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Room acoustics & decor considerations
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AmericanRadioHistory.Com
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Reduction
604
How to be a hero when you bring home
Scott's best receiver.
6'
-
remark about her great flair
Let your wife think you bought it for her
would enhance it. Don't
music
how
beautiful
and
for home decorating,
confuse her with technical talk about the Scott 388B's 3-FET front end or
simply point out that her favorite FM
integrated circuit design
broadcasts will never be spoiled by the electric mixer or the noise from
the 388B's 1.7 microvolt FM
your shaver. Talk about programs
sensitivity and wideband AM bring in more stations than she's ever heard
before. And the 7 -position input selector lets you record Baby's first
words, or save money by taping right off the air. And wouldn't connecting
a mike and electric guitar add a new kick to your parties!
She may think 120 Watts just means louder music. It really means
power enough for extra speakers in the den, the kitchen, and the sewing
room. And, you're just planning ahead for that big new house.
More? There's a scratch filter that makes the records you used to
dance to sound new again.
And a special control to cut out that annoying hiss between FM
stations. And a stereo/mono remote speaker switch that lets you have
background music throughout your house.
the handsome 388B itself. Does
Save your best convincer for last
your wonderful wife deserve any less?
If you need more details to convince yourself, send for Scott's new
-
-
-
1968 catalog.
35-06
Scotdt, Inc. Dept.tts
SCOTT H.H.
aynar, M assachuse 01754
C3
© 1968,
H.H. Scott, Inc.
Front Panel Controls: Dual bass, treble and loudness controls, balance control, rumble filter, dual microphone inputs,
volume compensation switch, tape monitor, noise filter,
muting control, dual speaker switches, rear panel remote
speaker mono stereo switch, front panel headphone output,
input selector, tuning knob, and tuning meter. Price, $559.95.
Check No. 100 on Reader Service Card
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,,
e
AUDI()
ARTHUR
P.
SALSBERG,
EDWARD TATNALL CANBY,
PETER RENICH
June 1968
Successor to
LEONARD FELDMAN
BERTRAM STANLEIGH
RADIO,
Est. 1911
Associate Editor
C. G. McPRoUD, Publisher
RICHARD CLIFF
SANF ORD
L. CAHN
Marketing Director
R. KENNETH BAXTER
Production Manager
JOSEPH GIOVANELLI
ALEXANDER ROSNER
STUART TRIFF
MARY CLAF'g'EY
Subscription Manager
FEATURE ARTICLES
Practical Aspects of
Audio Noise Reduction
A Custom Home Stereo Installation
Hello (Equipment) Dolly
ABZ's of FM-R.F. Front Ends
More About Negative Feedback, Part 5
Behind the Scenes-State of the Art
of Pre -Recorded Tapes
Ray M. Dolby
Michael J. Curry
James P. Holm
Leonard Feldman
32 Norman H. Crowhurst
19
24
28
30
50 Bert Whyte
MUSIC REVIEWS
Classical
Light Listening
Jazz
Tape Reviews
44
47
48
54
Edward Tatnall Canby
Stuart Triff
Bertram Stanleigh
Bert Whyte
EQUIPMENT PROFILES
Marantz Stereo FM Receiver
BSR Automatic "Total Turntable"
Jensen Bookshelf Speaker System
7
34 Eighteen
40 McDonald 600/M44 -E
42 Model TF -3B
AUDIO IN GENERAL
Audioclinic
What's New in Audio
Letters
Audio, Etc.
Tape Guide
Editor's Review
e
I,erIrUTC or
HIGH FIDELITY
MANUFACTURERS
INC
Number 57 in a series of discussions
by Electro -Voice engineers
Editor
Art Director
Design
Contributing Editors
HERMAN BURSTEIN
Vol. 52, No. 6
Classified
Advertising Index
2 Joseph Giovanelli
6
8
10 Edward Tatnall Canby
14 Herman Burstein
16
56
58
AUDIO (title registered U. S. Pat. Off.) is published monthly by North
American Publishing Co., I. J. Borowsky, President; Frank Nemeyer, C. G.
McProud, and Arthur Sitner, Vice Presidents. Subscription rates-U. S.
Possessions, Canada, and Mexico, $5.00 for one year; $9.00 for two years;
all other countries, $6.00 per year. Printed in U.S.A. at Philadelphia, Pa.
All rights reserved. Entire contents copyrighted 1968 by North American
Publishing Co. Second class postage paid at Philadelphia, Pa.
REGIONAL SALES OFFICES: Sanford L. Cahn, 663 Fifth Ave., New York,
N. Y. 10022; (212) 753-8824. Louis Weber, 5201 N. Harlem Ave., Chicago,
Ill. 60656: (312) 775-0755. Jay Martin, 9350 Wilshire Blvd., Beverly
Hills, Calif.; (213) 273-1495.
REPRESENTATIVE: Warren Birkenhead, Inc., No. 25, 2-chome, Shiba Hamamatsu -cho, Minato-ku, Tokyo, Japan.
AUDIO Editorial and Publishing Offices, 134 N. 13th St., Philadelphia, Pa. 19107
Postmaster: Send Form 3579 to the above address.
In recent years, considerable attention has been
drawn to electronically amplified versions of traditional reed and brass instruments. Of greatest
initial appeal has been the "new sounds" made
possible.by the electronic additions to conventional
instruments. But perhaps a more significant achievement to most musicians has been the vast increase
in dynamic range while maintaining the essential
character of the basic instrument.
This multiplication of available sound output differs
sharply from normal public address amplification,
since both volume and tonal quality remain solely
under the control of the player. Sound is predictable and uniform wherever the musician plays.
Development of the amplification system demanded
careful laboratory analysis, plus extended subjective
testing to achieve success. The Varitone* system,
available exclusively with H. & A. Selmer and
Buescher instruments, is a case in point, and an
examination of the trumpet system may prove
revealing.
Location of the microphone on the trumpet was
the most challenging phase of the design problem.
The obvious spot-the bell-was ruled out quickly,
as this would interfere with normal use of various
mutes. The alternative was at some point on the
wall of the trumpet itself. This, in turn, dictated a
microphone type and location that would not change
the playing characteristics of the trumpet. Element
choice was relatively easy, and a small, stiff ceramic
microphone that could withstand the high acoustic
pressures and high humidity encountered in the
trumpet was chosen. An element with relatively
low compliance was required so that the intonation
and acoustic resistance of the instrument was unaffected.
After extensive testing, a microphone location near
the mouthpiece of the instrument was chosen as
optimum. It minimized the problems of standing
waves whose nodal points vary with frequency
within the instrument. The final location represented a synthesis of both objective and subjective
testing techniques.
Since much of the characteristic sound of any instrument is determined by the relative strength of
overtones, the entire system-from microphone to
speaker-had to maintain flat overall response to
be musically effective. To this end, tape recordings
were made of the trumpet using a calibrated microphone placed in front of the bell, while simultaneous recordings were made with the instrument
microphone.
The recordings were then analyzed with a 1/10 octave band pass filter, and system response of
the instrument amplifier was adjusted to achieve
the desired trumpet sound. While the fundamental
range of the trumpet extends from 165 to 1175 Hz.,
the amplification system had to cover a much wider
range. High frequency response was added to maintain the correct harmonic relationship, while low
frequency response was needed to accommodate the
Octamatic** feature which provides output an octave below the note being played. Other features
included in the Varitone system include controls
for tremolo, reverberation, and voicing controls for
low, mid, and high frequencies.
The final system, available in 20 and 70 watt versions, has met with excellent acceptance among
musicians. It offers a means to play at high volume
where needed, without strain and without dependence on an outside sound system for amplification.
* Electro -Voice has assisted in the development
and production of Varitone systems for H. & A.
Selmer, Elkhart, Indiana.
** Varitone and Octamatic are registered trademarks of H. & A. Selmer.
For reprints of other discussions in this serles,
or technical data on any E-V product, write:
ELECTRO -VOICE, INC., Dept. 683A
602 Cecil St., Buchanan, Michigan 49107
gketercelir.
A
SUBSIDIARY
OF GULTON
INDUSTRIES, INC.
Check No. 101 on Reader Service Card
1
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AmericanRadioHistory.Com
Coming in
Audioclinic
July
JOSEPH GIOVANELLI
Audio/FM Test InstrumentsA roundup of test instruments used to examine audio,
FM and stereo FM equipment.
Electronic Crossover Networks Revisited C. G. Mc -
-
Proud discusses how to
modify his original three channel electronic crossover
construction project (Audio,
February 1968) to create a
two -channel unit. In addition, he provides information
on how to change values of
parts to obtain different
crossover frequencies.
Exotic Loudspeakers-Al Fanning surveys loudspeakers
other than moving -coil types
that are used by some hi -fiers.
Audio Noise Reduction-Ray
Dolby concludes his article
on audio noise reduction by
examining more aspects of
the Dolby professional system and by discussing some
practical applications.
EQUIPMENT PROFILES:
Fisher Model 200-T Stereo
FM Receiver
KLH Model Twelve Speaker
System
Regular monthly departments, music and record
reviews, and more.
Plus:
ABOUT THE COVER: The attractive cabinet
shown on the front cover, designed by Jerry
Joseph of Toujay Designs, Inc. for Edward
Greene of Baldwin, L. I., N. Y., is approximately eight ft. long by eight ft. high. It was
delivered in five sections, and said to take
less than 30 minutes to be set up permanently. The equipment it houses includes: a
Tandberg tape recorder, AR manual turntable, Dyna preamplifier, power amplifier
and tuner, and a pair of Bozak B302A speakers. Also accommodated are 400 LP records
and 300 reels of tape. Note that equipment is
at comfortable operating height.
If you have a problem or question on
audio, write to Mr. Joseph Giovanelli
at AUDIO, 134 North Thirteenth Street,
Philadelphia, Pa. 19107. All letters are
answered. Please enclose a stamped,
self-addressed envelope.
Silicon rectifiers
Q. I am one of the nation's first lifetime subscribers to AUDIO. I think my
membership card is No. 89. I have read
and enjoyed your column for many
years.
I am currently interested in building
oscilloscopes. I have had some success,
but I run into trouble with the high voltage supplies. I obtain the high voltage by combining the secondaries of a
couple of power transformers in series.
The problem is that in the circuitry,
this high voltage is applied to the filament windings. These windings are not
insulated for this high voltage. The result is, after a short time, a breakdown.
I am wondering about the possibility
of using silicon rectifiers in series instead of vacuum tubes as rectifiers, and
thus eliminating the need of the filament voltage. I get the impression from
my reading that it is possible to handle
higher voltages than individual silicon
rectifiers can withstand by connecting
them in series. I have been strictly a
tube man so far. The only time I tried
to use the silicon rectifiers, they overheated; it just did not work. Why, I do
not know.
For instance, I have some silicon rectifiers rated at 750, 500 mA. Could I
connect three of these somehow to
handle a negative 2,000 volts?
Are there any disadvantages in using
these silicon rectifiers? They are so
small and inexpensive and do not require filament voltage. It would seem
that no one would want to bother using
tube rectifiers.-Rev. Francis J. Jann,
Belfast, N. Y.
A. From your letter I gather that
the insulation between windings of one
or the other of your combined power
transformers is breaking down. What
you can do is simply employ a separate
filament transformer to heat the rectifier tubes. Be sure, however, that this
transformer has sufficient insulation
between its windings and its core to
avoid breakdown at the high voltage
used.
You can, of course, employ silicon
diodes. This is the better, easier course
to follow. When series -connecting
them, though, you should take the same
2
kind of precautions as you would if you
connected capacitors in series to obtain
a higher voltage breakdown rating. You
should shunt high -value resistors across
each diode. This will equalize leakage
currents and prevent one diode in the
string from taking most of the burden. Further, each diode should be
equipped with a shunt capacitor of perhaps 0.01 Z,t,F. This serves to hold down
certain transient peaks which come
along and often cause diodes to fail.
A full -wave rectifier system employing
these techniques is shown in Fig. 1.
From your letter it is not clear what
circuit you are using: bridge, voltage
doubler, etc. Therefore, I can only give
you some general guidelines on how to
make your circuit work in the best possible manner.
If your circuit employs a full -wave
rectifier from which you obtain 2,000
volts, you will need at least six diodes
in series in each leg of the circuit. I am,
of course, assuming you will be using
the diodes of which you wrote in your
letter, those having a 750-volt PIV rating. Actually, these six diodes will
handle a peak voltage of 4,500 volts,
dangerously close to the voltage which
may be present in this circuit during
times that the diodes do not conduct.
Further, one or more diodes in the
string may be incapable of handling
their rated peak voltage. Therefore, I
suggest that you use eight diodes in
series on each leg of the full -wave
bridge.
I suspect, though, that you are probably deriving your high voltage by
means of a positive and negative power
Fig. 1-Full-wave rectifier system.
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filter
network
117V
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AC
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supply system, with chassis ground
serving as the midpoint of the two supplies. Because there is little current
drawn from this high voltage supply, I
would assume that you might be using
a half -wave rectifier system for each
power supply. The typical halfwave
rectifier system is shown in Fig. 2. This
circuit shows a supply which will provide a voltage which is positive with
respect to ground. You would have to
reverse the connections to each diode,
and also reverse the polarity of your
electrolytic filter capacitors if this same
circuit were to be used to give you the
Check No.
www.americanradiohistory.com
AmericanRadioHistory.Com
rr4
3
on Reader Service
Card
dc
counterweight
Sliding counterweight is infiritey
adjustable, makes precise cynamic
balancing practical; locks inb dace,
isolated in rubber from the am
skating force
Patented anti -skating cont-c I, )f
spring -free sliding weight
design, has 1/2 gram
calibration to nullify
side pressure
on stylus and
groove walls.
Insert he most crit
rrost seisiive
partridge in the Garrard SL 95, and be
assured 1
travel the intricate =onvoutions of the grooves easily anc flawessly. The advanced jitra-low mass,
gyroscopically gimba ed tonea-m system has jusi three cor rcls, to balance it
exactly to the weight of the carridge,
adjust it prec sely to the recommended
stylus
and counteac the rateral
,
stylus
p
'sure
reading sty tus
,pre gauge sets
tracking force precisely
with audible/visible'
click stops a '4 gram'
pr
t ;
rvals.
-or
skatin3 tendency, p ovidiig perfect
Yackiig, distortion -free eprodupion.
The 9L 95 gives your records a perfect ride, toc. The sy-ic ironcus SyichroLab Motor" matched kinetica ly :o The
oversizec, ba anced Jrntable, giarantees a.bsolalely constant speec, unwav-
ering pitch, freedo-i from rumble.
Simplif ed cueing and rause contrcl, and
he exdusife safety record platfern, pro -
tact your -ecords bo'i in manual and
automatic e ay, making the SL 95 Autonatic Traracription T irritable the ulti nate it pe-formance anc depeidabil ty.
Price: 512=.50. less ease and cart-idge.
Other Garard models as love as $37.50.
For a canpl mentary Comparator Guide
to all modals, write Garrard, Dep-. AC-1,
Westbury N.Y. 11590.
cartridge
New cartridge
clip guarantees
safe, convenient
mounting, in perfect
alignment. Tone -arm
and "shell" are of rigid,
resonance -free, one piece
construction.
www.americanradiohistory.com
AmericanRadioHistory.Com
negative portion of the supply voltage.
The complete power supply circuit,
employing both a negative and a positive full -wave supply, is shown in Fig.
get the
NEWS
FREE!
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CV
Take into account that while the
voltage under load may be 2,000 volts,
the voltage without load (such as woùld
be true during times of tube warm-up,
etc.) might be close to 3,000 volts.
Hence, the filter capacitors must be
rated to handle at least a peak voltage
of 3,000 volts (and it is best to provide
a safety factor). Therefore, your filter
capacitors should be rated at 4,000
volts PIV.
I do realize that the oscilloscope tube
will not provide much of a load on your
power supply. It may be, therefore,
that you took this matter into account.
Possibly your power supply will deliver
1,500 volts under load, but will provide
the necessary 2,000 volts or thereabouts
when only lightly loaded by the CRT.
The symbols typically employed to
denote the anode and cathode connections of a silicon diode are shown in
Fig. 2. These are what you will find in
schematic diagrams. How the particular diode you plan to use is marked is
anybody's guess. Because of the lack of
a common standard in this matter,
measure each diode with an ohmmeter.
When the meter is connected to read
the lowest resistance, the positive
meter lead is the plate, or anode, of the
diode. The negative meter lead will be
the cathode connection of the diode. I
can't impress on you strongly enough
to be sure you know which is the positive meter lead. I very nearly came to
grief just the other day because I be Fig.
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2-Half-wave rectifier system.
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To
SEND TODAY
V
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--
3.
The new McIntosh 36 page catalog gives you all the details
on the new McIntosh solid state
equipment. In addition, you'll receive absolutly free a complete
up-to-date FM Station Directory.
z
01
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A.0
Anode Cathode
lieved that the common meter lead of
the VOM I was using was negative for
all functions. It wasn't, and I had to reverse the connections to 5 diodes.
If you know how to wire tube rectifiers, you can, most of the time at least,
wire up the silicon jobs in the same
way. Naturally, you must watch out
for the peak voltage. If the peak voltage in a given circuit is more than can
be withstood by the diodes, more than
one diode can and should be connected
in series, as I described earlier.
In addition to the advantages of no
heater voltage being required, such
diodes also offer the advantage that
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100k 100k
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and negative full -wave
rectifier system.
they have a lower voltage drop than do
tube rectifiers. Thus, the power regulation of the power supply is better
with these units than it is with tubes.
Like everything else, there are a few
disadvantages. If you replace a tube
rectifier with silicon diodes, the power
supply's higher voltage may be more
than certain circuit elements can withstand. Further, because silicon diodes
have such a low voltage drop, they will,
when connected to low - impedance
sources (such as the 117 -volt power
line), draw very high current. Often the
current drawn will be beyond the capability of the diode. These diodes,
therefore, must be protected by the insertion of a series, current -limiting
resistor. Even with this resistor included, the internal resistance of the
power supply will be better than it
would have been if tube rectifiers had
been used. The value of this resistor for
a.c. power line service is usually in the
order of 30 ohms for equipment such
as table radios.
A disadvantage which some people
have encountered results from the diode's ability to conduct and then switch
to a nonconducting stage extremely
rapidly. While this characteristic
makes diodes fine performers as
switches, this situation can, and often
does result in the production of transient voltage peaks which will damage
the diodes and/or introduce annoying
buzzing into certain pieces of audio
equipment. The shunt capacitors
shown in Figs. 1 to 3 are designed to
eliminate these problems.
Though the story of silicon diodes is
too long to tell here, it is my hope that
this information will be sufficiently detailed to enable you to design more
efficient, cooler -running power supplies.
Æ
Check No. 4 on Reader Service Card
Check No. 5 on Reader Service Card
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AmericanRadioHistory.Com
-Y
When Stanton engineers get together, they draw the line.
The frequency response curve of the new Stanton 681 erence to approve test pressings. They must hear exactly
Calibration Standard is virtually a straight line from what has been cut into the grooves. No more. No less.
But you don't have to be a professional to hear the
10-20,000 Hz.
difference a Stanton 681 Calibration Standard will make,
That's a guarantee.
In addition, channel separation must be 35 dB or especially with the "Longhair" brush which provides the
greater at 1,000 Hz. Output must be 0.8 my/cm/sec mini- clean grooves so essential for clear reproduction. The improvement in performance is immediately audible, even
mum.
If a 681 doesn't match these specifications when first to the unpracticed ear.
The 681 is completely new, from its slim-line configtested, it's meticulously adjusted until it does.
Each 681 includes hand -entered specifications that uration to the incredibly low -mass moving sysverify that your 681 matches the original laboratory stand- tem. The 681A with conical stylus is $55.00, the
681EE with elliptical stylus, $60.00.
ard in every respect.
For free literature, write to Stanton MagNothing less would meet the needs of the professional
studio engineers who use Stanton cartridges as their ref- netics, Inc., Plainview, L. I., N. Y.
www.americanradiohistory.com
AmericanRadioHistory.Com
pretty
clever...
those
fellows at
Superex
70 kHz
±1 dB; signal-to-noise ratio
(IHF),
65 dB; harmonic distortion, under 0.1%; channel separation, 37 dB at
1
What's New
In Audio
kHz.
The receiver, which includes an FET
front end and integrated circuits in the
i.f. section, has a full complement of
controls and switches. These include
high- and low -frequency filters, loudness contour control, tape monitor
switch, and bass and treble controls for
each channel.
Eight -track
CUT AWAY VIEW
of SUPEREX
WOOFER -TWEETER
STEREO PHONE
MODEL ST -M
First
they
put
woofer/
tweeter in their stereo headphones to provide a full range
of response without distortion.
a
They also added a complete
crossover network right in the
earpiece
for an authentically fine speaker system in
miniature. Just what the true
stereo buff ordered!
...
cartridge recording
Here's a real innovation that will
make many 8 -track cartridge tape
machine owners very happy-a device
capable of recording on standard 8track cartridges from a number of
sources!
Introduced by Sony/Superscope, the
unit, Model TC -8, has inputs for tape
recorder, phono or FM multiplex. To
record, the user tilts the cartridge panel
slightly forward, inserts the cartridge,
Communications use.
Now, they've developed a
great new model, the ST-PRO -B
just about the last word
in a professional quality head.
.
phone.
Pretty clever, those fellows at
Superex. All they do is give
you the edge in quality, value
and forward -looking audio engineering. Ask your dealer for
a demonstration.
Write for complete catalog.
SUPEREX ELECTRONICS
1 Radford Place, Yonkers, N.Y.
Check No.
12 on
Reader Service Card
AKG FET Condenser
Microphone System
Then they extended their line
in depth for the Hi-Fi enthusiast and for Education, Broadcast, Aviation, Marine and
.
Other important features include:
two magnetic phono inputs, tape recording/playback jack, stereo headphone jack, automatic stereo indicator
and a signal -strength tuning meter.
Price is $345.00.
and presses the "record" button. Power is automatically turned on when the
cartridge is inserted. If the cartridge is
inserted improperly, a cartridge-alignment indicator lights up and the TC -8
will not operate until it is properly reinserted. The unit features an automatic recording control, automatic
shutoff, and an indicator light which
identifies each channel being recorded.
Price is $99.50.
A new AKG modular condenser microphone system has been introduced
by North American Philips Company,
its distributor. Built around a new
C -451E preamplifier, which incorporates field-effect transistors, it has interchangeable pickup capsules: CK-1,
cardioid; CK-2, omnidirectional; CK-6,
switchable from cardioid to omnidirectional to figure -eight; and CK-9, "shotgun" attachment.
In addition to being able to be
powered directly from most amplifiers,
a dual a.c. power supply for two microphones is available (Model N -46E), as
well as a battery power supply for a
single microphone. The latter employs
a regular 9-volt battery.
Check No. 14 on Reader Service Card
Check No. 10 on Reader Service Card
Pioneer 170 -watt receiver
Pioneer's new SX-1500T AM -FM
stereo receiver features 170 watts total
music power (IHF) with a 4 -ohm load;
140 watts total with an 8-ohm load (the
usual speaker impedance). FM sensitivity is 1.7 microvolts, while other FM
specifications are: capture ratio, 1 dB
at 98 MHz; frequency response, 20 to
Check No. 6 on Reader Service Card
6
AUDIO
www.americanradiohistory.com
AmericanRadioHistory.Com
JUNE 1968
4
Back Power!
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Take a close look at the back of the powerful, exciting, Sansui AM/ FM Stereo 5000. You'll see the inputs
for 3 pairs of stereo speaker systems that can be played individually or in pairs-engineered quick holding
plugs that eliminate the need for cumbersome clips; selective monitoring for 2 tape decks so that you can
monitor while you record. Even the inputs for phono, tape, and aux. are grouped for easier access and to reThe Model 5000 Receiver features FET FM front end and
duce the chance of wires accidentally touching.
180 watts
4 Integrated Circuits, with a set of specifications that exceed Sansui's unusually high standards
(IHF) music power; 75 watts per channel continuous power; FM tuner sensitivity of .8µ,V (IHFI ; selectivity
greater than 50 db at 95 MHz; stereo separation greater than 35 db;
The front of
amplifier flat frequency response from 10 to 50,000 Hz.
the Sansui 5000? See it at your franchised Sansui dealer. Price $449.95
-
1
1:1_,Ls-ELE,2
SANSUI ELECTRONICS CORPORATION
34-43 56th STREET
Sansui Electric Company, Ltd., Tokyo, Japan
AUDIO
JUNE 1968
Check No. 7 on Reader Service Card
www.americanradiohistory.com
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WOODSIDE, N.Y. 11377
Electronic Distributors (Canada), British Columbia
7
Letters
elevation of antenna, since the higher
the elevation of antenna, the greater
the coverage or range of transmission
and reception." The sentence should
read: "Received field intensity will be
determined
Height of the transmitting antenna has no effect on transmitter power or effective radiated
power, but only on received field intensity. All other parameters being constant, the higher the antenna, the
greater the field intensity at a given
point.
On page 75, the first complete sentence reads: "As an example, a transmitter having a power of 20 kW will be
received with a signal strength of 1000
microvolts per meter at a distance of
32 miles if its transmitting antenna is
500 feet above sea level." There are
three misleading points in this sentence
and in the rest of the paragraph.
The figure of 1000 µV/m at 32 miles
has been computed from the chart in
Fig. 1 of FCC Sec. 73.333. Power is defined therein as effective radiated
power, not transmitter power. ERP is
equal to transmitter output power, less
transmission -line loss, times antenna
..."
In the article "ABZ's of FM," April
there is an error in Table I.
This refers to the various classes of FM
stations as defined by the FCC but it
actually lists the classes of AM stations
in the standard broadcast service.
Section 73.206 of the FCC Rules and
Regulations defines commercial FM
broadcast stations. Basically these are:
Max. Effective Antenna Ht.
Above Avg.
Radiated
Terrain
Power
Class
300 feet
3 kilowatts
A
500 feet
50 kilowatts
B
2,000 feet
100 kilowatts
C
As author Feldman points out, the
antenna height of an FM broadcast station has a lot to do with the station's
range. To correct for this and put all
stations on a competitive basis, as well
as minimize allocation and interference
problems, the FCC engineering standards provide for equivalent coverage.
When the antenna height is above the
standard specified for the class of station, the effective radiated power must
be reduced according to a formula. On
the other hand, no increase of power
over the maximum is permitted if the
antenna is below the standard height.
Average terrain, by definition, is the
average of all elevations between two
and ten miles from the antenna. It is
generally calculated along eight radials
which must include the most prominent topographical features within the
mileage limits.
Since very few antennas are at the
same height, station powers have many
different values. This has led to confusion on the parts of both listeners and
advertisers because some stations publicize their actual licensed rating
whereas others use the maximum ceiling value for that class of station. While
these larger numbers may appear to
make the station seem more powerful,
the simple truth is that all FM stations
operating with maximum facilities have
equivalent coverage.
AUDIO,
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your dealer or write Bogen for further details.
BOGEN
COMMUNICATIONS DIV.
LEAR SIEGLER,
Paramus. New Jersey
Check Na.
8
INC.
HAROLD A. DORSCHUG
Hartford, Conn.
On page 34, Table I of "ABZ's of
FM" purports to show the class, channel and power of FM stations. The
table is actually an obsolete version of
that information for AM stations.
Immediately below the table, the first
sentence in the paragraph is incorrect.
It reads: "Power will be determined by
gain.
For purposes of computing FM field
intensity, antenna height is always specified in feet above average terrain, and
never above sea level. The two are quite
different, and computing average terrain around an FM transmitter site is
a major task.
Finally, the author has omitted to
mention the fact that Fig. 1 of FCC
Sec. 73.333 shows received field intensity only when the receiving antenna is
30 feet above the ground. The antennas
of many FM listeners are probably
only around 5 feet above the ground.
PAUL NORMAN
New York, N. Y.
Here is the author's reply:
The AM Station Power Classifications were incorrectly copied as Table
I, as pointed out. With respect to comments on the relationship of power to
elevation height, I did not want to imply that effective radiated power is in
any way related to the height óf the
antenna. Mr. Dorschug read me correctly, as indicated in his third paragraph.
The comments about ERP and average terrain are correct, although my
reference to sea level was made only
in illustrating a comparison between
two antenna heights, not to setting a
new standard of average terrain measurement. In the May issue of AUDIO,
in a discussion of receiving antennas,
the point is made that elevation of the
receiving antenna has a direct bearing
on received field intensity of signal
strength.
LEONARD FELDMAN
on Reader Service Card
AUDIO
8
www.americanradiohistory.com
AmericanRadioHistory.Com
JUNE 1968
4
Acoustic Research announces a new speaker system.
first advertisement for the AR -3 stated, "it has the
most musically natural sound that we were able to create in a
speaker, without compromise." This judgment was supported by
distinguished writers in both the musical and engineering fields.
Hirsch -Houck Laboratories, for example, agreed that "the sounds
produced by this speaker are probably more true to the original
program than those of any other commercially manufactured speaker
system we have heard." For nearly nine years the AR -3 has been
the best speaker we could make.
In 1959, our
However, technical development at Acoustic Research, as at many
companies in the high fidelity industry, is a never-ending search for
improvement. After much effort we have found a way to better the
performance of the AR -3. The new speaker system, the AR -3a, has
even less distortion, more uniform dispersion of sound and still
greater power handling capability. The improvement can be heard
readily by most listeners; it has been brought about by the use of
newly designed mid -range and high -frequency units, and a new
crossover network. Only the woofer and the cabinet of the AR -3 are
retained in the new system. The AR -3a is priced from $225 to $250,
depending on cabinet finish, and is covered by AR's standard
five-year speaker guarantee.
Detailed information on conversion of an
AR -3
to an
AR -3a is
available from
ACOUSTIC RESEARCH, INC., 24 Thorndike St., Cambridge, Mass. 02141
Cieck No.
AUDIO
9 on Reader Service Card
9
JUNE 1968
www.americanradiohistory.com
AmericanRadioHistory.Com
AMU, EIT.
EDWARD TATNALL CANBY
The Visible LP
NO MATTER WHERE you look these
days, or where you listen, you'll find
audio entangling itself in other nearby
arts, crafts, and sciences. It's what's
going on everywhere.
Take an item that has been buzzing
around in my head ever since I saw
and heard a demonstration last autumn
(another product of the AES Convention). It is tentatively called Phonovid
and was developed experimentally (so
they say) by Westinghouse engineers.
The reason Phonovid interested me
was that its visible product and, in fact,
its whole central raison d'être, is an
LP record. Not a special one, but a
very ordinary, completely standard,
commercially pressable LP. On the
surface (and ignoring the label) you
couldn't tell it from a couple of billion others. It comes out of a standard
pressing plant, cut right along with all
the others on standard cutting heads,
off standard recorded tapes. It plays
on the usual good -quality LP playing
equipment, without any special differentiation-ordinary motors, cartridges,
styli. All quite routine.
But what "plays" from this LP record, with a bit of extra circuitry hooked
into the system, is pictures. Plus a
sound track, in sync.
Put the record on an ordinary LP
player with this system, lower your
ordinary stylus into the wholly standard groove, and you get a long, measured succession of still pictures in
black and white on the face of a TV
set connected to the system. Up to 400
"slides," to use the nearest conventional terminology, projected neatly
one after another from the LP record
with time to look at each one and listen
to the accompanying sound.
And, of course, you may hook in as
many TV sets as you want, if you need
to. That might be quite a number if,
say, you were a school. Or a school system. Or a business with a host of audiovisual messages to get over to a great
many people. Or a specialized training course, mass-production type. Or,
maybe, the U. S. Army or something.
10
In other words, here is a complete
built-in lecture on an LP record-the
lecture itself, the audible message, plus
really copious quantities of pictures,
each one "frozen" on the screen long
enough to look at, as the sound track
does the describing. Good TV stills,
too. I saw them on multiple rows of
TV viewers down the sides of an auditorium. They seemed to me to be just
as clean, just as steady and sharp and
undistorted, as any normal black and -white TV images you're likely to
achieve on standard commercial sets,
either broadcast or closed-circuit.
All this off a totally standard LP!
You see how clever the thinking was.
The actual recording system (I'll get
to it) is not really the vital point. The
LP record itself came first, and determined the parameters. Plus the standard TV screen. Anyone who knows
TV and cathode-ray technology can
figure out how you might derive pictures from a disc groove. Nothing revolutionary at all. Except, in Phonovid,
the specific choice of working parameters. What matters, you see, is the
medium. (Aren't we supposed to understand, today, that "the medium is the
message"?)
The LP record is one of the simplest,
the cheapest existing vehicle for mass scale information that we now have.
And it's available.
And the same with the associated
TV. Standard stuff. Though TV isn't
exactly cheap nor inherently simple, it
is also very definitely available. It exists. It is widespread and its presence
is increasing everywhere, and most
especially in the very places-schools,
industrial training centers, sales meetings, etc.-where this Phonovid system
might be most useful.
With standard equipment at either
end, Phonovid is off to a flying start.
All you need is the middle circuitry,
the minimum that can be added to
operate within the standard parameters
at the two ends. That was the experimental project.
Ah, how about all those "limitations"? There are plenty, if you insist
on looking at it that way. But in this
sort of fun -and -games project you start
at the far end and work backwards.
Phonovid is quite unlike, say, CBS's
new EVR (Electronic Video Recording) , which introduces its cannily designed new equipment to meet very
different basic parameters-a maximum
compactness of information content on
a much more demanding scale, recorded TV in full motion and in color.
Phonovid's LP disc contains no TV
motion. No color. Just pictures. And
sound.
As it has worked out, Phonovid projects slowly. Much too slowly for direct
continuity. It gives you, as the LP record plays, a good TV picture every six
sec )nds (though you may hook them
together for longer shots, when desired) And so you see what we have.
This is a system technically related to
the close -spaced moon shots we all saw.
Successive views, each a still picture,
each advanced in "motion" over the
previous one. But those were more rapidly projected. At a six -second spacing
even that sort of semi -motion is out of
the question.
Why stills only? To "move" a TV
image you need a very wide bandwidth,
as the videotape people know only too
well. To get TV in motion onto tape
you must resort to all sorts of inherently complex mechanisms providing in
one way or another the high tape -to head speed that is essential.
Your LP record has a hopelessly limited bandwidth from the moving TV
viewpoint. But given a bit of time, you
discover things aren't so bad. All you
have to do is to scan your picture more
slowly. Much more slowly. And store
up the information as you go along,
until you want to use it. A memory
.
device.
When each picture is complete, it is
presented on the TV screen, all at once
(as the eye sees it). Meanwhile, behind
1-The "Phonovid" still-picture/sound system is shown at left, playing a special LP
record on a Garrard automatic turntable. At right is Sony's magnetic -type video disc,
which records and plays back still pictures in black -and -white and color, as well as sound.
Fig.
Check No.
11
on Reader Service Card
The cartridge looms large
for a simple reason:
the point of contact between the enti~e hi-fi system and the recording. What happens at the tip of
its tiny stylus determines what will happen in all those big and impressive compon-:nts that are so obvious
to the eye and, in the aggregate, so apparent to the pocketbook. Worldwide, experts and critics have
hailed the discovery of Trackability as the definitive measurement of cartridge performance. When
evaluated against this measurement, the superb Shure V-15 Type II Super Track stands alone.
Shure Brothers, Inc., 222 Hartrey Ave., Evanston, Illinois 60204
It
is
The analog -computer -designed Shire V-15 Type II Super-Trackability cartridge maintains contact between the stylus
and record groove at track'ng forces from 3/4 fo 11/2 grams throughout and beyond the audible spectrum (20-25,000
Hz). Independent critics say it will make all of your records, stereo and mono, sound better and last longer.
Tracks 18 cr/sec. and up a^ 400 Hz; tracks 26 cm sec. and up at 5,000 Hz; tracks 18 cm sec. and up at 10,000 Hz.
This minimum trackacility is well above the theoretical limits of cutting velocities found in quality records. $67.50.
g
1968 Shore Brothers, Inc.
the electronic scene, another picture is
being slowly drawn by the scanning
beam, actuated by the record groove.
Takes that full six seconds to do it.
How do you store up picture info?
Via one of those tricky memory -type
storage tubes. Phonovid uses two tubes,
one to collect the slow playback info
and the other to accept the complete
fast -scanned image when the first tube
is ready. There's a slight degradation,
I gather, as this transfer system operates. But it isn't of serious proportions.
"No problem," the engineers said at the
demo. And that's the way it looked to
me. Surprisingly clear, steady pictures.
Sharp enough to read print and diagrams of considerable complexity. After all, how sharp is normal commercial
TV? Not very.
Let me be slightly more specific, as
per the notes I took at the time. The
onds maximum, of course.) A very odd
effect! You can stop anywhere and
hold.
The sound track, of course, reacts
exactly as on a normal LP record. The
voice stops, then starts in the middle
of a word. But the picture "hangs over."
Now the big one-how about mechanical distortions due to the record
and stylus? What do you see when
there is LP surface noise? Hiss, pops,
cracks, clicks? And, even worse, what
about wows, warps, ripples, off -center
grooving? There really ought to be unbearable degradation, yes? All sorts of
snow, flashings, picture distortions, all
the horrid TV "static" effects? An LP
record, strictly mass produced, isn't
that "clean." And, remember, no spe.
cial treatment.
These engineers were clever, I tell
you. They had this figured out from
"The whole thing [video disc] plays
as long as a normal LP plays."
basic nominal bandwidth for the picture is, if my handwriting is correct,
10 kHz, operating via a reconstituted
side band, laid out from 5 kHz upwards on the LP record. The sound
track uses the lower portion of the
spectrum. Not exactly hi-fi soundbut I found it a lot better than the
usual dreadful sound track we hear via
normal 16 -mm sound film. Actually
(my notes say), the system goes a bit
wider in practice, up as high as 181/2
kHz, giving a maximum bandwidth for
the picture of some 13 -plus kHz. That
little extra probably helps. Given that
much bandwidth, and the standard LP
playing speed and playback equipment,
you can come up with a good picture
at the six -second rate.
The whole thing plays as long as a
normal LP plays-which is a long time.
Maximum is, perhaps, 30 minutes a
-
side.
Now
for some urgent questions.
You've already been asking them, I am
sure.
What happens when you take the
phono stylus out of the groove in mid play? Really zany! The last picture just
stays on the screen. Sits there, unmoving, unfading.
When you put your stylus back in
the groove, things start going again,
though there may briefly be a split
image, half of one picture and half of
another. (Not more than the six sec 12
the word go. They thought ahead, and
solved the problem. Now how about
you closing your eyes right here and
taking a long, long minute to do the
same in your head, decisively, in one
major more. Got it?
So ingenious. Frequency modulation. An FM signal on the disc, containing the picture info.
There are minor distortion effects,
to be sure. But not as you might have
expected. Some wobbly lines. And
brightness may vary across the picture
in extreme cases. But it takes a large
amount of plain, blatant record wow to
produce any serious distortion at all.
Surface imperfections do not play back
as they would in a straight "pitch for
pitch" recording. FM treats them as
static. Indeed, the system is quite astonishingly efficient, I'd say. It seems
almost immune to distortion. The record plays its pictures as smooth as silk.
And that is a very big favorable factor
in potential mass-produced cheapness.
No special treatment needed.
Why use disc at all-why not tape?
Aha-there we go. Back to the first
premise. Tape is too limited in the
sense of a mass-produced and widely distributed medium. Tape, too, is clumsier and less convenient in a dozen
crucial ways. All the old factors operate, those that have kept the disc alive
and supreme all these years, in spite
of tape.
-
But wouldn't tape produce a better
picture? It could of course. Given
changed parameters. But since via the
frequency -modulated Phonovid system most of the mechanical disc crudities are by-passed in the reproduction,
the engineers say that within desirable
parameters the LP record has no trouble equalling tape quality.
Finally, how about those over-all limitations Motion is out as we know, and
not even considered in Phonovid. But
what of color? Color would be enormously helpful, in the very places
where Phonovid might be most useful.
Projected slides and film strips, after
all, do provide color as well as black
and white.
Well, lots of things might be useful.
Like optical sharpness equal to that of
an optically projected picture. TV
doesn't have it, in any shape.
You can't have everything. No system does. Better sound might be nice,
but the Phonovid sound is already superior to most 16 -mm sound, and it is
easily intelligible on speech, OK for
background accompanying music, too.
Stereo, in this situation, would be a
frill but not an important factor.
As for color, it might be managed
(the engineers suggested) by two channels of info; but they had not gone into
this possibility. Cross talk on the stereo
disc would present serious problems,
they said, for one thing .
I'll have to admit that the lack of
color does seem to me the only really
vital limitation in the Phonovid set-up.
Here's where Sony's "magnetic" disc
pulls ahead. The record -shaped video
disc announced by Sony back in '66 was
reported to play color still pictures on
TV. In addition, the video disc can be
recorded upon. This video concept requires an altogether different disc and
playback/record machine, unlike the
Phonovid, which in the photo here is
shown using a Garrard automatic turntable.
Then there are video tape recorders.
Why settle for "stills" when you can
have motion pictures, in color or black
and white? It's just that these devices
require, like the Sony video disc, a new
basic machine, compared to the familiar record turntable and LP record. So
let's wait and see if this particular
project ever gets out of the labs and
onto the turntable. I myself think that
Phonovid has something, even in face
of all the complex competition in the
picture world due to its mass-produced
simplicity, plus the fact that I've already got a record turntable, am partial
to using the medium of record discs,
and own a TV set.
AUDIO
JUNE 1968
ri
If saving money sounds "in" to you,
you' ought to hear
the sounds of University.
iéh qual"t', 'air prce. That's what makes University the "in" line. If the quality is ro good...why
even bVtier about the rice, r gti? R ght! But if the q_a':ity is c itstandinª, .vcu dn' ycu like to
save a little moola -ço? Tt:er you owe it to yoirse1 aid :your poc'cet- co< to check out
l niversity speaker; Here's t Off' te' do it the hard ,ray:
Take any one of Lhlive-s ty s many speaker sys-ergs. 'c- 3> s mple, try :he luxurious Eorrento
or the classic-s`yled IVed terraneat. Ask your beater -b pi ay either one along s ce another
speaker listed at th 3 same pri`e. Next, compare L 1 v_ -sity's gcalita wi-h alittle h gher
priced speaker. Tar -ry sti a highe pried speaker. Yocr ears will to t you to
stop conpar:na, 3rrd your eyes will tell }cu t -e Fsargain you got.
If you go along_ w th the idea that sai nç Homy is "in", ever with hi -f equipment, yoc'II ba amazad at how sertsa- ona Univers ty speakers really do
l
sx
nc, do lar -i ise and sound w se
While you're at it, check out _niiE sitti s one a -id an y Stcd e Pro -120
So id-S_ata FM/Stereo Receive-. -he specs aresc unoe ievably good,
we ha: them certified J7 an n:ependent testing lao. They meet or
baat any of the top -of-the lire r>ceivers of t -e Big E, at a most
a:-rac-ive middle of he lire p-cel
Now you know /my Lrivesity is the "in" ire. :.:heck it
oat. It's
a
good
ray t:
cash in.
1j) UNIVERSITISOUND
O'LISION OF LT [JAG A TE: INC.
Oklahora City C3kl3h:ma 73126
M)) e_= Rer,)
UNIVERSITY- saving money never sounded better
AUDIO
JJNE 1968
Check No. 13 on Reader Service Card
13
Tape Guide
HERMAN BURSTEIN
If you have a problem or question on
tape recording write to Mr. Herman
Burstein at AUDIO, 134 North Thirteenth Street, Philadelphia, Pa.19107.
Please enclose a stamped, selfaddressed envelope. All letters are
answered.
Compatibility of equalization
curves
Q. The European CCIR curve for 19
cm/sec (7.5 ips) now sets the standard
playback turnover at 70 microseconds.
But one cannot tell how many and how
far the manufacturers in Europe have
abided by this norm or the DIN norm,
which was 70 /.Ls before the new CCIR
norm was set. Before I came to live in
Europe I used to curse the North
American way of formulating norms
left and right, to eventually try some
other system, while the Europeans
seemed to be so fortunate in having a
body with enough authority to enforce
standards. Well, it seems that chaos is
here (Europe) as well. Added to the
various CCIR and DIN norms, all
European tape recorders usually include NAB playback; the result is that
they often use NAB for recording as
well.-Andre Thiverge, Geneve, Suisse.
A. The fact that the CCIR curve now
has a turnover of 70 f,t,s, compared
with 50 As for the NAB (and RIAA)
tape playback characteristics, indicates
that the difference between the two
characteristics is close to insignificant.
The maximum difference between the
two is not quite 3 dB. When one takes
into account the departures from flat
response deliberately introduced by
engineers and others in recording, the
departures from flat response of reproducing equipment, and the tolerances
of the nominal playback curves, a
difference of under 3 dB between two
equalization characteristics approaches
insignificance.
Interpreting specifications
Q. In the Abajian-Jones article in the
October 1964 issue of AUDIO on building a tape amplifier, the authors state
that the signal-to-noise ratio is 52 dB;
that total harmonic distortion is about
1% when a signal of 1,000 Hz is recorded at the 0 VU level; and that IM
distortion is then about 7%. I would
greatly appreciate your remarks on
these specifications with regard to how
they compare with those of high -quality professional equipment. A. J.
Steen, Los Angles, Cal.
A. I presume that for S/N measurement that Abajian-Jones are using 1%
harmonic distortion, corresponding to
0 VU in recording, as their reference
level. In this case the specifications for
their amplifier are excellent, comparable with top professional equipment.
If the S/N ratio is 52 dB at 1% distortion, it is about 6 to 8 dB higher at 3%
distortion, which is a frequently specified reference level for high -quality
machines. Thus the amplifier has an
S/N ratio of about 58-60 dB, which
puts it in a rather rare class.
Don't let the 7% IM distortion at
0 VU disturb you. This is quite normal
when the tape deck and the tape get
into the act. Because of the high IM
figures, very little is publicly said about
tape recorders' IM distortion. Only
harmonic distortion is mentioned, and
manufacturers don't even like to say
too much about it. At the same time,
keep in mind that most of the time you
are recording well below 0 VU, and
there is an appreciable drop below 3%
harmonic and 7% IM distortion at reduced level.
-
Ssssssshhh
Q. My new * * * tape recorder has an
annoying noise, best described as
ssssssssssshhhhh, when in the playback
mode. The noise is controllable by the
machine's volume control, and can be
almost eliminated by turning the treble
control of my audio amplifier all the
way down. The noise is of the same
magnitude on each channel, and occurs whether or not the tape transport
is in motion. If I remove all inputs from
the tape recorder, the noise remains.
The noise ceases when I disconnect the
recorder's output cables from my audio
amplifier. The noise comes through on
quiet passages of prerecorded tapes.
With no program material and with the
tape machine's volume control at maximum, it's eggs frying at their worst. I
have an older tape machine that displays less noise, but also does not have
as good high frequency response as the
new one. I recall several instances in
your column where you told your
readers that the * * * tape recorder is
known for its poor signal-to-noise ratio.
Is my machine one of those?-Fred J.
Petzinger, Jr., Portsmouth, Va.
A. Your tape recorder is not one of
those I had in mind when referring to
14
a poor signal-to-noise ratio. Inasmuch
as your new unit has a more ambitious
treble response than the old one, somewhat more hiss is to be expected from
the new one. In the absence of my having direct access to your new machine,
or of your supplying S/N measurements, it is difficult to say whether you
are getting excessive hiss. The answer
depends partly on how loud you play
your tapes; that is, on how far you advance the gain control of your audio
amplifier. If you play at quite a loud
level, it is normal to hear some hiss
from the tape playback amplifier.
If hiss is indeed excessive, the cause
might lie in noisy components in the
first stage. Or it might lie in improper
playback equalization. Do prerecorded
tapes have an overbright sound If so,
this suggests faulty playback equalization-not enough treble cut.
Another question: Do you get excessive hiss at all tape speeds? Or only at
lower speeds, such as 3.75 and 1.875
ips? At lower speeds, playback equalization involves less bass boost-that is,
less treble cut-than at 7.5 ips. Therefore more hiss will be apparent from
the electronics at the lower speeds.
Semantics
Q. Does a tape deck only play tapes?
Or can you record with one? Would I
be better off to get an all-purpose tape
recorder?-Russell E. Webb, APO San
Francisco, Cal.
A. The term tape deck is usually understood to signify a tape transport
plus preamplifier electronics for playback and recording. If the electronics
are confined to playback, the unit is
called a playback deck. If there are no
electronics, the unit is called a tape
transport. A tape deck does not include
power amplifiers and speakers; a unit
that includes these items is called an
integrated tape recorder. However, the
terms tape deck and tape recorder are
often used interchangeably; and the
term tape recorder also is often used to
designate an integrated machine. Thus
there is, unfortunately, some confusion
about the meaning of terms.
By an all-purpose tape recorder I
assume you mean one with its own
power amplifier(s) and speaker(s).
This, as I have said, is also called an
integrated machine. It can be advantageous if you want portability. For example, you might want to record something away from the rest of your audio
system, and you might want to listen to
the playback at the recording site to
make sure you have what you want on
the tape.
Æ
AUDIO
www.americanradiohistory.com
AmericanRadioHistory.Com
JUNE 1968
Have we got a Sony for you!
Scrape Flutter Filter. Special precision idler mechanism located between erase and record/playback
heads eliminates tape modulation distortion. This
feature formerly found only on professional studio
Non -Magnetizing Heads. Head magnetization buildup-the most common cause of
tape hiss-has been eliminated by an exclusive Sony circuit which prevents any transient surge of bias current to the heads !
equipment!
Vibration-Free Motor. An important new Sony
Three Speeds.
development utilizing "floating" shock
absorber action to completely isolate any
71/2, 33/4
and 1/8 ips!
motor vibration from the tape mechanism.
Ultra High Frequency Bias. The
very first popular-priced deck to
achieve true high fidelity re-
33/4 ips. Additional
features include: Four -track
sponse at
Stereophonic and Monophonic
recording and playback. Seveninch reel capacity. Stereo Headphone Jack. Automatic Sentinel
Shut-off. Two VU Meters. Pause
Control. Four -digit Tape Counter.
Record Interlock. Vertical or Horizontal Operation. And more!
Instant Tape Threading. Exclusive Sony Retractomatic pinch
rollers permit simple one -hand
tape threading. An automatic
tape lifter protects heads from
wear during fast forward and
reverse!
Sound -on -Sound. Individual
push-button selection of both
channels enables interchannel
transfer for sound -on -sound,
sound -with -sound, and other special effects recording!
Sony Model 255. Priced under
$179.50. For your free copy of our
latest tape recorder catalog,
please write to Mr. Phillips, Sony/
Superscope, Inc., 8142 Vineland
Avenue, Sun Valley, California
91352.
SONY®
You never
SUPERSCOPE ®
heard it so good.
Check No. 15 on Reader Service Card
AUDIO
15
JUNE 1968
www.americanradiohistory.com
AmericanRadioHistory.Com
natural growth without the assistance proposed
by Rep. O'Konski (who, it is reported, is the owner
of a TV station and a former owner of FM radio
stations) .
EDITOR'S
REVIEW
Hi-Fi and Liberalization
The political upheaval in Czechoslovakia coincides with an interesting event announced recently: the country's first international exhibition
of stereo equipment, "Hi Fi Expo Praha 68."
The exhibition will feature FM stereo receivers,
tape recorders, pickups, and other equipment of
both Czechoslovak and foreign make. According
to program information, there will be lectures by
leading technical specialists and industrial designers, public listener comparison tests, a technical and advisory service for visitors, and even a
corner for women. Interest in high-fidelity sound
is increasing in Czechoslovakia, as indicated by
the formation this year of a Czechoslovak Hi-Fi
Club, an independent organization that now numbers over 7000 music and high-fidelity enthusiasts.
All -Channel Radio Bill Introduced
A bill (H.R. 16523)
that requires all radios to
be capable of FM reception was introduced to
Congress recently by Rep. Alvin O'Konski (R.,
Wisc.) . This radio version of TV's all -channel law
(television receivers must be equipped to receive
both VHF and UHF broadcasts) would compel
manufacturers to include both AM and FM tuners
in their equipment if the bill passes.
AUDIO does not support this special -interest bill.
It would penalize the consumer who may not wish
to purchase (or may not be able to afford) two -in one radios. Further, FM radio is exhibiting a rapid
16
The Return of Carl LaFong
Record World, a music and record trade publication, has introduced a new weekly feature, "Notes
From Underground," bylined by Carl LaFong.
The column will be devoted to FM music stations
that "have become a potent force in broadcasting
pop music." Carl LaFong, as some readers might
recall, was a pseudonym used by comedian W. C.
Fields. Identity of the "new" Mr. LaFong was
not revealed.
Newport Jazz Festival
Jazz buffs note: July 4 through July 7 are the
dates set for the 1968 Newport Jazz Festival. This
year marks the 15th anniversary of the famous
Rhode Island event. Among the artists scheduled
to appear are Ray Charles and Dionne Warwick.
I
Hear Music
According to Graphic Communications Weekly,
an engineer servicing a Vario-Klischograph electronic scanner turned in a rather strange service
report. It seems that an engraving head on the
machine was producing music from a local radio
station. In the black -and -white position, two stations were mixed, and in the engraving -test -cut
position one station was heard with clarity.
Grounding the shield of the amplifier cabinet eliminated the trouble. Reading about it brought back
memories of picking up broadcast music from a
G.E. variable reluctance cartridge many years ago,
as well as a more recent problem where a nearby,
powerful FM stereo station's broadcasts were received whenever volume was raised to a normal
listening level, whatever the function selected. The
final solution to the latter difficulty was to move
out of the area.
A.P.S.
AUDIO
JUNE 1968
The X factor in the new Pickering XV15.
The X in tige new Pickering XV -15 stands for the
numerical solution for correct "Engineered Application." We call it the Dynamic Coupling Factor
(DCF).s"
DCF is an index of maximum stylus performance
when a cartridge is related to a particular type of
playback equipment. This resultant number is derived from a Dimensional Analysis of all the parameters involved.
For an ordinary record changer, the DCF is 100.
For a transcription quality tonearm the DCF is 400.
Like other complex engineering problems, such as
sM
AUDIO
JUNE 1968
the egg, the end result can be presented quite simply.
So can the superior performance of the XV-15 series.
Its linear response assures 100% music power at all
frequencies.
Lab measurements aside, this means all your favorite records, not just test records, will sound much
cleaner and more open than ever before.
All five DCF-rated XV -15 models include the patented V -Guard stylus assembly and the Dustamatic
brush.
For free literature, write to Pickering & Co., Plainview, L.I., N.Y.
Dynamic Coupling Factor and DCF are service marks of Pickering
Check No. 17 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
&
Co.
17
Siteidoect-the
lowdistor,
proud that Sherwood FM tuners were
selected because of their low distortion by
America's foremost heart -transplant pioneers
to receive telemetered EKG data in their critical research programs.
We are
tuner
Hirsch -Houck Laboratories evaluates the 0.15%
distortion Sherwood tuner shown above as
follows: "The tuner has a usable sensitivity of
1.8 microvolts, with an ultimate distortion
level of -48 db. This is just about as low as
we have ever measured on an FM tuner, ..."*
The S-3300 features our unique SynchroPhase FM Limiter and Detector with microcircuitry, field-effect transistors, a stereo
noise filter (which does not affect frequency
response), and of course, only 0.15% distortion at 100% modulation. Less case- $197.50
*
30.0
0.1
Amplifiers and speaker systems
best suited for low -distortion tuners!
Electronic World, Oct., 1967
Sherwood offers three low -distortion amplifiers precisely suited for your needs-led by
the Model S -9000a with 160 watts music
power (at 8 ohms). The 140 -watt S -9900a and
the 80 -watt S -9500b feature main and/or remote stereo speaker switching and separate
terminals for monophonic center channel or
extension speakers. All feature 0.1% distortion at normal listening levels. Prices from
$189.50 to $309.50.
Our acoustic -suspension loudspeaker systems
were designed to reproduce music with minimum distortion and coloration. You can hear
the difference low distortion makes. Hear
Sherwood's low -distortion Tanglewood, Ravinia, Berkshire, and Newport at your dealerthen take a pair home for a no-obligation
trial. Prices from $84.50 to $219.50.
SHERWOOD ELECTRONIC LABORATORIES, INC.
4300 North California Avenue, Chicago, Illinois 60618
Write dept. A-6
18
Check No. 18 on Reader Service Card
AUDIO
JUNE 1968
Audio Noise Reduction:
Some Practical Aspects
RAY M. DOLBY
Part I: Operating principles and details
of a professional noise -reduction system
A NEW GENERAL-PURPOSE, professional audio noise -reduction system
(Dolby Laboratories model A301)
was discussed last year in Aunio
Magazine.1 The design philosophy
of the system was subsequently presented in a technical paper.2 Intended as a continuation of this
discussion from a more practical
point of view, the present article will
examine the device itself and consider various operational aspects,
especially in relation to magnetic
tape recording.
The purpose of the noise-reduction system is to reduce noises-hiss,
print-through, hum, as examplesthat normally arise in the tape recording and playback process.
Beyond a certain point in the care
taken in designing, maintaining, and
operating recording equipment, any
gains in signal-to-noise ratio unfortunately become increasingly difficult. Such gains may be difficult not
only because of limitations imposed
by the physics of the matter, but because of expense or general impracticability. A 10 dB reduction in tape
hiss, for example, can in theory be
obtained by the use of tracks ten
times as wide. Or any desired reduction of print-through can be had at
the inconvenience and expense of
interleaving the layers of the recording tape with a suitable shielding
material.
Clearly it is a matter of great
practical significance to have a
method of side-stepping these difficulties, which is the intention of the
A301 system to be described.
Before going into the details of
operation, it is necessary to appreciate how the system is connected
into the recording chain. Referring
to Fig. 1, the signal is first treated by
the recording-processor half of the
noise -reduction system before being
recorded on tape. During playback,
AUDIO
the signal is fed through the other
half of the system, where it is restored to normal; at the same time,
hiss is reduced by 10 to 15 dB (depending on the frequency), and hum,
rumble, and print-through are reduced by 10 dB.
In general terms, the noise-reduction system must operate around or
enclose the noise-producing element
of the chain. Therefore, a requirement for use of the system is that
the signal must be available for preprocessing before being fed into the
noisy element and for post-processing after it emerges.
It should be appreciated that the
system is not capable of separating
the noise from the signal in the normal sense. All it does is pre- and
post -process the signal in such a way
that the signal effectively becomes
less susceptible to the addition of
noises. Pre -emphasis and de-emphasis and, in a somewhat different way,
frequency modulation and demodulation are further instances of complementary pre- and post-processing
systems which improve noise immunity.
In professional audio there are
many ways in which a noise -reduction facility can be utilized, but a
notable application is in the making
of master tapes for high -quality
phonograph records. When the original signal is put on tape in processed form it is protected from the
usual sources of noise encountered
in recording, dubbing, storage, and
final playback. In this connection,
hiss and hum are the most common
noises, but print -through is undoubtedly the most serious flaw when it
does occur.
Principles of operation
The A301 system may be thought
of from two points of view. First, it
is a compression-and -expansion sys-
tem operating in four frequency
bands. Second, it is an automatic,
signal-operated equalizer which con.
tinuously controls the recording and
playback equalization characteristics in such a way as to improve the
overall signal-to-noise ratio. From
both views, the A301 is a three-dimensional signal processing system
with an overall gain of unity, but
with intermediate transmission properties which are functions of amplitude, frequency, and time.
Viewing the device as a compressor -expander, the main feature which
distinguishes the system from previous ones along similar lines is that
the signal as a whole does not pass
through any variable -gain elements.
Referring to Fig. 2, high-level signals
pass straight through the direct path
of the system (amplifiers only) .
Thus, they are not altered in any
way whatever. By this means, the
usual distortions and tracking troubles of compressor-expanders are
avoided.
Low-level signals, which are of relevance for noise -reduction purposes,
are handled in a side chain (differential network) comprising four
band -splitting filters and low-level
compressors. Whenever the signal
amplitude is low in any band, the
output from the compressor is large
in comparison with the same component in the main path. The addition of the differential component
to the straight-through component
thereby results in a boosted output
signal. The situation at high levels
is that the differential component is
compressed substantially; being
small in comparison with the main
signal, its contribution is negligible.
A complementary operation is
performed during playback, with the
differential component in this case
being subtracted from the main sig19
JUNE 1968
www.americanradiohistory.com
AmericanRadioHistory.Com
nal. Since the gain of the playback
unit is decreased at low levels, the
desired noise-reduction effect is
achieved.
An important aspect of the system
is that identical differential networks
are used in both the recording and
playback modes. Inspection of Fig.
2 shows that, basically, an extra
component is added and then it is
subtracted; what is left must be the
original signal. Insofar as correct restoration of the signal is concerned,
the networks can have almost any
characteristics whatever, with the
proviso that they are the same.
A feature of the process, it should
be noted, is that no pilot signals are
used in controlling the playback operation. In effect, the signal is its
:
Fig. 1-Use of the Dolby noise -reduction
system in one channel of the audio chain.
The signal is processed before recording
and after playback; noise is reduced and
processing operations cancel out, restoring
the signal to normal.
ó°o
oó/ o
RECORDER
II
Processor
A
Processor
B
Recording
Playback
Mode
Mode
v-
NOISE
REDUCTION
SYSTEM
I
IT
\-.--:-\\\\\
STUDIO
FACILITIES
Gain Control
Mixing
Equalization
Filtering
Limiting
Reverberation
OUT
20
-
own pilot. The playback processor
contains full information on the
principle by which the recording
unit operated; this information, together with the processed signal itself, is sufficient for the playback
half to recreate the original signal.
The transfer characteristics of the
two processor units are shown in
Fig. 3. When the differential component, Fig. 3C, is added on a decibel (dB) basis to the input signal,
the recording characteristic in Fig.
3A results. It can be seen that at very
low levels the input signal is amplified, whereas at high levels the transfer characteristic essentially rejoins
the input signal line. The inverse
(playback) characteristic, shown in
Fig. 3B, is formed by subtracting
the differential component from the
input signal. The result is reduced
gain at low levels (noise reduction)
and nominally unchanged gain at
high levels.
A noise -reduction system with
transfer characteristics as described
above, but with only one full -frequency compressor band, would
have good characteristics with regard to distortion, tracking ability,
and so on, but it would suffer from
poor noise-reduction properties. Full
noise reduction would be obtained
only at low signal levels, while at
high levels the noise would have its
usual value. Moreover, "swishing"
and "breathing" would be produced
under dynamic conditions, a familiar
behavior of limiter and compressor
circuits in general.
There is a fairly widespread misconception of the reason for noise modulation effects; they are usually
attributed to excessive recovery time
in the limiter or compressor control
circuitry. In fact, such behavior is
evident even when extremely short
recovery times are used. A steadystate phenomenon, the effect arises
because of the inability of the signal
-which usually occupies the mid frequency portion of the spectrumto mask low- and high-frequency
noises adequately.
Fortunately, the masking effect
makes it difficult or impossible for
the ear to perceive noise in the same
frequency range as the signal. By
exploiting this naturally occurring
noise reduction and suitably fitting
compression and expansion noise re -
Differential
Network
B
Input
Output
Adder
Differential
Network
B
Input
Output
Subtractor
duction to it, it is feasible to provide
for all normally encountered eventualities of signal and noise and to
produce an overall reduction of perceivable noise.
The process of joining real noise
reduction to apparent noise reduction must take into account the diminishing efficiency of the masking
effect with increasing separation of
the noise and signal frequencies. To
this end, it is necessary to handle the
audio spectrum in several independent frequency bands. Figure 2
shows the arrangement used in the
A301 system, in which four bands
are employed.
The bands are divided as follows:
band 1, 80 Hz low-pass; band 2, 80
Hz-3 kHz band-pass; band 3, 3 kHz
high-pass; band 4, 9 kHz high-pass.
Conventional 12 dB/octave filters
are used for bands 1, 3, and 4, while
band 2 is designed to have a frequency and phase response which is
complementary to that of the other
bands.
In the recording mode, the outputs of all the bands are combined
with the signal in the main path in
proportions which result in a uniform low-level 10-dB boost up to
about 5 kHz. Above 5 kHz, the boost
rises smoothly to 15 dB at 15 kHz
and then levels out. The amount of
noise reduction follows the same pattern, since the frequency response in
the playback processor is complementary to that in the recording
processor.
For fairly low-level program material, the full amount of noise reduction is obtained in all bands. But
with increasing level, the noise re AUDIO
JUNE 1968
-
Filter
Band
Linear
Limiter
4
4
Filter
Band
Linear
Limiter
3
3
Mom.
Fig. 2 Basic block
diagram of Dolby
Non Linear
system. During re-
Limiter
4
--.
Non Linear
Limiter
3
Add,
Filter
Band
Linear
Limiter
2
2
Filter
Band
Linear
Limiter
r--
1
1
-
r
NonLinear
Limiter
2
-
Non
-
Linear
Limiter
Differential
Network
1
duction in band 2 decreases progressively, whereby the masking effect
then agsumes contrúl of mid -frequency noise perceptibility. Noise
reduction under etgnal conditions
thereeforr agises rnc)st of the time
from low-level preº -emphasis, followfd by compleme! ,dry
-em h à
sip, due to the actions of bands 1, 3,
and 4.
Because the bands do not have
sharply defined boundaries, they
produce useful noise reduction outside their nominal pass-bands, a
fact which has been taken into
account in establishing the frequency divisions. Thus, when band 2
is paralyzed, band 1 provides noise
reduction up to about 120 Hz, with
band 3 being effective down to about
1.8 kHz. With signals containing
fairly high-level high -frequency components, band 3 is also blocked, in
which case band 4 provides noise reduction down to about 5 kHz. Band
4 is rarely blocked, except by signals
such as loud cymbal crashes.
All of the bands work together, in
varying degrees of momentary noise
t
reduction, in their respective frequency ranges. The overall result is
a noise level which is less (or appears to be less) than the original
noise level and, equally important, is
constara (or appears to be constant).
R,eferriAg to Fig. 2, a further feaure of the system which should be
noted is the non-linear limiter following the compressor (linear limiter) in each of the four bands. In
practice, the non-linear limiter circuits are simply symmetrically
biased brie clippers. Without the
clippers, tone -burst applied to the
input of the system would normally
cause the output to overshoot by
10 to 15 dB during the attack time
(that is, the time taken for the
control -signal circuitry and compressors to respond) But the amplitude of the differential component is
so small in comparison with the signal in the main path, it is possible
to bias the diodes in such a manner
that any overshoots are confined to
2 dB with peak level inputs. Such
clipping may seem to be a very dubious procedure. In actuality, how .
Fig. 3-Transfer characteristic curves. Compression curve (a) is produced by adding the differential component (c) to the straight through signal. The expansion characteristic (b) is formed by
-40
a.
AUDIO
dB
-40dB
Input
Compression
cording, a differential network adds a
low-level signal to
the straight -through
signal. In playback,
the low-level component is subtracted. The differential
network (right) consists of four band splitting filters and
low-level compressors. Terminals A
and B show how
the network is connected.
b.
ever, the limiters operate linearly
except with the most percussive program material. When they do operate, the clippers are inaudible because of the masking effect of the
high-level transient components
present in the main path.
The attack time of the system is
variable in the range from about 1
to 100 ms, automatically adjusting
itself to the size of the amplitude
transition. For small transitions it
is an advantage to use long attack
times in order to minimize the generation of modulation products, but
for large transitions it is clearly best
to minimize the duration of the overshoot.
Non-linear control signal integration circuitry is similarly used to
provide optimum smoothing of the
rectified control signal, while minimizing the recovery time of the
noise -reduction action following cessation of high-amplitude signals.
Low-frequency distortion is thereby
held to a fraction of a per cent at
30 Hz, and the recovery time (less
than 100 ms) is short enough that
no "swishing" or "breathing" effects
are perceptible under even the most
difficult program situations, such as
"clap sticks" in a dead studio.
Block diagram
Turning to the block diagram in
Fig. 4, one of the two signal processors in an A301 unit is shown, together with the power supply. Each
processor consists of an amplifier
module, a control module, and two
compressor modules (each of which
contains two compressors)
The signal enters the unit through
the bridging input transformer,
T403 (or T404) It is fed to potentiometer RV101, which is adjusted
to give a standard operating level
.
.
subtracting the differential component (c) from the straight through signal according to the negative -feedback configuration
shown in Fig. 2.
Input
0
-4018
Input
C. Different al Component
Expansion
CO
CO
v
v
21
JUNE 1968
www.americanradiohistory.com
AmericanRadioHistory.Com
CONTROL
AMPLIFIER MODULE
RIGHT COMPRESSOR MODULE
MODULE
UPPER HALF
-Nnnv`
R303
OF BOARD
(INTEGRATOR
1
8
EF
AMP
E
30 MHz
LOW PASS
FILTER
0103
0102
EF
INTEGRATOR
FULL
E F.
WAVE
2
RV 201
6
0104
yeiRV 101
EF
FILTER
3 kHz
HIGH PASS
BAND 3
13
12
EF
DIODE
COMPRESSOR
NETWORK
0202
,
RV202
GAIN
--0
TP201
0204
0203
INPUT LEVEL
RECTIFIER
0201
LAW_
Q205
'
^
EF
CAMP
MP
0207
0206
fL
BS
0209
0208
ROC CAL
LOWER HALF
OF BOARD
REC
R304
V
(INTEGRATOR
31
B
PBICÁl.,/
(INTEGRATOR
2
E.F
E.F
O1V
07
-0108
0109_
>
E.F
Y
0106
/
27
29
25
26
23
24
19
20
1
Ef
RV201
LAW
/
FULL
0201
I
RV202
4-0 TP201
GAI N
V
FILTER
9 kHz
\0105
E.F.
HIGH PASS
2
0202
RAND
E.F
AMP
0205
0206
0100E
yt
COMPFESSOR
NETWORK
RECTIFIER
F
Q207
P
O`PLIT
0208
0209
I
RV 104
OUTPUT LEVEL
9
LEFT COMPRESSOR MODULE
13
R
301
v
UPPER HALF
OF BOARD
I2
(INTEGRATOR
I
(INTEGRATOR
2
9
9
FULL
POWER SUPPLY
MODULE
07
µ NVE
RV 201
7
RECTIFIER
LAW
T
RV202
GAIN
FILTER
60H3
E.F.
DIODE
COMPRESSOR
NETWORK
LOW PASS
BAND
1
R 302
(INTEGRATORI
TP201
SPLIT
F.
AMP
E.F
MP
0205
0206
-1207
0208
ó-t-e2º
1.209
LOWER HALF
OF BOARD
26
FULL
INTEGRATO
WAVE
24
20
TO
ARRANGEMENTS AND
RVAIN202
CONNECTIONS SIMILAR
E F
5. ALL COMPRESSORS
ARE
Fig. 4-The audio- noise reduction -system consists of two identical processors, one each for
left and right channels.
Q110.
The output amplifier itself is
fairly standard, having an output
impedance of 600 ohms and a clipping level a little over +18 dBm
(that is, 14 dB above 0 VU on the
normal +4 dBm standard) . As with
the input, the system output is left
floating to minimize line noises.
The control module coordinates
and controls the operation of the
four compressors. All functions
which differ from band to band are
contained in this module, an arrangement allowing identical compressors to be used for all bands.
Followirig band -splitting, the sig-
F
0202
NETWORK
0205
AMP
0206
E
0207
AMP
OSPLIT
02084-0209
L
SIMILAR
within the system. After passing
through the 30 -kHz low-pass filter,
which removes any tape recorder
bias or other undesired high-frequency signals in the input, the
signal is fed to the filter driver amplifier, Q103 and Q104. The output from the amplifier is passed 'to
the filters in the control module and
also to the output amplifier, Q107 -
DIODE
COMPRESSOR
30
RECTIFIER
4.-0 TP201
G
FILTER
60Hz - 3 kHz
BAND PASS
BAND 2
0201
0204
0203
4. PROCESSOR B
ye
20
PROZESSOR B
NOTES:
CONNECTION NUMBERS REFER TO
CIRCUIT BOARD EDGE CONNECTORS
2 EMITTER FOLLOWERS DESIGNATED OF
3 POWER AND EARTHING CONNECTIONS
NOT SHOWN
1,
RVj01
A Processor
is
(amplifier, control, and two compressor modules)
shown above.
nal is distributed to the four compressors, being fed in through the
emitter follower Q202, which in turn
drives the diode compressor network,
a combination of two germanium and
two silicon diodes.
The compressor circuit takes advantage of the fact that a diode's
dynamic resistance can be controlled
by the direct current flowing through
it; transistors Q203 and Q204 produce a control current which determines the impedance of the diodes.
The diodes form part of an attenuator network, a balanced configuration being employed to cancel the
d.c. component. Because of the low
signal amplitudes handled in relation to the curvature of the diode
characteristics, distortion produced
in the compressor is negligible.
The compression threshold in all
bands is 40 dB below peak operating
level, defined according to the European convention of taking the nominal 2% distortion point on magnetic
tape as peak operating level. In VU
22
terms, the threshold is 36 dB below
O VU.
The output of the compressor is
amplified by Q205 and Q206, passed
through the diode clipper circuit
(between Q206 and Q207) , and returned to the control module through
the emitter follower, Q207.
The output is also amplified further by the control -signal amplifier,
Q208, and passed to the phase split ter, Q209, and full -wave rectifier circuit. The fed -forward signal from
Q202 to Q208 should be noted. By
suitably combining this signal with
the output of the compressor, the resultant control signal produces the
down -turning characteristic shown
in Fig. 3C.
After being pre -integrated by the
fast time -constant integrator 1 in the
control module, the d.c. control signal is fed through emitter follower
Q201 and back again to the control
module for further integration. Integrator 2 is an RC circuit with a back (Continued on page 55)
Check No. 23 on Reader Service Card
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A Marantz
stereo component
isn't built
for
the mass market.
(That's what's so good about it!)
Marantz isn't the name that most people think of first when
they think of components. It's understandable. The price of
Marantz equipment is simply beyond them.
On the other hand, price is the very reason a Marantz
component can be as good as it is. (Nobody can give you
something for nothing.)
Quite frankly, our philosophy is to let our engineers
design a piece of equipment
as best as they know how.
performing stereo components available anywhere in the
world. The Marantz SLT-12U Straight -Line Tracking Turntable ($295). The Marantz 7T Solid -State Stereo Preamplifier Console ($325). The Marantz 15 Solid -State Stereo Power
Amplifier ($395). And the Marantz 10B Stereo FM Tuner($750).
As soon as you examine
these components, we know
you will appreciate what
goes into making a Marantz
a Marantz. That's why your
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dealer will be pleased to
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AmericanRadioHistory.Com
r
I
-MR
111111
Y
IBM
Ii
! Ir_
MOM
Fig.
RIM
.
1
-
View of
closed end of listening room shows
speakers concealed
above and behind
MEIN
furthest
wood
beam. Inset shows
how speakers were
placed.
BIM
r
Min 111111118_
A Custom
Home Stereo Installation
MICHAEL
J.
CURRY
The author stresses room acoustics, illustrating how he determined reverberation time in his
music -listening room.
science of archi-
EXTENDING THE
tectural acoustics to private residences can enhance the performance
of good -quality stereophonic home
music systems. The listening room
is the final link in the sound chain,
as most readers know, and plays a
significant role in the quality of
the final sound
There are three possible approaches to solving the problem of
the "right" stereophonic reproduction system; that is, integrating
music -reproducing equipment and
its environment. The ideal procedure
would be to design an acoustically
excellent listening room and then
custom -design the rest of the house
to fit.1 This is obviously a procedure
best suited to wealthy persons.
The second and perhaps most common method is to install stereo
equipment in an existing room wherever sufficient space can be found.
This is a makeshift arrangement
which rarely satisfies a discriminating stereo hi-fi enthusiast, though he
is often forced to adopt this approach. The third method, and the
.
best one in the author's opinion, is
to design the room and the audio
system together so that a harmonious accord between decor and sound
is achieved. This was the procedure
utilized by the author and described
here.
Construction
The basic objective of the stereo
installation was to provide good listening conditions and facilities in the
living room of the home, although
additional speakers were provided
in the master bedroom (see Fig. 3).
A 70-watt transistorized stereo amplifier provides the driving power,
fed from a stereo phono cartridge
installed in an automatic turntable.
The previously-determined plans
for the living room incorporated
three exposed beams running across
the room, as shown in Figs. 1 and 4.
The beam nearest the closed end of
the room was partially cut away over
two 3 -foot lengths to admit the
mounting of eight 8 -inch, wide -range
speakers, four per channel, in the
attic.2 Thus, the entire attic serves
as a common enclosure for both
speaker systems. The radiated sound
is reflected twice-once from the cutaway beam and once from the end of
the room-before reaching the listener. This results in an apparent
sound source across the end of the
room.
A specially -designed equipment
cabinet, doubling as an end -table,
houses the amplifier, turntable, and
controls, and provides record storage
space (Fig. 2). The result is a completely built-in system which is
readily accessible; yet it is pleasingly unobtrusive, not exhibiting an
"added -as -an -afterthought" look of
many built-in systems.
Summary of Background Theory
Despite the considerable volume
of work published in the field of
architectural acoustics, there re-'
mains a good deal of controversy
over the merits of precise acoustical
measurements as opposed to subjective evaluation when applied to a
given room3. 4, 5.6 Indeed, there
seems to be some doubt concerning
the ability of the present "state of
the art" to provide meaningful and
accurate descriptions of room acous-
Fig. 2-Photos of the equipment cabinet are shown with doors closed and opened. The
turntable and the record -storage bin are mounted on slides for easy access.
Check No. 25 on Reader Service Card
www.americanradiohistory.com
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For her, the PE -2020 is styled to fit beautifully
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And when you visit him, be sure to bring her
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of you. ELPA MARKETING INDUSTRIES, INC.,
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the Elpa PE -2020
tics in terms of measurable parameters.
Certainly an acoustical engineer
finds it imperative to be able to express his measurements and predictions in concise and well-defined
terms. However, no amount of well tabulated data will pacify a musician
or an experienced listener to whom
an audio reproduction system
"doesn't sound right." Therefore,
when the problem at hand is that of
designing listening environments for
separate section accompanying this
article to provide some objective
basis for evàluation of the completed
installation. The basic idea here was
to calculate reverberation time-the
key to a room's acoustic characteristic, barring resonances and the like
-using mathematical methods.
As previously stated, the real test
of the stereo system was a listening
test. The quality of the system's
sound reproduction proved to be
highly satisfying. The bass reproduction was entirely adequate, without "boom," and the highs were clear
and sharp.
It should be noted that the tone
and loudness controls of the amplifier provide excellent control of both
tonal range and brilliance. The
eight speakers were found to be capable of producing enough sound
intensity to create an uncomfortable
sensation without introducing noticeable distortion. In accordance
with the author's preference for subjective testing, actual recorded musical selections rather than test recordings were used for the listening
tests. The recordings used (all
stereo) were some with which my
"listeners" were reasonably familiar:
Fig. 3-Level
and balance functions are
provided for each of four speakers by constant -impedance "L" pads.
Living-room
speakers
Amplifier
t
Bedroom
speaker
a non -technical audience, the primary criterion for success should be
the realism of the sound produced
by the system. This is, unfortunately, a criterion which can be applied
only after the system is completed;
the a priori designing apparently has
to be done on the basis of experience
and intuition.
A considerable amount of work
has been done, however, to provide
the designer with limits within
which to work. A brief summary of
this theoretical work is given in a
1.
2.
3.
The Intimate Bach-Laurindo
Almeida (Capitol SP 8582)
Spanish Guitar-Tony Mottola and Orchestra (Command
RS841SD)
Bossa Nova USA The Dave
Brubeck Quartet (Columbia
-
CS 8798)
(Continued on page 54)
Fig. 4-Sketch plan of the music -listening room illustrates placement of speakers and significant furnishings. Note that the speakers in the master bedroom, separated from the
livir g room by the double fireplace, are mounted on the top shelf of a bookcase.
wmdows
Bookcase
Beam
Rug
Bookcase
Rug
Equipment
Cabinet
Settee
Fireplaces
m
Scale
0
26
Carpet
Rug
Des
t
2
mise is possible between the objectives. A brief summary of the
pertinent theory of acoustic room
evaluation and several excellent references are provided for the benefit
of those readers who wish to expand
their knowledge of this fascinating
subject.
Following the method of Stewart
and Lindsay,7 let us consider a room
in which there is a uniform sound
energy density, E, per unit volume.
Then it can be shown that the rate
of sound energy striking the room
walls per unit area is
Incident Rate =
4
Eu
(1)
where u is the velocity of sound.
Now, if we define the average absorption coefficient, a, as the fraction of the sound striking a wall
which is absorbed by that wall per
unit area, we see that the total
absorption is given by
a = a S
(2)
where S is the total surface area of
the room interior.
We pause momentarily at this
point to mention the units of absorption. For acoustic purposes, it
is assumed that an open window is
a perfect absorber, with a = 1;
that is, it is assumed that none of
the sound originating within a room
and passing through an open window is reflected back into the room.
Thus an absorber having a = 0.5 is
half as effective as an open window
of the same area. The unit of absorption is the open window unit
(OWU), defined as the absorption
of an open window of area equal to
one square foot.
From equations (1) and (2) we
see that the rate of absorption of
sound by the walls of the room is
Absorption Rate = EúaS (3)
'
4
Speaker
Positions
How to Evaluate a Room's
Acoustic Characteristics
THE MAIN PART of the article
describes the construction and performance of a custom stereophonic
system which was designed as an
integral part of a new home, both
acoustically and aesthetically. It
suggests that a satisfactory compro-
Cupboards
The rate of production of sound in
the room is assumed to be a constant, A. Then the rate of increase
of sound energy in the room is
equal to the rate of production less
the rate of absorption. This rate of
increase per unit volume is written
as dE/dt. Then the rate of increase
of sound energy for the whole room
feel
AUDIO
JUNE 1968
is V dE/dt. Writing the data of this
paragraph in mathematical terms,
we obtain the equation
-4 EuaS
V dE/dt = A
(4)
This equation can be solved, using
standard techniques,8 to give the
energy density, E, as
E
4A ri
e-(4V)t1 (5)
urS
-
L
J
where t is the time referred to the
commencement of the production of
sound and e is the base of the Naperian logarithms (e = about 2.72).
If the production of sound is suddenly stopped, the sound energy
density in the room will decrease
according to the relation
E =
a
ucTs
4Vt
(6)
Let us now define T as the time
necessary for this energy density to
decay to one millionth of its original
value,
E,a
That is,
Emas
E'
1,000,000
-
E'
e
(4V )T
(7)
Equation (7) can now be arranged
in logarithmic form. Evaluating the
logarithms and substituting the
value for the velocity of sound in
air we arrive at the expression
T = 0.049 V = 0.049 V
aS
a
(8)
where the volume V is expressed in
cubic feet and the absorption a in
OWU.
Equation (8) is the reverberation
equation, first determined experimentally by W. C. Sabine at Harvard University around 1900, and
the quantity T is called the reverberation time. This equation has,
however, been found to be inaccurate, especially for "dead" rooms
with high values of a. An improved
formula, presented by Eyring9, is
0.049 V
0.049 V
T =
-
a'
-S In (1 a)
In view of the difference between
equations (8) and (9) and as a matter of convenience, the total absorption has been redefined as
a' = -S In (1 - a) =
-2.30S log (1 - a)
(10)
When S is expressed in square feet,
the unit of a' is the Sabin. (Note
that this unit corresponds to but is
not exactly equal to the OWU.)
The reverberation time is the
parameter most often used to determine the acoustic quality of a
room. The optimum value for T, depending upon personal preference
AUDIO
JUNE 1968
and the use for which the room is
intended, has been expressed in several published works. Stephens and
Bates° experimentally developed
the relation
Top, = (0.0036V1 + 0.107)r (11)
where V is the room volume in cubic
feet and r has the values 4, 5, and 6
for speech, orchestration, and choral
music respectively. The Radiotron
Designers' Handbook" lists optimum reverberation times determined at 1000 Hz for living rooms,
while Beranek12 presents in graphical form optimum reverberation
times as compiled from the literature and from experience. Values
for Top, are also given by Knudsen".
The considerable variations in the
optimum values suggested by these
various workers render the choice of
a Top, figure difficult; however, a
basis for weighting the given values
for averaging purposes has been
provided by Knudsen", who observed that "over the period [from
1928 to 1954] there has been an unmistakable trend toward shorter
reverberation times in nearly all
types of rooms." Thus we are justified in attaching more significance
to more recently published values
of T,51.
Equations (8) and (9) tell us that,
for a given room with a fixed volume
V, the reverberation time is dependent upon a, a parameter which
can be varied by changing the substance of the interior of the room
and which can be calculated by
summing the contributions to the
total absorption by the various
components of the walls and furnishings16.
aS =
(12)
i=1
This equation enables us to calculate a, provided that we know the
area presented by each component
of the interior and the absorption
coefficient of that component. Fortunately, tables of the latter quantity are readily available,16,17,18 so
that, using equations (9), (10), and
(12), we can obtain a reasonable
estimation of the reverberation time
of a room without resort to complicated and expensive measuring
equipment.
Final evaluation
Measurements of the room and its
furnishings resulted in the following
values for pertinent parameters:
Volume, 2630 cu. ft.; total surface
area, 1350 sq. ft. Using available
tables for absorption coefficients to
complement the remainder of the
measured data, the total absorption
was calculated as shown in Table I:
Table I
Room Composition and
Individual Contributions
to Absorption
Material
Area
(sq. ft.)
CY:
a
(OWU)
163.0
168.0
87.6
0.03
0.25
0.03
4.89
42.0
2.63
445.0
328.0
21.1
10.0
73.6
0.20
0.05
0.05
0.7
0.03
89.0
16.4
1.05
7.0
58.6
0.5*
29.3
Floor, wood
Floor, carpeted
Walls, brick
Walls,
wood panelled
Ceiling, plaster
Wood, solid
Heavy Cushion
Glass
"Half -open"
(archways)
Chairs,
2.21
upholstered (4 chairs @ 3.25 13.0
OWU each)
Total Absorption 207.5 OWU
The remaining quantities of interest are easily calculated:
Average Absorption Coefficient:
a =
S
= 0.15
Reverberation Time:
T = 0.049 V = 0.58
a
sec.
Optimum Reverberation Time:
Top, = about 0.6 sec.
*No mention was found in literature of a
method of dealing with open archways. In
this case, the area of the archways is less than
5% of the total surface area of the room, and
the adjoining rooms are quite spacious. The
error introduced, therefore, by assuming for
these archways the value a = 0.5, is considered to be no greater than 0.04 sec.
References:
7. G. W. Stewart and R. B. Lindsay.
Acoustics (D. Van Nostrand Co., Inc.,
New York, 1950) Chapter IX,
"Architectural Acoustics "
8. See, for example: Differential Equations,
F. Ayres, Jr. (Schaum Publishing Co.,
New York, 1952) Chapter 6, p. 35
9. C. F. Eyring, Journal of the Acoustical
Society of America, Vol. 1, p. 217 (1930)
10. R. W. B. Stephens and A. E. Bate,
Wave Motion and Sound. (Edward Arnold and Co., London, 1950) p. 285
11. F. Langford -Smith, The Radiotron Designers' Handbook. 4th ed. (Radio Corporation of America, Harrison, N. J.,
1953) p. 863
12. L. L. Beranek, Acoustics. (McGraw-Hill
Book Co., Inc" New York, 1954) p. 425
13. V. O. Knudsen, Architectural Acoustics,
(John Wiley and Sons, Inc., New York,
1932)
14. V. 0.
Knudsen, "Review of Architectural
Acoustics During the Past Twenty-five
Years." Journal of the Acoustical Society
of America, Vol. 26, pp. 646-650 (19M)
15. N.
W. MacLachlan, Loudspeakers.
(Dover Publications, Inc., New York,
1960)
E. Kinsler and A. R. Frey, Fundamentals of Acoustics. (John Wiley and
Sons, Inc., New York, 1950)
17. L. L. Beranek, loc. cit. pp. 300-301
18. G. W. Stewart and R. B. Lindsay, loc.
cit. pp. 346-347
16. L.
27
(Equipment)
Fig.
1-Dolly-builder's stereo setup
for component identification).
(see text
Tape recordist puts equipment on
wheels to simplify transporting
gear from one location to another
"LIVE" MAGNETIC TAPE recording
is the shortest route to a high-fidelity
signal. A first (or master) tape is
free of several generations of loud-
ness limiting, transfer distortions,
and equalization. But the most difficult part of amateur live recording is
the transportation of the equipment
to the amateur live performers. This
usually involves many trips, sometimes of several blocks each, between parked car and recording site;
just one trip might require a safari
of bearers.
One day it occurred to me that
things move easier when you put
wheels under them. A first thought
was to simply put wheels on my
sixty -pound tape machine. The next
logical step was deciding to put
wheels under all of my recording
equipment. The resulting equipment
dolly carries my Magnecord tape
deck, among other things, and therefore was named the "Maggie -Dolly."
The Maggie -Dolly has space for
eight 101/2 -inch reels of tape, eight
Fig. 2-Front view of the dolly with drawers partially open is shown at left. A rear
view, with a microphone drawer on the
floor, is at right.
28
IDZLLUr
microphones, two Shure M-68 mixers, and a monitor amplifier. It is
currently equipped with two PML
EC -71 FET condenser microphones
and two EV 655-C omni-dynamics.
The space behind the mixers is open
for easy access to the mixer microphone receptacles. Next to the mixers is a small stereo amplifier which
drives the Koss Pro-4 earphones.
This amplifier also has a silicon control -rectifier (SCR) peak detector I dreamed up to reduce recording distortion on material that
has an abnormally low rms (VU meter reading) characteristic. The
peak detector reads both channels
simultaneously, and its alarm light
is mounted in place of the original
pilot light.
The large upper drawer in the
Maggie -Dolly holds all the loose incidental equipment one must have
when recording in the field. The
smaller middle drawer is compartmentalized for microphone storage,
while the small lower drawer holds
the microphone power supply, 10 dB line "H" pads and line transformers for recording without the
mixers.
The cable tray attaches to the
dolly, as does the Maggie, with window locks. This permits removal in
several seconds, and thus allows
rapid breakdown of the system for
transport in my car trunk. The cable
tray holds enough cable to permit
running two microphones out about
120 feet or four microphones out
about 70 feet. The cables are wound
in a figure -8 configuration around
end blocks that have swinging retainers on them. This enables me to
run the cable off in "fire -hose" fashion upon my usually tardy arrival at
a recording session. The tray also
holds four collapsible microphone
stands. The elastic rope helps to
hold baby booms, etc., to the tray.
The Maggie-Dolly's box is made
JAMES P. HOLM
of %-in. plywood, and its frame is
11/2 -in. x 11/2 -in. x 1/8 -in. angle aluminum. The box was fastened together
with spiral nails and glue. The frame
was welded together on a radio frequency welder. The drawers are
specially designed to prevent small
items from falling out when the dolly
is lying on its back during transport.
The handles are swing -down motor Fig. 3-The dolly is shown
all set to roll at right.
Note cable
-
retaining
swivel fingers. The dolly
and
cabinet are
''sw..,it
transported in an
auto trunk, while the
recorder and cable
tray are placed inside
the car as a safety
precaution.
cycle foot-rests mounted upside
down. Wheels are from Sears, Roebuck & Co.
My stereo system at home is situated for convenient transfer to the
dolly, as shown in a photo here. The
speaker enclosures are based upon a
design article published in the April,
1960 issue of AUDIO. Each speaker
system contains two 15-in. woofer/
whizzers with a DuKane Inovac
tweeter topping it off. Program
sources are: (a) Dual 1019 changer
with a Shure V15 -II cartridge, (b)
Magnecord "728" 71/2- and 15-ips
1/2 -track tape deck, (c) Viking "88"
71/2- and 31/4-ips 1/4 track tape deck
with a hysteresis drive motor for improved pitch accuracy. The preamplifier is a Dyna PAS -3, driving a
Dyna Stereo 70 basic power amplifier.
AUDIO
JUNE 1968
PAS -3X PREAMPLIFIER
69.95 KIT, 109.95 ASSEMBLED
FM -3 TUNER
99.95 KIT, 154.95 ASSEMBLED
UNC M P
M ISEO QUALITY
This combination of PAS -3X preamplifier, FM -3 tuner,
and Stereo 120 amplifier represents the highest level of
quality which can be attained with high fidelity components. It combines the virtues of both tubes and transistors in a flexible modular system without skimping
to squeeze it into one unit.
Two of these components have passed the test of
time
years of increasing public acceptance. The
Stereo 120 is an all new design. All have been engineered and produced with the same underlying Dynaco
philosophy of offering superlative performance at the
lowest possible cost-when you buy it, and as long as
you own it. Everyone recognizes that Dynaco is "best
for the money." We know that it should be judged regardless of price-Dynaco quality has never been compromised by cost considerations.
Our sole concern is sonic perfection. We don't follow
the herd in engineering, styling or promotion. Fads,
status and "revolutionary new sounds" never enter our
planning. We avoid regular model changes and the
planned obsolescence they engender. We take the extra
time to do things right the first time. That probably ex -
-
plains why our limited product line has become increasingly popular each year. It's why our kits are so easy to
build; why maintenance is so easy; and service problems so few. We constantly strive to improve our products though, and when we do, these changes are available to our customers to update existing equipment at
low cost.
Our detailed literature, available on request, gives
the full specifications which help to explain why the
Dynaco components illustrated (PAS -3X, FM -3 and
Stereo 120) will provide the finest sound possible. Specifications are important, but the most complete specifications cannot define truly superb sound. Go to your
dealer, and compare Dynaco with the most expensive
alternatives, using the very best speakers and source
material you can find. Be just as critical, within their
power limitations, of our best-selling Stereo 70, Stereo
35 and SCA-35.
Of course, if you are now a Dyna owner, don't expect us to convince you to replace what you already
have.
But your friends might benefit!
STEREO 120 AMPLIFIER
159.95 KIT, 199.95 ASSEMBLED
alyAraI0
AUDIO
JUNE 1968
3060 JEFFERSON
IN
EUROPE WRITE:
STREET,
DYNACO A -'S,
Check No. 29 on Reader Service Card
PA. 19121
HUMLUM, STRUER, DENMARK
PHILADELPHIA,
29
Antenna
Front End
30
E
C
Fig. 1-Block diagram of an FM tuner, with
shaded portion indicating section discussed here.
LEONARD FELDMAN
HAVING EXAMINED some general characteristics of FM in past articles, we
are now ready to begin a step-by-step
analysis of the "blocks" used to make
up a typical, high -quality FM tuner.
First, let's define the word "tuner,"
because it means different things to
different people. In high-fidelity terminology, the "tuner" is all the circuitry
needed to convert the received signal
at the FM antenna into audio information suitable for application to an audio
amplifier. "Package" or console manufacturers often refer to a "tuner" too,
but they mean just the early portion of
the receiver devoted to amplifying the
radio frequencies and converting them
to an intermediate frequency of 10.7
MHz. It is this section of a "tuner" that
we call a "front-end"; and it is this section to which we shall now devote our
attention.
Figure 1 is a block diagram of a typical "tuner" (by our definition). The
shaded block is the one we will study
first. Each month, we shall repeat this
diagram, featuring a different "block"
of study.
Today's tuners almost invariably
employ solid-state amplifying devices
in the front end, as well as in the i.f.
section. More recently, many manufacturers are using Field -Effect Transistors in at least the r.f. stage of the
front end. These solid-state devices
more nearly approximate the performance of the highly perfected r.f. tube
designs that were popular a few years
ago. If this seems a bit paradoxical, one
must realize that the pressures of marketing forced designers into complete
transistorization a bit too soon. Only
now are the solid-state devices used for
front-end design catching up with some
basic performances capabilities long
associated with vacuum -tube performance. For this reason, we shall first
examine an "old fashioned" cascode
r.f. amplifier, as used in a Fisher Radio
receiver some years back.
The ability of a receiver to amplify
a signal is not limited by the ampli -
Limiters
Detector
A.
Front Ends
Amplifiers
A.G.0
ABZs ofFM
R.F.
I.E
fication atttainable from the vacuum
tubes or transistors, but rather by the
noise which arises from these devices
and their associated circuitry. Further,
the noise developed in this first r.f.
stage is actually the most significant:
whatever noise voltage appears at the
grid of this stage will be amplified
along with the signal. The best choice
for low noise (confining the discussion
to tubes, for the moment) is a triode
amplifier tube. Unfortunately, the gain
of most triodes is less than that obtainable from pentode tubes.
The circuit shown in Fig. 2, known
as a cascode amplifier, combines the
gain features of a pentode with the
low -noise features associated with triode operation. Ll and L2 constitutes a
matching transformer arrangement
known as a "balun." While most antenna transmission lines used for home
FM receivers is the familiar 300 -ohm
twin -lead type, coaxial transmission
line has been shown to be more advanFig.
Audio Out
tageous when fighting local man-made
noise, such as ignition from vehicles,
etc. Coaxial transmission line sold for
this purpose has an impedance of 72
ohms, and if no provision were made
for impedance match, the signal lost by
virtue of the mis -match to a 300-ohm
receiver input might well off -set the
gains resulting from the use of coaxial
lines in the first place. Some high -quality sets provide inputs matched for
either 72 or 300 ohms for this reason.
The signal from secondary L2 is applied to the first tuned circuit, which
in turn connects to the control grid of
the first triode section. The signal at
the plate of the first triode is coupled
to the cathode of the second triode section, while the grid of the second triode
is grounded (so far as r.f. is concerned)
Thus, the first stage is operated as a
conventional amplifier, while the second stage is employed as a grounded
grid amplifier.
The non -detailed blocks (local oscil.
2-Good-quality front end from the vacuum -tube
era, featuring
a
popular "cascode"
dual -triode r.f. stage of the period (courtesy of Fisher Radio Corp.).
RF Cascode
Stages
Mixer
Z
470
Stage
500
1M
10
5000
Antenna
470k
Plug
Inductive
`Coupling
A.F.C.
Amplifier
Local
Oscillator
From Detector
Check No.
31 on
Reader Service Card
-ÿ
The most
independent, independent
testing laboratory
in the business.
Fifty of the toughest critics are putting a
new cartridge through one of the
most demanding tests ever conceived.
Cur own meticulous laboratory tests show one hirg: the new ELAC 444-E is a superb cartridge_
Still, impressive specifications aren't enough. We didn't want to rest can our laurels.
So the tirs: fifty 444 -E's off the line.vere sen- to50 of the leading high ficelity sales-nerThe roughest,toughest critics in the busines-.The people who,daily,work wi_h hi-fi.
They're testing it right now. On every kind of system.
We are anxiously Cand co:ifideitly) awaiting the results
You wi be learning more about the ELAC 444-E and a new series of E -AC ca-tridges
priced fron $69.50 to a modest $24195. Ma -(e yojr own test. Hear the ELAC at your dealer
or write for the reports. Benjamin Electronic- Sound Corp., Farmingdale, N.Y. 11735
I
ELAC 444-E
It may be the finest cartridge you ever heard.
lator and mixer) constitute the rest of
this "front end"; operation of these
blocks will be discussed in more detail
at a later date. At this point, however,
before we present analogous transistorized r.f. stages, it would be well to
examine some of the other features of
this first section of an FM tuner. For
one thing, we glossed over the means
of "tuning."
Tuning is generally accomplished by
means of a variable air capacitor, much
like those used in AM receivers. Over
the years many other schemes of tuning or changing frequency have been
devised. For example, coaxial variable
capacitors were tried by one manufacturer some years ago. Instead of the
plates meshing, as in a conventional
capacitor, a coaxial capacitor consisted
of a stationary cylinder into which is
plunged a movable cylinder. The two
are separated by a dielectric (usually
a glass cylinder, onto which the outer
conductive plate is heat shrunk or
vacuum plated) .
Permeability tuning (where the inductance rather than the capacitance
of the resonant circuits is varied) in
various forms has also been used in a
great many designs over the past two
decades. Somehow, however, the good
old air-dielectric variable capacitor
seems to have won out, at least insofar
as high-fidelity front ends are concerned (diode tuning has of late been
adopted by some manufacturers, however). Permeability tuning is still used
in automotive receivers, perhaps due
to space requirements and because
some physical arrangements of inductance tuning are a bit more stable and
less susceptible to dust and road shock.
Confining the discussion to variable
capacitors, then, the next question is:
"How many sections, or tuned circuits,
are needed for quality performance?"
As you peer underneath FM tuners,
examining construction, you are likely
to find some having only two-gang capacitors, others using three gangs
(these are by far in the majority) and
even a few employing four sections.
The minimal -quality sets employing
only one tuning section for r.f. frequency selection (the second gang
tunes the local oscillator frequency)
will, of course, have minimum selectivity. More selective sets have a three gang capacitor for tuning the input antenna circuit, the interstage coupling
circuit (as in the example of Fig. 2),
and the local oscillator. Four-gang capacitors will be found in sets which
employ more than one r.f. stage or in
designs where the interstage coupling
is accomplished by means of a double-
tuned circuit.
AGc or "Automatic gain control" is
More About
Negative
Feedback
NORMAN H. CROWHURST
PART 5
(Conclusion)
Supply Circuits
A CAUSE OF variation in amplifier
performance often overlooked is sup-
ply circuit impedance. For simplicity of calculations, supply voltages
are usually considered to have zero
impedance,, sources. But in actual
amplifiers they don't. The fact that
some a.c. impedance is present in
supply circuits modifies feedback or
provides feedback loops additional
to those intended (Fig. 1).
Proper treatment can often offset
this by changes in the intentional
feedback, or with decoupling or isolating networks (Fig. 2). Most of
these approaches assume supply circuit impedance is constant, or that
voltage drop is within a predictable
range. These assumptions may prove
tree with steady-state test conditions, using test frequencies that
don't give time for the supply voltage or current demand to fluctuate,
but be invalid under certain program
sequence conditions.
Whenever supply fluctuates, a
change in supply source impedance
occurs. If the source of power is battery, internal resistance changes
with momentary current drain and
even more with the state of charge of
the battery. If the source is rectified
a.c., the output impedance of the
1-How supply circuits can cause instability due to unintended feedback.
Fig.
Supply
Supply
source
Z
Supply bus
a
Feedback voltage
into low level
stage
Heavy signal
cur rent, high
level stage
(Continued on page 57)
rectifier changes with momentary
current handling.
Put all these effects together, and
we find that feedback isn't the simple
thing it looked at the beginning.
Even a computer won't give you the
correct answers, unless you put in
all these variables. In my opinion,
the better way is to start with the
more important facts you know,
keeping aware of the others we have
mentioned, which you hope may not
bother you until you've investigated
the more important ones. Then if behavior does not come up to expecta2-Methods of offsetting unwanted
supply -circuit coupling: (a) conventional
decoupling; note that no three stages involving phase reversal should be fed from
a common, undecoupled point; (b) isolation provided by emitter follower; here
the high -current stage can fluctuate supply -circuit voltage, provided it doesn't dip
below that for the low -current stages.
Fig.
DECOUPLING
,
1st
STAGE
-
2nd
STAGE
3rd
STAGE
SUPPLY
TO
HIGH
CURRENT
STAGE
VOLTAGE
LOW
CURRENT
TO
DIVIDER
STAGE
EMMITTER
CATHODE
OR
FOLLOWER
ideas to work
from in looking for the reasons. Applying the various pieces of information we have covered, as they prove
relevant, checking possible causes to
eliminate those that are not relevant,
and adjusting or changing your design to overcome problems successively as they appear, will eventually
care for all the possible deviations.
In this article, we have taken
feedback apart and looked at it
in a way that is a little closer to the
practical circuits that use it than
was the theory of previous articles.
Now we have a better overall picture
of the whole bag of tricks. A nearfuture series of articles will take
some specific types of circuits and
Æ
explore them.
tions, you have some
AUDIO
32
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AmericanRadioHistory.Com
4th
STAGE
JUNE 1968
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AUDIO
JUNE 1968
Check No. 33 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
33
$695, rings the bell as the highest-
Equipment
Profiles
priced receiver available at this time.
With Marantz' line of separate components costing twice as much, however, the new receiver's price might be
considered to be startlingly low.
This Month:
Features
Marantz Model Eighteen
Stereo FM Receiver
BSR Model 600/M44 -E
Automatic Turntable
Jensen Model TF3B Speaker System
Marantz Model Eighteen
Stereo FM Receiver
Fig.
1
-
MANUFACTURER'S
SPECIFICATIONS
(AMPLIFIER SECTION) Power Output per
channel (both channels operating): 40.
watts rms at 4 and 8 ohms. Power Bandwidth (IHF): 10 Hz -30 kHz at 0.2°/o THD.
Frequency Response: 20 Hz -20 kHz ±03
dB. Total Harmonic Distortion (at rated
power): 0.2% max., less at lower power.
IM distortion (at rated power): 0.2°/o max.,
less at lower power. High -Level Hum and
Noise: -80 dB. Damping Factor: 30 min.
(TUNER SECTION) FM Sensitivity (IHF usa able): 2.8 /,t,V. Total Harmonic Distortion
(400 Hz, 100°/o mod.): 0.2°/o max. Multiplex Separation: 45 dB at 1000 Hz. Sub-
carrier Suppression: 65 dB Min. (GENERAL)
Dimensions: 18'/4' W x 6" H x 53/4" D.
Price: $695.00.
A Marantz FM/FM stereo receiver!
Six - hundred - and - ninety - five dollars!
And therein lies drama.
Marantz was more cautious than
most manufacturers in combining on
one chassis preamplifiers, power amplifiers, and a multiplex FM tuner. The
company had always traveled the
separate -component high road with a
few other manufacturers of truly elite
equipment. Here the rally was for the
buyer who wanted the best, hang the
cost and the problems attendant with
greater space requirements of separate
components.
Now Marantz has introduced an all in -one component receiver which, at
The Marantz Model Eighteen receiver is imposingly big, as you might
expect it to be. It's about an inch or
two more in length, width and height
than most other high -power receivers.
This does not detract from its general appearance, however, since the
front panel is tastefully designed. Embossed sections in black complement
gold -colored surfaces at the top and
bottom of the panel. The entire panel
is a solid casting, hinting at the quality
of construction lying behind it.
The lower half of the panel contains
the usual selector switch with positions
for phono, FM, tape, Aux 1 and Aux 2.
Next in line are the balance control
and volume control, followed by clutch operated separate bass and treble controls, a speaker selector switch, stereo
headphone jack and the power on -off
toggle switch. At the extreme lower
left of the panel are two additional
jacks used for dubbing from one tape
recorder to another-an extremely useful feature for the user who wishes to
copy tapes without going to the rear
of the receiver each time this dubbing
attempted.
The upper section of the panel contains the tuning dial, which is itself
unique to this equipment. Instead of
the usual control knob, the tuning dial
consists of a horizontally mounted flywheel, the front edge of which protrudes through the front panel. This
edge is knurled or serrated, so that by
passing one's thumb or forefinger
across this edge, tuning from one FM
station to another is effected with far
less effort than is required for the twisting motion of a conventional tuning
knob. The dial scale itself is fully ten
inches long, permitting extremely accurate fine-tuning. This demands precise calibration and alignment on the
manufacturer's part so that this capability can be fulfilled. To Marantz'
credit, we found that frequency calibration was never off by more than a
pointer width, despite the expanded
dial scale. The upper portion of the
panel also incorporates a stereo light to
indicate stereo FM reception. In addition, Marantz' famous oscilloscope display and its associated centering controls are located here, of which we shall
have much to say shortly.
In the interest of clean appearance
and functional design, the many secondary controls have been blended into
the black center strip which divides
the upper and lower sections of the
dress panel. These take the form of
eight black push-button switches of the
"push to actuate-push to release" type.
The first of these buttons, when depressed, connects a second phono input
pair of jacks, for the many users who
have both a record changer and a
manual turntable. The second button
creates a monophonic or mixed L and
R signal, useful for cancelling out noisy
Fig.
3-Rear panel of the Marantz Eighteen
stereo FM receiver.
is
2-Pushbutton-activated low -and high frequency filters are unusually effective, as
shown here by their characteristics.
Fig.
o
-5
Ca
-10
-15
ow hlter
high filter
-20
20
100
1k
10k 20k
FREQUENCY (HERTZ)
34
stereo FM reception. The third button
effects the necessary circuit break for
"tape monitoring" when used with
three -headed tape decks or recorders.
The next button provides for an alternate use of the 'scope display. When
depressed, the scope displays combined
left and right audio information; when
released, the scope is used for accurate
center -of-channel tuning of FM stations and many other analyses of reception quality which will be discussed
later. The fifth button causes a blending of left and right channels to take
place at high frequencies only. Much
of the noise associated with weak stereo
FM reception can be cancelled with the
aid of this feature, with only a moderate reduction in apparent stereo separation.
High- and low -frequency filters are
inserted in the circuit by means of
Check No. 35 on Reader Service Card
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-
»ALLTO WALL SONY
Practically eve -y conporent part ii the new
ST-5000FW FM stereo tuner is Sony -engineered
and Sony -made [spec al y the held -effect
trans stors. Is that so :maarter? We think so
Because they're made to br rip out the best in our
unique circuit cesigi.
Such as what?
FET's (particularly Sine's'. a -e innerently mcch
less susceptible to cverlcad b7 strong signals.
Used n the Sont froit erect -hey are impregnab e.
You can enjoy even the weate;t FM stations
without annoying cres<_maduláicn interferene.
The best FET's (Soiy again) lave noticeably less
noise than conventional silicor transistors. In the
Sony front end they increase toe usable sensit vity
(1.5,uV) right out to its theoretical mit.
Three unique sohd-s-ab f,ltors ae used in the
i.f. amplifier -stages. They cal eve go out of
I
adjustment, so they never neec realignment.
They contribute :o the tuner': tatulous select vity
(better than 90db) and stereo separation. Yot :an
zero in on a weak station rigid next to a strong one.
Another Sony innovation is tte unique sele::ive
circuit in tie multiplex sectica. This prevente
triggeriig of automatic stereo cperation whe-e the
quality of the multiplex signa can not assure
noise -free, distortion -free sterei reception.
We use Sony FET's at manycitical points.
In the Iccal oscillator in the f owl end, to keep
drift to an absolute minimum_ Ail in our n fly
muting circuit, (which has 9 coruenticnal
transistors, too).
Hear the new ST-5000FW at your high ficelit7
dealer. Suggested list is $44953.
Sony Corpo-ation of America, ;7-47 Van Dam St,
Long Island City, V.Y. :1101
New Sony FET
Stereo FM Tuner
2.5
THD& IM - one channel
load both
channels driven
2.0
8 -ohm
aº
Z
1.5
O
25-40
~
ce
O
tn
1.0
IM
5
W
20
3
10
á
THD
15Hz
27
8Hz
kHz'
33 kHz /
5
0
10
20
POWER
Fig. 4
- Harmonic
30
40
50
60
,
noisy.
As for the rear connection panel, it
contains the necessary input jacks and
a pair of tape recording output jacks.
These output jacks are always connected in parallel with the "Dubbing
our" jacks on the front panel. The tape
input jacks at the rear, on the other
hand, are automatically disconnected
when a tape recorder is connected to
the "Dubbing IN" jacks at the front
panel.
There is a single 21/2 -ampere fuse on
the rear panel, since speaker line protection and output transistor protection
is afforded by self -resetting circuit
breakers. An unswitched a.c. outlet for
auxiliary equipment is provided, and
can be used for equipment requiring up
to 500 watts. Speaker connections are
made on a barrier terminal strip, as is
the FM antenna. Proper matching of
both 75 -ohm and 300 -ohm antennas is
Fig.
per channel
grounding terminal post completes the
layout of the rear panel, which can be
seen in Fig. 3.
Performance
Measurements on the Marantz receiver indicated that specifications published by the manufacturer were very
much on the conservative side. For example, the power rating which we would
apply to the amplifier section would be
50 watts/channel rms with both channels operating, whereas the specs claim
only 40 watts/channel. It is at 50 watts
(continuous power) that we reached
the incredibly low total -harmonic -distortion (THD) figure of 0.2%! IM distortion reached the 0.2% point at 45
watts. Curves of IM and THD referenced to an 8 -ohm load may be examined in Fig. 4.
Two power bandwidth curves are
shown in Fig. 5. The lower curve is
referenced to 40 watts at 0.2% distortion, extending from 8 Hz to 33 kHz.
Note that it exceeds the published
6-Tone-control characteristics illustrate how "customized" compensation is
achievable.
Fig.
-maximum
bass E.
treble -boost 8 cut
-10
....... bass &
20
treble -boost
6 dB at 50 Hz &
50
500
FREQUENCY
100
1k
(HERTZ)
5-Power bandwidth, referenced to both 40 watts and
provided for by means of a balunmatching transformer. A convenient
-20
100k
10k
1k
FREQUENCY
distortion and IM distortion of the Marantz
Eighteen's amplifier section.
the sixth and seventh buttons and, as
can be observed in Fig. 2, they are
designed with a 12-dB/octave slope,
beginning at 8 kHz and 70 Hz, respectively. Unlike many so-called filters which exhibit only a 6-db/octave
slope (and are thefefore really nothing
more than a second set of fixed tone
controls) these filters are very effective in reducing rumble and high -frequency record hiss without seriously
affecting overall tonal response.
The last button in this secondary
control grouping defeats the interstation muting feature which is otherwise
present. Normally, with the muting
feature in the circuit, signal strengths
of approximately 15 microvolts will
overcome the muting and provide
noise -free reception. But there are
doubtless some DX'ers who prefer to
receive distant stations even if they are
100
10
OUTPUT (WATTS)
10
& cut
kHz
5k
10k 20k
(HERTZ)
36
(8 -ohm
claim of 10 Hz to 30 kHz. For consistency, we also plotted power bandwidth
for a 50-watt level (which is the power
rating we would assign to this amplifier) and came up with end points of
15 Hz and 27 kHz. Remarkable!
Tone control action is illustrated by
the double set of curves shown in Fig.
6, in which the dotted curves represent
partial rotation of the bass and treble
controls. From these curves you can
see that the variable crossover, feed Fig.
7-Square-wave response
at 10 kHz
(left) and 100 Hz.
back type of tone -control circuit is
used, enabling a degree of "customized" tonal compensation not possible
with less expensive "losser" circuits.
As for frequency response, rather than
resort to special graph paper, suffice it
to say that we measured flat response
from 8 Hz to 46 kHz (+0,-1 dB),
again surpassing published specifications.
The FM section of the receiver
proved to be an excellent match for the
audio amplifier section. For example,
the tuner section's harmonic distortion
figure for 100% modulation at 400 Hz,
which is stated as 0.2% maximum,
measured 0./% on our sample.
FM sensitivity (IHF) read 3.0 microvolts at 98 MHz. A passive front end
-that is, one that provides no amplification whatsoever-holds down the sensitivity a bit, but more than makes up
for it in other areas, as will be dis -
AUDIO
www.americanradiohistory.com
AmericanRadioHistory.Com
50 watts
load).
JUNE 1968
1
m
-
-0
0
u.._>
a
-
I- -30
O -40
-o
o
co
m
v
30 -dB % at 2.2NV
r.
Dise
-80
0.2
1.0
41.
1
k
Fig. 8-FM quieting sensitivity of the Model Eighteen receiver with
100°/o modulation, 400 Hz. The 80-dB quieting figure at 100 microis
the greatest figure AUDIO has observed to date.
cussed later. Quickly, though, the design innovation makes it possible to
receive more listenable stations than
previously possible. The quieting sensitivity is plotted in Fig. 8. It ties in
very well with published claims, exceeding the claims at 10 and 50 microvolts and reaching the incredible quieting figure of 80 dB at 100 microvolts
and up. This is the greatest figure of
quieting we have ever observed with
any FM receiver!
Stereo FM performance and separation is plotted in Fig. 9. Only the left
output is shown with respect to residual right output, since the reverse plot
is so close to this one that the lines
would be superimposed upon one another. The dashed -line area of the
lower (separation) curve is a bit embarrassing-for us, that is. You see, our
stereo FM signal simulator has a guaranteed separation capability of 40 dB.
This is fully 10 dB more than is required of stations transmitting FM
stereo, and we always thought it would
be adequate for any equipment tests
we might have to make. But here is the
Marantz Eighteen, which claims separation of 45 dB MINIMUM at 1000
Hz! They probably make it or come
close-but we will have to accept their
word for it, since our equipment cannot confirm anything beyond 40 dB.
Invariably, when a prospective customer is confronted with a receiver retailing at around $700.00 in the face of
competition in the $300, $400 or even
$500 price class, he will ask, "What
makes this one worth that much
more?" or "Is it really that much better?" There is no "pat" answer to these
questions, but here are some facts that
may help you to decide for yourself.
With the exception of the Cathode
AUDIO
JUNE 1968
"R"out
-40
100
10
MICROVOLTS
volts and up
-20
-30
ai
J
lz
-10
m
M
"Lout
0
I
-10
D -20
-50
f= -60
Q
- -70
out ut (audio)
-dB limiting (3.5pV)
20
100
10k 20k
1k
FREQUENCY
(HERTZ)
Fig. 9 -FM stereo separation, left -channel output only (right channel is identical). See text concerning dashed line. Scope traces
show separation at 1 kHz (left) and 10 kHz.
ray tube (`scope tube), the Model
Eighteen is an all -transistor receiver,
embodying some of the same circuits
and design philosophy as the Marantz
Model 10B tuner, the 7T Preamplifier
and the Model 15 Power Amplifier
(combined cost: $1470, less cases). Its
circuitry uses 73 transistors and 76
diodes, or a total of 149 solid-state de-
ered this receiver-but would it have
run as cool to the touch after several
hours of use as this one does?
The i.f. section and limiter section of
this receiver does not use conventional
i.f. transformers. To quote the Marantz
manual:
Examination of the insides of this
unit (see Figs. 10 and 11) discloses the
use of parts such as electrolytic capacitors, toroidally wound inductors, precision resistors (often having power
ratings four and five times greater than
would be required in the given circuit)
and even mechanical parts more often
associated with the reliability and durability of military or industrial electronic equipment. The power trans-
"The i.f. section is a modified Butterworth -type filter configuration. The characteristics ... are ideal in that the 200 kHz
pass -band is phase linear with sharp cutassures the elimination of a
off slopes
major source of high -frequency distortion
permits
and loss of stereo separation
reception of adjacent channels under adverse reception conditions. This i.f. filter
permits performance which is unobtainable
with conventional i.f. transformer coupled
circuits."
By way of illustration, a single such
filter circuit is shown in Fig. 12. A
glance at the number of components
involved suggests the number of coils
former, which can be seen in the photos
of Figs. 10 and 11, is larger than any we
have seen since the days of high-powered tube -type power amplifiers. One
half the size might easily have pow -
and capacitors usually found in many
entire i.f. strips. Yet there are FOUR
such interstage circuits in the Marantz
i.f. strip, as distinguished from the
limiter strip, which is a separate circuit
Fig. 10 -The Marantz Eighteen receiver's
outsize power transformer, seen in this
top -side photo, runs exceptionally cool.
Fig. 11 -The underside reveals high -quality
components more often associated with
vices.
...
.
.
.
industrial or military equipment.
FT
71TM
llilRit i
37
100
Q-203
Fig. 12-One of several complex band-pass
filters which are used instead of conventional i.f. transformers in the Marantz i.f.
strip.
module containing four additional limiter stages!
Then, of course, we have the oscilloscope display. Is it just a "gimmick" or
is it, indeed, an aid to better listening?
Having had an opportunity to use it for
several weeks, we can say without
equivocation that it is a great aid to the
serious FM listener intent upon achieving the best reception he can. The various traces of Fig. 13 tell the whole
story. Trace A represents an FM station, with audio information applied,
properly and centrally tuned. Had the
station been detuned, the trace would
appear either to the left or right of the
vertical center line. (Up to this point, a
"center of channel" tuning meter would
do just as well.) The traces of Fig. 13,
labelled B and C, show various degrees
of "multipath" or signal reflections
which cause a change in amplitude to
the received signal. Such multipath reflections can seriously impair reception
of stereo FM, causing distortion, decrease in separation and even momentary shifting of left 'and right channel
information. The solution? Re-orientation of an adequate FM antenna to reduce the "multipath." But except for
spotty aural detection, how would you
ever know without this visual aid?
38
The traces of Fig. 14 illustrate the
visual displays that might be seen when
the alternate function of the display
'scope is used-the one engaged by depressing the front -panel pushbutton
described earlier. Here, left- and right channel amplitudes, singly or in combination, are visually apparent. Note
that monophonic reception is indicated
by a sloping line, denoting equal left
and right information. An interesting
fact is that we caught a station ostensibly engaged in stereo broadcasting
playing a monophonic recording on
four occasions. Ordinarily, the stereo
light would have contributed nothing to
our knowledge since it is illuminated
whenever the station's 19 -kHz pilot
carrier is turned on. Once, when we
were sure the recording involved was
only issued in stereo, we actually telephoned the broadcast station and, sure
enough, someone had failed to throw
the "mono-stereo" (19 -kHz pilot
switch) in the studio.
All right, so the Marantz Eighteen
enables the user to monitor a station's
proficiency or deficiencies. But how
does the equipment sound?
We found that the Marantz receiver
provided a subtle superiority in performance over other modern receivers
examined. This is not always immediately discernible, but it becomes clearly
evident after awhile. For example,
though 3 microvolts (IHF) usable sensitivity is not the best figure we have
ever encountered in a receiver's tuner
section, we were able to listen to 42 FM
stations with satisfactory quieting and
low enough distortion to make them
truly listenable. This is four more than
we have been able to receive on receiv-
ers measured heretofore. Conclusion: it
takes more than just "sensitivity" to
receive noise -free, distortion -free FM.
Perhaps this is due to the elaborate i.f.
system or the passive FM front end (no
transistors, not even FETs; all the
"gain" is accomplished at conversion or
in the i.f. section-hence, no "cross
modulation" problems or spurious responses attributable to non-linear characteristics of front-end amplifiers), or
both.
In the presence of a strong signal,
the Model Eighteen imparts a cleanness of stereo in FM listening that approaches listening to master tapes.
Obviously, separation, per se, is not the
only criterion. When we increased the
vertical gain of our scope, after photographing the separation characteristics
of the stereo FM portion of the receiver at 1 kHz and 10 kHz (Fig. 8),
we noted that what little "cross talk"
there was (not visible in the photos because of the scale used) was not made
up of second and third harmonic components, but was primarily a fundamental of the signal in the opposite
channel.
Records were reproduced on the
Model Eighteen with much less apparent IM distortion than we were used
to hearing. Truly, it can be said that
whatever IM remained was a function
of the cartridge and not the preamplifier or amplifier. We tried, in vain, to
tax the dynamic range of this amplifier
during our LP -record auditioning, employing everything from intimate string
quartet ensembles (full of pauses and
quiet passages) to large orchestral
works. With some of the better -quality
Fig. 13 (below)-The Model Eighteen's
built-in' oscilloscope can pinpoint the
spot on a dial where minimal distortion
is present.
Fig. 14 (right)-Here are some of the
various audio displays which are observable on the Model Eighteen's scope.
/
left channel
only
right channel
only
z
zero separation
(monophonic)
A
ideal trace
multipath
Fig. 13
very severe multi path resulting in
partial cancelation
of signal
both
channels
Fig. 14
stereo out
of phase
passage with less
separation such as
centrally placed
soloist
AUDIO
JUNE 1968
Gua-adm. 2eade4442, m2440114. Me
EW
Computer Logic Control
Pro 800 Transport
the league of nimble -fingered tape -handlers there
exists a recurrent problem. It has been demonstrated time and again that anyone can ruin a
valuable tape by absentmindedly outsmarting the
interlock system of an otherwise safe tape recorder.
In
MODEL CX 822
For the studio where flexibility
means creative productions.
In answer to this problem and similar problems arising in automated and remote control
applications, the CROWN Pro 800 was designed.
This recorder has a computer logic system using
IC's which prohibit all such destructive operations.
The CROWN computer stores the last command
given it in its memory (forgetting all previous commands) and by a continuous knowledge of the
operating state of the machine (motion and direction), it takes all the necessary measures and
executes the command. This is all done without
time -wasting delay mechanisms.
Computer logic control brings to you rapid
error -free tape handling. It is actually
impossible to accidentally break a tape.
Call your CROWN dealer NOW!
MODEL CI 844
Four channel recorder for
perfect mastering.
FINEST TAPE HANDLING
MOST PERFECT REPRODUCTION
Performance as yet unequalled
Computer smooth operation
True straight line threading
Four years proven Solid
State circuitry
Extremely low noise electronics
THE HALLMARK OF CROWN
-
Patented Electro -Magnetic brakes
never need adjusting
QUALITY CRAFTSMANSHIP THROUGHOUT
MADE
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IN
AMERICA
AUDIO
JUNE 1968
BOX 1000, ELKHART, INDIANA 46514
Check No. 39 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
PHONE (219) 523-4919
39
recordings, there was the wonderful
feeling of transparency that good solidstate amplifiers impart.
Based on the foregoing tests and observations, the Marantz Eighteen receiver appears to bridge the gap
between separate components and today's increasingly popular receivers.
It looks like a receiver, combining all
electronics on one chassis, while it performs like good -quality separate components. Though it is not quite the peer
of Marantz' own line of separate components, the Marantz receiver shares
many of its design and long -life construction virtues. And it's half the
price! So if you've aspired to own
Marantz equipment in the past and
could never swing the price, there's
another turn at bat for you.
Addenda to Sony/Superscope
Model 230 Stereo Tape Recorder
Equipment Profile (May 1968)
It was erroneously stated in reviewing the Sony/Superscope
Model 230 four -track stereo tape
recorder that it had a signal-tonoise ratio lower than that
claimed by the manufacturer,
where, in fact, S/N was higher.
This variance in measurement
was due to using different references. Whereas AUDIO employed
a reference point of 0 VU at 1%
distortion,
Sony/Superscope's
specifications clearly note that
measurements were taken at peak
level, which would be at the 3%
mark commonly used by many
tape recorder manufacturers. This
would indeed enable the machine
to easily meet its signal-to-noise
specifications since it increases
the ratio by 6 to 8 dB.
Also worth noting is omission
of mention of the machine's inclusion of a "scrape flutter filter."
Usually found only in professional recording equipment, the
"scrape flutter filter" is a special
idler located between erase and
record/playback heads. Its purpose is to eliminate tape -modulation distortion.
Check No. 34 on Reader Service Card
arm descent is proportional to the
speed with which the lever is thrown.
While this method works well, it is not
quite as effective as the pneumatic -type
systems used in more expensive tone arm designs. However, this cueing device is an especially useful feature,
meeting all but very precise. tape re-
McDonald
Model 600/M44 -E
Automatic Turntable
BSR
-
MANUFACTURER'S SPECIFICATIONS
Speeds: Four. Platter Diameter: 11". Wow
(at 33'/3 rpm): 0.1°/o rms. Flutter (at 33'13
rpm): 0.04% rms. Tracking Error: Two deg.
max. Stylus -Force Range: 0-6 gms. Arm
Resonance: 15 Hz. Price: $89.50, including Shure M44 -E cartridge, WB -6 deluxe
base and DC-3 deluxe dust cover.
The BSR 600/M44 -E is a complete
record -playing unit. That is, it consists
of an automatic turntable with a Shure
Model M44 -E elliptical -stylus stereo
cartridge already installed, and a ,walnut -finish wood base topped by a plastic dust cover.
The Model 600 changer used here is
the top unit in a line of moderately
priced BSR McDonald record changers. The changer itself has a retail
price of $74.50. In contrast, the whole
package is available for only $15.00
more (if bought separately, the components and accessories would total
$128.00.)
The turntable incorporates most of
the features of higher -priced automatic turntables, though in some cases
in a more simplified way. The changer
40
unit features a low -mass tubular arm
that comes with a sectional counterweight to balance against a wide range
of cartridge weights. Both counterweights are resiliently mounted and are
easily adjustable for see -saw balance
before the tracking force is "dialed."
The arm's ball -bearing pivot is angled
parallel to the plane of the clip -in
cartridge shell. There are 2 spindles:
One short one for manual play and a
long one for automatic play. Tracking
force is set by dialing a number next to
the arm pivot. The dial is calibrated in
1/3 -gram increments. And it is pretty
accurate once a good zero reference is
established by sliding the rear counterweight to the proper place for balance.
A most handy feature is the arm lock
that automatically clamps the arm
after shut-off and releases it during
start. A muting switch shorts out the
cartridge output during record changing and a "pop" filter eliminates motor
cording needs.
Drive and changing mechanisms are
rugged and simple. A four -pole induction motor has a stepped pulley
mounted to its shaft, which drives a
rubber interwheel. The wheel drives
the inside of a sub -platter (7 -in. diameter) that is riveted to the main 11 -in.
cast -aluminum platen. A novel speedchanging mechanism uses a nylon rack
and pinion linkage to smoothly raise
and lower the interwheel with the
speed selector control, thereby lining
it up with the different pulley steps.
The entire mechanism was found to be
jam -free and reliable in operation.
Performance
The BSR 600/M44 -E performed as
follows: Rumble, including vertical and
lateral components, was measured at
-27 dB referred to 1.4 cm/sec at 100
Hz (or 3.54 cm/sec, 45 deg. velocity
Fig.
2-View of the BSR 600 with turntable
platter removed.
on -off noises.
The cueing mechanism, which allows
one to handle a lightweight tone arm
manually without fear of dropping it
on a record, operates with mechanical
linkages. Therefore, the rate of tone -
AUDIO
JUNE 1968
KENWOOD is made for lovers
...those who seek the ultimate
in pleasure
...perfect fidelity
...a warm dependable
companion
... discriminating taste
...fall in love with KENWOOD
because KENWOOD is made
for lovers ...music lovers.
Set your heart on KENWOOD
for the heart of your
hi-fi stereo system
TK -140
AM/FM
FET
SOLID STATE
130 WATTS
RECEIVER
$339.95
Whether you select the elegant TK -140 (shown) with all the Iuxury features
including the feather -touch control cr any of the other KENWOOD models
...it's bound to be love at first sight.
TK -88
TK -66
TK -55
TK -40
AM/FM
AM/FM
$289.95
239.95
199.95
189.95
249.95
695.00
89.95
(all prices include cabinets)
SOLID STATE 90 WATTS RECEIVER
SOLID STATE 60 WATTS RECEIVER
FM
FET
SOLID STATE 60 WATTS RECEIVER
AM /FM SOLID STATE 30 WATTS
RECEIVER
TKS-40
COMBINATION TK -40 RECEIVER and 2S-40 SPEAKERS
SUPREME 1 3 -CHANNEL 165 WATTS STEREO AMPLIFIER
KA -2000 40 WATTS SOLID STATE
STEREO AMPLIFIER
FET
FET
the sound approach to quality
3700
S.
Broadway Pl., Los Angeles, Cal. 90007
AUDIO JUNE
1968
/ 69-41 Calamus Ave., Woodside, N.Y.
11377
/ Exclusive Canadian
Check No. 41 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
Distr.
- Perfect Mfg. & Supplies Corp. Ltd.
41
at 1000 Hz) the standard NAB method
for rumble measurement. With the
vertical-rumble components cancelled
by paralleling the cartridge outputs,
the rumble was -31 dB. This is satisfactory for all but speaker systems that
can exhibit great output in the very
deep bass region. Wow was checked at
0.15% and flutter was about .04%. The
speed at 331/3 rpm was more than 1%
fast, as well as running fast at the other
speeds. Speed remained constant over
,
a range of 85 to 135 volts, however,
which is excellent. There was no arm
Jensen Model TF3B
Speaker System
-
MANUFACTURER'S
SPECIFICATIONS
Frequency Response: 25 Hz -20 kHz. Crossover Frequencies: 2000 Hz, 10 kHz. Impedance: 8 ohms. Power Rating: 25 watts.
Woofer Resonance: 30 Hz. Dimensions:
131/3" H x 233/4" W x 1134" D. Shipping
Weight: 40 lbs. Price: Oiled Walnut,
$122.00; unfinished, $109.00.
The model TF -3B, a 4 -speaker, 3 way bookshelf -size unit, is the least
expensive one in Jensen Manufacturing's new series of five loudspeaker
systems.
It contains four speakers-a
10 -in.
woofer, two 31/2 -in. midrange units, and
a spherical -radiator tweeter. Housed in
a dark walnut cabinet (an unfinished
model is also available), it features
dark olive -color cloth that matches walnut strips which divide the front into
three sections. The outside two sections
are covered with a gold metal grille,
giving the unit a modern -style appearance. The metal grille also offers extra
protection against accidental poking to
the two mid -range speakers which are
mounted behind one section. Two screw
resonance down to 20 Hz and the unit
mounted to its base was not particularly sensitive to shock and vibration or
acoustic feedback.
The Shure M44 -E stereo cartridge
which comes fitted to this BSR unit is
the $34.50 member of the Shure family
of high-performance ellipticals. It has
the highest output voltage and, as an
excellent performer at just under 3
grams of tracking force, appropriately
complements the BSR 600 automatic
turntable.
The sculptured walnut base of the
BSR 600/M44 -E package has an attractive metal sash around its girth,
and the matching tinted plastic cover,
w.th its distinctive walnut stripe, is effective in protecting the unit from dust
and other hazards. In addition to presenting an attractive appearance, the
BSR Model 600/M44 -E succeeds admirably in filling the need for a modest -priced all -in -one record playing
unit that incorporates many refinements normally found only in more
expensive automatic turntables.
terminals (color -marked for polarity
identification) are recessed in the rear
of the enclosure, together with knurled
shaft of a high -frequency level control.
The cabinet of the TF -3B is made of
a plywood-flakeboard walnut veneer
combination, 3/4 -in. thick. The backs
of the mid -range and tweeter speakers
are sealed with metal, an integral part
of the speaker "basket" assembly. The
woofer, which has a 11/4 -lb. magnet,
utilizes the enclosure's ducted port (a
heavy cardboard tube, 7-in. long and
about 3 -in. in diameter) for bass loading; a rubber gasket ensures a tight seal
of the enclosure rear. Crossovers are of
the L -C (inductor -capacitor) type. The
high - frequency - level
potentiometer
controls both mid -range and tweeter
level, since mid -range crossover takes
place at a high 2000 Hz.
levels. At low levels, we could measure
output down to 30 Hz. There were no
significant peaks or dips in the response. Tone bursts, shown in Fig. 2,
back up the excellent transient response of the speakers, with no evidence of ringing anywhere. The high frequency dispersion was good, as
would be expected from th_ ome-type
super tweeter. In a haroom, one
might turn down the HF level control
just a bit. Otherwise, full up is OK.
Efficiency of the speaker system is low.
Therefore, we recommend a 25 -watt
Check No. 40 on Reader Service Card
Fig.
2-Tone bursts taken at 250
Hz and
10 kHz.
Performance
With the HF level control turned up
all the way, the measured frequency
response of the TF -3B averaged about
±6 dB between 60 and 16,000 Hz. This
is particularly fine. Response dropped
off below 60 Hz and doubling could be
induced below 50 Hz at high input
Modbookshelf
speaker system.
Fig. 1-Jensen
el TF3B
(rms) amplifier for use in a 12 by 18 ft.
room. In a smaller room, a lower -power
amplifier would suffice, of course.
In listening tests, we found that the
TF -3B had a full, warm sound. There
was a slight tendency to be boomy at
very high listening levels, but a speaker
of this type should not be used to produce sound pressure levels that can
burst ear drums. It offered its best
sound in a small room, at medium and
lower acoustic output levels. When
listening to a stereo pair of TF3B's, we
observed excellent stereo balance, with
no wandering or peaking, which denotes close similarity in the two units.
The TF -3B, therefore, turns out to
be an excellent performer in its class.
It should serve well in complementing
a medium-priced sound system. Persons who want a moderate -sized bookshelf speaker system with a little more
sculptured face to go along with fine
performance will find the TF -3B very
appealing, indeed.
Check No. 42 on Reader Service Card
AUDIO
42
www.americanradiohistory.com
AmericanRadioHistory.Com
JUNE 1968
THE
UNBELIEVABLES
If we told you that your present
speakers are not producing
their fullest potential, you
wouldn't believe us, would you?
If we told you that the minute
you hooked them up to a CM
amplifier things would happen
to you that would spoil you
for anything less, you still
wouldn't believe us, would you?
Even if you're sophisticated
enough to read the CM specs
and compare them tc the specs
of any other quality amplifier,
you still wouldn't be_ieve us.
You will only believe your ears!
We suggest, then, that you
write us for the name of a CM
dealer near you who has been
authorized to loan you a CM
amplifier or a CM amp/preamp for testing in your own
home wit_ your present
equipment. Just :isten ... for a
change. Then you'll believe us.
Even the 3ffer is unbelievable,
isn't it?
14,
Front, .n:CC-1; Top Left, #911; Right, #CC -50S
AUDIO
JUNE 1968
LABORATORIES
C/M Laboratories, 327 Connecticut Ave., Norwalk, Conn. 06854
Check No. 43 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
43
AUDIO
)Il'SIÙ
KEVIEtiV
Classical
Light Listening
44
Jazz
Pre -Recorded Tapes
48
Classical
Record
Reviews
EDWARD TATNALL CANBY
Baroque Organ
Music of Frescobaldi, Sweelinck, Bach.
Lawrence Moe, organist.
ately biting dissonance; just pleasantly
solid after the hors d'oeuvre of Side 1.
A good album, period; and who cares
what official category it's filed under.
Maybe we ought to call it mood music.
Darned good mood music!
47
54
Performance:
organ in the high Baroque style, offers
a Bach program, a prelude and fugue
(A major) followed by the Christmas
Canonic Variations on "Vom Himmel
Hoch," a familiar chorale melody.
Again, excellent phrasing and shaping
of every detail and none of that arbitrary staccato playing that too many
organists do by habit, after years of
dull -toned and blurred church organs.
(Only way to punch the melody
through the murk-but not on this instrument.)
Note RCA's better-known Weinrich
recordings on a similar Holtkamp organ in New York-this man Moe is a
far finer organist. Only RCA's big live
acoustics are superior; this organ is in
a somewhat lifeless small hall.
Sound: B -}-
Performance: A
Cambridge CRS 2513 stereo
This is a first rate "Baroque" organ
record, from the University of California, offering not only excellent hi-fi
sound but two very different organs
and music to match each. Plus an organist, who for once, is really musical
in his playing, shapes each line with
care, gets through to the meaning of
every section, plays a superb legato
and a dynamic staccato and registers
the music with splendid color structural sense. Cambridge Records is well
known for this kind of excellence. It is
one of those rare, small companies that
continue to exist on a very few releases,
every one of real interest. Don't know
how they do it.
Side 1 offers a lovely little "chamber
organ," built in 1783 but using pipes
fabricated even earlier. The appropriate music is by Frescobaldi and Sweelinck; Frescobaldi, one of the very earliest true organ composers, seldom has
sounded so convincing and the lovely
Sweelinck variation (Dutch) on a folk
song, "Mein junges Leben hat ein End"
are faultlessly set forth, with never a
note unphrased or uncalculated yet
with human warmth rare on the organ
mechanism that must always, of
course, be forcibly "humanized."
Side 2, on a larger modern Holtkamp
-a
44
A Jazz -Classics Mix
Charlie Byrd-Music of Villa-Lobos. (Preludes Nos. 1-5; Etudes Nos. 1, 5, 6, 8,
11). Guitar solo.
Columbia
CS 9582
stereo ($4.79)
I haven't kept up with the raft of
previous Byrdish albums that are in
the Columbia "popular" catalogue. All
I know officially is that here is a famed
jazzman playing "classical," all by himself, not even a lush orchestral backing.
Easy enough to pass judgment! It's
excellent. Maybe even better than Columbia knows. Jazz or no jazz, this man
is a first rate "classical" guitarist, technically very much on top but, more important, with an easy musicianship that
makes the music sing with really effortless grace and naturalness. A thorough pleasure, absolutely unqualified.
Not that Villia-Lobos (Brazilian) is
very heavy "classical." Far from it.
Like so many Latins, he was prolific
and eclectic, with no great worries
about being either profound or difficult.
The early Preludes (1929) are more or
less modified Spanish -school, diomatic
for the guitar and totally easy on the
ear. The later Etudes on Side 2 (1940)
are more complex, with some moder-
A-
Sound: B
The Music of Omette Coleman (Saints
and Soldiers; Space Flight, Forms and
Sounds). With Phila. Woodwind Quintet, String Quartet of Ch. Symph. of
Phila.
RCA Victor LSC 2982 stereo ($5.79)
This jazzman isn't playing classical
producing "classical" music
(maybe) for a classical performers.
And boy, is he trying hard.
Frankly, I found the stuff pretentious and self-conscious. By which I
mean simply, that though it is full of
extreme dissonance and makes a very
important -sounding impact, what with
the Philadelphia classical players and
all, the music itself leaves me classi-
-he's
cally very cold.
I suppose this is partly because I am
never happy when jazz people desert
their relatively advantageous informality for the outward formal wear of the
classical scene, white tie, black tails and
all. That stuff is on the way out in
"classical" music. Jazz is putting on
the dog too late. In many ways, jazz is
much stronger in its own style of music
making. Reminds me of the "primitive"
folk singers who want to give up their
own genuine music in favor of show
tunes and television.
Beyond the mere fact of this extremely dissonant and difficult classical
idiom, played by such a forbidding array of ultra -ultra chamber players-a
string quartet, mind you-is simply the
music itself. I don't make any sense of
it. Maybe you will, so better try. My
ear is too popular -oriented, I guess.
Performance:
?
Sound:
B-
Checkmate Farewell
Wagner: Siegfried Idyll. Brahms: Serenade
No. 2 in A, Op. 16. South German Philharmonic Orch., Ristenpart.
Checkmate C-76010 stereo
Here, much delayed, is seemingly the
last of the Checkmate releases from
Nonesuch-Elektra, sealing what apparently was a miscalculation of considerable proportions-considering the
enormous success of the original None -
Check No. 45 on Reader Service Card
-
Most of the features of this $89.50 Dual were designed for more expensive Duals.
You'd expect a big difference
So. though we're about to describe
the ':9.50 Dual, the Model 1015,
everything we say about it is also true
There isn't a big difference.
of the more expensive Duals.
The higher -priced models have a
The 1015 has a low -mass,
few more features, but no more precision_ counterbalanced tonearm that tracks
Play all three through comparable
flaw: essly with a force as low as
hi-fi systems and we defy you tc tell
half a gram. (Vertical bearing friction
which is which, from the sound alone.
is .01 gram; horizontal bearing
To achieve this similarity, Dual simply friction is .04 gram.)
did what other manufacturers would get
The tonearm settings for balance,
sued for doing. We copied the most
tracking force and anti -skating are conexpensive Dual.
tinuously variable and dead -accurate.
We eliminated some things that
The cue control Ls gentle
weren't essential to the good performance. and accurate, and works on both
But we kept everything that was essential_ automatic and manual start.
in performance between the $129.50 Dual,
the $109.50 Dual, and the $89.53 Dual.
www.americanradiohistory.com
AmericanRadioHistory.Com
(Rate of descent is 0.5 cm/ sec.
The cueing is silicon-damped and
piston -activated.)
The motor maintains constant speed
within 0.'. % even if line voltage varies
from 80 to 135 volts.
Rumble, wow and flutter are inaudible,
even at the highest volume levels,
If all we say about the $89.50 Dual
is true, you may wonder why anyone
would pay the extra $40 for the Dual 1019.
Perhaps there's something appealing
about owning the very best there is.
United Audio Products, Inc.,
535 Mad: son Avenue,
New York, N.Y.10022. Dual
®
such label. So be it. I wrote the linear
notes for these Checkmates, and I
write them no more! Down goes the
crew with the ship.
I wrote about the music but, by a
technical quirk (no pressings yet), I
never got to hear them. So this is my
own first try at the release, liner notes
or no. Interesting. Now just what does
this disc (like the others in the series)
have to offer? What is its problem, if
any?
Technically it is a lovely job, an original recording (not merely licensed
from other outfits, as are many Nonesuch releases), and it was done via the
Dolby system, cut direct from the original non -mixed master tapes, recorded
for stereo only. Fine idea, and still
good as ever.
But musically there are problems.
The big works of nineteenth century
music-even these on the side-belong
to the first -line orchestras and the
powerhouse conductors, at least as we
hear them in the U.S.A. We are in a
sense spoiled. We have heard such
music, if we know it well, in a long series
of superbly tailored performances over
the years, with all the advantages of
the great -name leaders from Toscanini onwards. Though we may not know
it, we can tell the difference, when we
hear merely a good, solid "small-town"
performance. It's like a local "South
Pacific" or "My Fair Lady"-excellent,
but the original performance echoes
through every note, in the mind.
Worse, sight unseen, we are equally
spoiled; we'll buy the big names (especially in the low-cost reissues!) in preference to the small names, when it
comes to the famous warhorses. That's
the big -name problem.
Frankly, I found Ristenpart's Wagner very amateurish. He is not a specialist in this music; his best work is
in the steady solidity of Baroque music,
than which nothing could be more opposite than the "Idyll," with its sensuous, perfumed exoticism! It is nicely
played here, on the surface. But there
is no tension; it plods, it loses its way,
its insides are poorly balanced, its marvelous changes of key and mood are
perfunctory. The big conductors win by
a mile.
Brahms, much more gemütlich, more
friendly and German in this early Serenade, fares a good deal better. Nice
contrasts, strings vs. winds. But even
here, the tension is lacking, the music
rather oddly paced (for those of us who
have heard it elsewhere numerous
times) .
Good try, good idea; so-so realization.
-
Performances: C+, B
-
Sound: B+
Violin Concertos
Haydn: Violin Concertos (No. 1 in C; No.
3 in A, "Melk"). Nell Gotkovsky; Toulouse Ch. Orch., Auriacombe.
Nonesuch H-71185 stereo
In the summer of 1929 I was taken
through the library of the fabulous
monastery of Melk, on the Danube
near Vienna-plastered cherubs and
angels galore, a most un -librarian
decor! Within a few feet of me lay the
lost manuscript now known as the
Melk concerto, discovered there almost
twenty years later and recorded on one
of the early LPs of the 1950s. It is a
work of the first ten years of Haydn's
composing life, that sprightly period
now becoming so popular on discs, and
will remind you of Mozart as much as
of the later Haydn. Mozart was a child
when it was composed. The other concerto on this record is from the same
period, a bit earlier. Both make lovely
and effortless listening, either foreground or background as you wish.
Miss Gotkovsky is an ideal Haydn
violinist, superbly accurate in her pitch
and rhythm and in her effortless double
stops, entirely free of the flamboyant
Romantic trickery that so many older
violinists still employ, yet a persuasive
performer of expressive melody. Excellent! Even her cadenzas (by herself)
are believable, which is something.
Good orchestral backing, too, if in a
rather over -large, though pleasing,
acoustical surround.
Performance:
A-
Sound: B+
Roger Sessions: Violin Concerto (1935).
Paul Zukofsky; Orch. Philh. de la Radiodiffusion -TV Francaise, Gunther Schuller.
Composers Recordings CRI 220 USD
stereo
Composers Recordings is the electronic arm of the contemporary American composing fraternity (classical division). The label covers a cross section
of current and recent production in the
area. Faithfully reflecting the musical
scene, the CRI offerings are wildly varied, in every imaginable style and of
all degrees of content and accessibility
-just so the CRI pro judges feel the
music is representative of their collective art. The choices are authoritative,
definitely, and many are widely valuable for listening, like this one. Others,
perhaps, are musician's music, for the
profession. That is to be expected.
Not this one, though you may never
have heard of Roger Sessions. (I once
studied with him, and taught as his
assistant.) It isn't popular music, to
be sure, but if you like, say, Prokofieff,
and can take Stravinsky and Bartók,
you will find the big Sessions Concerto,
now already more than thirty years old,
an easy work to listen to in terms of
idiom. It is no longer very modern
(though it is dissonant), of an elegant
effect, neither jazzy nor twelve-tone,
nor folksky. Solid symphonic concert
stuff, the best of its kind, and sympathetically performed by a knowledgeable young violinist and a powerful
young conductor.
Sound: B
Performance: A
Harpsichordist
e
Rameau. Pièces de Clavecin 1724, Nouvelles Pièces 1728). Kenneth Gilbert,
harpsichord.
Pirouette
JAS 19036
stereo
This fòrthright young Canadian
harpsichordist plays an interesting instrument; modern but with its "quills"
and all the rest modeled directly on
17th -century Flemish construction. It
sounds more brilliant and bell -like than
most modern instruments, and the annotation wisely suggests that playback
volume be turned a bit low. Sounds
much better that way since the instrument isn't as loud as it seems with full
groove modulation. (It would be good
if this admonition were more widely
used in recordings of small -voiced intruments.) Turn it down and it is
lovely. Up and it becomes unnaturally
strident.
Gilbert is technically a whirlwind of
a finger man, and musical, though his
playing is far removed from the dramatic Romanticism of such as old
Landowska-who played Rameau too.
In the young style, he plays rather metrically, with a minimum of hesitations
and ritards. But in the long run, after
two sides, one comes really to respect
him. The music is alive and expressive.
Note a typical scrambled omelette of
commercial attributions here-it's a
Pirouette record; on the cover, and a
Janus, on the label, an "Everest production" distributed by Ambassador
Record Corp., pressed for Baroque
Records (that's what it says) by RCA
Victor Custom Division. And it comes
from Canada! What next?
Performance: B+
Sound: B+
AUDIO
46
www.americanradiohistory.com
AmericanRadioHistory.Com
-e
JUNE 1968
Light
Listening
STUART TRIFF
Leontyne Price: "Right As the Rain" and
eleven other songs. Leontyne Price,
soprano; arranged and conducted by
André Previn.
RCA Victor LM/LSC-2983 ($5.79)
Dear Miss Price:
Just heard your new album of pop
songs, so let me say right off that we all
love you and think you're great! And
you don't have to prove to us what a
regular gal you are by singing songs
like "My Melancholy Baby " With that
superb vocal instrument of yours, it's
sporting, but really unnecessary for you
to resort to imitations, such as that
camp rendition (in German, yet!) of
"Falling In Love Again."
Admittedly, "Hello, Young Lovers,"
"Sleepin' Bee," and "Sunrise, Sunset"
are all fine songs, but don't you think
they've been somewhat over -exposed?
To be quite honest, I feel that you're
not entirely at home in many of these
numbers, judging by the manner in
which you alter your style and timbre
from song to song, sometimes, within
the framework of the same song.
I hope we can meet someday soon,
over one of my special martinis (nobody makes 'em drier-no vermouth),
and talk about some of the wonderful
and unduly neglected things by Gershwin, Weill, Arlen, etc., that would make
excellent material for your second album of light repertoire. By the way,
I'd like to nominate that song by the
Previns ("Where, I Wonder") as the
"sleeper" of this collection ... a haunting and beautiful ballad, beautifully
sung! With all good wishes.
S.T.
Performance: B
Sound: B+
New Year's Concert-Music of Johann and
Josef Strauss. Vienna Philharmonic
Orch./Willi Boskovsky.
London
CS-6555 ($5.79)
This is the seventh collection of
music by the Strauss Family recorded
by the Vienna Philharmonic under its
concertmaster, Willi Boskovsky. It is
every bit as welcome as the previous
half -dozen and long may the series continue. Included in this present survey
are three orchestral excerpts from
rarely -heard operettas by the Waltz
King: the Czardas from the third act of
"Ritter Pásmán," and the Overtures to
AUDIO
JUNE 1968
"Cagliostro In Vienna" and "The
Queen's Lace Handkerchief." Tunes
from the latter work are contained in
the waltz, "Roses From the South."
Another Johann Strauss item of
special interest is the waltz, "Karnivalbotschafter," which I believe is here
making its debut on long-playing discs.
Josef Strauss, a fine musician, overshadowed by his more celebrated
brother, is represented by two waltzes
("Dynamiden" and "Village Swallows") and two polkas ("Dragon -Fly"
and "Windmill") which exemplify his
expert craftsmanship.
The performances of all these works
leave nothing to be desired. The Vienna Philharmonic is one of the world's
great orchestras. And it sounds it here!.
The conducting is both authoritative
and affectionate. London's reproduction is first-rate. Stereo effects are discreet except in the "Ritter Pásmán"selection, where violin and cymbalom
solos are distinctly defined left and
right. All in all, a thoroughly enjoyable
record.
S.T.
Performance: A
Sound: A
AN ASTOUNDING NEW
AUDIO NOISE REDUCTION
SYSTEM WHICH IS
MAKING BACKGROUND NOISE
YESTERDAY'S PROBLEM.
The Dolby System gives
10dB increase in
usable dynamic range
A 10-15dB hiss reduction
A 10dB print -through and
cross -talk reduction
A 10dB hum reduction
A
PLUS generally cleaner, more
transparent recordings-with
unaltered frequency response
and signal dynamics.
Recording engineers and musical directors are
so enthusiastic about the Dolby S/N Stretcher
system that the network of users is growing at
an astonishing rate-on an international scale.
Master tapes made with the system now fly
regularly between the major recording centers of
the world, such as New York, London, Rome,
and Vienna.
The basic principle of the system is simple.
Low-level signals are amplified in four independent frequency bands during recording and
attenuated in a complementary way during playback-recording noises being reduced in the
process. High-level signals are unaffected by
this procedure (no distortion or overshooting),
and the symmetrical design of the circuitry
ensures that the signal is restored exactly in all
details-high-level and low-level, amplitudes and
phases. The result is a noise reduction system
with ideal characteristics-perfect signal handling
capability which can pass any line -in, line-out
A -B test, arid a genuine 10dB noise reduction.
In short, the Dolby system offers an entirely
new area of sound for the recording engineer.
Get to know more about it fast by writing directly
to Dolby Laboratories or contacting your nearest
agent.
DOLBY
333
LABORATORIES
SIXTH AVENUE
Telephone:
(2121 243-2525
-
INC.
N.Y. 10014
NEW YORK
Cables: Dolbylabs New York
Check No. 47 on Reeder Service Cord
47
New Sonicspectaculars!
by STUART TRIFF
LONDON -DECCA CREATED quite a
sensation among sound buffs several years ago with the establishment of its Phase -4 Series, designed
primarily to exploit the potential of
the then novel medium of stereo.
The accent was on sound; musical
content was a lesser consideration.
To a certain degree this is still true,
but aural advances made by other
companies have now reduced the
novelty value of Phase -4. Realizing
this, London has wisely been paying more attention to substantial
repertoire, and more ambitious recent releases have been leaning
heavily on symphonic chestnuts,
performed by major British orchestras under well-known conductors.
With the inauguration of its new
Deram label, London has more or
less entered into competition with
itself in the sound sweepstakes. Six
discs, devoted mainly to current pop
material, comprise the initial release. Once again, as with early
Phase -4, the sound is the thing. The
music, though pleasant and expertly
played, is inconsequential, and the
performing artists are something
less than celebrated. So, there is
little to divert the attention from the
Series' sonic delights ... which are
considerable.
Now, for a brief description of the
"Deramic Sound System" and what
it is, and what it is not (advance
publicity releases, notwithstanding)
The recording technique employs
two adjoining studios (for differing
ambience) with a variety of microphones, each with different characteristics-the various sections of the
orchestra requiring a minimum of
four mikes. Twenty-two or more
magnetic tape tracks are used during the process, along with twelve
reverb systems and twelve British made signal-to-noise reduction systems. I was somewhat more amused
than impressed over this procedure
on learning that the Deram people
insist on referring to it as not being
"mechanically -contrived" (!)
In common with Phase -4, the reproduction bears little real resemblance to the way an orchestra
actually sounds in a concert hall. It
is, however, a fabulous phonographic achievement. The record
.
.
surfaces are exceptionally quiet and
clean; each instrument is reproduced with X-ray clarity. The
stereo perspective is broad and fullbodied. Another plus factor is the
excellent sound quality obtainable
at low listening levels. This will be
a boon to the enthusiast who wants
to show off his rig to friends, without making their conversation compete with the volume control-and
this is as it should be in music which
is of the background -mood variety.
Good as these records are, I cannot indulge their makers in two bits
of wishful thinking made for them.
As stated, the sound has very effective depth and dimension, but it
most certainly does not "wrap itself
around you." The other claim:
"... as effective when moving around
as sitting in one place," is true just
so long as you don't move any further than from one end of the sofa
to the other. I also feel obliged to
point out that the playing time of
these discs, which are not budget priced, averages approximately 16
minutes per side.
Orchestral in the Night-Gordon
BERTRAM STANLEIGH
Hank Jones & Oliver Nelson: Happenings
Impulse Stereo A-9132 ($5.98)
The Oliver Nelson band, with Clark
Terry featured on trumpet, provides
some supple backgrounds as Hank
Jones creates delicate filagree patterns
:
Franks
Orchestra (You Only Live Twice; A
Walk in the Black Forest; Love in the
Open Air; Brazil, etc.). Deram (stereo
only) SML-13701 ($4.79).
Voices in the Night-Peter Knight OrWere a Rich
chestra & Chorus (If
Man; My Cup Runneth Over; Puppet
on a String; A Whiter Shade of Pale,
etc.). Deram (stereo only) SML-13702
I
($4.79).
Latin in the Night-David Whitaker Orchestra (The Look of Love; Corcovado;
I
Will Wait for You; Summer Samba,
etc.). Deram (stereo only) SML-13703
($4.79).
in the Night-Tony Asborne's
Three Brass Buttons (All You Need Is
Love; Thoroughly Modern Millie; Helados; Cornflake; Sunspot, etc.). Deram
(stereo only) SML-13704 ($4.79).
Brass
Piano in the Night-The Pianos of Tony
Osborne (Volare; Exodus; Sentimental
Journey; Elmer's Tune, etc.). Deram
(stereo only) SML-13705 ($4.79).
Strings in the Night-Gordon Franks Orchestra (Viva Maria; A Man and a
Woman; Umbrellas of Cherbourg; The
Young Girls of Rochefort, etc.). Deram
(stereo only) SML-13706 ($4.79).
Performance (for all): B+
Sound (for all): A+
yfaslaVhallaa\a1aaaeaYalaaVaasaas....
48
Jazz, etc.
on his new Baldwin electronic harpsichord.
Jerry Hahn Quintet: Ara-Be -In
Changes Stereo 7001
First release of a new offshoot of the
Arhoolie label, Changes Records will
concentrate on contemporary music.
Hahn's quintet, comprised of former
members of the John Handy and
Charles Lloyd groups, integrates Afro Indian influences into expressive, well paced performances Sound is clean
with a balanced spread. Changes Records is at P. O. Box 9195, Berkeley,
California 94719.
Performance:B+
Sound: A
Phil Woods: Greek Cooking
Impulse Mono A-9143 ($5.98)
Saxophonist Phil Woods supplements a seven piece jazz combo with
performers on the bazoukie, dumbeg,
and oud to achieve a new tonal palette.
Themes from Zobra the Greek, A Taste
of Honey, Antony & Cleopatra, and
Samson & Delilah all respond well to
the treatment, and the Woods group
show themselves as interesting innovators.
Performance: B
Sound: A
Wild Bill Davis: Midnight to Dawn
RCA Victor Stereo LSP-3799 ($4.79)
Recorded live at Grace's Little Belmont in Atlantic City, the locale of his
recent collaboration with Johnny
Hodges, this platter features the same
tenor, guitar, and drums combo of the
earlier disc and much the same uninterrupted background of audience
chatter. The group swings brightly, and
the sound is about what one can hope
for under the circumstances. But are
such circumstances necessary?
Performance: A
a
Sound: A
Performance: A
Sound:
C-
..-._.s......a.-.,a-ah,l-,.as,
AUDIO
JUNE 1968
Bill Evans at Town Hall, Volume
Verve Stereo V6-8683 ($5.98)
1
A Sound
Investment
Wonderfully communcative performances by the outstanding keyboard
impressionist in jazz. His solo, in memory of his father who died two weeks
before the concert, is one of the most
profound jazz statements on disc.
Performance: A
The 711B FM Receiver. For real music to
your ears. Every touch of sound from FM,
tape or record player, arrives with
distortion -free reproduction whether it's
the softest whisper of a muted guitar or
the rolling crescendos of tympani.
100 watt power rating (IHF) with frequency response of ±1dB, 15 to 30,000 Hz,
the 711B is fully silicon transistorized, has
the Iatest FET front end, integrated circuits,
automatic reset circuit breakers. Between station noise is completely eliminated by
Altec's new muting circuit.
The professional look. Certainly the professional touch. (Professional sound engi-
Sound: A
Poetry, Rock, etc.
Tim Buckley: Goodbye and Hello
Elektra Stereo EKS-7318 ($5.79)
In his second album, Buckley displays a more poetic, atmospheric personality than appeared in the vigorous
initial platter. Ten eloquent, anguish
tinged poems are chanted to an exotic,
unearthly accompaniment.
Performance: A
Sound: B
Malachi: Holy Music
Verve Stereo V6-5024 ($5.98)
More psychedelic music with an
East Indian influence, this disc offers a
variety of slow, clear plucked sounds
that provide an adequate background
for some other activity but fail to keep
the attention of this listener for more
than a few minutes.
Performance:
?
neers have installed Altec quality in
broadcast and recording studios for over
three decades.) That's why it's the very
sound buy at $399.50. See your Altec dealer.
Or send for our 1968 Hi-Fi Catalog.
Sound: A
Big Jim Sullivan: Sitar Beat
Mercury Stereo SR -1137 ($4.98)
A rocking beat, well -spread stereo,
and a pleasant balance of exotic sounds
combine to make most of this disc
among the most engaging of the current flock of pop -rock -sitar recordings.
Only the few bands with oboe and
string arrangements keep this from being a total delight.
Performance: A to B
Sound: A
Movement Soul
ESP Mono ESP 1056
Selections from mass meetings, sermons, rallies, and demonstrations, together with a number of individual
interviews. Recorded in 1963 and 1964
in Alabama, Mississippi, Georgia, and
Washington, D. C., these recordings of
the spirit and music of the freedom
movement are a well -prepared document with a full text in an accompanying booklet. Sound is remarkably good
for field recording.
ALTE[
LANSINGe
Sound: B
A
AUDIO
JUNE 1968
division of
"
s
Ling Altec, inc.,
1515 S.
Manchester Ave., Anaheim, Calif. 92803
Check No. 49 on Reader Service Card
www.americanradiohistory.com
AmericanRadioHistory.Com
49
RCA Victor
became the first major record company
to issue a pre-recorded stereophonic
tape. The work was Richard Strauss'
"Also Sprach Zarathustra," conducted
by Fritz Reiner with the Chicago
Symphony Orchestra. The format was
open reel two -track stereo at a speed
of 71/2 ips. For all practical purposes
it can be said that the stereo tape industry began with that remarkable
recording.
Among the audio buffs of those days,
"Zarathustra" and subsequent stereo
tape releases created a sensation. It became a very "in" thing to "go stereo."
But the price of admission to this exclusive club was high. You may recall
that the tapes were astronomically
priced (for example, a Tchaikovsky
6th Symphony was $18.95). Then there
was the matter of the stereo tape machine, plus an extra amplifier and
speaker. Unquestionably, stereo tape
was for the affluent at that time, but
backed by strong promotional pushes
from manufacturers, this medium
flourished although the growth pattern
was steady rather than spectacular.
By 1957, which can be considered the
"high water mark" of two -track stereo
tape, sales were reported to have
passed 5 -million dollars a year. In spite
of such drawbacks as poor signal-tonoise ratio and the "sput-phut" of d.c.
nodule noise, stereo tape was exciting
and offered a unique listening experience not obtainable from a disc. Near
the end of the two -track stereo tape
era, better quality control of the duplicating process and improved tape oxides gave us some tape recordings of
remarkably high quality. The venerable phonograph disc, often the target
of pundits predicting its demise,
showed its amazing market vitality by
adapting to stereophonic reproduction
in 1958, and came very near to sounding the death knell for stereophonic
tape. As you know, stereo tape survived with the introduction of the 4 track format.
Stereo on disc and on tape has now
co-existed for 10 years, yet I am continually astonished that so many
people insist on the two mediums competing with each other on a "warlike"
basis. This attitude is especially prevalent since the advent of stereo tape in
such new formats as open reel at 33/4
ips, the 8-track cartridge and the cassette. The general feeling is that technological advances in stereo tape have
out -distanced the stereo disc. This
posture is patently rediculous, of
course. One can make a formidable
case for the merits of stereo on tape or
FOURTEEN YEARS AGO,
50
uwuuuuuuiomuumnuuomnwuuuuuuuunnuuouuunmmuinuuu
Behind
the
Scenes
BERT WHYTE
thusiast may sneer at such ineptitude
on the part of the "general public."
The factor of price has always been a
thorny point with pre-recorded tape.
The gulf between the price of a disc
and the identical program on a 71/2-ips
stereotape is considerable, and must
certainly be reckoned as one of the reasons for the increasing interest in open reel 33/4- ips tapes. Even taking into
consideration the discount practices
prevalent in most large cities, many
3% - ips pre-recorded tapes have
achieved a price parity with the stereo
disc.
The State of Open -Reel
Pre-recorded Tape
vumnuuuuunuuuununnnunnuuuuunuuunnnnuuuuuuumunuunur.
on disc, and an equally strong case for
their respective disadvantages.
For the last ten years, stereo tape has
meant the familiar open -reel 4 -track
format operating at 71/2 inches -per second. It is generally conceded that
this type of pre-recorded tape affords
us the highest quality of stereophonic
sound available to the mass market.
Given a carefully duplicated open -reel
tape made from a really good master
recording, we can enjoy wide range
30 Hz to 15 kHz sound on a remarkably consistent basis.
The 71/2-ips speed bestows the advantages of good transient response,
and lessens the problems of wow and
flutter and scrape flutter. To a somewhat lesser extent, the speed improves
the signal-to-noise ratio. Dynamic
range can be quite wide, and a common advantage shared by all tape formats is that there is no distortion of the
type caused by the inner grooves of a
disc.
Needless to say, the longevity of
to play the program
repeatedly with virtually no audible deterioration-is a plus factor of all prerecorded tape over discs. Tape escapes
some of the distortion -causing factors
inherent in record -playing equipment,
such as inner -groove distortion. And
some tape machines can reverse a
tape's direction automatically-equivalent to flipping over a disc automatically-which puts tape ahead on this
score. As to the disadvantages of open reel 71/2-ips tapes, there are some that
are trivial and some that are trouble-
tape-the ability
some.
The statement that open -reel tapes
are "hard to handle" and "difficult to
thread" must be given some relevancy,
even though the experienced tape en-
From the strictly technical viewpoint, the open -reel, 4 -track, 71/2-ips
stereo tape suffers from two maladies.
Crosstalk is one of the bugaboos, defined as a transformer -coupling phenomenon between adjacent pairs of
head stacks. On a 4-track tape, tracks
one and three, and two and four, are
recorded in opposite directions. When
one pair of tracks is producing music
at a pianissimo level and the juxtaposed other tracks are unleashing a
mighty fortissimo passage of music,
crosstalk is at its worst. Most of the
crosstalk is in the lower frequencies, but
mid -range and even high frequencies
can be involved. The severity of crosstalk varies with the type of music and
the degree of quality control which was
exercised in duplicating the tape. The
application of a separate bias supply to
each track in recent years has resulted
in less crosstalk and in lower levels of
crosstalk. Nonetheless, crosstalk remains an all too frequent accompaniment to the recorded program, and is
often cited by many professionals and
advanced audio buffs as the reason for
their preference for two -track stereo.
The other technical shortcoming of
open -reel pre-recorded stereo tape and,
unfortunately, of every pre-recorded
tape format, is the matter of signal-tonoise ratio (or if you prefer, tape hiss).
More than anything else, tape hiss has
been and is today, pre-recorded tape's
chief flaw. The amount of tape hiss one
perceives is subject to many variables.
The size of the room in which the
listening takes place, the acoustic characteristics of that room, the response
and efficiency of the loudspeakers, and
the sound level at which one plays back
his tape can have a profound effect on
what the auditor hears as a degree of
tape hiss (and for that matter, of crosstalk and any other noises and distortions) .
If a person lives in one of today's typically thin -walled apartments,
which perforce imposes a limit on his
playback levels, and he listens in a
AUDIO
JUNE 1968
A copy of this Test Report
on the Tandberg Model 64X
small room highly damped with carpeting and draperies, utilizing small
speakers with limited bass/treble response, he can report with honesty that
he does not hear tape hiss nor crosstalk. Contrast this with the audio buff
who lives in a house and plays his tapes
in a large living room through a widerange system at a relatively high room filling level. We can go a step further
here, for if this person favors the use
of some of the fairly inefficient acoustic
suspension -type speakers, he must turn
up his gain control more than if he
used highly efficient theatre-derived or
horn -loaded loudspeakers. Quite obviously there is a difference in hiss level,
but even with the high -efficiency system, he might find the amount of tape
hiss somewhat objectionable.
Admittedly, all the variables involved
complicate the job of the reviewer of
pre-recorded tape. Nevertheless, the
critic should establish some frame of
reference as to the level of tape hiss,
crosstalk and other extraneous noises.
I have used a sound -level meter to take
readings in a number of locations in my
listening room, of peak levels in the
loudest portions of the music as played
at a given level. By averaging these
readings, I can get a decibel reference
point at which I can assess the degree
of noise. By adjusting the playback
level of various recordings to this reference point, the differentials in tape
hiss, crosstalk, etc. among the competing brands of pre-recorded tape can be
ascertained with reasonable accuracy.
Stereo Tape Recorder
is yours for the asking:
EQUIPMENT TEST REPORTS
By Hirsch -Houck Laboratories
Tm outstanding petformance of past Tandberg record.
Other differences between the new Model 6AX reed the
older Model nt include changes in the equalization at
33/a. ips and a reduced reeording-bias current at the IT tps
speed. The most important change is the addition of a
separate cross -held hiss head facing the uncoated side of
the tape opposite the recording bead. This is largely responsible for the improved frequency response and signalto-noise ratio of the Model 6IX.
At 71/2 ips, we measured the ov.nall record -playback
frequency response of the Tandberg Model 64X as an ex.
cellent +0.5, -2.5 db from 40 re 20,000 Ha. The play
se from the Ampex H321-04 test
bar
i in
smoothly
natter of record. In our comments on the oregmal
)963), we
pointed out that, almost alone among hone tape recorders
of that time, the Tandberg 64 at 7y ips did not in any
way change the sound of a recorded program, whether
from discs or FM
It es difficult to Improve on this sort of performance,
but Tandberg engineers have done so. The new Model 64X,
externally identical to the older Model 64, is substantially
tarter in its frequency response, particularly at the lower
tape speeds, and has an even better signal-to-noise. ratio
than did
et model.
The T
cis is
Model.
l 04 (HrFs/STEREO Revsew, October.
Hz.
back
separate
aprplihcr 4
A stogie mat play
frees the
changed
the eeron
Each c
pressed
lever in
allows
tape,
separate
Presten
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such
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fact that
nil
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sound rc
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fece
the
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when a
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-
"The 64X offers the highest
caliber of performance
presently obtainable
in a home tape recorder
...we could not find
fault with it in any respect.
The Tandberg 64X sells
for $549 and is well worth it'
As appearing in
HI Fl STEREO REVIEW
February 1968 issue
reg,lenti
The
tubes
Transition
Acknowledging all the merits and
drawbacks of open -reel 71/2-ips prerecorded stereotapes, what is the present status of this medium and what of
its future? These are not easy questions to answer. The entire field of prerecorded tape is in a transitional phase.
The backers of the newer tape formats
are all trying to gain ascendency and
become the dominant medium. They
are thinking in "mass -market" terms,
and I respectfully submit that this approach is not valid in respect to open reel 71/2-ips stereotape. I have always
maintained that this product is for a
quality -conscious market, especially for
the devotee of classical music. Ampex
evidently agrees with me. They are now
the biggest producers of 71,2-ips tapes,
and I was told that they are in this
market to stay. They are very positive
in their convictions that the 71/2-ips
tapes are the preferred medium for
their classical catalog as well as for
high -quality pop material. The only
33/4-ips tapes in the Ampex classical
t
creases
cap' qu
recordin
use to
The
awdberg Mo
line outputs ttrom. lowdmped asce cathod
the rear and IS intended to be connected to
program source and amplifier system for recor
playback. The recorder is supplied installed i
teaks -nod base.
The electronics of the &1X are hybrid in nature, using
tubes for most Iancrions. The beat mediator and
ns associated output stages (which are separate for each
track) are transistorized, az s the center -channel output
mpirYrer that supplies
volt of mixed output signºI to
the re, ,ark
w
-
cm
+I.
better
ers.
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Tyr-ips machine with the Tandberg Model
í14X operating at iv/a ips.
The 6-1X orders the highest caliber of performance pres.
ently obtainable in a home tape recorder. It Is unquestionably a high-fidelity recorder at asp ips, which. cannot he
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t fault its performance en any respect- The Tandberg
6IX sells for $549 and es well worth it.
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Hear this superb 4 -track stereo
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AUDIO
tape
how-
lf. Ar
JUNE 1968
51
on Reader Service Card
51
www.americanradiohistory.com
AmericanRadioHistory.Com
catalog are productions made from
such labels as "Everyman" and "Parliament," which are from low-priced
stereo discs.
As far as open -reel 71/2-ips stereo tapes from companies other than Ampex are concerned, the picture is very
bleak. Most surprising is that stereo
pioneer RCA Victor has completely
abandoned 71/2-ips tapes. All their new
material, both classical and pop, will
be issued at the 3%-ips speed. Catalog
items will continue to be furnished at
71/2 ips. For some time now, Capitol/
Angel has been issuing all of its tape
product at the 3%-ips speed, and from
what I can determine there is no plan
to revive 71/2-ips tapes, even for the
classical catalog. Presumably, Columbia has some interest in the 3%-ips
market, as they have issued a few tapes
at this speed. What their intent is in
regard to the slow-speed material or
their future plans for 71/2-ips tapes I
don't know.
It would appear on an overall basis
that, although there seems to be some
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TIME IT NOW
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Install multiple microphones as
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©
52
1967
movement away from 71/2-ips pre-recorded tapes, the massive strength of
the Ampex conglomerate of labels will
ensure a good supply of this product.
There also seems to be a general feeling that if the problems of tape hiss
and crosstalk could be overcome, the
71/2-ips tape would not only stage a
"comeback," but would win many new
converts for this medium. Fortunately,
there has been some progress in this
direction. A few months ago Ampex introduced 71/2-ips classical tapes duplicated with their new process called
"EX -Plus." By optimizing their mastering equalization curve, the use of
specially built record and playback
amplifiers and a new type of monitoring meter that can accurately indicate
maximum recording level, this permits
the elimination of the 6 dB "safety
buffer" formerly necessary to avoid distortion. This means that at the same
listening level you used with conventionally duplicated tapes, the EX-Plus
tapes permit a 50 per cent reduction of
your volume control setting and a corresponding reduction in noise.
Does it help? Most assuredly, but
with variable results. This is not so
much a shortcoming of the new process,
as it is with the quality of the masters
that are furnished. With a good, quiet
first -generation master, the EX -Plus
tapes are excellent, with the best signal-to-noise ratio I have ever encountered on commercially pre-recorded
tapes. The company has informed me
that all of their classical material will
now be duplicated with this process.
They added that certain selected pop
recordings will be given the EX-Plus
treatment in the near future. Unquestionably, this type of duplication is a
valuable ally in the battle against tape
noise, but it is not the total answer.
Happily, the EX -Plus process will
soon be augmented by the highy efficacious Dolby system. Ampex is awaiting delivery of their Dolby A-301 and,
when it is installed, we will have at
hand the means for the production of
exceptionally quiet tapes. It is fairly
safe to say that most major record companies are now, or shortly will be
equipped with the Dolby system. It appears likely that those companies which
are members of the Ampex tape combine will furnish them with copies of
their masters in the Dolby "compressed" mode, and Ampex would prepare their dubbing masters from the
"expansion" signal output of their
Dolby A-301. If the record companies
involved had made their original recording with the Dolby system, this
would be ideal. On the other hand, it
still would be possible to produce very
quiet tapes even if the original recording was non -Dolby, providing the company made Dolby copies of the original
master or at the very least, the working master, since the vast majority of
either original or working masters have
a signal-to-noise ratio of at least 60 dB.
That there are other possible noise reduction applications inherent in the
Dolby system goes without saying. At
the moment, the Dolby/EX-Plus combination appears to be the most practical key to the revitalization of the
71/2-ips pre-recorded tape medium.
As previously noted, the open -reel,
4 -track, 3%-ips stereotapes are appear-
ing on the market in appreciable quantities. As far as I can determine, the
advantages of this medium are twofold. One is that they are the first
variety of stereophonic tape able to
compete price -wise on a nearly equal
basis with the stereo disc. The other is
that the slower speed affords great continuity, especially of value in operatic
and certain other types of recordings.
As is true of 71/2-ips tapes, there is a
considerable variation in the quality of
pre-recorded 3%-ips tapes. Some productions are impossibly noisy. I have
heard a few ... very few
3%-ips
classical tapes in which the tape hiss
was low enough to be "tolerable." In
common with 71/2-ips "pop" tapes, the
3%-ips pop productions have such a
limited dynamic range and are recorded at such relatively high levels
that tape hiss is fairly low. In general,
the 3%-ips classical productions have
...
Shure Brothers, Inc.
AUDIO
JUNE 1968
You may have
perfectly good tonearm
but here are some
sound reasons to replace it.
more tape hiss, crosstalk, etc. than
their counterpart at the higher speed.
The reason for this is that the recording equalization used for the slower
speed makes the tapes more susceptible
to overload, so the engineers keep the
peak levels appreciably below the maximum recording level. Acid to this fact
that 3%-ips playback equalization is
tipped up a bit on the high end, this
combination of factors causes more
a
noise.
As far as classical tapes are concerned, the 3%-ips productions have
handle,
without audible distortion
the higher velocities present on
todays better recordings.
The Ortofon RS-212 is the most advanced, superb professional tonearm on
the market. It will accept every standard cartridge made. It will accommodate the lightest cartridge manufactured, and it supplies automatic, antiwith an added
skating and correct stylus pressure simultaneously
fine anti -skating adjustment control. No tonearm in the world can
track or compare to the performance of the Ortofor
RS -212. The Ortofon RS-212; $90.00.
For the FREE Record Omnibook and demonstration,
see your hi-fi dealer; or write directly to
ELPA MARKETING INDUSTRIES, INC.,
other limitations in addition to their
noise problems. Compared to 71/2-ips
tapes, they have less brilliance and
clarity. They simply are not as clean sounding. This is not so much a matter
of frequency response, as many of the
tapes extend to 9 or 10 kHz. Rather it
is the area of transient response, the
"fuzziness" and blunting of percussives, the dulling of attacks, that erodes
the quality of the slow -speed tapes.
This is particularly apparent with
piano sounds.
The gremlin behind all this is "scrape
flutter." This longitudinal oscillation of
the tape occurs around 3000-3500 Hz,
and in original recordings or one-to-one
dubs, is not normally of much concern.
However, the 3%-ips pre-recorded
tapes are dubbed at an 8 -to -1 speed
ratio and, unhappily, this drops the
scrape flutter frequency to 240-280 Hz,
right around middle C (256 Hz) and
coincidentally the center of the piano
keyboard. At 280 Hz, scrape flutter,
with its phase modulation and frequency sideband distortions, raises hob,
dulling transients and thus the clarity
of the recording. To those who might
be a bit skeptical about this, I will say
that it is necessary to have a high quality, wide -range playback system to
fully appreciate this problem. To those
who own such systems, if you can compare a piano recording on 3%-ips tape
with the same recording on 71/2-ips
tape, stereo I'm sure your ears will confirm the difference.
As far as eight -track stereo cartridges and the two-track stereo cassettes are concerned, they share the
technical problems which afflict open reel tapes, especially the noise, and may
surpass them in severity. In addition,
there are special problems peculiar to
these new tape formats.
Deficiencies in pre-recorded tape
notwithstanding, the tapes do offer
many redeeming attributes, as mentioned earlier. Further, a tape recorder
-that is, a tape unit with recording
facilities-opens up a bright, new world
of sound and fun for users.
Æ
AUDIO
Even if your tonearm was the best on the market just a few years ago, it
is probably unable to take full advantage of today's better cartridges.
For example, any tonearm developed two or three years ago is unable to
accommodate or take advantage of today's new cartridges which track at
1 gram or less. Nor can
it track today's stereo recordings properly. Or
-
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If you can read English
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And the best way to own an organ is
to assemble your own from Schober's 100
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that thousands of entirely untechnical
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If you want to play everything from
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Recital Organ (right), physically and
tonally so like a fine pipe organ that many
people can't tell the difference. Everything you need (if you use your own hi-fi
or stereo system for the sound) costs only
$1725. You can pay as you build, to
spread the expenditure, and you couldn't
buy the equivalent elsewhere for less than
twice that price. Or you may choose
another Schober Organ model. They start
at $645. Schober's enjoyable self -teaching
courses give you musical results immediately, and the more you play the better
you get.
Over 50% of Schober Organ owners
never handled an electronic job before
and didn't play a note, yet assembled
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D Enclosed please find $1.00 for 12-inch
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NAME
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CITY
Check No. 53 on Reader Service Card
JUNE 1968
STATE
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J
53
STEREO INSTALLATION
(Continued from page 26)
Pre-recorded Tapes
BERT WHYTE
Leontyne Price: Prima Donna, Volumes
One and Two. RCA Victor TR35018, 4
tr.-33/s ips stereo open reel ($11.90)
... AS
EASILY AND
COMPETENTLY AS
ONE
MICROPHONE
The Shure M68 Microphone Mixer
enables you to teach inexperienced users how to operate a multiple -microphone sound system in
seconds! It is your best tool for
selling Total Communications*.
(* A superior sound system in
which everybody who needs a
microphone has one at his fingertips.)
MICROPHONE
MIXER
,..YOUR KEY TO TOTAL COMMUNICATIONS
.,!) 1967
54
Shure Brothers, Inc,
For fans of Leontyne Price, this is a
bonanza. No less than 18 excerpts are
presented from operas ranging from
Purcell's "Dido and Aeneas" and Handel's "Atlanta" to Puccini's "Suor
Angelica" and Barber's "Vanessa." As
a demonstration of this artist's versatility, it is a veritable tour de force.
Her power is astonishing and seemingly limitless. Only at the extreme
bottom of her lower register does she
have a little trouble in projecting the
voice, as was noticeable in her recording of the "Final Scene from Salome"
on stereo disc. Otherwise she summons
those golden tones with consummate
ease and the singing is always pristine
pure and dead on pitch.
Throughout this tape the voice is
very bright and articulate with fine
projection. There is good vocal localization and a judicious left/right orchestral balance. Vocal/orchestral balance okay. The acoustics are spacious
and definition is such to ensure a lot of
presence. Dynamics are moderately
wide. When Leontyne hits some of
those "high hard ones," however, we
get some print -through. Sorry to report
that the hiss level is too high in Volume One, and crosstalk frequent, although fortunately at relatively low
level. Volume Two is much the same
technically, with somewhat less hiss
and the addition of some extraneous
low -frequency noise that sounds like it
might be "room -rumble."
This is beautiful singing, though,
and once again one must say that the
advantages of a higher -speed recording
is sorely missed. I have long been one
of the most ardent boosters of magnetic tape, but at the risk of being
drummed out of the "tape corps," let
me say that I have this identical album on stereo disc and, forgetting the
factors of wear and "scratchability,"
in its present unsullied state it speaks
for Miss Price more quietly and more
eloquently than this tape does. B.w.
CAPSULE COMMENTS:
Jacqueline Du Pre playing the Elgar and
Delius Cello Concertos. Angel Y1S36490
open reel, 33/4 ips-Beautiful music, lovely
performance and good sound. Worthwhile
if you can check your copy for an annoying hum.
have two copies ... both have
hum ... maybe you'll be luckier.
I
Big Band Bossa Nova-Enoch
Light (Command RS844SD)
5. Concertos by Bach, Vivaldi,
4.
Handel-Yehudi Menuhim and
the Bath Festival Orchestra
(Angel S36103)
Sacre du Printemps
6. Le
7.
-
Or-
chestre National de la R.T.F.
(Nonesuch H-71093)
Beethoven Symphony No.
Otto Klemperer and the Philharmonia Orchestra (Angel
5-
S35843)
These recordings provided a variety of types of music from soft, intimate, classical guitar to crisp,
modern jazz to full symphony orchestra; the system performed admirably under all these conditions.
It can be seen from the calculation
of reverberation time in the accompanying section (even though both
the calculated time and the computed optimum time are approximate values, subject to subjective
interpretation) that the room is well
suited to general listening. It is possible, however, that "crisp" music
such as piano selections might demand a slightly more reverberant
environment. Reference to Fig. 4 reveals that there are three small rugs
and one larger carpet on the hardwood floor. The appropriate calculations show that removal of the
three smaller rugs would increase
the reverberation time to about 0.61
sec., while removal of all four rugs
would increase it further to about
0.7 sec. Such transformations are
easily made, should the requirement
arise; however, the lower time (0.58
sec.) would appear to be more suited
to a general-purpose living room.
References:
I. J. K. Hilliard, "Acoustic Measurements on
a Home Stereo Installation." IRE Transactions on Audio, Vol. AU -9, March-April
1961. pp. 41-43
2. The author is indebted to Mr. David J.
Thomson, Bell Telephone Laboratories,
Murray Hill, N. J., for invaluable advice on
placement of loudspeakers.
3. T. Somerville. "Subjective Comparison of
Concert Halls," B.B.C. Quarterly, Vol. 8,
No. 2, pp. 125-128 (1953)
4. J. Blankenship, R. B. Fitzgerald, and R. N.
Lane. "Comparison of Objective and Subjective Observations on Music Rooms,"
Journal of the Acoustical Society of America, Vol. 27, pp. 774-781 (1955)
5. A. F. B. Nickson and R. W. Muncey. "The
Acoustic Conditions Accepted by Listeners in
an Auditorium," Acustica, Vol. 9, pp. 316320 (1959)
6. R. W. Muncey and A. F. B. Nickson,
"The
Listener and Room Acoustics." Journal of
Sound and Vibration, Vol. 1, pp. 141-147
(1964)
AUDIO
JUNE 1968
GLOSSARY
Here are some of the terms used
in Dr. Dolby's article on audio noise
reduction, which starts on page 19
of this issue.
Attack time-The time elapsing
from the initial signal which inaugurates a control until the control is
fully in effect. Usually expressed in
milliseconds (ms).
Breathing-The sound caused by
variation in gain of an amplifier if
the filtering is not optimum. (See
Swishing.)
Bridging input-Describing the
input circuit of an amplifier which
is designed to be connected across a
line of a specified impedance, but
not terminating the line, nor appreciably affecting its loading.
Compressor-A variable -gain amplifier designed to reduce the dynamic range of a signal by limiting
the difference between the loudest
and the softest sounds.
De-emphasis-A controlled
change in frequency response applied to a signal which has been pre emphasized previously. In FM radio,
for example, a pre -emphasis is apNOISE -REDUCTION SYSTEM
plied to the signal to boost the high
frequencies in the transmitter, and
a complimentary de-emphasis is introduced in the receiver to result in
a flat signal in which noise is reduced appreciably.
Diode clipper-A diode arranged
in a circuit that cuts off hence
"clips"
peak excursions of signal
voltages to prevent overloading of
succeeding circuits.
Expander
variable -gain amplifier arranged to increase the dynamic range of a signal. Opposite of
compressor. Both functions are often combined in one unit.
Filter-A circuit element designed to eliminate a specific range of
frequencies from a signal. Low-pass,
passes low frequencies and eliminates those above the specified
frequency; band-pass, eliminates
frequencies above and below the selected band; high-pass, eliminates
low frequencies and passes highs.
Floating
Describes a circuit
which has neither terminal at
ground potential, nor does it have a
center -tap ground. Used when the
device may be connected to a circuit
which may have a ground at some
-
-
-A
-
other point. Usually employed to
eliminate ground loops.
Pre-emphasis-See de-emphasis.
Print-through-Each signal recorded on a magnetic tape represents a series of permanent magnets, which may affect the coating
on adjacent layers of the tape. This
undesirable effect is called "print through."
Recovery time The time, express Pd in milliseconds (ms) that a
circuit requires to return to normal
after a controlling signal is terminated. (See attack time.)
Swishing Noise generated by
varying the gain of an amplifier
rapidly. So-called because it is descriptive of the sound, which is more
pronounced than "breathing."
Threshold-Signal level at which
a control action is inaugurated. Below this level, the amplifier is in a
normal linear condition.
Tone burst
Short, regularly
spaced groups of a limited number
of cycles of a continuous tone used
in testing amplifiers and loudspeakers. Usual bursts contain 4, 8, or 16
cycles of the testing frequency, and
output is viewed on an oscilloscope.
-
-
-
COOeMMMQikäOriMMOMQ4ärc
kX
(Continued from page 22)
to -back combination of germanium
and silicon diodes in parallel with
the resistor. This configuration provides the desired non-linear integration properties. Finally, the
smoothed control signal is returned
to the compressor and is used to control the current in the compressor
diodes by means of Q203 and Q204.
The four compressor output signals returning to the control module
are combined by the precision resistors R301 -R304 and are fed back to
the amplifier module. After being
amplified by the feedback amplifier,
Q105 and Q106, the resultant noisereduction signal is fed to a switch
which determines whether the processor operates in the recording or
playback mode. For recording, the
noise-reduction signal joins the main
signal additively between Q104 and
Q107; during playback, the noisereduction signal is combined subtractively at Q102 -Q103.
REFERENCES
1. E. T. Canby, "Audio ETC.," Audio Magazine, March 1967 and April 1967.
2. R. M. Dolby, "An Audio Noise Reduction
System," J. Audio Eng. Soc. 15, 383 (1967).
Dr. Dolby discusses applications of the noise -reduction system.
NEXT MONTH:
AUDIO
JUNE 1968
Save $100.
During our "Own the Best" sale, buy
the world's finest portable tape recorder for $340. instead of $440. The
Uher 4000 Report -L is the choice of
professionals. 7 lbs. light, solid state,
it records and plays back 4 speeds,
uses
rechargeable or ordinary bat-
teries and has a 3 -digit index counter
with push-button reset.
Sale offer includes Dynamic Microphone-#M514; Long Life Accumulator Dryfit Batteries-#433; AC power
supply and battery charger-#880,
Genuine Leather Carrying Case -#861.
Now that we've made it $100.
easier to "Own the Best," take this
ad to your Uher dealer and walk off
with
7
pounds of greatness...the
Uher 4000 Report -L.
Offer expires midnightJunel5,1968.
D5
Uher by Martel
Martel Electronics Inc. Sole U. S. Importers
2339 South Cotner Avenue, Los Angeles,
California 90064; New York: 1199 Broadway
Chicago: 5445 No. Lincoln
Check No. 55 on Reader Service Card
55
;
CLASSIFIED
MIX
FOUR
Rates: 25¢ per word per insertion for noncommercial advertisements; 50¢ per
word for commercial advertisements. Frequency discounts as follows: 2 times,
less 15°/o; 6 times, less 209o; 12 time s, less 30°/o. Closing date is the FIRST of
the second month preceding the date of issue.
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FOR SALE
RECORDING SERVICES -Tape, Disc, and
Duplication. Reasonable Rates. Jones and
Associates, Box 142, Dayton, Indiana 47941.
DON'T THROW YOUR OLD CARTRIDGE
AWAY. Send us $19.95 and any old
cartridge. We will ship PREPAID any one
of the following top rated elliptical dia-
HIGH FIDELITY SPEAKERS REPAIRED
AMPRITE SPEAKER SERVICE
168 W. 23rd St., New York, N. Y. 10011
CH 3-4812
PROTECT YOUR LPS-Heavy poly sleeves
for jackets 5¢, Round bottom for records
3'/4 ea. New LP jackets, White 20¢, Colors
25¢. Min. order $5.00. LP Supplies, Hillburn, P.O. New York.
11.20
ONE
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FOR EACH
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Shure M68 Microphone Mixers
can be stacked and interconnected to accommodate virtually
any number of microphones regardless of impedance. They are
unusually compact, singularly
flexible, and modest in cost. They
make Total Communications a
practical reality.
MICROPHONE
MIXER
CUSTOM RECORDING SERVICE -Tape or
disc recordings made from live or recorded material. High quality. Reasonable
rates. Audio -Tech Laboratories, 2819 Newkirk Avenue, Brooklyn, N. Y. IN 9-7134.
M. RETTINGER, Consultant on Acoustics.
Analysis. Room Design. Noise Reduction.
5007 Haskell Ave., Encino, Calif. Tel: (213)
784-3985.
RENT STEREO TAPES-75¢ week. Catalog.
Art's 16131/2 N. Mariposa Ave., Hollywood, Calif. 90027.
FOR SALE
-
-
KIT EXPERTS Dynaco Specialists Kits at
reasonable prices are our specialty. Also
custom -wired kits guaranteed to exceed
factory standards at substantial savings.
Beautiful handcrafted walnut cases for
complete Dynaco line, plus everything in
audio. Kitcraft, Dept. A168, 738 Washington Avenue, Brooklyn, N. Y. 11238. Tel:
MA 2-5230.
mond stereo cartridges NEW: Pickering
V15AME3, Empire 888SE, Shure M55E,
Stanton 500E, Shure M80ED (for Lab 80),
M80ED19 (for Dual 1019). Write for lowest quotations all stereo components.
DEFA ELECTRONICS, 2207 Broadway, New
York, N. Y. 10024.
ACOUSTIC RESEARCH, Dynaco, Koss,
Shure specialists; free listing. Stereo Component Systems, 95 Vassar St., Cambridge,
Mass. 02134.
MUSIC LOVERS, background music, continuous, uninterrupted, from your FM
radio, using new inexpensive adaptor. Free
literature. R. Clifton, 11500-E N.W. 7th
Ave., Miami, Florida 33168.
DISC RECORDING EQUIPMENT: Cutter heads, Recording Amplifiers, and Lathes.
New and used. From Rek-O-Kut to Scully.
Send requirements. Wiegand Audio Labs,
221 Carton, Neptune, N. J. 07753.
SCULLY Professional Tape Recorders, from
1 to 12 tracks, complete recording studios
available in prewired console cabinets
starting at $8,000.00. 70°%o financing. WIEGAND AUDIO LABORATORIES, 221 Carton, Neptune, N. J. 07753.
for money saving stereo catalog AM and lowest quotations on your individual component, tape recorder, or system requirements. Electronic Values, Inc.,
200 West 20th St., New York, N. Y. 10011.
FREE! Send
cost. Arkay Sales Company, 1028-H Commonwealth Avenue, Boston, Mass. 02215.
FOR SALE: 2 E.V. 666 Mikes, $90.00 each;
Neumann U67 Mikes with wind screens,
$298.00 each; 2 Westrex (just rebúilt) 2B
cutters, $1,095.00 each; 1 HEACO 2B
driver amplifiers, $685.00 each, 1 Westrex
2B driver amplifier, $450.00; 8 Cinema Engineering 101 AX pre-amp with trays,
$40.00 each; 2 Heathkit amplifiers 30 watt,
$20.00 each. Contact: Hank Waring, 1456
Cahuenga Blvd., Hollywood, Calif. 90028
or phone HO 3-9804.
HAMMOND reverberation! New mechanism-$4.-CAL'S! Box 234, Dearborn,
Michigan 48121.
JAPANESE PRODUCTS CATALOG by air
mail $5, sea $3. Intercontinental, CPO
1717, Tokyo, Japan.
HARPSICHORD: Same as owned by Philadelphia Orchestra and RCA Victor. In kit
form for home workshop assembly, $150.
Clavichord kit, $100. Free brochure. Write:
Zuckermann Harpsichords, Dept. R. 115
Christopher St., New York, N. Y. 10014.
TAPE RECORDER SALE. Brand new, na-
tionally advertised brands, $10.00 above
2
...YOUR KEY TO TOTAL COMMUNICATIONS
SHURE BROTHERS, INC., 222 HARTREY AVE.
EVANSTON, ILL. 60204
©.1967 Shure Brothers, Inc.
Check No. 56 on Reader Service Card
56
AUDIO
JUNE 1968
MARANTZ-7, $160. w/wal. cab. Acoustech-1, $140. KLH-18, $90. All mint condition. Dinaro, 44-20 Ketcham St., Elmhurst,
N. Y., 212-426-0934.
WANTED: Western Electric 594A DriverFor sale or trade Western Electric 555
drivers, JBL 175 DLH. Charles Johnson, 21
Holly Hill Dr., Mercer Island, Washington.
SCOTCH RECORDING
TAPE,
lowest
prices. Tape Center, Box 4305, Washington, D. C. 20012.
McINTOSH Mc 60, Like new 60 watt amplifier $115.00. F. Breidbart, 405 Beach 122
St., Rockaway Park, N. Y. 11694.
MAGNECORD 1024, 1/4 track, 33/4 and
71/2 in./sec. Tape Deck. New Sept. '67. Excellent Condition. 36 81/4 reels in boxes.
Best offer. Steve Shepard, Box 4302, State
College, Miss. 39762. Phone 601-323-2756.
AMPEX AG -350-2 Stereo Recorders. Both
unmounted. Like New condition. One machine has standard track heads, $1,550.00.
Second machine has additional quarter track playback, $1,600.00. J. M. Edelman, M.D., 4550 North Boulevard, Baton
Rouge, Louisiana, Phone 504-927-3553.
RECORDS. 40 different new 45's many
recent hits. $3.95 postpaid. Jack Armstrong, 52724 Francis Rd., So. Bend, Ind.
46637.
TWO 16" TURNTABLES, weighted and
balanced, with mounting plates, suitable
for custom recording lathes; cork suction
chuck available. Box 324, Bayville, N. J.
08721
TAPE RECORDING MAGAZINE-Enthusiasts monthly magazine for amateurs and
professionals. Send $3.75 for 1 year subscription to 14-18 Holborn, London, E.C.1.
England.
EQUIPMENT WANTED
WANT TO BUY: Fairchild conax-1 mono,
1 stereo; Westrex 3C cutters-need not be
in working order; V.P. Scully lathe. CONTACT: Hank Waring, 1456 Cahuenga
Blvd., Hollywood, Calif. 90028 or phone
HO 3-9804.
WANTED-Fisher MPX-100. Goodman, 516
Kenmore, Los Angeles, Calif.
S.
MAGNECORD P-75 record or play head
mount needed. Please state mounting
method. Reply to: Richard McCleary, 4534
Blount Ave., Jacksonville, Florida 32210.
HELP WANTED
HI-FI, HAM, CB salesmen
wanted. J. S. Draper, Lafayette Radio Electronics All Cape Shoppers Bazaar, Rt. 132,
Hyannis, Mass. 02601.
EXPERIENCED
Be an
ABZ's of FM
FOR SALE
expert
(Continued from page 32)
often applied to the r.f. stage to prevent overload of the stage when particularly strong signals are applied. This
means that the first stage must have
the capability of exhibiting varying
gain with different bias settings. This
was easily accomplished with "variable
mu" vacuum tubes and is equally easy
to accomplish with today's transistors,
which depend on bias for varying figures of gain. Note that this feature is
called Automatic Gain Control, rather
than AVC (Automatic Volume Control), the term used in AM receivers.
This is because changing the amplitude
of the r.f. signal in an FM receiver does
not alter the volume or "loudness" of
the resultant output unless we are
speaking of signals so weak that they
do not cause full limiting in subsequent i.f. stages.
Other features of an FM r.f. stage
which are not apparent from examining the schematic alone should be
noted. Coils represented in the usual
manner in the schematic become just
four or five turns of heavy wire, with
rather large spacing between turns, often using air as a dielectric. The variable capacitor sections themselves usually have just two or three plates in
the rotor or stator, since we are dealing
with total capacitances of just a few
picofarads. Dress and layout of parts
is much more critical than in AM r.f.
stages, because even an inch or so of
excess wire length implies a significant
amount of additional inductance.
Proper grounding is very important,
too.
The techniques used to design and
lay out r.f. sections of an FM receiver
have evolved over a great many years.
It is not the sort of thing a novice kit builder should attempt to do from simple referral to a schematic. It is for this
reason, incidentally, that most tuner
kit manufacturers supply the front end
in pre -assembled form, often even prealigned. To really appreciate the differences between a broadcast-band r.f.
design and one intended for FM reception, you should examine the front-end
construction of an FM tuner. Note the
overall shielding (good FM tuners usually enclose the entire front end in a
metal shield to preclude excessive
radiation from the local oscillator and
to prevent accidental or intentional
tampering with precisely -aligned coils,
trimmers, etc.).
Next, we shall bridge the great gap
from tubes to solid state and discuss
considerations in transistorized r.f.
amplifier design which forced the reeducation of a whole population of FM
Æ
design engineers.
to
on how
select the best
automatic
turntable.
A true hi -fidelity automatic turntable
precision built mechanism with many
many parts, each of which has a very special function to perform. Very often. to
is
a
save money in manufacturing, some com-
panies either compromise on the quality
of these parts, or leave certain of them
out. The turntable will still operate of
course but forget about getting maximum
high-fidelity. How can you tell when a turn-
table has everything? Use our
BSR
McDonald 600 as an example of perfec-
tion. It has all of these essential features
that a professional quality automatic
turntable must have to insure peak
performance.
MICROMETER
STYLUS
PRESSURE
ADJUSTER
DYNAMIC
ANTI -SKATE
AUTOMATIC
CONTROL
VERNIER
ADJUSTABLE
COUNTERWEIGHT
CLIP-IN
TONE ARM
LOCK
CARTRIDGE
HEAD
.\
CUE
NG AND PAUSE CONTROL
1
Please send FREE detailed literature on
all BSR McDonald automatic turntables.
-
Name
Address
City
L
State
Zip
Mc DONALD
J
PRECISION CRAFTED IN GREAT BRITAIN
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JUNE 1968
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Finished in select walnut and
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Altec Lansing
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Benjamin Electronic Sound Corp.
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WILLIAMSBURG EA -3
These fine furniture space savers are also available in
easy to assemble kits. Choose from 20 different decorator
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Electro -Voice, Inc.
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Erath,
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PHONE (212) 752-2354
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Kenwood Electronics, Inc.
41
Marantz Company
Martel Electronics, Inc.
23
Morhan National Sales Co.
McIntosh Laboratory, Inc.
58
Ot-
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Sharpeii Pencih
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ON
HI-FI
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invite your test of our
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Scott, H. H., Inc.
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Shure Brothers, Inc.
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