Packburn Model 325 Owners Manual

Packburn Model 325 Owners Manual
electronics inc.
AUDIO NOISE SUPPRESSOR
MODEL 325 OWNER’S MANUAL
Packburn is Registered in U.S. Patent and Trademark Office
REV 16-1
electronics inc
AUDIO NOISE SUPPRESSOR MODEL 325
A single-ended noise suppressor designed to eliminate or reduce noises due
to imperfections in and damage to sound recordings in all analog audio media
and their digital reproduction, including cylinder, disk, film wire and tape
recordings, both monophonic and stereophonic
Model 325 contains three processors designed to suppress
transient noises (ticks, pops, clicks, crackle, scratch)
encountered in some 100 years of phonograph recordings,
wherever and however made, as well as the audible hiss
familiar in all audio media prior to the development of
successful encode/ decode noise suppression systems and,
more recently, digital audio.
Model 325 also incorporates a number of
necessities and conveniences for the optimum playback of
disk and cylinder recordings for best quality of sound.
The Switcher:
The first noise reduction processor in the Audio
Noise Suppressor is the Switcher. This is designed specifically
for the reduction of noises from monophonic disk and cylinder
recordings, taking advantage of the redundancy that exists in
these media: the same signal is engraved on each of the two
side walls of the groove. However, the distribution of
particulate matter in the record material (one cause of noise) is
random. Also, dirt, mildew and scratches do not affect each
side wall identically.
Prior to the development of the Packburn Switcher,
a monophonic disk or cylinder, if played back with a
stereophonic reproducing system, was best played by
summing (in the appropriate polarity) the signals from the left
and right channels. The Switcher does this when in the rest
position. However, at any moment when the reproduction from
the left or right channel is quieter (more noise-free) than the
sum signal, the Switcher can elect to reproduce just the quieter
groove wall. The Switcher switches among these three
possibilities (left, right, or sum) at a very rapid rate with
astonishing results. At lower frequencies (from 300 Hz down)
where switching would not accomplish anything, the two
channels are mixed to minimize rumble.
The idea of using the Switcher on vertical-cut
recordings may seem strange at first since there is only one
signal engraved in the bottom of the groove. However, the
vertically modulated signal is affected by disturbances in the
side walls of the groove. The Switcher is not as effective for
vertical recordings but it has a part to play.
The switching process is generally not applicable for
noise reduction of stereophonic records or of monophonic tape
recordings or broadcast. For these, transient noise
suppression must be achieved by the Blanker alone.
The Blanker:
The second noise reduction processor is the
Blanker. This is designed to cope with transient noises from
any source: whether from the output of the Switcher, where
noises remain that were common to both side walls of the
groove, or from a stereophonic disk recording. Also, it is
applicable to a monophonic tape, a broadcast or a CD record
of a disk recording that has transient noises. Note that the
Packburn Blanker works from any program source, in contrast
to some devices that require the vertical component of a
stereophonic disk to trigger their action.
The Blanker clips the amplitude of each individual
positive-going or negative-going pulsation of the noise
transient whenever it exceeds a threshold value determined by
the peak program level in the vicinity of the transient.
The Switcher plus the Blanker comprise the
Transient Noise Suppressor of the Audio Noise Suppressor.
The Continuous Noise Suppressor:
The third noise reduction processor reduces audible
hiss-or white noise, whatever one prefers to call it. It is a
constant annoyance in just about every cylinder, disk, wire,
analog tape or film recording made prior to the development of
successful encode/ decode systems of noise suppression,
followed by digital mastering.
This noise is perceived by the human ear as being
of a fairly continuous nature in contrast to the pops, ticks, and
clicks of transient noise and therefore, we call our third
processor the Continuous Noise Suppressor. This processor
comes third because it is expeditious to suppress the transient
noises first. In the case of recordings containing no transient
noise, such as analog master tapes and copies thereof, the
Continuous Noise Suppressor will be the only one needed.
The Continuous Noise Suppressor is a variable lowpass filtering circuit that responds in accordance with the
nature of the program material. When the program material is
quiet and contains little in the way of high frequency energy,
the high frequencies that the listener is aware of are almost
entirely those in the noise. The cutoff frequency of the filter
closes down to its lowest value. In loud and/ or brilliant
passages when the signal is effectively making the noise, the
cutoff frequency assumes intermediate values. The operator
controls the extent to which the filter closes down and opens
up, so a substantial reduction of hiss can be achieved without
audible degradation of the program material and without the
swishes and pumping that have been the undesirable byproduct of similar devices.
REMOVABLE
19 INCH RACK
MOUNT EARS
TABLE TOP
DESIGN
HALF THE
HEIGHT
(3.5 INCH)
FACILITIES ADDITIONAL TO AND SUPPORTIVE OF THE
NOISE REDUCTION PROCESSORS
A number of necessities and conveniences are included in the
Audio Noise Suppressor to assist the user in achieving
optimum performance with disk and cylinder playback as well
as other signal sources, as follows:
Playback from either channel: There is the ability to play
from either channel separately of a monophonic disk or
cylinder with the lower frequencies of the two channels mixed
so as to eliminate rumble. This is a necessity in reproducing
those occasional recordings in which one side wall is
consistently noisier than the other. Such a condition can
indicate that the optimum stylus is not being used, but some
recordings persist in this behavior with any stylus that one may
try. For these recordings it is preferable to play from just the
quieter side wall of the groove and use just the Blanker for
transient noise suppression.
Transient Noise Suppressor can be switched out: The
Switcher plus the Blanker, which constitute the Transient
Noise Suppressor, can both be switched out by means of a
single toggle switch whenever one wishes to process a
recording only through the Continuous Noise Suppressor
.
Metering of the input: The two input channels are metered to
assure that the proper signal levels are provided to the Audio
Noise Suppressor. Metering takes place after the input level
control and before the channel balance control.
Channel balance control and audition of difference signal:
the balance control is needed for balancing of signals into the
Switcher when playing monophonic disk or cylinder recordings.
In reproducing vertical-cut recordings, the balance control also
serves as a canting control. Audition of the difference signal
as well as of the sum signal allows one to set the channel
balance or canting adjustment with accuracy.
Test Switch: This switch enables selection of either the
quieter or noisier groove wall by the Switcher. It is useful for
demonstration and diagnostic purposes. Also, in the case of a
full-width monophonic tape recording in which the oxide is
flaking off, one can play it with a two-track head and use the
Switcher to choose the momentarily louder channel and thus
avoid dropouts.
ERGONOMIC
CONTROL
LAYOUT
EQUALIZATION
SETTINGS FOR LP
AND EARLY
RECORDS
(8 TURNOVER,
6 ROLLOFF)
THREE NOISE
REDUCTION
STAGES
Eight position bass equalization switch:
This allows
selection of the commonly used bass equalization curves for
78s manufactured prior to the recording industry’s
standardization on the RIAA curve in 1953. Also includes the
RIAA curve.
Six position treble equalization switch:
This allows
selection of the commonly used treble equalization curves for
78s as well as for those long playing records that were
manufactured prior to the recording industry’s standardization
on the RIAA curve in 1953. Also includes the RIAA curve.
Cutoff frequency meter: This meter displays the everfluctuating value of the cutoff frequency when the Continuous
Noise Suppressor is operating.
Bypassing the Audio Noise Suppressor: The Audio Noise
Suppressor is provided with a bypass relay. This connects the
output terminals to the input terminals when the power is OFF
or when the ANS switch is in the “0” position. Thus, the Audio
Noise Suppressor is easily removed form the circuit when it is
not needed.
SOME
USERS
OF
THE
PACKBURN
AUDIO
NOISE
SUPPRESSOR
Customers are telling us “Simple to use…just sit back and listen!”
“Good hiss, pop and click elimination!”
“Improved musical clarity!
“The controls are easy to operate!”
“Preserves the original sound – serves archival purposes
well”
And for those who have returned their Packburn machines
for upgrading to the model 325 performance level * “The blanker and continuous noise suppressor are more
effective even on LP records.”
“There is less low frequency rumble on older records
including vertical-cut records.”
* Consult factory for details
APPLICATION NOTES
78s:
The success of the Audio Noise Suppressor is most
spectacularly demonstrated with noisy 78 rpm disks, as these
present a continuous stream of ticks, pops, etc. the
suppression of which is immediately demonstrable. The same
applies to excessively ticky, scratchy or dirty 45s and long play
disks. You can instantly hear how the Switcher reduces the
crackle. Next you can turn on the Blanker and hear the major
role that it plays in eliminating or reducing noise from
scratches and cracks. Then you can adjust the Continuous
Noise Suppressor for the final improvement. You can even
operate the TEST switch and hear the effect of choosing the
noisier groove wall.
45s and long play disks. You can instantly hear how the
Switcher reduces the crackle. Next you can turn on the
Blanker and hear the major role that it plays in eliminating or
reducing noise from scratches and cracks. Then you can adjust
the Continuous Noise Suppressor for the final improvement. You
can even operate the TEST switch and hear the effect of
choosing the noisier groove wall.
Long Play and Stereo Disks: The improvement of these
requires more patient observation if they have not been abused,
as these have only occasional and pops, some of which,
however, can reproduce as loud as a pistol shot. The Blanker
reduces the pistol shots to innocuous thumps. Lesser noises are
turned into slightly noticeable thuds when they are not totally
eliminated. The Continuous Noise Suppressor effectively and
unnoticeably reduces the hiss.
45s and polystyrene long play records, with their higher hiss
level, are nicely served by the Continuous Noise Suppressor.
Acetates: These can range from worn and deteriorating disks
to extremely quiet, mirror-surfaced beauties. The Audio Noise
Suppressor handles the difficult ones like bad 78s, the good
ones like fine long playing disks.
Vertical-cut Recordings: This includes acoustical disks and
cylinders and electrical broadcast transcriptions. Both the
Switcher and Blanker have a major effect in reducing transient
noises from broadcast transcriptions. With acoustical disks and
cylinders the Blanker plays the major role in reducing the
transient noises. The Switcher can be turned up slightly for some
assistance in the noise reduction. The Continuous Noise
Suppressor can be applied to good effect in reducing the
remaining hiss.
78 Transfers to tape or long playing records: Many tape
copyists and record producers mistakenly transferred 78s with
the RIAA curve, which reduced surface noise but also took much
of the life out of the sound of a voice or instrument. In playing
back from such a source, one can restore the treble equalization
and then use the facilities provided by the Audio Noise
Suppressor to suppress the noises in the proper manner.
Analog Master Tapes and Film: The Continuous Noise
Suppressor is very successful at unobtrusively reducing the hiss
level of analog master tapes or copies thereof.
CDs: We claim no applicability of the Audio Noise Suppressor
to CDs mastered from original digital tapes. However, CDs
derived from 78s, from old movie sound tracks or from master
tapes that antedate the introduction of encode/decode noise
reduction devices all are instances where the Audio Noise
Suppressor has a role to play, whether on the part of the CD
producer or the consumer. If the producer chooses to ignore
what the Audio Noise Suppressor can do to improve his
product, the consumer can do it on his or her own!
Broadcast reception in general can benefit from use of the
Continuous Noise Suppressor if there is audible hiss, whether
the source of the hiss is in the program material or in the
conditions of the reception. Broadcasts of historical material, if
equalized with the RIAA curve (as it often is) can be corrected
and transient noises can also be suppressed.
Regarding copies, In general: The Blanker has to be relied on
to provide whatever transient noise suppression is to be
achieved. However, it must be recognized that recordings
processed into long playing disks or into radio broadcasts are
subject to equalization, compression and limiting and probably
are also several copying generations removed from the original.
All of these circumstances can tend to soften the leading edge of
a noise transient with the result that the detectability of the noise
transient by the Blanker circuit is lowered. Thus, as a general
rule, the Transient Noise Suppressor will be at its most effective
when it can be applied to the original recording.
The Continuous Noise Suppressor will not be affected in the
same way. It will just have more to do.
Carefully made stereo tape transfers of a monophonic disk or
cylinder—especially a digital tape—can provide good results,
as the Switcher can be employed and there should be no
appreciable degradation of the noise transients that would
reduce the effectiveness of the Blanker.
Record Restoration: Application of the Continuous Noise
Suppressor is best deferred to the final stage of processing by
those doing record restoration. In such applications, one would
use the Transient Noise Suppressor at the start. After filtering,
equalization, volume expansion, adding reverberation, etc., one
can then use the Audio Noise Suppressor a second time, this
time by-passing the Transient Noise Suppressor and using only
the Continuous Noise Suppressor.
Quadraphonics — Surround Sound — Ambience Systems
— Electronic Reverberation: The spatial illusion of these
systems is seriously degraded when pops and "pistol shots"
disclose the presence of the ambience loudspeakers. With the
Audio Noise Suppressor one can even play 78s without any loss
of the spatial illusion.
Audio Noise Suppressor Model 325 Technical Specifications
Designed for professional installations and for quality home
sound systems
Outfitted to interface with 600 ohm balanced line systems or with the more customary single-ended Hi Fi systems;
Provided with XLR professional connectors as well as with RCA-type phono connectors for all signal input and
output terminations.
Power Line Voltages:
U.S./ Canadian 105 volts 120 volts, 50/60 Hz
International: 210 volts-240 volts, 50/60 Hz (consult factory)
Power Consumption:
20 Watts
Size:
Width: 19" (483 mm) for rack mount, 17” (432 mm) with mounting ears removed
Depth: 13" (332 mm), Height: 3.5" (89 mm).
Inputs and Outputs:
There are two separate electronically balanced input channels. Separation throughout the
audio frequency range is maintained in processing stereo signals, in which each signal path
is provided with a Blanker, a Treble Equalization network and a Continuous Noise
Suppressor and then routed through a dual OUTPUT LEVEL control to the separate output
terminations.
In processing lateral-cut or vertical-cut recordings, the signals applied to the two input
channels are routed through a balancing circuit to the Switcher. Or, at the operator's choice,
with lateral-cut records, the signal of either channel may be individually selected for
processing. To reduce the audibility of low frequency disturbances, the bass portion of the
two input channels, is mixed in the proper polarity. The output of the Switcher is connected
to both of the Blanker + Equalizer + Continuous Noise Suppressor channels, and the fully
processed signal may be taken from either or both of the output channels.
Electronically balanced input. Single-ended input impedance is 100k ohms.
Electronically balanced output. Single-ended output impedance is less than 1 ohm.
Sensitivity:
With INPUT LEVEL control all the way up, a 0 VU (1.23 v.) reading of the processing
level meters will be achieved by an input signal of — 6 VU or less from a 600 ohms line or
by 0.4 v. or less from a single-ended source. Range of control of INPUT LEVEL
potentiometer is 20 db.
With OUTPUT LEVEL control all the way up, there is unity gain from the metering circuit to
the output terminations.
Frequency Response:
Bass response is within ± 1/2 db to 10 Hz.
Treble response is determined by the setting of the Treble Equalization switch and the
action of the Continuous Noise Suppressor.
is provided by the Audio Noise Suppressor by means of a six-position selector switch which
enables you to match the treble portion of published equalization curves of records, old and
new. Includes FLAT, FFRR, AES, RIM, LP.
Treble Equalization:
Continuous Noise
Suppressor Action:
The Continuous Noise Suppressor is a low pass filter. Cutoff frequency varies from 2.5 kHz to 18 kHz
in accordance with the dynamics of the program material and the nature of the surface noise.
Alternatively, a fixed cutoff frequency may be selected. Meter on front panel reads the cutoff
frequency. Filter has a slope approaching 12 db per octave.
IM Distortion:
60 Hz and 7 kHz, 4:1 at + 4 vu (1.23v.) input: Less than .05%
S/N Ratio:
(Unweighted) – At least 75 dB with reference to + 12 vu (3 v.).
Warranty:
A full five year’s warranty on both parts and labor.
About your Record
Playback Equipment:
To take advantage of the Switching process, you must have equipment to play back discs or
cylinders stereophonically. The two channels of reproduction must be closely matched in
frequency response.
Demonstration CD:
Available on request
electronics inc. P.O. Box 226 Syracuse, NY 13215 U.S.A.
Ph 315-476-9121
Covered by one or more of the following US patents: 4,151,471; 4,155,041; 4,259,742; 4,322,641; 7,035,417
TABLE OF CONTENTS
Foreword
Pg: 3
Installation of the Audio Noise Suppressor
4
Controls (Front Panel Description)
7
Getting Started
12
Technical Principles of Operation
15
Suggestions for Optimum Processing of Historical Recordings
17
Vertical Cut Records (Edison Diamond Disc, Hill and Dale)
20
Recommendations for Preserving Historical Media
21
CD’s – Tapes – Broadcasts
22
The VU Meters
24
Optimizing Other Components in Your Audio System
25
Trouble-Shooting Procedures
28
Equalization Settings for Early Recordings
31
Interface Diagram
36
1
2
Foreword
Packburn Electronics, Inc. has been in business for over 25 years, inspired by the late
Richard C. Burns. What got the company running was Dick’s passion for historical sound
recordings and inventive playback equipment that would rescue musical nuances in a safe
and effective manner from the assault of unwanted noise. Our modest goal was to improve
the sound quality of our personal record collections but it was quickly discovered that our
noise suppressor was of interest to others. Our founding principles of safe noise reduction
and ease of operation are still alive and carry into our latest patents and our Model 325
Audio Noise Suppressor.
We appreciate your purchase of our product, and we want this unit to work for you as well
as it has for us in the time that we have spent with it. The unit has gone through extensive
testing, a one week run-in, and a listening session with test records.
The instruction manual describes how to use the Audio Noise Suppressor with a wide variety
of historical sound recordings. For casual listening you will probably develop settings that
apply to a given recording format. For meticulous copying of records, you will want to
check the settings for each individual recording.
The Audio Noise Suppressor consists of three noise reduction stages called the ‘Switcher’,
the ‘Blanker’, and the ‘Continuous Noise Suppressor’ (or CNS.) As you gain experience and
confidence in its operation, you will learn that the Audio Noise Suppressor is perpetually on
guard, acting to suppress noises as they occur. Those who already have a reasonably welladjusted audio system usually get the unit quickly connected and working and proceed to
"enjoy".
Wishing you pleasurable listening,
Thomas N. Packard
President
3
4
Installation of the Audio Noise Suppressor
A. The Turntable
A stereo cartridge needs to be used even for monophonic phonograph records.
If a
monophonic record is played back using a monophonic cartridge, the first noise reduction
stage (Switcher) won’t operate to remove noise.
For those using the PACKBURN for
playback of 78 RPM records, stylus suggestions are provided on p. 17.
B. The Pre-amplifier (for providing turntable signal to the PACKBURN)
The preamplifier needs to be a stereo. For optimal playback of cylinders and records of all
speeds the pre-amp should have a flat high end frequency response and preferably a flat low
end frequency response as opposed to RIAA rolloff and turnover equalization. 1
If the
preamplifier has treble and bass controls they should be set flat and if it has a balance
control, to the center of adjustment. The Packburn’s own rolloff and turn-over equalization
controls subsume those of the pre-amp.
The preference is to play all phonograph records using a pre-amplifier set as described
however some only have factory-fixed RIAA roll-off equalization. Here are suggestions
about what to do:
(a)
We may be able to offer suggestions for a replacement pre-amp.
(b)
The PACKBURN Audio Noise Suppressor has an inverse RIAA curve feature that
can be factory enabled to counteract the pre-amplifier equalization.
(c)
Install a stereo equalizer between the preamplifier and the Audio Noise Suppressor
to counteract the rolloff curve of the preamplifier. For information on how to adjust
the equalizer, refer to Stereo Equalizer Ahead of the Audio Noise Suppressor on p.
25.
1
For 33 speed records, noise becomes easier for the Packburn to detect without high frequency rolloff. Also, some early
33 speed records do not follow the RIAA curve (refer to p. 32 of the owner’s manual.)
5
.
(d)
A flat high end frequency response can be approximated by your pre-amp if it has a
treble control. Listen to a 33 speed record with the Packburn’s ROLLOFF control at
0 dB and notice the loss of high frequencies when turning it to 14 dB. Boost your
preamplifier’s treble control to restore the original sound. The treble control is
then left at that setting for all records. This is only recommended for non- exacting
work.
(e)
Install a pair of passive equalizers between the preamplifier and the Audio Noise
Suppressor.
For an example of a design, refer to Installation of a Passive
Equalization Network Ahead of the Audio Noise Suppressor on p. 25.
C. Equipment Following the PACKBURN A u d i o N o i s e Suppressor:
Signal processing devices such as equalizers, filters and sonic enhancers may be connected
to the output of the Audio Noise Suppressor to further improve the signal that is being
reproduced.
D. Input and Output Connections to the PACKBURN Audio Noise Suppressor:
The Audio Noise Suppressor accommodates typical high fidelity systems and professional
audio installations.
The stereo pre-amp output or other stereo signal processing device
connects to the input of the PACKBURN. The PACKBURN installs in the audio system much
as one would install a stereo equalizer.
The RCA connectors are used for a typical high fidelity system. For professional audio
systems, the three prong connectors are used. Pin 1 of the three prong connector is
grounded and for single-ended (unbalanced line) systems, signal may be provided on either
pin 2 or pin 3. For 600 Ohm balanced line systems, signal is provided on both pins 2 and
3.
When utilizing the RCA connectors, it is prudent to insert the grounding adapters
provided by PACKBURN into the three prong input connectors. The adapters ground the
unused pin 2 inputs.
6
Front Panel Controls
1
2
3
4
12
13
5
14
15
1 L - left input level
2 R - right input level
6
16
7
8
17
9
10
11
18
19
20
11 Power - Packburn on/off
12 Mode - selects how input signals to be processed
13 TNS – transient noise suppressor (switcher and
blanker) on/off
14 Test - normally leave in “0” see instructions
15 Switcher - on/off
3 Input Level - adjusts meter readings
4 Bal - balances inputs if Mode in Mon or Ver
5 Rate - Switcher sensitivity
6 Rate - Blanker sensitivity
7 Low - CNS minimum cutoff frequency
16 Blanker - on/off
17 CNS - continuous noise suppressor on/off
18 Turnover - low frequency equalization
8 CNS cutoff frequency
9 Rate - CNS sensitivity
19 Roll-off - high frequency equalization
20 ANS - audio noise suppressor (TNS and CNS) in
or out of system
10 Output Level - adjusts output terminal levels
A. Enablement Controls (INPUT/ OUTPUT LEVELS, POWER, ANS, TNS, CNS)
INPUT LEVEL is set for proper readings on the L (left input) and R (right input) VU meters.
Music or speech should have peak readings at about or slightly above 0 VU. If an occasional
tick causes the meter needle to go off scale or the meter readings to mismatch, do not worry
about it if the program levels are correct. The input level control boosts the input signals up
to +20 dB.
OUTPUT LEVEL sets an output level that is convenient for the user, the input level already
having been set for proper VU meter readings. The PACKBURN provides unity gain (input
and output terminal signal levels match each other) when the two controls are at 12:00 and
also for other settings.
7
POWER provides line voltage to the PACKBURN. When in the off position, the left input
is directly fed to the left output and also the right input is directly fed to the right output.
This means that even when the PACKBURN is not powered, your audio system will have
signal continuity.
ANS (audio noise suppressor) sets the PACKBURN in or out of your audio system. When
switched out (‘0’) the left input is directly fed to the left output and also the right input is
directly fed to the right output. When switched to ‘1’ the left and right inputs are fed to the
outputs through the PACKBURN.
This switch allows the user to perform a full “A - B” comparison test on the PACKBURN.
However, in order for this test to be valid, the signal levels at the input and output terminals
of the PACKBURN must match one another and the PACKBURN equalization curves must
be flat (turnover control set to RIAA, and rolloff set to 0 Hz.) Further, for a comparison
involving the mode switch in “mon”, the amplifier following the PACKBURN should be
switched to monaural. All of this makes for a “complete in-out” comparison of the device.
There is a less complete but much easier alternative: An “A - B” comparison is performed
on just the noise reduction stages of the PACKBURN by simply turning the TNS and CNS
switches on or off, no other adjustments being needed.
TNS (transient noise suppressor) turns the Switcher and Blanker noise reduction stages on
or off, overriding the individual Switcher and Blanker on-off switches. These noise reduction
stages reduce ticks and clicks and may reduce hiss if made up of a succession of small
clicks, all of this referred to as transient noise.
CNS (continuous noise suppressor) turns the CNS noise reduction stage on or off. This
stage reduces hiss.
8
B. MODE Switch
This switch determines how the PACKBURN is to process the input signal. In the ST
(stereo) position, the PACKBURN treats the input as having two different musical signals
and so feeds stereo to the L and R outputs. When the switch is set to all of its other
positions L (left), R (right), MON (monaural) or VER (vertical), the PACKBURN treats the two
musical input signals as having little and usually no stereo content and so converts the input
signals into a matched, monaural signal at the left and right outputs. The signal on each of the
two output channels is predominantly the following:
L
Left input signal,
R
Right input signal,
MON
Mix of Left and Right input signals,
VER
Mix of Left and Right input signals phased for vertical-cut (Edison)
cylinders and discs,
ST
Left input signal provided to left output,
Right input signal provided to right output.
The “MON” position is normally used for monaural tape, film, 78, 45 or 33-1/2 RPM records
or signal sources.
The “VER” position is used for monaural 78 RPM vertical cut records such as Edison
cylinders or diamond discs.
The “L” or “R” positions are normally used for purposes of adjusting the BAL (balance)
control or selecting the correct stylus size for the most exacting work, as will be described
below. However, you may find occasions when the L or R positions provide best noise
reduction, so feel free to use them.
The “ST” position is used for CDs, tape, film, 33-1/3 or 45 RPM records, or other signal
sources having noticeable stereo imagery.
.
C. Switcher Controls (BAL, RATE, TEST, SWITCHER-on/off)
The Switcher is the first noise reduction stage. The Switcher reduces pops and clicks and
may reduce hiss if made up of a succession of small clicks, all of this being referred to as
transient noise.
This stage is active only in the “MON” and “VER” positions of the mode
switch.
9
TEST is normally kept in the off (‘0’) position. This switch provides a way to check the
effectiveness of the Switcher. In the off position the quietest input signal is always selected
by the Switcher for playback, whereas in the ‘1’ position the nosiest signal is always selected!
The comparison should be made with the Blanker and CNS stages turned off. The TEST
switch has some playback utility as well.
Some customers have used it for monaurally
recorded reel-to-reel tape or film reproduced stereophonically. The “nosiest” input is always
selected, in this case the input not having a brief drop-out! Transient noise or continuous
noise on the tape or film is taken care of by the other noise reduction stages.
BAL (balance) matches the levels of the left and right input signals, something that is
important for optimum use of the Switcher. BAL. can be set by comparing the mode L and
mode R signals and adjusting until the two signals are equal.
Alternatively, turn the
BLANKER and CNS off and MODE to “VER”. Set BAL. to the music null (cancellation of the
music). If the transient noise is canceling, the switcher won’t operate properly (see p. 15.)
Also, if there isn’t a null, make sure the treble and bass control settings in the pre-amp ahead
of the PACKBURN are the same. BAL. corrects up to a 6 dB mismatch between the input
signal levels.
(SWITCHER) RATE increases the sensitivity of the Switcher when it is adjusted clockwise.
As the sensitivity increases, the L, R, and M (mixed L and R) lights increasingly flicker,
indicating that the L and R input signals are being selected with increasing frequency over
the mixed monaural signal as the quietest signal for playback. If the L and R lights don’t
flicker to the same extent, make sure the input signals have been properly balanced. If the
balance is correct, the lights are just indicating that there is more noise in one input signal
than the other. The control is often operated at 5:00 (full clockwise rotation).
D. Blanker Controls (RATE, BLANKER-on/off)
The Blanker is the second noise reduction stage. The Blanker is a complimentary strategy for
reducing transient noise. The Switcher and Blanker form collectively the TNS (transient
noise suppressor).
(BLANKER) RATE increases the sensitivity of the Blanker when it is adjusted clockwise. As
the sensitivity increases, the L, R lights increasingly flicker, indicating that the left and right
input signals are being independently noise suppressed. These lights are conservative. It is
10
normal for them to respond to louder passages of music. A 3:00 control setting is a good
starting place for most records in fair condition. For 78 rpm records with hiss or long playing
records with scratches, higher settings are often beneficial.
E. Continuous Noise Suppressor Controls (LOW, RATE, CNS-on/off)
The CNS (continuous noise suppressor) is the third noise reduction stage.
The CNS
reduces hiss, referred to as Continuous Noise.
LOW sets the lowest frequency in the input signals to be noise filtered. When the (cns) rate
control is set to 8:00 (fully counter-clockwise), LOW operates like a treble control and is set
to where the hiss is removed. The setting is best made during quiet passages of music. The
setting is displayed on the frequency meter. Typical LOW settings are 8:00 to 10:00.
(CNS) RATE sets how the CNS should react to louder or more brilliant passages of music.
The control is adjusted in the clockwise direction until these passages are not dulled. For
records in fair condition, the frequency meter should display a reading of 10 to 15 kHz during
loud or brilliant passages. It is okay for the frequency meter to go off scale. The optimum
setting of RATE may require LOW to be increased from its initial setting. Typical RATE
control settings are 10:00 and 12:00.
F. Equalization Controls (TURNOVER, ROLLOFF):
TURNOVER provides the most common eight low frequency (bass) equalization curves for
playback of 78, 45 and 33-1/3 RPM phonograph records, and also for cylinders. Refer to
Equalization Settings, pp. 31-35. For CDs, magnetic tape, video, film, broadcast or other
media, set turnover to “RIAA”. If you change the TURNOVER setting, it might be necessary
to change the input level setting.
ROLLOFF provides the six most common high frequency (treble) equalization curves for the
playback of 78, 45 and 33-1/3 RPM phonograph records, and also cylinders.
Refer to
Equalization Settings, pp. 31-35. For CDs, magnetic tape, video, film, broadcast or other
media, set rolloff to “0”.
If you change the ROLLOFF setting, it might be necessary to
change the CNS control settings.
11
Getting Started
1.
Install the Packburn between your pre-amp and the stage of your audio system to
which the pre-amp was connected.
Don’t connect the PACKBURN to the line
voltage just yet.
2.
Preset these controls as shown :
POWER
Off
Start with the power switch off.
12:00
12:00
12:00
ST
MON
VER
For stereo music (CDs, tape, film, 45’s, 33-1/3 speed)
For monaural music (78’s, 45’s, 33-1/3 speed discs,film)
For vertical-cut (Edison) cylinders or discs
TURNOVER
ROLLOFF
>>
>>
Set the bass equalization. See pp. 32, 34-35.
Set the treble equalization. See pp. 32, 34-35.
TNS
TEST
SWITCHER
BLANKER
CNS
ANS
0
0
0
0
0
1
>>
INPUT LEVEL
BAL.
OUTPUT LEVEL
MODE
3.
Connect the PACKBURN to 120 VAC (unless factory-set for 230 VAC).
POWER
4.
Start playing music. You should hear sound through your audio system
which is now bypassing the PACKBURN. If you don’t hear anything, check
your patch cables.
On
At least one light should light. Also, you should still hear music, otherwise,
make sure that the output cable has not been plugged by mistake into the
input terminals.
Adjust the level controls:
INPUT LEVEL
>>
Adjust the preamp ahead of the PACKBURN or INPUT LEVEL until the left
and right meters are reading 0 VU on the program (music).
OUTPUT LEVEL
>>
Adjust OUTPUT LEVEL for level match when the ANS is switched
between ‘0’ and ‘1’, or to your liking.
12
5.
Turn on just the SWITCHER (noise reduction stage 1)
MODE
TNS
TEST
SWITCHER
BLANKER
CNS
ANS
6.
MON or
VER
The switcher applies only to the MON and VER modes. Stereo records
not having much stereo imagery to sacrifice may be played in MON.
Stereo recordings are normally played in the ST mode. When the ST
mode is selected, the SWITCHER stage is automatically bypassed.
1
0
1←
0
0
1
BAL.
>>
Select VER mode. Adjust BAL. for a null. Just the music should null, not
the noise, see p. 15. Alternatively, adjust BAL. for equal music levels
between mode R and mode L.
(switcher) RATE
>>
Adjust clockwise for best noise reduction without musical disturbance.
is often set fully clockwise.
L, R and M lights should be flickering.
Turn on just the BLANKER (noise reduction stage 2)
MODE
TNS
TEST
SWITCHER
BLANKER
CNS
ANS
(blanker) RATE
L
R
MON
VER
ST
Select as desired.
1
0
0
1←
0
1
>>
Adjust clockwise for best noise reduction without musical disturbance. A
3:00 setting is typical for records in fair condition. L and R blanker lights
should be flickering.
13
It
7.
Turn on just the CNS (noise reduction stage 3):
MODE
L
R
MON
VER
ST
Select as desired.
TNS
0
TNS overrides the Switcher and Blanker switches.
CNS
ANS
1←
1
(cns) RATE
8.
LOW
>>
Select a quiet passage of music. Adjust LOW as you would an ordinary
treble control to remove hiss. Ignore for the moment any dulling of the
music.
(cns) RATE
>>
Select a loud passage of music. Adjust (CNS) RATE so the music is not
dulled. In newer recordings, the frequency meter should read about 10
kHz to 15 kHz during the most brilliant passages of music.
Turn on the noise reduction controls in combination (the Switcher, Blanker and CNS
stages are all turned on in the following example):
MODE
TNS
TEST
SWITCHER
BLANKER
CNS
ANS
9.
Start at the 8:00 (full counter-clockwise) position.
MON or
VER
1
0
1←
1←
1←
1
Adjust switcher, blanker and CNS rates in combination
for the optimum result.
Turn on the noise reduction controls in combination for a Stereo recording (the
Blanker and CNS stages are turned on):
MODE
TNS
BLANKER
CNS
ANS
ST
When MODE is in ST, the Switcher is automatically bypassed.
1
1←
1←
1
Adjust blanker and CNS rates in combination
for the optimum result.
14
Technical Principles of Operation
A. Mode Switch
In all settings of the MODE switch except the ST (stereo) setting, the lower frequencies of the
left and right input signals to the PACKBURN are mixed below 300 Hz turnover at a 6 dB/
octave slope. This pretty much eliminates the rumble component. In the L, R and MON
settings, the low frequency mix is phased for lateral-cut records, not vertical-cut records. The
mix is phased for vertical-cut records only in the VER setting.
MODE lets you audition the “difference component”, that is, the difference between the two
input signals. For monophonic records played back stereophonically the two signals are
ideally the same so the signal after one is subtracted from the other is ideally “zero”. Thus
for monophonic records the difference component helps you obtain optimum channel
balance. The difference component is obtained by playing lateral-cut records in VER and
vertical-cut records in MON.
The Switcher operation is activated only in MON and VER. In the L, R and ST settings, the
Switcher stage is bypassed and the signal is applied to the Blanker and CNS stages, a pair
of them in each channel.
For single channel non-disc recordings, use the ST setting.
B. Switcher
The Switcher process relies on L and R input signals having identical program material but
different transient noise. This is what occurs when monophonic records (lateral or verticalcut) are played stereophonically. For lateral-cut records, the two input signals are derived
from the two sidewalls of the record groove, the sidewalls having identical program material.
By setting BAL for equal input levels, the two signals differ only by the transient noise, since
transient imperfections in the recording medium seldom disrupt both sidewalls at the same
time. (Switcher) RATE adjusts the threshold sensitivity of the Switcher. The TEST switch
determines whether the Switcher selects the noisier sidewall or the quieter groove wall for
playback.
The operation of the Switcher is visible in the blinking of the three LEDs,
depending on whether the Switcher has chosen L, R or M (center mix) for playback.
15
C. Blanker
Impulse noises on records are characterized by a high amplitude and a short duration. Their
duration is so short that it is chiefly by virtue of their high amplitude that they are perceived
as acutely as they are. Thus, a device that will limit noise impulses so that the amplitude
does not appreciably exceed the level of the music (or other program material) at the
moment of occurrence of the noise will reduce these noises to inaudibility or to a sufficiently
low value so that they no longer constitute an annoyance.
The Blankers
clip noise impulses as soon as they exceed the amplitude of the wave
envelope of the program material. At each of those points in time the instantaneous level is
held until the amplitude of the noise impulse comes back to the program level. Thus, a
separate clipping action occurs for each positive or negative noise pulse. The Blankers are
designed for maximum preservation of the program material and the ability to cope with even
the high rate of incidence of noises on 78 rpm records.
The (blanker) RATE control
establishes the sensitivity threshold.
D. CNS (Continuous Noise Suppressor)
The Continuous Noise Suppressor is designed to reduce high frequency noises of a
continuous nature (hiss).
It is, basically a dynamic low-pass filter with a variable cutoff
frequency between 2.5 kHz and 15 kHz. Thus, its action is confined almost exclusively to the
overtone region of the musical spectrum, as its lowest cutoff frequency exceeds the pitch of
the highest note of most musical instruments. The rolloff approaches 12 decibels per octave.
The cutoff frequency, rather than being responsive to the signal level only, is determined by
the relation of the velocity component of the total local signal-plus-noise to the peak local
signal-plus-noise in a selected octave bandwidth. The CNS is able to detect the difference
between a noise transient to be dulled and a musical transient.
As a result, the cutoff
frequency as displayed by the frequency meter normally remains unchanged due to a noise
transient but rises rapidly upon the occurrence of a musical transient.
16
Suggestions for Optimum Processing of Historic Recordings
A. Cleaning
Optimum reproduction of a phonograph record requires that it be clean. We are not able to
recommend one cleaning method or product over another but in general whenever cleaning
“caution” is the rule. If the record appears to have deteriorated, consider creating a safety
copy before proceeding. If you have a record of similar condition but of lesser value, you
might want to use it for practice. Record labels should not be unduly exposed to the cleaning
solution, the inks and the adhesives being at risk.
A web search will show much thought has been given to cleaning, options ranging from
household supplies (mild detergent and distilled water) to methods employing cleaning
machines and proprietary cleaning solutions. If you are seeking expert guidance, you might
consult an archive, preservationist, or the Association for Recorded Sound Collections
(ARSC.)
B. Centering and Flatness
It has been our experience that most low-frequency thumps in the reproduction of 78s are
due to warped or off-center records. In addition, off-centeredness may cause a once-perrevolution swish. Centering and flattening of the disc are recommended for the elimination of
these noises. The Audio Noise Suppressor will not remove thumps but will frequently reduce
swish.
C. Choice of Optimum Stylus
An audible indication that the stylus size is not optimum is an unequal distortion in the left or
right input signals revealed by comparing MODE “L” and “R”.
Other indications are a
distortion even when MODE is in “MON” or excessive rumble. The stylus should be chosen
that gives the minimum noise and clearest sound with the Transient Noise Suppressor in
operation.
It has been our experience that conical styli reproduce some records with less hiss than do
17
elliptical styli although with louder reproduction of the ticks. Since the Packburn Audio Noise
Suppressor suppresses the ticks, some owners have found that the conical stylus is optimum
in those cases where harmonics greater than about 7 to 8 kHz are not present (early
acoustical recordings, for example). The elliptical stylus, having a superior resolving power,
is best when high frequency harmonics and musical transients are present (electrical
recordings and late acoustical recordings.)
It is also advisable to audition the two sidewalls of the groove to determine that they sound
alike. If one side wall sounds hissier than the other, try changing styli. It has been our experience that the hiss of the two channels will match each other, in most cases, by proper
choice of stylus.
We have encountered cases especially with lacquer discs (sometimes erroneously referred
to as acetates) where one sidewall of the groove reproduces with more hiss than the other
sidewall, regardless of stylus choice. Sometimes the hiss even shifts from one sidewall to the
other. In such cases, it is especially advisable to experiment with the Switching rate.
If one sidewall is consistently hissier than the other, you may find it preferable to set the
MODE switch to L or R to select the quieter channel and using just the Blanker and CNS
stages.
D. TEST Switch
This switch is useful in diagnosing what the Switcher is accomplishing. When TEST is set to
“1” position, the switching action of the Switcher is reversed such that the noisiest
instantaneous signal from among the L, R or M input signals is played back (M is the
monaural mix of L and R.)
E. The Vertical Component
In monophonic lateral-cut recordings, the vertical component of stylus motion is caused by
noise components, such as surface noises of all kinds, turntable rumble, record warpage, off-
18
center playback, surface uneveness and by signal components introduced by tracking error
and tracing error including "pinch effect".
Listening to the vertical component can be a
valuable diagnostic procedure: Turn the MODE switch to VER, rotate (Switcher) RATE fully
counter-clockwise, and switch the Blankers OFF. If your playback equipment is in proper
alignment and you are using the Transient Noise Suppressor according to instructions, the
vertical component of any reasonably noisy record should consist almost entirely of noise.
By adjusting BAL, you should be able to find a position where the program signal nulls. In
fact, that is where the control should normally be set. Once the two signals are in balance,
the vertical component can be auditioned for difficulties such as record wear.
19
Vertical-Cut Records
A. Switcher
Vertical-cut records such as Pathe and other hill and dale discs, Edison cylinders, and Edison
Diamond Discs differ fundamentally from lateral-cut records in that the signal is recorded in the
bottom of the groove rather than on the two sidewalls. Thus there are not two legitimate signal
channels for the Switcher to choose from. However, those who work extensively with vertical
recordings tell us that the Switcher in the newest PACKBURN Model 325 is more able to remove
noise with that type of groove. The Switcher RATE may need to be set below 12:00 if the lateral
component is strong in comparison to the music level. The lateral component is audited by setting
the mode switch to MON.
B. BAL (balance)
BAL should be carefully adjusted for the best cancellation of the lateral component. This process is
referred to as “canting”. Comparing the MON and VER positions of the MODE switch can help
you determine the best setting for the BAL control. The optimum setting can be different from
record to record.
Vertical-cut recordings are intended to be played only in the VER setting of the mode switch. The
L and R settings normally are not appropriate because for vertical-cut records the low frequency
components (frequencies below 300 Hz) are improperly mixed.
C. With and without (A/B) Comparison
Turn the TNS and CNS switches on and off together.
Using the ANS switch for A/B
comparison is possible but involves effort: Either the left or right signal fed to the Packburn will
need to be inverted, the PACKBURN MODE switch operated in MON instead of VER, and the
signal from the PACKBURN monaurally mixed.
comparison also.
20
The ANS switch will then provide A/B
Recommendations for Preserving Perishable Media
A.
First Generation Media
First generation media with limited life expectancy are often transferred in as close
to their original forms as possible to non-perishable, often digital media for
archiving. The PACKBURN’s MODE switch settings L, R, MON and VER will help
reproduce first generation discs or cylinders with optimal stylus, cleaning, antiskating adjustment, record centering or disc flattening, or magnetic tape with optimal
head alignment.
We suggest that whenever possible, both monaural and stereo
media be transferred in stereo. Later when the transfer is played back, the signal
can be noise-reduced through a switcher stage either in the PACKBURN or a future
analog or computerized system that comes along.
B.
Reel-to-Reel Tape
If the perishable medium is monophonic reel-to-reel tape, azimuth alignment of the
tape head is critical. To make the alignment use either a phase monitor oscilloscope
(see below) or audition the difference component (MODE switch in VER.)
If the tape happens to be a second or third generation, it must be recognized that the
intervening work could have involved a lot of equalization, compression or limiting. Generally
the Transient Noise Suppressor is the most effective when processing first generation media.
C. Digital Transfers
Carefully made stereophonic transfers of monophonic discs or cylinders using digital
methods can provide good results. Since the transfer is in stereo, the Switcher stage will be
able to function.
D. Half Speed Transferring
If you have to play a record at half speed or at some other speed considerably removed from
normal to make the transfer, it is recommended that the transfer be played back on pitch into
the Audio Noise Suppressor. This takes advantage of optimized time constants in the noise
suppression circuits.
21
Compact Discs - Tape - Broadcasts
A. Compact Discs
CDs derived from 78s, from old movie sound tracks or from master tapes that antedate
the introduction of encode/decode noise reduction devices are some examples of where
the Audio Noise Suppressor has a role to play. Re-equalization of the signal before the
Audio Noise Suppressor might be required. Copyists sometimes transferred 78s using
the RIAA playback curve if that was the only equipment that was available.
When
playing CD records that do not require noise reduction, the Audio Noise Suppressor can
be bypassed by turning the POWER switch off.
B. Magnetic Tape and Broadcasts
Broadcasts, both live and on tape, and magnetic tape recordings in general can be
processed very successfully using the Audio Noise Suppressor.
Stereo tapes and
broadcasts can be processed with the MODE switch set to ST (stereo). The Blanker removes
transient noise if there is any to suppress, and the CNS removes white noise (hiss.) The
Switcher is bypassed in the ST position.
If the tape or broadcast is a copy of a 78 rpm record, re-equalization of the signal before
the Audio Noise Suppressor may be required. Copyists sometimes transferred 78s using the
RIAA playback curve if that was the only equipment that was available.
Tape is susceptible to random dropout. The Switcher may address this problem for full-width
monophonic tapes played back in stereo. With the MODE switch in MON and TEST in the “1”
position, the Switcher will select the momentarily louder of the two channels, i.e., the channel
having the least drop-out.
The Blanker and CNS noise reduction stages then remove
transient noise (if there is any) and continuous noise.
The tape recording may have been made with an intervening acoustic link such as the coupling
of sound from a loudspeaker to a microphone. Neither the Switcher nor Blanker will be able to
remove transient noise, however, the CNS will remove continuous noise.
22
C.
Film Recordings, Wire Recordings
Although we do not have experience with processing either of these media, the Blanker should
be able to reduce transient noise and the CNS should be able to reduce continuous noise.
For film whose audio track is monaural, the Switcher might have a role to play if the audio
track is played back stereophonically.
First, set the MODE switch to VER to audit the
difference component between the two signals. After balancing the two inputs if transient
noise seems the most problematic, TEST should be set to ‘0’. If there are random bursts in
the program material due to drop-out, TEST is perhaps better set to ‘1’. After the (Switcher)
RATE has been adjusted, the L, R and MON settings of the MODE switch should be
compared, choosing for playback the setting that provides the best sound quality.
23
The VU Meters
The VU Meters are, strictly speaking, peak reading meters. They are connected following the
INPUT LEVEL and TURNOVER controls but preceding the balance (BAL) control.
The
purpose of the meters is to assure that the Audio Noise Suppressor is not overloaded. BAL
has no effect on the meter readings, rather, it serves as a fine level setting whose setting is
best left to the ear.
The VU meters also follow the anti-RIAA equalization circuit when this circuit has been
activated at the factory (refer to Installation Instructions for more information.)
The anti-
RIAA (75 s) circuit emphasizes the high frequencies of the input signals. Since the VU
meters follow the equalization circuits (a circuit provided in each channel), they are
displaying the true input signal being processed.
The balance control on your pre-amplifier ahead of the Audio Noise Suppressor should be
adjusted so that the VU Meters yield approximately equal readings on the program material.
If one channel has louder ticks than the other, its meter can be expected to register a higher
level. Your adjustment should be to the program material: music or speech, whose peak
readings should be at about or slightly above 0 VU. If an occasional tick causes the meter
needle to go off scale, do not worry about it if the program levels are correct.
24
Optimizing Other Components in Your Audio System
A.
Pre-Amplifier Ahead of the Packburn
The frequency response of the left and right signals from the pre-amplifier ahead of the
Packburn need to match if the Switcher is to operate to best advantage.
1
Set the treble and bass controls on your pre-amplifier “flat.”
2
While playing a monophonic record, adjust your pre-amplifier balance and
level controls, and the INPUT LEVEL control on the Packburn for good meter
readings.
3
Set the MODE switch to VER.
4
Adjust BAL. for best signal cancellation.
5
Adjust the treble control on just one channel of your pre-amplifier to see if you
can exact better signal cancellation.
6
Readjust BAL. if necessary.
B. Stereo Equalizer Ahead of the Packburn
If an equalizer is inserted after the pre-amplifier and ahead of the Packburn, its two channels
should be matched band by band using the above procedure or alternatively, a phasemonitoring oscilloscope (see next section.)
One purpose for the equalizer is that it can provide the desired flat treble response to the
Packburn even if you have a pre-amplifier that only avails the RIAA high frequency rolloff
curve. The equalizer should be set as follows:
1kHz (0 dB), 2 kHz (+2.6 dB), 3 kHz (+4.8 dB), 5 kHz (+8.2 dB), 6 kHz (+9.6 dB), 7kHz (+10.8 dB),
8 kHz (+11.9 dB), 9 kHz (+12.9 dB), 10 kHz (+13.6 dB), 11 kHz (+15.3 dB), 12 kHz (+17.1 dB)
(Tremaine, Audio Cyclopedia, Howard W. Sams, Indianapolis, p. 668.)
This equalizer may also be used to compensate tapes or discs having frequency imbalance
between the two channels, or insufficient high frequencies.
25
C. Phase Monitoring Oscilloscope
The cathode ray oscilloscope is a valuable tool for accurately aligning a stereo system used to
play back monophonic records or stereo tapes of monophonic records into the Audio Noise
Suppressor.
Setting the Phase Monitor Oscilloscope:
1.
Adjust the input signals to the Audio Noise Suppressor for approximately
equal levels.
2.
Connect the vertical and horizontal amplifier inputs of the oscilloscope to the L
input of the Audio Noise Suppressor.
3.
While playing the record, adjust the controls of the oscilloscope until the
display (the vector sum is about 45 degrees from the vertical.
4.
Now, connect the horizontal and vertical amplifier inputs to L and R inputs two
audition the vector differences between the two input signals.
For a monaural disc or tape played with a stereo pick-up, the program component will lie on
the 45 degree incline whereas transient noise is a “difference component” and so appears as
vectorial bursts at other than the 45 degree incline. It is these bursts that can be suppressed
by the Switcher. The Blanker can suppress star bursts in all directions.
Mistracking of a record will cause the oscilloscope to display an ellipse rather than a straight
line.
A relative mistracking is when the signal strengths of the two channels do not
consistently match. This type of mistracking will cause the line to vary from the 45 degree
angle.
A frequency response mismatch will display as an ellipse usually at certain audio
frequencies. Matching the two channels of your pre-amplifier or equalizer is similar to the
procedure outlined above except that the treble, bass and frequency band controls are
adjusted until the oscilloscope displays the straight line. A series of tones may be used as
the signal source. For each tone, the pre-amplifier or equalizer is adjusted so the signal is
displayed along the 45 degree line.
26
Alignment of a tape recorder playback head is most accurately accomplished by prerecording simultaneously in both channels a series of oscillator tones starting at the low
frequency end of the audio spectrum.
27
Trouble - Shooting Procedures
1.
There is no output signal. POWER is 1 (on), and ANS is 1 (engaged.)
Make sure the cables are not crisscrossed, i.e., the one that feeds signal to the Packburn
has been connected to the L and R input receptacles and the one that feeds signal from
the Packburn has been connected to the output receptacles of the Packburn.
2.
The Switcher is not reducing noise at all. The Audio Noise Suppressor is being fed
signal from a noisy monophonic record through a stereo pre-amplifier with proper
equalization. The Switcher controls have been properly adjusted including the test
switch.
Set the MODE switch to VER. If there is a reduction in both the signal component and
transient noise component, the incoming signals are in fact monaural. The record itself
might be a 78 rpm dubbing in which the ticks are equally combined in both channels. Try a
different record. If this doesn’t work, check your equipment. The phonograph cartridge
might be monaural. Check its terminals. The cartridge could be stereophonic but operating
in monaural due to a shorting wire between two of its terminals. Follow manufacturer
instructions for converting the cartridge to stereo.
3.
There is a dull output signal when MODE is MON. The L and R Switcher lights
never light.
This probably indicates that there is a bad connection, perhaps a bad cable, in the circuit
ahead of the Audio Noise Suppressor and/ or an extremely out-of-balance signal level.
This should be indicated by little or no signal in one of the VU meters. The dull sound is
due to the low frequency components in the lone signal feeding into the Packburn being
fed into the disconnected channel through the low frequency mixing circuit. The Switcher
then chooses that signal for playback. Solid, non-intermittent connections are important
especially for proper operation of the Switcher.
28
4.
There is no setting of the BALANCE control that produces a good null. The MODE
switch is in VER and a monophonic record is being played. The equalization
curves of the two input signals being provided to the Audio Noise Suppressor are
matched.
The Audio Noise Suppressor is provided with professional balanced XLR input sockets. If
the RCA connectors are being used, it is good practice to ground the unused inputs (pin 2
of each of the XLR input sockets.)
5.
The noise worsens when the SWITCHER RATE control is turned up (clockwise
rotation.)
Make sure that the TEST switch is ‘0’ (off.) The Switcher will then be choosing the quieter
instead of the noisier of the two input signals for playback.
6.
The Switcher is distorting the sound when the signal source is a stereo tape recording
made from a monophonic record.
Check the azimuth alignment of the playback head with reference to the tape that you are
playing by using the VER position of the MODE switch or a phase monitor oscilloscope.
See pp. 18, 26.
7.
The Switcher and Blanker are not operating. The pre-amplifier to the Audio Noise
Suppressor has the correct equalization per instructions, and the INPUT LEVEL
control has been properly adjusted.
The TNS switch could be in the ‘0’ position, de-activating the Transient Noise Suppressor
(i.e. Switcher and Blanker.)
29
8.
There is not much Frequency Meter action even though the CNS switch is ‘1’ (on) and
CNS RATE is fully clockwise.
This could be an indication that the record is especially hissy, or that the high frequency
levels in the signal to the Audio Noise Suppressor have been unduly exaggerated.
This
could happen, for example, if your pre-amplifier has a flat treble characteristic and you
have had the PACKBURN factory set for RIAA cancellation.
This factory setting is
intended for use with a pre-amplifier having an RIAA treble rolloff characteristic.
The following test determines whether the factory setting has been activated: Set the
ROLLOFF switch to 0, the CNS switch to ‘0’, and use the ANS switch to find a brighter
sound when it is in the ‘1’ position.
9.
The sound is garbled when playing a stereo record or CD, especially during loud
passages. The level readings are proper.
Make sure the MODE switch is in ST. If the MODE switch is in MON or VER, the Switcher
can chop up the music as it tries to play the instantaneously quieter of the two stereo input
signals.
10.
None of the above applies.
Before contacting us, we recommend having certain information on hand, preferably taking
down a few notes while observing the problem. Here are some questions we will ask you:

What problem is being experienced?

What are the control and switch settings on the Audio Noise Suppressor (described
in terms of clock setting)?

Is the problem in just one output channel? If so, which channel (L or R) is it in?

If you swap the input conductors, does the problem follow the conductor (in which
case the problem is very likely to be ahead of the Audio Noise Suppressor.)

If you try varying each of the controls, are there any that have an effect on the
problem?

What is the serial number of the machine?
30
Equalization Settings
Traditionally, the inherent equalization curves used for cutting electrical recordings have
been specified in terms of a “bass-turnover frequency” and “treble pre-emphasis.” It is
intended that the playback equalization curve be the inverse of the equalization curve used
during manufacture of the record.
The Packburn rolloff and turnover controls perform as intended only if the pre-amplifier
ahead of the Packburn is properly set. See Installation Instructions, p. 5.
A. Turnover
Bass-turnover is the attenuation of low frequencies during record manufacturing in order to
limit groove modulation. Bass limiting was introduced with early playback equipment in
mind to maintain satisfactory groove tracking and to reduce record wear. Most of the
published recording curves for 78 rpm records indicate that the bass attenuation (or
"constant amplitude") portion of the curves had a 6 dB/ octave slope.
The playback
equipment was designed to accentuate the frequencies below the turnover setting to
restore the bass signal. TURNOVER settings are the frequencies in Hz where the bass is
boosted 3 dB.
B. Treble Pre-emphasis/ Rolloff
Treble pre-emphasis is the accentuation of high frequencies during record manufacturing.
During playback, the high frequencies are “rolled off” to restore the treble characteristic
whereas high frequency noise becomes attenuated. Treble pre-emphasis appears to have
been first used for reducing noise in broadcast transcriptions. It was eventually applied to
78 rpm records and to all long playing records. The historical drawback was that millions
of record players were in service by then having a permanent flat treble characteristic that
caused the later recordings to sound shrill.
The rolloff slope is 6 dB/ octave except for the 8.5 dB setting where the slope is 2.5 dB/
octave. Rolloff settings are the attenuations (in Decibels) occurring at 10 kHz.
31
C. Equalization Curves by Name
Name
Turnover (Hz)
Published
Setting
Rolloff (dB)
Nearest Packburn
Setting
Published
Setting
Nearest Packburn
Setting
AES
400
400
12
12
FFRR (1949)
250
250
5
6
FFRR (1951)
300
300
14
14
FFRR (1953)
450
500
11
12
500 (LP)
LP
16
16
NAB
500
500
16
16
Orthophonic (RCA)
500
500
11 (8.5)
12 (8.5)
629
629
700
RIAA
500
500
13.7
14
LP/ COL
Some of these published curves additionally include a low frequency "shelf" below which
the attenuation in the recording process is leveled off.
The benefit is that the
corresponding leveling in the playback equalization curves reduces turntable rumble. The
Columbia LP shelf is 100 Hz whereas the RCA Orthocoustic, RCA Orthophonic and RIAA
shelves are 50 Hz.
D. Records Made After 1955
Set TURNOVER to 500 Hz and ROLLOFF to 14 dB.
In 1953 the recording industry standardized on the RIAA playback curve.
E. Records Made Before 1925
Set TURNOVER to 0 Hz or as needed, and ROLLOFF to 0 dB or as needed.
Some maintain that acoustic discs and cylinders should be played back “flat” since
electrical manipulation of the recording characteristic was unknown in the era of acoustical
recording. When played in this manner there is almost non-existent bass due to the
inherent mechanical equalization of the primitive recording process. Others want to hear
more bass. Using a 250 Hz turnover does not exactly reverse the mechanical equalization
32
but may offer a better starting place. Some use a rolloff of 5 dB to reduce surface noise.
F. Records Made Between 1925 and 1955
Set the TURNOVER and ROLLOFF per the following tables.
The need for equalization curves for playback of electrical records has never been
controversial but there is still some disagreement as to what curve should be used on
what company’s records made at what time. In addition, the equalization curves may be
one among several factors that transformed the bass and treble response during the
recording process. For reasons such as these, the equalization tables should be treated
as a good starting place. The trained ear might be the best final judge.
33
Records Made Between 1925 and 1955
TURNOVER (T) and ROLLOFF (R) Settings
78 ↓
T
78 ↓
T
R
78 ↓
T
R
Banner Perfect
Inconclusive
Odeon (early)
(pre 1947)
300
300
0
8.5
Vitaphone
(motion picture)
300
950
0
18.5
Blue Bird
800
10
Mercury
400
12
Brunswick (rare)
(early)
(1946-)
1000
500
300
8.5
0
16
MGM
500
12
Cameo Pathe
Inconclusive
Montilla
500
12
Capitol
400
12
Musicraft
700
14
Columbia (1926-)
(1938-)
(European)
250
300
300
5
16
5
Oriole Romeo
Incon
Coral
400
750
12
16
OKEH
300
8.5
Decca (early)
(1934-)
(ffrr)
150
400
250
0
12
5
Parlophone
(pre 1947)
300
500
0
8.5
Deutsche
Grammophon
300
5
Polydor
300
8.5
Disc
300
16
Radiofunken
400
0
Diva
300
16
RCA Victor
See Victor
Edison
0
0
Schirmer
1000
24
Electrola
800
10
Supraphone
400
0
Good Times
Jazz
400
12
Telefunken
400
0
Gramophone
300
10
Transcriptions
Vertical
500
300
16
14 **
Harmony
300
16
Ultraphon
400
0
Hit of the W eek
500
5
Vanguard
500
16
HMV (1925-)
(1946)
(1946-)
250
400
800
0
10
16
Victor (1925-)
(1938-)
(1947-52)
300
500
500
500
0
0
8.5
12
King
500
16
Vocalion
300
0
Linguaphone
300
0
Vox
500
16
London ffrr
250
5
W estminster
750
16
Majestic
500
16
Velvet Tone
300
16
R
** Vertical transcriptions have a 12 dB/ octave rolloff. Use the 14dB setting and apply the
following corrections using a third octave equalizer: 5 kHz (+2 dB), 6.2 kHz (+1 dB), 8
kHz (-1 dB), 10 kHz (-4 dB), 12.5 kHz (-6 dB), 16 kHz (-8 dB), and 20 kHz (-12 dB.)
Reference:
34
45 ↓
T
R
33 ↓
T
R
33 ↓
T
R
Columbia
500
16
Colosseum
400
LP
12
16
Oxford
750
16
Decca
750
16
Columbia
LP
16
Odeon
300
8.5
Mercury
400
12
Concert Hall
400
LP
LP
12
16
8.5
Parlophone
300
8.5
MGM
500
12
Cook
500
12
Period
500
16
RCA Victor
800
10
Philharmonia
400
12
33 ↓
Coral
400
12
Polydor
300
8.5
Decca
12
16
14
14
Polymusic
500
16
(FFRR ’51)
(FFRR ’53)
400
LP
300
450
Dial
750
16
Rachmaninoff
750
16
Electra
630
16
RCA
500
500
500
10.5
12
14
1948
1949
1953
Allegro
750
16
EMS
400
12
Remington
500
16
Allied
500
16
Epic
750
16
Renaissance
750
12
American Record
Society
500
12
Esoteric
500
400
12
12
Stradivari
750
16
Angel
500
12
Festival
750
16
Telefunken
400
0
Arizona
400
12
Folkways
630
16
Ultraphone
400
0
Atlantic
500
16
Good Time Jazz
400
12
Urania (Most)
(New)
LP
400
16
12
Audio Fidelity
500
16
Handel Society
750
16
Vanguard
LP
16
Bach Guild
750
16
Haydn Society
750
16
Vitaphone
300
0
Banner
750
16
HMV
800
10
W estminster
500
400
16
12
Bartok
630
16
London
750
10
Boston
630
16
Lyrichord
16
16
16
Transcriptions
(new)
LP
400
630
Blue Note Jazz
400
12
Mercury
400
12
BBC
300
0 or 5
Caedmon
630
11
MGM
500
12
Orthacoustic
500
16
Capitol
400
12
Montilla
500
12
RCA Program
700
500
0
0
Canyon
400
12
New Records
750
16
Pre WW II
500
0
Cetra-Soria
400
500
12
16
Oceanic
LP
16
Vertical
New
300
16
Okeh
300
8.5
Vertical
Old
300
5
35
Input/ Output Schematic and Block Diagram
For models 323 AA, 325
electronics inc.
P.O. Box 226, Syracuse, NY 13215 USA
Ph. 315-476-9121
36
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