Orban 464A User manual

Operating Manual
The Co-Operator
Gated Leveler/Compressor/High-Frequency Limiter/Peak Clipper
Model 464A

IMPORTANT NOTE: Refer to the unit’s rear panel for your Model Number.
Model Number: Description:
464A/U
464A/E CO-OPERATOR Level Control System, 2ch 115V CO-OPERATOR Level Control System, 2ch 230V
OPTIONS:
Model Number: Description:
SCI Security Cover (CLEAR, BLUE, or WHITE)
CAUTION: TO REDUCE THE RISK OF ELECTRICAL SHOCK, DO NOT REMOVE COVER {OR BACK).
NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
WARNING lTO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK, DO NOT EXPOSE THIS
APPLIANCE TO RAIN OR MOISTURE.
This symbol, wherever it appears,
alerts you to the presence of uninsulated
dangerous voltage inside the enclosure —voltage
that may be sufficient to constitute arisk of shock.
This symbol, wherever it appears,
alerts you to important operating and
maintenance instructions in the accompanying
literature. Read the manual.

Operating Manual
The Co-Operator
Gated Leveler/Compressor/High-Frequency Umiter/Peak Clipper
Model 464A

Co-Operator is atrademark and Orban is aregistered trademark of AKG Acoustics, Inc.
Dolby is aregistered trademark of Dolby Laboratories, Inc.
This Orban product has been manufactured by AKG Acoustics, Inc.
This manual is part number 95059-000-03
300 -FB -1/93
©Copyright 1993 by AKG Acoustics, Inc.
1525 Alvarado Street, San Leandro, CA 94577 USA
Telephone [phone]
Fax [phone]
orban
adivision of AKG Acoustics, Inc.

Orban 464A
The Co-Operator
Operating Manual
page contents
1-
iSection 1: Introduction
Orban's Co-Operator
Applications
Registration, Warranty, Feedback
2
-
1Section 2: Installation
Installation and Set-up
Level-matching
3-
1Section 3: Operation
Controls and Meters
Recommended Control Settings
More About Co-Operator Audio Processing
4
-
1Section 4: Maintenance
Routine Maintenance
Getting Inside the Chassis
Performance Evaluation
5-
iSection 5: Troubleshooting
Problems and Possible Causes
Technical Support, Factory Service
6-
iSection 6: Technical Data
Specifications
Circuit Description
Parts List, Schematics, Assembly Drawings
Abbreviations
INDEX on next page

index
abbreviations 6-26
accessories 2-13, 6-2
applications 1-4
assembly drawings 6-20
audible distortion 3-8, 5-3
audio
connections 2-5
input 2-5
output 2-5
tape recorder 3-4, 3-1
0
audio/video production 1-4
automatic gain control (AGC) 3-8
average modulation, increasing 2-10
balanced inputs 2-7
balanced output transformer 2-7,8
bargraph driver 6-9, 6-12
bi-amped systems 1-4, 3-7
block diagram 6-21
buzzes 5-2
cable shielding 2-5, 2-7
cassette duplication 1-4, 3-6
chassis, getting inside 4-2
chassis ground 2-7
circuit boards
access to 4-2
front panel 4-2
circuit description 6-4
circuit ground 2-7
clicks 5-2
clipper-defeat jumper 2-2, 2-9
clipping 2-10, 3-10
bias 2-10,3-4,5-3,6-10
increasing 2-1 0, 5-3
level calibration 2-1
1
transient 3-8
common-mode rejection 2-7
component
numbering system 6-4
vendors 6-19
compression 3-8, 6-8
connectors, audio 2-5
constant-directivity horns 1-4
controls 3-2
control settings 3-4
BetaCam/MII VCR 3-5
broadcast cart machine 3-5
broadcast transmission 2-12,3-4
cassette duplication 3-6
FM subcarriers 2-12, 3-6
Quad VTR 3-5
satellite uplink 3-5
sound system protection 3-7
STL protection 2-12, 3-4
type BVTR 3-5
type CVTR 3-5
U-Matic VCR 3-6
covers, removing/replacing 4-2
customer service 5-3
dBu (definition) 4-5, 6-26
de-essing 3-9
distortion 3-8, 5-3, 6-6
dual mode 3-10
factory service 5-4
FM subcarrier generators 1-5
protection 2-9
front panel 1-2, 3-2
fuse 2-4, 6-2
gain reduction 3-8
meter 3-8, 6-8
gating 3-8, 5-2, 6-8
control circuits 4-3
grounding 2-6,7, 5-2
difficult situations 2-8
ground loop 2-7,8
harshness 5-2
high-frequency
limiter 3-9,4-3,6-10
pre-emphasis 3-9
saturation 1-4
high-SPL environments 1-4
hum 5-2
impedance 2-5
input
attenuator 3-8, 6-5
balanced 2-7
buffer 6-5
impedance 2-5
level 2-5, 6-8
stages 4-3
overload point 2-5
unbalanced 2-8
installation 2-1
FM broadcast 2-9
jumpers
access to 4-2
positions 2-3
leveling 3-8, 6-8
loudness 3-4, 3-8
maintenance, routine 4-2
meters 3-2, 4-3, 6-8, 6-1
1
calibration 2-10, 2-14, 6-11
red zone 3-8
nastinesses, various 3-8
noise rush-up, pumping 3-8, 5-2
options 2-13, 6-2
ordering parts 6-13
output
impedance 2-5
level 2-5
matching to toad 2-1
4
stages 4-3
unbalanced toad 2-5
overheating, thermal failure 1-4
overshoot 5-2
packing for shipment 5-4
parts list 6-13
peak
clippers 5-2
control 5-2, 6-10
level 3-8
overload point of toad 2-15
analog tape recorders 2-15
audio power amplifiers 2-15
USA-standard phone lines 2-15
output level meter 6-1
1
calibration 2-10, 2-14
performance evaluation 4-3
phone jacks 2-5
physical dimensions 6-2
power
cord 2-4
requirements 6-2
supplies 4-3, 5-2, 6-12
pre-emphasis 3-9,10,5-2,6-10
jumper 2-2, 2-9
LF/HF drivers 3-10
problems 5-2
product features 1-3
rack-mounting unit 2-4
rear panel 1-2
recording studios 1-4
registration card 1-6
regulated voltage 6-1
2
regulator dropout 6-12
release shape 3-8,9, 6-8
release time 3-8, 6-8
retrofit kit 6-2
return authorization 5-4
RF suppression 5-2, 6-5
ringing 5-2
SCA channels 1-5
schematics 6-20
security cover 2-13, 6-2
service 5-4
shipping
damage 2-2
instructions 5-4
shrillness 5-2
sound systems 1-4, 3-7
specifications 6-2
stereo mode 3-10
STL protection 1-5, 2-9
swept sine wave tests 3-10, 6-1
0
tape 3-1
0
technical support 5-3
thumps 6-6
tilt 5-2
timing module 6-8
transmitter
pre-emphasis 2-9
protection 2-9
troubleshooting 5-1
unbalanced input 2-8
unbalanced load 2-5
unregulated voltage 6-12
user feedback 1-6
VCAs 4-3, 6-6
voltage regulators 5-2, 6-12
warranty 1-6
XLR connectors 2-5

page contents
1-3 The Orban Co-Operator
1-2 Fig. 1-1: Front and Rear Panels
i-4 Applications
i-6 Registration, Warranty, Feedback

in
CAUTION
OltCttON AOAit
1TMf JAMf IYMvA
Orban
Model
464A

Co-Operator INTRODUCTION 1-3
The Orban Co-Operator
The Orban Model 464A Co-Operator™ Leveler/Compressor/HF Limiter is an inte-
grated automatic gain control (AGC) device of the highest professional quality. The
Co-Operator is afriendly, automatic “assistant operator” that smoothly and unobtru-
sively rides gain, controls high-frequency levels, and limits peaks.
The Co-Operator achieves its outstandingly transparent audio performance through
the use of finely-tuned control loops which eliminate the dynamic distortions that are
the downfall of most conventional compressors and limiters, and through the use of
aclean, class-Aproprietary VCAto ensure negligible static distortion and noise.
•Asmooth leveler function provides transparent gain riding —without long-
term distortion-producing overshoots.
•Afaster “compression” function can be switched in to provide additional
transient overshoot protection for material with abrupt level changes or un-
usually high peak-to-average ratios. The compression function is available
without leveling for applications that require safety limiting only.
•Release time and release shape are adjustable to optimize processing for
music or voice.
•Adefeatable “silence gate” prevents noise rush-up, holes, pumping, and
breathing by inhibiting sudden gain increases once the signal level falls below
apreset threshold (during pauses or low-level program material).
•Six switchable HF limiter pre-emphasis/de-emphasis curves (25 to 150|is)
allow the HF limiting to react optimally for the medium or device being
protected and guard against excessive sibilance.
•Adefeatable clipper follows the HF limiter for absolute peak protection.
•Either stereo-tracking or independent two-channel operation can be selected.
•The least-used controls are concealed behind asecurity panel to avoid con-
fusing non-technical operators, and to permit tamper-proof calibration.
•Two LED bargraphs per channel simultaneously display gain reduction and
peak output levels.
•Output level meter can be calibrated to match the overload point of the device
being drivea
•Balanced, floating inputs and outputs are EMI-suppressed; the Co-Operator
is compatible with the levels and impedances found in both professional and
semi-professional applications.
•25dB gain reduction range is achieved with alow-distortion, class-A VCA.
•Two channels packaged in aspace-saving, rugged, all-metal, 1%-inch chassis.
•Hard-wired bypass switch is included.
\

INTRODUCTION Orban Model 464A
Applications
The flexibility and natural sound of the Co-Operator are ideally suited to recording
studio, sound reinforcement, broadcast, motion picture, and video sound applications.
The defeatable high-frequency limiter can be used to prevent pre-emphasized mate-
rial from overloading tape recorders, disk cutters, high-frequency drivers in sound
systems, broadcast STLs (studio-transmitter links), FM SCAs (“subsidiary commu-
nications authorization”), and for controlling cassette masters which have excessive
high-frequency energy. Controlling high-frequency energy permits average recording
or transmission levels to be increased, yielding improved signal-to-noise ratios.
Recording Studios
With the RELEASE SHAPE control set to SOFT, the Co-Operator will subtly reduce the
dynamic range of an entire mix. The HARD setting provides effective gain riding on
single tracks, increasing “punch” and intelligibility while retaining the basic feel of
the performance and the apparent dynamic range of the voice or instrument. The
RELEASE TIME control is useful in governing the uniformity of loudness in the final
result.
Audio and Video Production
The Co-Operator can be used to protect VTRs, ATRs, or cart machines from overload
during transfer. On mic channels the Co-Operator’s smoothness and silence-gating
guarantee uniform, punchy voice quality without noise rush-up during pauses.
Cassette Duplication
Even with the latest advancements, such as “hot” tape and Dolby® HX Pro, there
are still some masters which can cause high-frequency saturation in cassette dupes.
The Co-Operator’s high-frequency limiter can be set to eliminate problems caused by
synthesizers, cymbals, and sibilance, while still permitting high average modulation
on the cassette. The broadband AGCAeveler can be defeated to permit use of the HF
limiter alone when automatic gain riding or broadband peak protection is not desired.
Sound Systems
The Co-Operator provides colorless protection for your system —whether it be a
fixed installation or traveling PA. For example, in an unattended bi-amped system,
the slow AGC leveler can efficiently ride gain while the faster compressor protects
the system from abrupt increases in level.
Placed after the mixer and equalizer and before an active two-way crossover, the
Co-Operator will protect power amps from excessive clipping and high-frequency
drivers from thermal overload.
Especially with constant-directivity horns, the selectable pre-emphasis of the HF
Limiter can protect the horn from the boost that is required to compensate for the
constant-power high-end roll-off. When horns and drivers are located 75 feet in the

Co-Operator INTRODUCTION 1-5
air, this becomes critically important. The Co-Operator guards against overheating
and subsequent thermal failure.
In an attended bi-amped system, the Co-Operator can be placed after an electronic
crossover. The two channels of the unit are arranged to separately feed the power
amps for LF and HF drivers. In this application the leveler is defeated (so it does not
fight with the mixing engineer), leaving the compressor, high-frequency limiter, and
peak clipper to guard the system from overload. In particularly high-SPL environ-
ments, the compressor may be uncoupled so that each channel of the Co-Operator can
operate independently to deliver the maximum level to each driver without distortion.
Similarly, the Co-Operator’s controlled clipping avoids clipping of the power ampli-
fier, which can cause “sticking”, instability, and other audible problems.
Broadcast Studio/Transmitter Link Protection
The STL is often the weak link in the broadcast chain due to barely adequate signal-
to-noise ratio. Clean protective limiting ahead of the pre-emphasized STL transmitter
helps maximize the signal-to-noise ratio at the receiver and prevents overload. The
selectable pre-emphasis ensures matching of the high-frequency limiting function to
the STL’s overload characteristic.
FM Subcarriers
Voice or music SCA channels are typically pre-emphasized at 150ns. In addition to
providing transparent gain riding and level control for the subcarrier, the Co-Operator
can also provide the rarely found 150ns HF limiting function, which permits more
efficient use of the SCA channel by eliminating overmodulation on HF peaks.
See Section 3for specific information on setting the controls for your application.

1-6 INTRODUCTION Orban Model 464A
Registration, Warranty, Feedback
Registration Card
There are two good reasons for returning the Registration Card shipped with this
product:
1) It enables us to inform you of new applications, performance improvements, and
service aids which may be developed, and
2) It helps us respond promptly to claims under warranty without having to request
acopy of your bill of sale or other proof of purchase.
Please fill in the Registration Card and send it to us today. If it is lost (or you have
purchased this unit used), please photocopy the duplicate below, fill it in, and send
it to Orban at the address on the inside of the front cover.
Registration Card
Model #Serial# Purchase Date
Your name Title
CompanvTelephone
Street
City, State, Mail Code (Zip), Country
Nature of your product application
How did you hear about this product? Purchased from
Comments
Which magazines do you find the most useful to your job?
dB Magazine
Mix
Radio World
TV Broadcast
95101 -000-07 1/91
Audio
Electronic Musician
Post
RE/P
TVTech
Broadcast Engineering
EQ
Pro Sound News
Sound &Communications
Broadcast
Millimeter
Radio &Records
S&VC
Warranty
The warranty, which can be enjoyed only by the first end-user of record, is stated
on the separate Warranty Certificate packed with this manual. Save it for future
reference. Details on obtaining factory service are provided on page 5-4.
User Feedback Form
We are very interested in your comments about this product Your suggestions for
improvements to either the product or the manual will be carefully reviewed. A
postpaid User Feedback Form is provided in the back of this manual for your con-
venience. If it is missing, please write us at the address on the inside of the front
cover. Thank you.

page contents
2-2
2-3
2-5
2-5
2-7
2-6
2-9
2-14
Installation —Most Applications
Fig. 2-1 :Pre-Emphasis and Clipper Defeat Jumpers
Fig. 2-2: AC Power Cord Color Code
Audio Wiring, Connectors, Levels
Grounding: Power, Audio, Difficult Situations
Fig. 2-3: Some Possible Grounding Schemes
Installation —FM Transmitter, STL, Subcarrier
Generator Protection
Matching Output Level to Device Being Driven

2-2 INSTALLATION Orban Model 464A
Installation —Most Applications
Allow about 20 minutes for installation.
If you will be using the Co-Operator to protect an FM transmitter, STL, or subcar-
rier generator use the “Installation —FM Transmitter, STL, Subcarrier Generator
Protection” instructions on page 2-9.
Installation consists of unpacking and inspecting the Co-Operator, optional resetting
of clipper-defeat and pre-emphasis jumpers, mounting the Co-Operator in arack, then
connecting audio and power.
1) Unpack and inspect.
If obvious physical damage is noted, contact the carrier immediately to make a
damage claim.
If you should ever have to ship the Co-Operator (e.g., for servicing), it is best to
ship it in the original packing materials since these have been carefully designed
to protect the unit. Therefore, make amental note of how the unit is packed and
save all packing materials.
Packed with the Co-Operator are:
1Warranty Certificate
1Registration Card
1Operating Manual
2) Reposition clipper-defeat and pre-emphasis jumpers.
(optional)
Alist of recommended jumper positions for various applications begins on page
3-4.
If you want to reposition these jumpers, you will need to remove the top cover
of the Co-Operator to access the main circuit board. Remove all screws holding
the cover in place, then lift it off. When replacing the cover, replace all screws
snugly. (Be careful not to strip the threads by fastening the screws too tightly.)
a) If you want to enable the peak clippers, reposition jumper Aon the main circuit
board to the “OPERATE” position (see Fig. 2-1).
The Co-Operator is shipped with this jumper in the “DEFEAT’ position.
In general, the clippers should only be activated if the device being
driven has an absolute peak overload point (a broadcast transmitter, for
example). The HF LIMIT buttons must be set to OPERATE for the peak
clippers to be active.
b) If you want apre-emphasized output, reposition jumpers Band Con the main
circuit board to the “PRE-EMPHASIZED” position (see Fig. 2-1).
The HF LIMIT PRE-EMPHASIS switches determine the pre-emphasis
curve that will be used.

Co-Operator INSTALLATION 2-3
Fig. 2-1: Pre-Emphasis and Clipper Defeat Jumpers

2-4 INSTALLATION Orban Model 464A
3) Mount the Co-Operator in arack.
The Co-Operator requires one standard rack unit (1 3Ainches, 4.4 cm).
There should be agood ground connection between the rack and the Co-Operator
chassis —check this with an ohmmeter.
Mounting the unit directly over large heat-producing devices (such as avacuum-
tube power amplifier) may shorten component life and is not recommended. Am-
bient temperature should not exceed 113°F (45°C) when equipment is powered.
4) Connect audio input and output.
See the hook-up and grounding information on the following pages.
5) Check the line voltage, fuse and power cord.
The Co-Operator is shipped ready for 115-volt, 50/60Hz operation —unless a
label on the power cord indicates otherwise.
aQ DO NOT connectpower to the unit yet!
bQ Check the value of the fuse and change the fuse if the value is incorrect.
For safety, the fuse must be 3AG 250V Slow-Blow, V2-amp for 115V,
or 250mA “T’-type for 230V.
oQ Connect power cord.
AC power passes through an IEC-standard mains connector and an RF
filter designed to meet the standards of all international safety authori-
ties.
The power cord is terminated in a“U-Ground” plug (USA standard), or
CEE7/7 plug (Continental Europe), as appropriate to your unit’s Model
Number. The green (or green/yellow) wire is connected directly to the
Co-Operator chassis.
If you need to change the plug to meet your country’s standard and you
are qualified to do so, see Fig 2-2 on page 2-6. Otherwise, purchase a
new mains cord with the correct plug attached.
WARNING
If the ground is defeated, certain fault conditions in the unit or in the
system to which it is connected can result in full line voltage between
chassis and earth ground. Severe injury or death can then result if the
chassis and earth ground are touched simultaneously.
6)
Complete the Registration Card and return it to Orban
(please).
The Registration Card enables us to inform you of new applications, performance
improvements, and service aids which may be developed, and it helps us respond
promptly to claims under warranty without having to request acopy of your bill
of sale or other proof of purchase. Please fill in the Registration Card and send it
to us today.

Co-Operator INSTALLATION f-
Audio Input and Output Connections
Wire:
We recommend using two-conductor shielded cable (such as Belden 8451 or
equivalent), because signal current flows through the two conductors only. The
shield does not carry signal, is used only for shielding, and is ordinarily connected
to ground at one end only.
Because use of single-conductor cables virtually eliminates any possi-
bility of carefully controlling the system grounding scheme, it is NOT
RECOMMENDED! Even so, it often does work adequately.
Sometimes, particularly if you are using the Co-Operator with musical in-
struments or home-type equipment, single-conductor shielded cable may
be the only practical alternative. In this case, connect the inner conduc-
tors of the shielded cables to the HI sides of the Co-Operator inputs and
outputs. Connect the shield of the Co-Operator input cable to the LO
input, and connect the shield of the Co-Operator output cable to the Co-
Operator’s IX) output terminal on the rear-panel barrier strip. Connect
both IN LO and OUT LO terminals to ^.
Connectors:
•Input and output connectors are either barrier strip terminals (with #5
screw), ‘A-inch tip/ring/sleeve phone jacks, or XLR-type jacks.
Levels:
•Nominal input level is between -10 and +8dBu. The absolute overload
point is +20dBu. (OdBu =0.775V RMS; for this application, the dBm @
60012 scale on voltmeters can be read as if were calibrated in dBu.)
•The electronically-balanced input of each channel is compatible with most
professional and semi-professional sound equipment, balanced or unbalanced,
with asource impedance of 600 ohms or less. If the source impedance is
greater (as in some vacuum-tube audiophile preamps), remove capacitors
C102 (left channel) and C302 (right channel), and connect the hot side of the
driving equipment’s outputs to the Co-Operator’s HI inputs.
•The two electronically-balanced and floating outputs of each channel sim-
ulate atrue transformer output. The source impedance is 30 ohms (93 ohms
for units with serial numbers below 1306000 —see note on page 2-14). In
addition, there is alOOOpF capacitor between each output (HI and LO) to the
chassis for RFI suppression. The output is capable of driving loads of 600
ohms or higher.
•If an unbalanced output is required (to drive imbalanced inputs of other
equipment), it should be taken between the HI and LO outputs. No special
precautions are required even though one side of the output is grounded.
Connect the LO output terminal to ^.

2-6 INSTALLATION Orban Model 464A
CONDUCTOR WIRE COLOR
Normal Alt
LLINE BROWN BLACK
NNEUTRAL BLUE WHITE
EEARTH GND GREEN-YELLOW GREEN
Fig. 2-2: AC Power Cord Color Coding
Iout! r~iNout! Hn i
.OUT1
(UNBALANCED)
DRIVING EQUIPMENT
I
nIN OUT1
(UNBALANCED) I
—HI (+) (+) HI —»—
|ORBAN I
UNIT I
-»~LO(-) (“)LO —»—
I-i o--. *I
/~h M1rfrJ
CHASSIS GROUND j(RACK OR POWER LINE)
*lf Orban unit is equipped with optional output transformer, then install this jumper.
Fig. 2-3: Some Possible Grounding Schemes

Co-Operator INSTALLATION
Grounding
Very often, grounding is approached in a“hit or miss” manner. But with care it is
possible to wire an audio studio so that it is free from ground loops (which induce
hum and can cause oscillation) and provides maximum protection from power faults.
•All units in the system must have balanced inputs. In amodem system with
low output impedances and high input impedances, abalanced input will
provide common-mode rejection and prevent ground loops —regardless of
whether is driven from abalanced or unbalanced source. (The Co-Operator
has balanced inputs.)
•All equipment circuit grounds must be connected to each other, all equipment
chassis grounds must be connected together.
•Cable shields must be connected at one end only —preferably the source
(output) end.
Power:
•Ground the Co-Operator chassis through the third wire in the power cord.
Proper grounding techniques never leave equipment chassis unconnected to
power/earth ground. Aproper power ground is essential to safe operation.
Lifting achassis from power ground is asafety hazard. If there is apower
fault to the chassis, death could result!
Circuit:
To maintain the same potential in all equipment, the circuit (audio) grounds must be
connected together:
•In asimple one-studio system, the connection through power ground (via
the power cord’s third wire) will suffice, Connect the Co-Operator’s circuit
ground (^)terminal to its chassis ground )terminal. Also connect the
circuit and chassis grounds of other equipment.
•In larger systems, it is common to establish an isolated circuit ground system
that is insulated from the power ground except at one point (usually the studio
power distribution panel). In this case, disconnect the Co-Operator’s circuit
ground (^)terminal from its chassis ground )terminal, then connect
the Co-Operator’s circuit ground (^)terminal to the isolated circuit ground
system.
Audio Output:
•Use two-conductor shielded cable (Belden 8451, or equivalent).
•At the Co-Operator’s output (and at the output of other equipment in the
system), connect the cable’s shield to the ^terminal for that channel.
Connect the red (or white) wire to the channel’s HI terminal, and the black
wire to the channel’s LO terminal.
•To interface units with unbalanced inputs in aprofessional system, install
abalancing transformer (Jensen JE- 11 P-1, or equivalent) to prevent ground
loops.

2-8 INSTALLATION Orban Model 464A
Grounding (continued)
Audio Input:
•Input connections are the same whether the the driving source is balanced or
imbalanced.
•Do not connect the cable shield —it should be connected at the source end
only. Connect the red (or white) wire to the appropriate minput terminal,
and the black wire to the corresponding LO input terminal.
•If the output of another unit is unbalanced and does not have separate ^
and LO (or -) output terminals, connect both the shield and the black wire
to the common (-) or ground terminal. It is rarely necessary to balance an
imbalanced output with atransformer. As long as it is feeding abalanced
input, the system will work correctly.
(The only situation where the addition of an input transformer is war-
ranted is one in which the source equipment is powered from aseparate
mains transformer and power ground. Terminate the transformer’s sec-
ondary with a20K resistor.)
Difficult Situations:
Because it is not always possible to determine if the equipment driving or being
driven by the Co-Operator has its circuit ground internally connected to its chassis
ground (which is always connected to the ground prong of the AC power cord, if
present), and because the use of the AC power ground often introduces noise or other
imperfections such as RFI, hum, clicks, and buzzes, the wiring techniques in Fig. 2-3
are not universally applicable.
If you follow Fig. 2-3 and hum or noise appears, don’t be afraid to experiment. If
the noise sounds like alow-level crackling buzz, then probably there isn’t enough
grounding. Try connecting the LO input of the Co-Operator to achassis ground
terminal on the barrier strip and see if the buzz goes away. You can also try strapping
the Co-Operator’s chassis and circuit grounds together, and see if this helps.
Aground loop usually causes asmooth, steady hum rather than acrackly buzz. If
you have aground loop, you can often break it by disconnecting the jumper between
circuit and chassis grounds on the Co-Operator’s rear-panel barrier strip. In either
case, think carefully about what is going on, and keep in mind the general principle:
one and only one circuit ground path should exist between each piece of equipment!
(Bear in mind that the circuit grounds of the two channels of die Co-Operator are
connected together internally, and could conceivably introduce aground loop if you
do not take this connection into account in planning your wiring.)
When asingle-conductor shielded cable is used for audio connections, the shield will
ordinarily receive chassis ground from the external equipment which it is connecting
to the output of the Co-Operator. The chassis ground/circuit ground jumper on the
rear barrier strip of the Co-Operator should be left in whichever configuration gives
minimum hum or buzz. To minimize hum or buzz, it may be necessary to jumper
one or more shields to chassis ground, and/or to jumper the Co-Operator’s LO output
to chassis ground.