The small amount of
shift in values can readily be tolerated
without apparent effect, but most constructors will wish to take advantage of
the 10 per cent tolerance of this type of
component. The two inductances listed
may be any type of toroid available. If
the entire installation is to be used at
some distance from any hum -producing
fields -such as a phonograph motor-
-a
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for complete freedom from the effect of
any external fields, the toroid is the
answer.
The original unit built by the author
takes the place of one which has been
in service for several years, and is
powered by the same supply that has
been in service since it was originally
described in the series on "Residence
Radio Systems," published in 1948. This
supply was designed to furnish 12 volts
d.c. at a maximum drain of 1.0 amps,
and with a relatively low ripple. The
unit has been tested with a 6.3 -volt a.c.
supply and has been found entirely satisfactory, provided the latter is suitably
center- tapped to ground the circuit as
near to the zero -potential point as possible.
While the circuit shown makes no
provision for switching between phono.
radio, TV, tape recorder, or any other
possible source, there is no reason why
the builder could not place another
switch in the circuit and arrange to accommodate any desired number of signal sources. However, most modern
20
so
3000
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Fig.
8.
Curves of
5000
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20000
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filter action.
tuners provide switching facilities, and
this unit is designed to furnish only the
basic requirements of a sound system
the preamp, the tone -control facilities,
and some means for controlling the
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Reference to Fig. 7 will show the
arrangement of the components-except
the inductance -used in the low -pass
filter circuit. The four capacitors at the
left are shown with their shunting resistors, and are-from left to right
Cs. to CN respectively. The next four
-
IIIIII
111111I111111RI
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-
FREQUENCY
IN
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
NNW
CYCLES FER SECOND
JANUARY, 1954
capacitors are C.. to C. respectively.
One end of each of the capacitors and
resistors is grounded, and leads connect
from the other terminals to the two arms
of Sws. Construction is not critical,
since the impedances are low at this
point in the circuit.
Special Components
Special units are listed for several of
the components, but all are available.
The preamplifier switch -consisting of
two 5-position decks, one with one arm
and one with two, and both being actuated by a dual- concentric assembly
is listed as part number SPP -3002, a
Centralab Type 30c switch. The Baxendall tone control unit is available completely assembled as Centralab part
number C3-300, and consists of the two
pots assembled as a dual -concentric unit
together with the Couplate. The combination presence control and filter
switch is available as Centralab part
number SPB -3001. The Senior Corn pentrol is already available as Centralab
part number C2-100. All units have
in. long,
standard bushings (a-32)
with the inner shaft 1 9/16 in. long,
measured from mounting surface, and
the outer shaft 1 1/16 in. long, measured
from the mounting surface. This provides sufficient room for any panel up
to ;,¡ in. thick.
Several types of knobs are obtainable for these controls, since the dualconcentric control has become quite
common on TV sets. The writer's TV
set is a "home- made" Techmaster 630
mounted in a bleached oak corner
speaker cabinet, and the knobs used are
those normally used on the RCA 8TS30
receivers. To have matching knobs, the
same type were used. Tan knobs are
obtainable as stock numbers 73227 and
73231; the dark brown knobs are stock
numbers 73226 and 73230. Four of each
are required. Other types of knobs may
be obtained from various sources, but
may entail some searching. All of the
Centralab units may be obtained on
order from any Centralab distributor.
-
1600 µµf, mica
3000 µµf, mica
5600 µµf, mica
20-20 pf, 350 v., electrolytic
something worthwhile, and the time Co, Cn
and money have not been spent in vain. C,,, Co
Co, Co
C,,,
C
PARTS LIST
CI
C,
C,, C.
C,, C,., CH
Co, C,.
Cl, Cl, Cu
Cr
C.
C,.
C
Cu
C
.05 pf 600 v., Aerolite
.002 pf, molded paper
0.5 µf, 600 v., paper
0.1 pf, 600 v., Aerolite
L,
L,
R,
2000 µµf, mica
1200 µµf, mica
3300 µµf, mica
200 µµf, mica
620 µµf, mica
1000 µµf, mica
3500 µµf, mica
R,
R,
R,
R,
R.
Rs,
C,.
R.
CH, C..
0.47 meg,
R,.,
R
R,,.
R
R
0.25 pf, 600 v., Aerolite
1100 µµf, mica
Ct,
R", R,e,
R,., Rt.
Re
150 µµf, mica
50 pf, 6 v., electrolytic
Cu
(Mallory FP-227)
H, toroid inductance
0.45 H, toroid inductance
47,000 ohms, 1/2 watt
3900 ohms, % watt
0.5 meg, 1 watt, low noise
1.5 meg, 1 watt, low noise
1.2 meg, 1 watt
1200 ohms, % watt
.0.1 meg, 1 watt, low noise
1.0
0.1 meg,
1
1/2
watt
watt
33,000 ohms, V2 watt
watt
1.0 meg,
27,000 ohms, 1 watt
y
(Continued on page 62)
From
Station Break
to
Feature...
the NEW
et'
coil--
doing a
whale of a job
every day!
is
"BALANCED"
TV
TRIPOD
mounted on
3 -wheel
portable
collapsible
dolly
illustrated.
THREW THE book away and engineered o
brand new "BALANCED" Tripod for every photorevelagraphic and video need. The result
tion in effortless operation, super- smooth tilt
and 360° pan action.
We
-a
BALANCE prevents mishap if the lock
lever is not applied. Quick release pan handle
locks into desired position. Mechanism is enclosed,
rustproof, needs no lubrication. Tension adjustment for Camera Man's preference.
Built -in spirit level. Telescoping extension pon
handle. We defy you to get anything but the
PERFECT
Performance
The performance curves of the several
functions of this amplifier have been
shown in Figs. 5, 6, 8, and 9. The presence control may appear to be another
example of painting the lily, and in this
era of attempting to obtain a response
curve which is completely flat from zero
to infinity may appear to be unnecessary, but it is only suggested that a
quick trial be made of the idea before
passing judgment. Like many circuit
arrangements, it is not always possible
to pass upon their effectiveness until
one has an opportunity to listen to the
results, and it is this writer's opinion
that "somthing new has been added"
when the presence control is turned
from off to on. The effect is neither
ear shattering nor eye opening, but as
one approaches the optimum in performance it requires only a small change
to outwit the law of diminished returns.
If we can "cheat" the response curve
just enough to make the change reasonably perceptible, we have accomplished
AUDIO ENGINEERING
smoothest, most efficient operation out of this
tripod beauty.
WE DESIGN and manufacture Lens
Precision T' STOP CALIBRAWE CALIBRATE LENSES
Mounts and camera equipment for
method
is
Our
focal
length.
lenses,
any
TION of all type
35mm and TV cameras.
16mm
approved by Motion Picture Industry and Standard Committee of SMPTE. Lenses rooted for photography.
Special TV coating.
FRANK C. ZUCKER
'
WE
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CAMERAS
DOLLIES
SERVICE
HOWELL:
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Complete line
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MITCHELL:
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MOVIOLA:
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available for rental.
BNC,
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16mm.
Editing machines,
JANUARY, 1954
www.americanradiohistory.com
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MAURER:
8
16mm
Synchronize rs.
C.
...
YOU WORK WITH FILM
It will pay you to get to know us.
foremost
The country's
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portable,
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57
FACTS YOU
A Perfect Loudspeaker:
A New Reproducer Philosophy
SHOULD KNOW
ABOUT U H F
CONVERTERS
LEUNG CHO YUK
Many converters on the market today
are unsatisfactory in fringe and
shadow areas where signal strength
is low. Before you install a UHF
converter in these areas you should
know these facts:
Signal power loss in the preselectot
seriously affects picture quality.
Most UHF converters use sliding.
contact shorted line tuners in the
preselector with a fixed power loss
of 6 db. The Turner uses High Q
i
coaxial cavity tuners with no sliding
contacts. Signal power loss is cut
to 3 db. The resulting low noise
figure keeps picture quality high.
2
3
Oscillator radiation often causes in
terference with neighboring sets. In
the Turner converter the oscillator
tube socket and all associated circuits are inside the coaxial cavity,
self -shielded. Removable covers provide a second shield against radiation.
High amplifier noise figure can further damage picture quality. The
Turner converter uses a special
broadband amplifier with Cascode
circuit. It retains the preselector sig.
nal savings without appreciably increasing the noise figure. The Turner
amplifier noise figure is only 4 db.
Whether installing converters in
shadow and fringe areas, or putting
one in your own home, remember
the Turner often means the difference between good reception and
bad reception.
EXCLUSIVE TURNER FEATURES
Higher sensitivity
Extremely low noise figure
Exceptional frequency stability
Double shielding
Hi -Q silver plated coaxial cavities
No sliding contacts
OTHER MAJOR TURNER FEATURES
Illuminoted
Continuous single -knob tuning.
slide-rule dial. Smaller size: 8 "x6 "x6 ". Use
with UHF or combination antennas. Self powered, uses channels 5 or 6. Complete installation instructions. For 110 -120 volts 50 -60
cycles AC. Schematic included.
List price
$49.50
In VHF fringe and
shadow areas, the
Turner Booster is a
superior performer;
too.
r.......= =.
The TURNER Company'
929 17th St., N.E., Cedar Rapids, Iowa
Gentlemen: Please send complete infor -p
motion on the Turner UHF Converter Op
Turner Booster
Name
Address
City
State
II-
-I
I
I
58
1
.J
Export: Ad Auriemo, Inc.,
89 Broad St., New York 4, N. Y.
Canada: Canadian Marconi Co.,
Toronto, Ont. & Branches
Many a valid concept long precedes the technology necessary to
make it a reality. This writer's concept is interesting despite the
fact that present -day techniques could not make it a product.
TRE
CONTROVERSY AROUSED in the
article, "The Great Loudspeaker
Mystery, makes the writer feel that
the art of loudspeaker designing is still
in its infancy. No wonder it is being
looked upon as a kind of mysticism. Before the perfection of any art or science
it is always a mystery to our bewildered
minds. Its understanding may, of course,
be regarded as a kind of metaphysical
philosophy.
It seems that there are two schools
of opinion about the construction of a
perfect speaker diaphragm. It is a pity,
however, that they both tend towards
the two extremes -the infinitely rigid
cone, and the very flexible one. It seems
to this writer they are both right in a
way, but, inconceivable as it may seem
to adherents of either group, they both
lack something. How,,ever, before putting
forward a new argument, let us have
a little discussion about nature and the
way we often try to imitate her.
It is undeniably evident that our ears
hear and that our mouths speak. This
may lead one to the assumption that our
ears and mouths are, electromechanically
speaking, equivalent to the microphones
and loudspeakers in an electro- mechanical acoustic transmission system; many
designers, indeed, carry out their designs according to this principle. The
idea sounds reasonable enough. But in
the writer's opinion, only the ear is
good enough for us to imitate. This does
not mean that we should only design
microphones. On the contrary, we
should also design loudspeakers-by
imitating some of the special features
of the ear mechanism. The reason why
we should not imitate the mouth (the
human voice producer) in designing
speakers is that the way in which our
mouth produces sound is too complex
to imitate. It is, after all, a generator,
not an imitator ; yet it requires an air
flow of variable intensity and velocity,
stretched vocal chords with variable
length and tension, very involved cooperative movements and effects of various muscles, teeth, tongue, lips, nose,
larynx, and so on. And with all of this
the mouth can produce sounds only
within a very limited frequency band
and over a very limited range of various
types of characteristics.
'
s 6 Rednaxela Terrace,
Caine Road,
Hong Kong.
I H. A. Hartley, AUDIO ENGINEERING,
Jan., 1953.
Certainly the highest standard we
ought to demand of speaker design is
nothing more than to satisfy our ears,
so that when we listen to a speaker we
may have as nearly as possible the same
feeling we would have if we were hearing the real thing. Actually, what we
want from a system (from microphone
to speaker) is to have it do the work
of "acoustical space shortener" or
"acoustic energy preserver" so that it
can, electronically or otherwise, take
our ears to, or back to, the actual scene
-the origin of the sound.
The translation of acoustical or mechanical vibration to electrical nerve impulse in our human hearing apparatus
takes place in the cochlea. The electrical
impulses are then sent to the brains,
so that we can feel the sensation of
sound. The cochlea is a coiled, liquid
filled tube divided longitudinally by the
basilar membrane into an upper and
lower gallery.' The basilar membrane
is composed of about 24,000 tightly
stretched fibres. It is assumed that each
fibre is resonant to a certain frequency,
whereupon we may assume that these
24,000 fibres are resonant to 24,000
different frequencies, which can well
cover the audible frequency range, from
20-20,000 cps. This explains why we
can hear clearly and vividly and distinguish two almost similar tones.
Though there is some nonlinearity in
our hearing systems, the deficiency is
tolerable, since we are born like that and
probably would be very unhappy if the
nonlinearities were somehow miraculously straightened out.
In the designing of a perfect speaker,
the diaphragm should be made to resemble that of the basilar membrane in
that it should be composed of about
24,000 individual units. Each unit should
then be made to resemble the rigid disc
described by one school of opinion as
the perfect diaphragm (though the
construction of such a disc is still an
enigma) so that each unit can respond
to one frequency only, as claimed by
the mastermind of the perfectly flexible
diaphragm. The units should, however,
be connected together in such a way
that each of the individual units should
have no influence on and not be
influenced by any other unit. In such
a case, the whole diaphragm resembles
' Edgar M. Vilichur, "Handbook of
Sound Reproduction," chap. 6, AUDIO ENNov., 1952.
GINEERING,
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
a really flexible diaphragm, yet consists
of thousands of individual and independent rigid discs.
Though the perfect speaker diaphragm described above seems at the
moment very difficult or even impossible
to construct, it is strictly sensible, and
before rejecting the idea the reader will
do well to remember that before any
problem is solved it begins as an enigma.
Scientifically speaking, nothing is impossible. Our forefathers would certainly have been willing to swear that
you could never see a man who is 1,000
miles away; today we call it television
and think the old ancestor was terribly
backward!
Even
in designing
present -day
speaker systems we are following my
trend of thought. Look at the coaxial
and triaxial speaker systems. Each of
the two or three units is mechanically
and electronically separated and decoupled from the other unit or units, so
that each may work independently
within its own frequency range. Results
so obtained have been found to be much
more satisfactory than a single unit.
There is no reason why development
cannot be extended to the perfect
speaker diaphragm described. Though it
may still be a long time before our
technology is equal to the task, it is
certainly worthwhile to think about this
principle and try it when we can. So
let us go back to our labs and start all
over again!
Some salient characteristics:
REFERRED PRIMARY LOADING. The stand-
ard models cover the requirements of all
popular tubes. Each half primary is brought
out separately to posts and is tapped at
43o/d of the turns.
POWER RATING. Peak SO watts at 60 c.p.s.
or 14 watts at 30 c.p.s. for less than 0.5%
harmonic distortion without feedback.
LEAKAGE INDUCTANCE . . 10 mH. SELF
CAPACITY . . 500 PF. full primary.
Edited by Richard F. Shea. New York:
John Wiley and Sons, Inc., 535 pages,
illustrated, 1953. $11.00.
While some of the material in this book
may be familiar to those who have followed
the technical reports on transistors issued
by Bell Telephone Labs, there is a large
amount of new material which has not been
published before. Heretofore the best available material on transistors all in one place
was the famous November 1952 issue of the
Proceedings of the IRE. This text is the
work of nine engineers at General Electric.
The task of harmonizing all the manuscript
into a uniform easily readable text, was
undertaken by Richard F. Shea.
For those not familiar with matrices
there is a separate chapter on matrix methods of circuit analysis and there is additional information on the fundamentals of
matrix algebra in the appendix. Since many
engineers are more familiar with vacuum
tubes than with these new substitutions for
electron tubes, the editor has gone to special pains to indicate the resemblances to
vacuum -tube circuits. The introductory
chapter on semiconductor principles plus
the second chapter on forms, types, and
characteristics of transistors, both read in
conjunction with Chapter 14 on circuit design by duality will help the engineer with
little knowledge of transistors.
The level of the book is graduate school
but the practicing engineer will be able to
read this text with understanding and
profit.
-D.
AUDIO ENGINEERING
* For "Williamson" enthusiasts there is the well proven type WWFB -the originally specified trans$26 Duty Paid
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For those seeking 'C' Core technique at its best
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there is the now famous C.F.B
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Sealed in a deep drawn case.
AMPLIFIER KIT
FEATURES
Practically distortienless. Harmonic and inlermodulation distortion
both less than one hall of I9} at 5 watts.
I db hem IB cycles to 100 kilocycles.
Frequency response
Attec Lansing PEERLESS or ACROSOUND Iranstnmers available.
First Wllkamson type Amphfiei wished with matching preamphñer.
When selecting an amplifier for the heart of
a
fine high-
fidelity audio system, investigate the outstanding advantages
offered by the Heathkit Williamson type Amplifier. Here is
an amplifier that meets every high -fidelity audio requirement and makes listening to recorded music a thrilling new
experience through naturally clear, lifelike reproduction of
sound at all tonal levels. Wide acceptance of the Heathkit
Williamson type Amplifier by the most critical purchasers
clearly demonstrates that high -fidelity can be coupled with
low cost. For factual information regarding the Heathkit
Williamson type Amplifier, consult "CONSUMERS RESEARCH ANNUAL CUMULATIVE BULLETIN 1952 -53."
This outstanding amplifier is offered with the optional
choice of the ACROSOUND output transformer or the PEERLESS output transformer. ACROSOUND features ULTRA LINEAR circuitry, which is the exclusive development of the
Acro Products Company and provides a. greater margin of
reserve power efficiency and increases power output. PEERLESS features additional primary taps to permit the optional
choice of either the extended power circuitry. now enjoying
current popularity. or all of the advantages of the original
Williamson type circuit.
The construction manual has been simplified to the point
where even the complete novice can successfully construct
the amplifier without difficulty. Write for a free catalogue
containing complete specifications and schematics of the
Heathkit Williamson type Amplifier.
HEATH COMPANY
BENTON HARBOR 25, MICH.
PRICES OF VARIOUS COMBINATIONS
Amplifier Kit Ilnrl. M., in AnipiM.r
with peerless Output Transform.
W-a
r. Power Sulmry anti WA-PI
lbs. Shipped express
only.
W -aM Amplifier Kit (ind. Main Amplifier
with Peerless Output Transformer
Power Supply) Shipping :4915
W1
eight 29 lbs. Shipped express
only.
W -3 Amplifier Kit land. Main Amplifier
with Aerosound Output Trans.
former, Power Supply and WA- feeda
PI Preamplifier Kit) Shipping faa961
weight 39 lbs. Shipped express 1111U
only.
W -3M Amplifier Kit (Ind. Main Amplifier
with Arrosound Output Trans.
former and Power Supply) ship
ping Weight 29 Ms
e
press only.
WA -P1 Preamplifier Kit only. Shipping
Weight 7 Ms. Shipped express
or parcel post.
Preamplifier Kit) Shipping f 6950
Weight 39
p
T. Armstrong
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
59
SAVE
PROFESSIONAL TAPE RECORDER
33,E
(from page 22)
This is
our
GROUP SUBSCRIPTION PLAN
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The more men in a Group, the more
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1
AUDIO ENGINEERING is still
the only publication devoted
entirely to
Audio
Broadcasting equipment
Acoustics
Home reproduction systems
Recording
PA systems
Psychoacoustics
Please
print)
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.
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U.
Company
S
,
Posw,ti,or
and Cana la only.
RADIO MAGAZINES, INC.
P. O. Box
60
629, Mineola, N. Y.
Fig. 9. Schematic of the cascode preamplifier
stages in the amplifier section.
Valley and Wallman' and shown in Fig.
9. The use of this input stage results in
lower equivalent input noise than most
microphone preamplifiers commercially
available. The production units have
shown an input noise figure of the order
of -127 dbm. The newly developed 6BK7
tube is used. The high amplification
factor and low plate impedance of this
tube make it well suited for cascode application. The input stage is capable of
handling input levels at high as -20 dbm
without exceeding 1 per cent total harmonic distortion. The large input signal
handling capability and the low noise
figure result in an ideal microphone
amplifier input stage. Approximately 6
db of inverse voltage feedback is carried
around the input stage to increase the
level handling capabilities.
The output stage V. consists of a
constant-current, inverse-feedback amplifier, with a large cathode resistor to
provide the feedback. Equalization is
accomplished in the cathode circuit by
employing a small bypass capacitor
across the cathode resistor, resulting in
higher gain with higher frequency. This
method is used for the 15 -inch tape
speed. At
inches a greater slope of
the equalizer curve is required and a
series resonant circuit is used to shunt
the cathode resistor. Equalizations are
of the order of 8 db at 15 kc for 15 ips,
and 16 db at 15 kc for
ips.
The response of the recording amplifier is flat from approximately 30 cps to
the point where the high -frequency pre emphasis begins. It is the opinion of the
authors that low- frequency pre- emphasis
should not be used in the record amplifier, to eliminate the possibility of overloading the tape with high- level, low frequency tones.
The plate of the output stage connects
7/
7/
' Valley and Wallman, "Vacuum Tube
Amplifiers," McGraw -Hill Book Co., 1948.
directly through an 0.5 µf capacitor to
the record head. A potentiometer is provided in the ground return of the record head circuit. The bias current passes
through this potentiometer, and a voltage
proportional to the bias current is developed across it. A portion of this voltage is tapped off and fed to the VU
meter as the bias reading.
A second voltage amplifier also feeds
a cathode- follower stage which supplies
record monitoring voltage to the VU
meter and to the phone jack. The output
impedance of the cathode follower is approximately 600 ohms. This impedance,
together with the 3,300 -ohm VU meter
series resistor, constitutes the proper
impedance and time constant for proper
damping of the VU meter. The over -all
apparent gain of the record amplifier
at the microphone input is 95 db. This
means than an input level of -95 dbm is
required for a zero level recording.
Reproduce Amplifier
The output voltage from the reproducer head is fed directly to the first
grid of a 12AU7 input stage connected
in a cascode arrangement. Several types
of tubes were tried in the input stage;
these included a low -noise pentode and
various dual triodes. However, it was
found that the 12AU7 connected in the
cascode arrangement resulted in the
lowest over -all noise figure. The output
of this stage feeds the first section of a
12AX7 dual-triode cascode amplifier.
The output of the first section of the
12AX7 is fed back through an inverse
feedback loop to the cathode of the input
stage. This is a frequency -selective voltage feedback network which results in
over-all frequency characteristics very
closely in agreement with the standard
NARTB playback curve. This curve
consists of approximately 25 db of additional gain at 50 cps above the 1000 -cps
gain, while the gain at 15 kc is approximately 10 db below the 1 -kc gain.
The over-all gain of the playback amplifier is approximately 75 db at 1000
cps. There is an additional gain of approximately 25 db at 50 cps. Since most
of the noise consists of low -frequency
components, the gain affecting the noise
output is of the order of 95 db. Calculations will show that the equivalent input
noise due to the input stage is phenomenally low. This is a criterion which
must be satisfied to achieve over -all high
record -playback signal -to -noise ratios. It
may be safely stated that with any highquality recorder the determining noise
should be confined strictly to the tape
output noise, and the amplifier noise
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
JANUARY, 1954
Battery- Operated
Long -Play Spring -Motor
Portable Recorder j
Spci dl...Ilt designed for maximum professional
performance with greatest operating ease. Friction free, ball -bearinged drive system enables
tape transport mechanism to run 15 minutes on
a single wind (at 744 ips). Dynamically balanced
hidden flywheel reduces Butter and wow, equivalent to studio equipment. Incorporates high speed
motor rewind (100 seconds). Built-in spring motor meter continually indicates condition of
spring motor. Single knob controls tape and playrecord functions. Safety "Record" interlock. 4
Models available in speeds of 344, 74 & 15 ips.
Check These Unusual Features:
* High -speed
rewind
*15 Minute play per wind
* Hidden high-speed flywheel
* Ultrasonic bias
* Meets NARTB standards
*100 Hours battery life
* Size: 7 z 10 z 11
* Weight: 14 lbs.
inches
Write for complete technical literature
and direct factory prices to Dept. AE
AMPLIFIER CORP.
of AMERICA
398 Broadway, N. Y. 13, N. Y.
should be held at least 6 db below that.
The playback gain control is located
between the second and third stages of
the amplifier. The gain control is followed by two stages of triode amplification and an output stage consisting of
one -half of a 12AU7. The output transformer has two 600-ohm secondary windings, one of which is carried directly to
the output terminal, a barrier strip on
the rear of the chassis. The other secondary winding is used for developing
constant -voltage inverse feedback around
the output and driver stage, and also to
supply voltage to the monitor jack and
the VU meter. There is approximately
20 db of feedback around the output and
driver stages, which results in distortions of less than 1% at the full rated
output of +16 dbm.
When the equalizer switch is in the
7.5 position an R -C network is connected
across the cathode of the driver stage to
increase the high- frequency response by
about 6 db at 15 kc so that frequencies
up to 15 kc may be played back at 7%
inches per second.
The power supply for the amplifiers
consists of a transformer -fed, single phase, fullwave rectifier, followed by an
R -C low -pass filter. Filament voltage
for the input stages of each of the two
amplifier sections is supplied from a
rectified 18 -volt winding of the power
transformer to maintain low hum content. A.c. power for the amplifier is obtained from the tape transport unit
through a power cable and connector.
The plate and filament voltages are supplied to the bias oscillator on the tape
transport unit through this power cable.
Performance Figures
...before it TALKS
...is the way our doctors put
-
it "Our chances of curing
cancer are so much better
when we have an opportunity
to detect it before it talks."
That's why we urge you to
have periodic health checkups that always include a
thorough examination of the
skin, mouth, lungs and rectum
and, in women, the breasts
and generative tract. Very
often doctors can detect cancer in these areas long before
the patient has noticed any
symptoms.
For more life - saving facts
phone the American Cancer
Society office nearest you, or
write to "Cancer "-in care of
your local Post Office.
The over -all performance of the M-80
is well within professional standards, not
only in an electrical and mechanical
sense, but also in terms of fulfilling pro
fessional operational requirements. Starting time for the tape is less than 0.1 second and stopping takes place within 2
inches of tape when using the operating
speeds. Flutter and wow are under 0.1
per cent r.m.s. at 15 ips and less than 0.15
per cent at 7.5 ips. The signal -to-noise
ratio is better than 58 db, based on a
level giving a maximum of 3 per cent
harmonic distortion.
The frequency response for the overall recording- playback operation is
shown by the two curves of Fig. 10 to be
within 2 db from 30 to 15,000 cps at 15
ips, and within 4 db at 7.5 ips. The total
harmonic distortion for maximum indicated level of 0 VU on both record and
playback is less than per cent.
TERMINAL
Direct Factory Distributor
(in Downtown N. Y. C.)
for all MAJOR Lines
including:
McIntosh
LAEORATORY, Inc
Amplifiers or 99. 96,'.00% per
led amplification.
afFneandi,INC.
Tape Recorders for profess onal
recording the world around.
SOUND, Inc.
Speakers-End esurss for match.
lest reproduction.
RADIO ENGINEERING
LABORATORIES, In_.
designers of
profess onal
FM Tuners -Receivers
the first and finest
FM receivers.
Recording Equipment for price.
less "presenze" and perform.
AMPEX
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First for Values!
Because TERMINAL stocks
MORE of the World's finest Ni -Fi, Audio, and
Sound Equipment) You owe it to yourself to visit
Terminal Sound Studios. See, Hear, Compare all
makes, from basic units to special equipment for
every application
communications, industry, and
the home.
-
Over 130 pages packed with
sound values. A ready refer.
ence to everything in audio
for audio engineers and
-
music lovers
Amplifiers,
Speakers, Radio & TV Tuners,
Retard Changers, Recording
and Playback Equipment,
Furniture,
Custom
Public
o
Address and Sound Equipment.
If you can't visit
our Sound Studios, send for
your FREE copy today.
.5
RESPONSE CURVE
RESPONSE CURVE.
15"/ SEC
Audio
Radio
7.5' /SEC.
5
-10
20
Fig.
Video
ilecteonic Equipment
Phone: WOrth 4 -3311
50
100
10.
500 1000
CYCLES
PER
5000
10000
SECOND
Response curves of the M -80 at 7.5
and
AUDIO ENGINEERING
NAMES AT
1
FREQUENCY IN
American Cancer Society
FAMOUS
15
inches per second.
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
I
t'
mina
RADiC CORP.
85 Cortlandt St.
New York f, N. Y.
61
Now!
A COMPLETE
GUIDE TO
HIGH
FIDELITY!
glom
.. for listeners
...builders
,
...
experimenters
service technicians
This big, new authoritative
book by one of the nation's
leading experts brings you
JUST OUT!
the "low down" on every
HIGH
phase of high- fidelity reproFIDELITY
TECHNIQUES duction and equipment. In a
way you can easily underby John H. Hewitt D.I.C. Staff stand, it shows how to get
Member, Dept. of best results at minimum cost
Electrical
Engi- -discusses all details of "hi
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494 pages,
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chock full of how-to -do-it
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ANSWERS YOUR QUESTIONS
ABOUT "HI Flee- Covers both
construction and service problems
-
a few
of the subjects covered:
What to look for in high -fidelity equipment
what to avoid
Getting reproduction to suit your
taste
Some unusual "hi -fi" combinations
Matching the reHi -fi vs. P.A. type speakers
Loudspeaker conproducer to its environment
Adjusting bass -restruction and performance
A novel
flex cabinets
Controlling distortion
Letting rid of "overBaffles
horn system
Selecthang"
The best reproducer enclosure
Sounding a woofer -tweeter combination
How grillwork affects atproofing materials
Proper crossSpecial hi -fi circuits
tenuation
over frequencies for dual- channel amplifier systems
Do's and don't's of volume expansion
A good tone control
Ways to suppress noise
Negative feedback and how to use it
system
Amplifier construction
Pre -amps and equalizers
Commercial amplifiers and how to judge
hints
MiniF -M tuners and how they work
them
Avoiding chatter and
mizing tuner distortion
Limiter- discriminator vs. ratio deteccrosstalk
All about records
tor FM circuits
A comprehensive
and record players
Pickcourse in magnetic recording
up resonance, its cause and cure
Tips for cusChoosing a recorder
Custom -building techtom builders
Special
nical problems and solutions
Typical "hi -fi"
installation problems
Bass -reflex calculations
installations
charts
design
and
Acoustical horn design
Here are just
data
.
and dozens of
other subjects. Read it
for 10 days AT OUR
RISK! Use coupon.
50,000 ohms, linear pot, (combined with SW))
1800 ohms, % watt
18,000 ohms, 'A watt
R
R,e
Rua,
R
R
Centralab Senior Compentrol
1000 ohms, 1 watt
6800 ohms, 1 watt
13,000 ohms, '/2 watt
11,000 ohms, 'A watt
8200 ohms, % watt
12,000 ohms, '/2 watt
10,000 ohms, % watt
7500 ohms, % watt
5600 ohms, % watt
10,000 ohms, 1 watt
5600 ohms, 2 watt
3900 ohms, 2 watt
1.8 meg, 1 watt
Preamplifier switch, Centralab
b
R
R
R
R
R
R,.
R,e
R
R.
Sw,, Sw,
30c type, special (see text)
Centralab 30a type, combined
with Ru, special.
Amphenol 80 -PC2F receptacle
Amphenol 80 -C receptacle
Centralab Couplate No. 12614,
with 1.0 -meg front section
cad 0.5 meg tapped rear section dual- concentric controls
Genelex Z729
Ste,
J,. J,, J,
JI
Tone Control
VI, V,
V,
12AX7
12AU7
vI
III(;ll FIDELITY TECHNIQUES
Newitt for 10 -day FREE examination, If
decide to keep the book, I will then remit
$7,50 plus postage. Otherwise, I will return
book postpaid promptly and owe you nothing.
(If you send cash with order, we pay postage
-same return privilege with money refunded.)
Name
Send
by
I
Address
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OUTSIDE U.S.A, -Price $8,00 cash only
Money back if book is returned postpaid to
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62
AUDIOPHILES wanted for part or ful
time work. Technical or secretarial expert
ence desirable. Location : north suburban
Philadelphia. Send resume of education and
experience to Box CJ -1, AUDIO ENGINEERING.
VIRGIN Presto thermostyli. Box 101, St.
Albans, N. Y.
ELECTRO -VOICE 950 "Cardai" mike, no
Astatic WR-40, $20 ; Shure 55 dynamic, $30.
Guaranteed new condition. HEIN, 418 Gregory, Rockford, Ill.
INCOME TAX PROBLEMS -Personal, bustness tax returns. Low cost service. Mail $1
for Tax Saver Guide. Donald Hilliard, 1697
Broadway. Dept. F-11, New York 19, N. Y.
PACIFIC NORTHWEST FANS -why not
own a Klipsch corner speaker. Telephone me
for a free demonstration featuring latest
Scott, Browning, Fairchild units. Trade-ins
accepted. William T. Raymond & Associates,
17 Oak Park Drive, Tacoma, Wash. Phone
LA 9265.
AUDIOPHILE WANTED, thorough knowledge high -fidelity, aptitude for administration
and sales. I.Q. at least 140-no exceptions.
Good typist, excellent vocabulary. Man or
woman of executive calibre will he business
manager within six months at $6000- $8000.
$15,000 within three years, High -Fidelity
House. 536 South Fair Oaks, Pasadena 1,
Calif. Telephone RYan 1 -8171.
FOR THE FIRST TIME-Guaranteed aystem response of 30- 20,000 cps including
speaker and pickup, NICELY ASSOCIATES,
Kenton, Ohio.
WANTED: Western Electric 728 -B speakers, Stanley Ruttenberg, 13650 Valley Vista
Blvd., Sherman Oaks, California
ALTEC 604E 15 -in. speaker, $100; Altec
A-433 -A front end, $45, for Williamson Amp.
3M, 34-35 76th St., Jackson Hts., N. Y.
IL 7-8649.
TANNOY SPEAKERS, available NEW
YORK area. Call (New York) PLaza 7-8569
(evenings REgent 7-2642) for opportunity to
hear one in typical high -fidelity custom music
Installation. You will be impressed. BOHN
Music Systems.
HEAD ALIGNMENT and record level ad-
justment tape, $4.00 postpaid. E. J. Lesher,
2730 Heatherway, Ann Arbor, Mich.
You got troubles? Let us fix them!
COMPETENT ENGINEERS
FULLY -EQUIPPED AUDIO
LABORATORY
Distortion, frequency -response, and other
measurements; hum elimination. correction
of faulty operating conditions, performance
improvement to your requirements. Write,
describing your problems for estimate.
Box PV -1, AUDIO ENGINEERING
Dept. AE -14, Rinehart Books, Inc..
Technical Division,
232 Madison Ave Now York 16 N. Y.
per Word per insertion for noncommercial
i a
adveradvertisements; 25e per Word for corn
tisements. Rate, are net, and no discounts wi II be
al lowed. Copy must be accompanied by rem ìttance in
full. and must reach the New York office by the
first of the month preceding the date of issue.
Rates: IOC
page 57)
I
K
R,.
R.,, R,e
.
-CLASSIFIED
"PRESENCE"
HIGH -FIDELITY
-
536 South Fair Oaks, Pasadena 1, Cal.
5
-4118
RECORDING ENGINEER -Three years experience with small, well -known company.
Can do mastering. maintenance, editing, construction, etc. References on request. Box
CJ -2, AUDIO ENGINEERING.
FOR SALE Altec 604C speaker, network,
used several weeks, ;120. Stephens Tru -sonie
enclosure, modern mahogany, fancy grille,
$45. Wm. Tannenbaum, 160 Bennett Ave.,
New York 33, N. Y. TOmpkins 7 -1698.
:
RECORDING FANS -Join world -wide club;
swap tapes, make friends everywhere! Details free. P. O. Box 1404 J, San Francisco,
California.
HOUSE
Offering the World's Finest Home
Music Systems, created by experts
with years of experience.
High Fidelity is our only business
not a sideline. Complete stock of every
worthwhile component at all times.
SY
THE AUDIOPHILE BULLETIN, monthly
confidential consumer hi -fi equipment reports.
Year's subscription, $2.00. Dept. B, 1379 E.
15th St., Brooklyn 30, N. Y.
RY
1
-8171
YOU
IF
I
Circulation Department
RADIO MAGAZINES, INC.
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0.
Box
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Please lot ity our Circulation Department at least
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Please cooperate? when notifying us. please give
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629
Mineola, N. Y.
JANUARY, 1954
FULL
DIMENSIONAL SOUND
RECORDING TAPE
Triad Transformer Corporation, Venice.
Calif., has put into operation a profitsharing plan for which all employees, except major executives, are eligible. The
plan takes into consideration earnings, accumulated seniority, and position. It is
part of a continuing employee participation program which already includes a
federally- chartered employees' credit union. Approximately 400 persons will be
affected.
THE ULTIMATE IN
HIGH FIDELITY
RECORDING
Look for this symbol on record albums you buy
oration, with headquarters
in Pasadena, Calif., celebrated the inauguration of its new eastern plant in Mountainside, N. J., on December 3. Some 500
prominent guests attended at the invitation of Dr. A. O. Beckman, Helipot presi-
dent, and Donald
ager.
U. S. Recording Co.
1121
Vermont Ave., Washington
Llaman 5.2705
S,
D. G.
"EVERYTHING IN HIGH FIDELITY"
From Primary Components
to Completed Custom Audio Equipment
KIE
F
Sound Cor'p.
820 West Olympic Blvd.
Richmond 7 -0271
Los Angeles 15, Calif.
ZFnith 0271
"WE HAVE IT"
HI
- FI
COMPONENTS EXCLUSIVELY
HOLLYWOOD
ELECTRONICS
7460
MELROSE AVE.
HOLLYW000 46
C
A L
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F O
WEesTaw
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N
I
Information on tradinç Hl -FI
o
components on request. Ydri'e
o
or call for free catalog
o
AE
exchave exchoiaes audio
the audio exchange
Jamaica 32,
-0445
AUDIO ENGINEERING
purchase
tapes.
of
I2
new
Recording tudios, schools, radio stations
and other arge quantity users-write for
bulk price.
* **** 'kW * * * ** drink * driest* ****
USED RECORDING TAPE
(PLASTIC BASE)
7" -1200 foot
1.99
for
.99 for
5
.59 for 4
for
3
Plastie reels
"600 loot
""- with
300 foot
150 foot
Included
all above sizes.
New empty
labeling.
30e; 7"
plastic reels in boxes for
Professional reel
45e ea. EMPTY BOXES: 3"
5" 5e: 7" 10e
We
easy
3" 10e; 4" 22e; 5" 24e: 7"
(21"
hub)
30; 4" 5e;
ea.
carry new recorders. recording blanks, tape.
recorders. etc.
at large savings.
SUFFICIENT POSTAGE.
PLEASE
ape
LNCLUDE
COMMISSIONED ELECTRONICS CO.
2503 Champlain St., N.W., Washington
9,
D.
C.
For The Ver y Finest
in High Fidelity
James R. Lansing sonad, Ino.,
Angeles, has expanded its facilitiesLos
to include a new building for housing offices,
cabinet and paint shop, research laboratory, and warehouse. Located adjacent to
the company's main building, which will
be devoted entirely to production, the
new structure will permit
the
number of factory and officedoubling
employees.
MASCO
Allied Radio Corporation, Chicago, was
host at the December 16 meeting
of the
Chicago Acoustical and Audio Group.
In
addition to a sumptuous dinner, members
were treated to a variety of impressive
demonstrations by Ampex Corporation
and Electro-Voioe, Inc. Speakers included
Electro- Voice's Howard Souther. Allied
president A. D. Davis, and CAAG president George Bonvallet.
A
the audio exchange exchanges audio
the audio exchange exrhnn,,.r ..+:a
8
FREE! A 7.95 tape carrying case included with
3-10
the audio exchange exchang3s audio
the audio exchange exchanges audio
159.19 Hillside Avenue
Olympia
ATAPE?
tape with plastic reel.
Choice of nationally famous top quality
brands such as:
Webtor (2906) 3.20; Reeves (SPN -12) 3.20;
Audio (1251) 3.23; Scotch (111 -A) 3.25;
Panacoustic (711 -A) 3.25; Irish, Professional grade (211 RPA) 3.30.
.29
One of the electronics industry's oldest
trade marks will soon become
evident in
the hi -fl field when Preed- Rissmann
duces a complete line of home musicintrotem components. Initial production syswill
include AM -FM tuners, preamp-control
units, amplifiers, and complete AM-FM receiver chassis.
90zhabut
the audio
Afafnetic
BE MORE RED
1200 ft. plastic
Duncan, general man-
Ampex Corporation is planning to prove
that high -speed duplication
of recorded
tape is as practical and economical
as
pressing discs in a tape duplication exhibit at the Loa Angeles Audio Fair. Fair
visitors will be offered the opportunity of
having a duplicate of their favorite tape
made on- the -spot at no cost -all they need
do is bring the recorded tape and an equal
roll of blank tape to the Ampex exhibit.
A 1200 -ft. spool can be copied in four
minutes.
Custom -Built Equipment
WHERE ELSE WOULD THERE
WASHINGTON, O. C.:
RCA Victor Division of the
Corporation of America has startedRadio
tion on a group of ultra-modern construcbuildings
In Camden, N..1., to serve as administration and laboratory headquarters for its
Home Instrument and Service Company
activities. Scheduled for completion
this
Fall, the project will contain five interconnected buildings and will occupy a
58 -acre tract in Camden's Cherry Hill section. The new buildings will house 1400
employees.
Helipot Co
PROFESSIONAL
DIRECTORY
(PLASTIC BASE)
PRICES
in Cartons of 12
at NET
inc.
N.
Y.
nom...
Dr. Leslie Hill has been appointed director of research for the Pentron Corporation-formerly developed electronic
equipment for the British and Egyptian
governments
Changes in sales organization of Browning Laboratories,
Inc.,
find Ralph L. Torrington as vice -president
and director of sales; Roy R. Lonnberg as
sales manager of high -fidelity equipment;
Lee Slaserian as sales manager of industrial test equipment, and Robert L.
Gagnon as applications engineer ... Management promotions at Brush Electronics
Company include Douglas C. Lynch who
becomes executive vice -president; C. J.
Stayers, vice- president and treasurer; R.
H. VanRonten, vice- president and director
of employee relations; A. J. W. Novak,
general sales manager; W. C. Hall, controller, and P. W. Anderson, budget director . . . Thomas D. Walsh and George
Lotto have been named vice -presidents R.
of
The National Company.
...
JANUARY, 1954
www.americanradiohistory.com
AmericanRadioHistory.Com
20-Watt Amplifier
with Remote Pre -Amplifier
unequalled realism of tone. The ultimate in high
fidelity for the critical music lover. A few of its
outstanding features:
Less than 0.2% harmonic or Intermod
tatlon distortion at 20 watts, from 20
cycles to 40,000 cycles.
Frequency response 10 to 50,000 cycles
±44 db at 20 watts.
List Price
CM -20 20-Watt High -Fidelity Amplifier
Call -20 20 -Watt High-Fidelity Amplifier $186.50
with remote preamplifier In
hand -rubbed mahogany cabinet
with 6-foot cable and plug
$295.00
Mu.
Writ. ter Catalog
*
NV
ra`
`
T
F. E. T.
CM -853
MARK SIMPSON Mfg. Co., Inc.
Long Island City 3. New York
63
ADVERTISING
AtLast!
THE
SPEAKER
INDEX
THAT
PRODUCES
loSou nA
Fiddles, trumpets, drums ... these are
Allied Radio Corp.
Altec Lansing Corp.
Amplifier Corp. of America
Arnold Engineering Co.
41
Asco Sound Corp.
56
33
Audak
Audio
Audio
Audio
31
resonance...
General
system. Instantly you will hear the
difference . - . clean bass, smooth highs
and a sense of realism and presence
that will amaze you.
...
Only $65
new
THE
NEW
,:nd
other conventional encÌosures
are tuned resonant systems.
For best results the Hartley
BOFFLE Enclosure is recommended...available in single,
dual, and 4-speaker models, in
kit forni or finished, and
priced from $35.00.
HARTLEY
215
H. A. HARTLEY CO., INC.
2
62
43
63
Hartley, H. A. Co., Inc.
64
Harvey Radio Co., Inc.
Heath Co.
Hollywood Electronics
45
36, 59
63
53
48
Hubbell Mfg. Co.
Hycor Sales Co.
Research
and
Development
Laboratories
Interelectronics Corp.
46
Kingdom Products, Ltd.
51
Kierulff Sound Corp.
63
Leonard Radio, Inc.
54
Cover
3
Partridge Transformers, Ltd.
Peerless Electrical Products
Pickering and Co., Inc,
Precision Film Laboratories, Inc.
Presto Recording Corp.
Professional Directory
59
Radio Corporation of America
35
55
10
15
12
9
63
Rauland -Borg Corp.
Reeves Equipment Corp.
Rek -O -Kut Co.
Rider, John F., Publisher, Inc.
Rinehart Books, Inc.
Rockbar Corp.
52
13
58
62
48
Shure Bros., Inc.
Simpson, Mark, Mfg. Co., Inc
Stancil- Hoffman Corp.
Stromberg- Carlson
37
63
TAB
49
Terminal Radio Corp.
Thermador Electrical Mfg. Co
Tung -Sol Electric, Inc.
Turner Company, The
61
United Transformer Co.
University Loudspeakers, Inc
U. S. Recording Co.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
63
38
39, 47
Co.
At franchised dealers or write to:
521 EAST 162nd ST., BRONX 51, N. Y.
LUdlow 5.4239
64
Electric
57
4
Orradio Industries, Inc.
Substitute a HARTLEY 215 in any
nee,
16
40
Electro- Voice, Inc.
Treat yourself to an earful.
ould
53
50
firmed this fact, time and time again.
AB comparison listening tests have
likewise revealed the superior performance of the HARTLEY 215.
be used. The bass-re
2
63
Bell Telephone Laboratories
Bozak Co., The R. T.
Hughes
a non -resonant baffle
Cover
Duotone Company, Inc.
D G R, Ltd.
Laboratory measurements have con-
Hartley 215 has no res
Co.
Devices, Inc.
Exchange, Inc.
Fair, The
The loudspeaker, however, is not a
The HARTLEY 215 has no
'e
5
Camera Equipment Co.
Capitol Records. Inc.
Chicago Transformer Division
Cinema Engineering Co.
Classified Ads
Collins Audio Products Co., Inc. ..
Commissioned Electronics Co.
, and produces no distortion.
t
61
musical instruments. They produce
sound. And resonances are deliberately
created to give the sound timbre and
identity.
musical instrument. Its specific function is to reproduce sound. It must
in no way add to the sound it reproduces. It must be free from resonance,
and free from distortion.
NOTE: Because
42
11
3
34
8
58
Cover
4
7
63
JANUARY, 1954
)i
hat Mirrors the Original Sound
iris
BRAND
GREEN BAND
THE
FINEST TAPE YOUR
Just as the reflection of a perfect
mirror is faithful to the original
image, in every detail, so too does IRISH
Green Band RECORD. RETAIN and REPRODUCE
the original sound with flawless fidelity.
This can be confirmed by tests. Instruments
will reveal :hit IRISH Green Band offers
lower noise level, uniform sensitivity, minimum amplitude variation, less distortion.
But instrument tests are only the landmarks
1
Professional
RECORDER CAN
USE
of good design and production. The final
proof is in the hearing. Therefore, to know
and appreciate the quality of IRISH Green
Band Tape, it must be used, listened to, and
compared with other tapes on the same
recorder.
You will find that the only limitation to
IRISH Green Band quality is the limitation
of the tape recorder itself : it is the finest
tape your recorder can use.
ish
An,")
BAND
GRE
Prof ssional
is fast becoming the choice
of audio engineers in broadcast stations,
recording studios and wherever sound
quality is of paramount importance.
1200 feet an plastic ree
$ 5.50
12.85
2400 feet on metal reel
One day you will surely use IRISH ... so
write today for free test sample reel.
irish
BROWN BAND
for Popular Priced Recorders:
Brown Band, expressly designed for home
ar,d office recorders. Reprod aces with true fidelity
the frequency range from 100 to 8000 cycles. A
high quality, plastic base tape for the price of
ordinary paper tape!
1200 feet, plastic base, on plastic reel
$3.75
At all leading
-adio parts distributors
IRISH
ORRADIO INDUSTRIES, INC.
OPELIKA 8, ALABAMA
World's Largest Exclusive Magnetic Tape Manufacturer
EXPORT DIVISION
Morhan Exporting Corp., New York, N. Y.
www.americanradiohistory.com
AmericanRadioHistory.Com
Linear Standard
THE
4;/rj!
SERIES
The eve- increosin_, use of wide range equipment for broadcast service Fos reached the point where the major limiting factor
is the frequency range of the transformers employed
UTC Ungar
Standard components represent the closest approach to Ih
transformer from the standpoint of uniform frequency re
a4,
low wave form distortion, high efficiency, thorough shielding?
dependability. Typigpl LS snits are described blow".
LS-IS
Case Size
LS-1
Length
Width
Height
LS-2
4:..
258 "
3Sz"
INPUT TRANSFORMERS
Type
No.
r
RD
AO
00
Rá<,C-c<us.i:
040
400
043
See MO
4000
101.
N
,
sxcmo
30
70
no
(40 Os
Primary
Impedance
Agplication
Low
impedance
70.
LS-15X
Three isolated lines or
pads to me or two grids
i
Secondary
mike, 50. 125/150,
pickup, ar multiple line 200, 250, 333,
to grid
500 /600 ohms
IS -10X As above
As above
LS-12
Low impedance
mike, 50,125/150,
pickup, 3r multiple line 200, 250. 333,
500 /600 ohms
to push pull grids
LS -12X As above
As above
LS-10
30, 50, 200,
250 ohms
each primary
1
db
Impedance
from
60,000 ohms in 20-20,000
two sections
50,000 ohms
120,000 ohms
overall, in two
sections
80,000 ohms
overall, split
60.000 ohms
overall, in two
sections
3f4..
Relative' Unbal.
Max.t
Level
h
List
Cr e
Na.
Price
LS -1
$25.00
.5 MA
LS-1
.5 MA
LS-1
35.00
26.00
DB -Q
.5 MA
LS-1
35.00
DB-Q
.5 MA
LS-1
37.00
prim'y
Case
No.
Price
DC
prim'y
in
,m
+10
DB
-74
DB
.5 MA
20-20,000
20-20,000
+10
+10
DB
-92
-74
DB-0
DB
DB
20-20,000
+10
DB
-92
20-20,000
+10
DB
-92
INTERSTAGE AND MATCHING TRANSFORMERS
Primary
Type
No.
LS-19
,0 Ob
GO
NO
WO
WO
VIKOODC,C.I.L3
000
POI
ad
SILO.
Jr
VA
1,10
4:04
041
n44
LS -25
LS-t2
n s
x n
s
fPM
LS -21
MO
100 NO
i
R
am
SEW.
r
v
r sr
LS -30
aa
LS -33
Replication
Single p ate to push pull
grids like 2A3, 616.300A.
Split secondary
Single pate to push pull
grids. Split pri. and sec.
Push pu I plates to push
pull grids. Medium level.
Split pr mary and sec.
Mixing, low impedance
mike, p ckup, or multiple line to multiple line
High level line matching
LS-:.0
---.....,
rRe.c.-c<LC, Re
30,000 ohms
plate to plate
50,000 ohms;
50,125/150,
50,125/150,200,
±1
200, 250, 333,
500/600 ohms
1.2, 2.5. 5, 7.5
10, 15, 20, 30, 50
125, 200. 250,
333. 500 '600
250, 333,
500 /600 ohms
50, 125, 200,
250, 333,
500 /600 ohms
±
Primary
Impedance
koplication
No.
LS -52
LS-SS
LS-63
r,ee4cKS-CF Cs
135,000 ohms;
3:1 overall
R SM.. x
Level
hum
in
DC
+12
DB
-50
DB
0 MA
LS -1
$26.00
± 1 db
20-20,000 +10
± 1 db
DB
20-20,000
-74
DB
0 MA
LS -1
28.00
+15 DB -74
DB
1
MA
LS-1
32.00
-74
DB
.5 MA
LS -1
26.00
LS -2
30.00
Case
No.
Price
LS -1
$26.03
LS-2
35.00
LS-2
35.00
LS-2
25.00
LS-1
27.00
db
20-20,000
+15
DB
.2 db
20- 20,000 15 watts
,w[
»c ,a.
Single t late to multiple
Secondary
Impedance
plate to plate
LS-151
Max.t
Response
!
Level
50, 125/150,
1 db
line
200, 250, 333, 20-20,000 +15 DB
500 /600
± .2 db
Push pill 245, 250, 6V6 8,000 ohms
500, 333, 250,
or 245 A prime
200, 125, 50, 30. 25. 20,000 15 watts
20, 15, 10, 7.5,
5, 2.5, 1.2
± .2 db
Push pull 2A3's. 6A5G's, 5,000 ohms
500, 333, 250.
300A's, 275A's, 6Á3's, plate to plate
200,125,50,30, 25.20,000 20 watts
6L6's, 6AS7C
and 3,000 ohms 20, 15, 10, 7.5,
plate to plate
5, 2.5, 1.2
± .2 db
Push pell 6F6, class B 10,000 ohms
30, 20, 15, 10,
46's, 4AS7G,
807 -TR, plate to plate
7.5, 5, 2.5, 1.2 25-20,000 15 watts
1614-TR
and 6,000 ohms
15,000 ohms
Bridginc from 50 to 500
16,000 ohms,
ohm
bridging
lin! to line
50, 125/150,
200, 250, 333,
± 1 db
15-30,000
+18
DB
Relative' Unbar. DC
hum
in prim'y
-74
0 MA
DB
-74
DB
1
MA
500'600
The values of Inbalanced DC shown will effect approximately 1.5 DB loss at 30 cycles.
Comparison of hum balanced unit with shielding to normal uncased type. Q Multiple alloy magnetic shield.
1
40/(C0JOICV-CKI. CS
et
list
OUTPUT TRANSFORMERS
Type
100
15,000 ohms
turn ratio
1.3:1 overall
Relative ' Unbal.
Max.t
Response
95,000 ohms;
± 1 db
1.25:1 each side 20-20,000
ref.0.e
1S -50
w
Secondary
Impedance
Impedance
15,000 ohms
0DB reference.
6 MW as
SUONO
en ate
ONLY audio units with a GIARANTFEO uniform
response... L.. 1 DP from 20 to 20.000 cycles.
1
5
0
V A
R
I
C
EXPORT DIVISION
K
S T
R
E
E
T
13 EAST 40t11 STREET, HEW YORK 16, N. Y.
www.americanradiohistory.com
AmericanRadioHistory.Com
Ill
YORK
13,
CABLES:
ARIAe'
List
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