Orban 424A User manual

422A/424AGated Gompressoi/
Limrtei/De-Esser
OPERATING MANUAL
orbon
adivision of AKG Acoustics, Inc.

422A/424AGated Gompressoi/
Limiter/De-Esser
OPERATING MANUAL
95028-000-05
erbon
adivision of AKG Acoustics, Inc.
645 Bryant St., San Francisco, California 94107 USA
Phone [phone] Telex 17-1480 FAX [phone]
©1989, AKG Acoustics, Inc. 5/89-7P

GAIN REDUCTION:
Reads the gain of the VCA,
from 0to -25dB. Shows
the effect of any control
but OUTPUT TRIM and DE-
ESSER. v
r
INPUT ATTEN.:
Adjusts drive to compres-
sor/limiter, determining
amount of G/R.
-
ATTACK TIME:
Adjusts speed of response
to input level increase.
Fast: peak limiter &
compressor
Slow: compressor only
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0-SHO>«-fO-?3
0»-«0-l9-tO-?S
GATE THRESH.:
Determines the input level
that causes “gating"; VCA
gain moves slowly to IDLE
GAIN control setting.
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DATED COMPREBBOR/LIMITER
OUTPUT TRIM:
Adjusts VCA gain to control
or prevent clipping; its ef-
fect is seen on VCA LEVEL
meter; not an output at-
tenuator (Output Attenuator
located on rear).
DE-ESSER OPERATE/
DEFEAT:
Activates or defeats de-
esser control circuitry.
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Couples Aand Bgain and
gating circuits for stereo
tracking.
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COMPR. RATIO:
Adjusts compression from
“looser’’ (2:1) to
“tighter" (°°:1).
REL. SHAPE: Lin: com-
pressor releases at cons-
tant rate
Exp: release starts slower,
then speeds up
REL. TIME:
Adjusts speed of gain in-
VCA LEVEL:
Reads peak operating level
crease when output level is of VCA. Clipping occurs
below threshold of com-
pression.
above approximately
“+2”.
IDLE GAIN:
Determines VCA gain when
unit is gated (OPERATE
mode) or anytime unit is
DEFEATED.
OPERATE/DEFEAT:
Activates or defeats comp/
lim control circuitry. Does
not bypass any circuitry.
DE-ESSER SENSITIVITY:
Adjusts threshold of de-
essing.
CAUTION
OPELECTRICAL SHOCK
DO NOT PEWOVn COVER. NO USER
SERVICEABLE PARTS INSIDE
REFER SERVICING TO QUALIFIED
SERVICE PERSONNEL Hi
^WARNING
TO REDUCE THE RISK Of FIRE
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EXPOSE THIS APPLIANCE TO
BAIN OR MOISTURE
-OR CONTINUED
PROTECTION AG»'N«,t
FtWE HAZARD RfPlACf
ONLY WITH SAME TYPE
FUSE SAC, S/S
FOR 115V MAINS I/4A
FOR JJOV MAINS I/I A
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MODEL 424A SHOWN

Table of Contents
About This Manual
Registration Card
Warranty
ICondensed Operating Instructions
5Part A: Introduction
5Performance Highlights
6Front-Panel Description
6Rear-Panel Description
7Part B: Installation
7
Mechanical Installation
7Electrical Installation
AC Power
Control Loop Bass Rolloff
Audio
Output
Preferred Wiring
Table I: General Input/Output Connection Rules
Wiring The 424A With Single-Conductor Shielded
Cable
1 1 Part C: Operating Instructions
II Description and Function of Front-Panel Features
Using The Compressor/Limiter
Using The De-Esser
Adjusting The OUTPUT ATTEN Control
19 Some Specific Applications
Adjusting The 424A To Provide Peak Overload
Protection
Stereo And Multichannel Operation
Speech-Activated Ducking Of Music
21 Part D: Maintenance
21 Introduction
21 ALIGNMENT AND PERFORMANCE VERIFICATION
General
Power Supply
Signal Processing Circuitry
27 MAINTENANCE AND SERVICE
Preventive Maintenance
Corrective Maintenance
Service Access
Lamp Replacement
Component Replacement
Replacement Parts
Replacement Of Components On Printed Circuit
Boards
Removal
Installation
Troubleshooting 1C Opamps
Factory Service
Shipping Instructions
31 CIRCUIT DESCRIPTION
General
Input Buffer
Voltage-Controlled Amplifier (VCA) Operation
Current-Controlled Gain
Exponential Converter
Compressor/Limiter Circuitry
General
Rectifier With Threshold
Timing Module
Threshold-Setting Circuitry and RATIO Control
Gating Circuitry
Gain Reduction Meter
De-Esser Control Circuitry
VCA LEVEL Meter
Power Supply
40 APPENDIX A: INTERCONNECTIONS AND GROUNDING
43 APPENDIX B: SPECIFICATIONS
44 PARTS LIST
53 SCHEMATIC
54 PARTS LOCATOR

ABOUT
THIS MANUAL
REGISTRATION
CARD
WARRANTY
Except for the first few sections, the information contained in this manual is
primarily for reference and to aid maintenance. The unit has been designed to be
straightforward and intuitive to use, and most experienced compressor/limiter users
will be able to use it easily without instruction.
However, anumber of subtle features have been included. Full understanding of
these will enable anyone —beginner or pro —to get the most of the unit. Time
spent with the manual will often yield substantial rewards.
The original purchaser should have received apostpaid Registration Card packed
with this manual.
Registration is of benefit to you because it enables us to tell you of new
applications, possible performance improvements, service aids, etc., which may be
developed over the life of the product. It also provides us with the date of sale so
that we may more promptly respond to possible claims under Warranty in the
future (without having to request acopy of your Bill of Sale or other proof of
purchase).
Please fill in the Registration Card and return it to us.
If the Registration Card has become lost or you have purchased the unit used,
please photocopy the image of the card reproduced below and send it to us in an
envelope. Use the address shown on the title page.
Model #Serial #
Name or Title
Organization
Street
City/State/Country
Zip or Mail Code
Purchased from City Date of Purchase
Nature of your application
How did you hear about it?
Comments:
Fig. A- 1:REGISTRATION CARD
The Warranty, which applies only to the first end-user of record, is stated on the
Warranty Certificate on aseparate sheet packed with this manual. Save it for
future reference.
Details on obtaining factory service are provided in Part D.

Condensed Operating Instructions
These instructions are primarily designed to help you get started using your
422A/424A. (The later parts of your OPERATING MANUAL contain much more
detail, and will help you get the most from your 422A/424A after you have
become familiar with the basics.)
Operationally, the 422A/424A can be considered to be abasic compressor/li miter
with enhancements. If you are just beginning to learn about it, or if you only need
basic compressor functions, you needn't worry about these enhancements.
Most of the enhancements are associated with the Gating function. If the GATE
THRESHold control is turned OFF (fully counterclockwise), these enhancements are
not operative and need not concern you now.
To Use The Compressor/Limiter: Preset the following controls:
REL SHAPE
GATE THRESH
OUTPUT TRIM
IDLE GAIN
COMP/LIMITER OPERATE/DEFEAT
DE-ESSER OPERATE/DEFEAT
LIN
OFF
0(at the detent)
0
OPERATE
DEFEAT
You then need to deal with only four familiar controls: INPUT ATTENuator,
RATIO, ATTACK TIME, and RELEASE TIME. These controls are always adjusted by
ear to obtain the desired sound. If you have used any common professional
compressor or limiter before, these controls should operate intuitively:
I) Adjust the INPUT ATTENuator control until the GAIN REDUCTION (G/R)
meter indicates the desired amount of G/R. Don't let the G/R meter enter the
red section of the scale.
2)
Adjust the RATIO control to determine if compression will be "tight" or
"loose". "Tight" means that alarge increase in input level will produce asmall
increase in output level. As the ratio becomes "looser", the output level will
change more and more for agiven change in input level. 2:1 is the "loosest"
ratio; infinity: Iis the "tightest". "Looser" ratios tend to give more natural,
dynamic sound at the expense of lower loudness and less consistent levels.
(Adjusting the RATIO control to "looser" settings automatically lowers the
compression threshold to prevent peak overload of the 422A/424A circuitry or
of the device being driven by the 422A/424A when high amounts of gain
reduction are used.)
3)
Adjust the ATTACK TIME control to determine how quickly the 422A/424A
responds to an input level increase. Fast attack times produce the most
consistent control of peak levels (and therefore produce highest loudness).
However, their effect tends to be more audible than that of slow attack times.
Slow attack times permit transient material to pass through the 422A/424A
unaffected, so that transient definition is retained.
(To prevent transient overshoots permitted by slow attack times from
overloading either the 422A/424A circuitry or devices being driven by the
422A/424A, the threshold of compression is reduced as the attack time is made
slower. This way, the peak level at the output remains approximately constant
as the ATTACK TIME control is adjusted.)

The ATTACK TIME control is calibrated with an arbitrary scale because the
attack time is automatically varied according to the nature of the program
material. This minimizes audible compression-induced side-effects.
Because the range of the ATTACK TIME control has purposely been made very
wide, certain sounds can cause the 422A/424A to produce distortion when
operated with fast attack times. Such sounds include certain male voices,
Hammond organ, and some types of bass (particularly synthesizer-produced). Such
distortion can be totally eliminated by operating with slower attack times —
usually between "5" and "SLOW" on the dial.
4) Adjust the RELEASE TIME control to determine how fast the 422A/424A gain
recovers toward maximum during those times when its output level is below the
threshold of compression.
Fast release times produce the greatest "density" and most consistent output
levels. However, they also create the greatest risk of audible side-effects. They
are most useful in recording studios or production situations where the program
material being processed is asingle track and is to be mixed with other
material.
Slower release times generally produce amore natural sound on mixed program
material. Accordingly, they are more useful in such applications as broadcast
production or cassette duplication.
The RELEASE TIME control is calibrated with an arbitrary scale because the
release time is automatically varied according to the nature of the program
material. This minimizes audible compression-induced side-effects.
(The RELease SHAPE switch determines if the release proceeds at aconstant
number of dB per second (LINear), or if it starts more slowly and then speeds
up as it progresses (EXPonential). LINear usually sounds most natural, but
EXPonential can be useful if you want to create the "open" sound associated
with slow release times, yet gain-ride quickly during pauses or low-level program
material. Like the other controls, it should be adjusted "by ear" to your taste.)
5) It is important to note that the OUTPUT TRIM control should not be treated
like afamiliar "output attenuator" control: It is ordinarily left at "0". Its
purpose is to permit you to operate the Voltage-Controlled Amplifier (VCA) in
the optimum part of its range for your application. You can use the OUTPUT
TRIM control to create controlled clipping in the VCA, to prevent VCA clipping,
or to optimize the signal-to-noise ratio. Refer to the OF*ERATING MANUAL for
further details.)
Astandard OUTPUT ATTENuator control is located on the rear panel.
Compressor/Limiter Enhancements: The IDLE GAIN control determines the gain of
the Compressor/Limiter when the COMP/LIM OPERATE/DEFEAT switch is in
DEFEAT. If the IDLE GAIN control is set close to the average amount of gain
reduction, the Compressor/Limiter can be defeated and reactivated in the middle
of program material without obvious side-effects such as sudden gain changes. (The
control also has asecond function which will be explained below.)
2

The gating features permit the 422A/424A to handle noise or low-level program
material differently than it handles high-level program material. The gating feature
is not the same as aconventional "noise gate": It is not intended to reduce noise
or other undesired sounds below the level at which they exist in the original
program. Its purpose is to prevent compression from unnaturally exaggerating such
material. If needed, aconventional noise gate can be used before the 422A/424A.
The gating feature is activated whenever the GATED lamp is on. This lamp will
turn on whenever the input level drops below athreshold set with the GATE
THRESHold control. (In its OFF postion, this control totally defeats the gating
feature.)
When the GATED lamp is on, the gain of the Compressor/Limiter moves slowly to
apoint set by the IDLE GAIN control. This gain change is indicated on the GAIN
REDUCTION meter. If the IDLE GAIN control is set at apoint equal to the
average amount of gain reduction occurring, then gain will neither increase nor
decrease during low-level program materal or pauses. In particular, noise will not
be "pumped up" as in aconventional compressor. For example, if you are
compressing aparticular track in amultitrack mixdown, tape hiss or low-level
material below the gating threshold will not be increased in level at the beginning
of the mix (before high-level program material first appears on the track), or
during pauses in the track.
If the IDLE GAIN control is set lower than the average gain reduction, then it
can leave a"hole" when high-level program material reappears and turns the
GATED lamp off. This is because the Compressor/Limiter must recover to ahigher
gain to produce full loudness, and this cannot happen instantaneously: The time
necessary for recovery is determined by the RELEASE TIME control.
To Use The De-esser: To use the De-esser, switch the DE-ESSER
OPERATE/DEFEAT switch to OPERATE and adjust the De-esser SENSITIVITY
control until "esses" sound naturally balanced with the rest of the voice.
The threshold of de-essing is fixed by the SENSITIVITY control, and does not track
the average vocal level (as in the Orban dedicated de-essers). For consistent de-
essing, it is important that the level presented to the De-esser be relatively
constant. This is ordinarily achieved by compressing the voice with the
Compressor/Limiter, which is functionally ahead of the De-esser.
It is sometimes possible to de-ess vocals which have been mixed with other
material. Each case must be evaluated by ear. The DE-ESSER OPERATE/DEFEAT
switch does not introduce clicks, pops, or discontinuities into the program, so the
De-esser can be keyed in or out in the middle of program material as required.
This may be the best way to handle afew problem "esses" in mixed program
material.
3

PERFORMANCE
HIGHLIGHTS
Part A: Introduction
The Orban Model 422A/424A Compressor/Limiter/De-Esser is an integrated AGC
device of highest professional quality. It can perform compression, peak limiting,
and vocal de-essing functions simultaneously with unusual freedom from side-effects.
It can thus serve either as ageneral-purpose no-compromise compressor/limiter, or
as acomplete dynamic processor for conditioning vocals. However, it is not
optimized for over modulation protection of broadcast transmitters, and the Orban
OPTIMOD-AM, -FM, or -TV should be used in such applications.
The flexibility and natural sound of the 422A/424A make it applicable in other
areas of professional audio as well: recording studios, sound reinforcement, public
address, motion picture sound, etc.
The product is available in both single- (422A) and dual- (424A) channel versions.
(For clarity, only the 424A will be referenced in this manual.) The dual-channel
version is equipped with acoupling switch which forces the gain of both channels
to be equal, tracking the channel demanding the greatest amount of gain reduction.
This preserves correct imaging in stereo applications. However, the stereo coupling
switch does not couple the operating controls, and these are ordinarily set
identically in stereo operation.
Attack and release times are both program-controlled, but can be scaled faster or
slower by means of front-panel controls. This results in maximum flexibility, plus
extremely natural sound over awide range of control settings.
The 424A Compressor is equipped with electronically-balanced inputs and outputs
and is compatible with the levels and impedances found in both professional and
semi-professional applications. RF suppression applied to the input, output, and
power leads enables use in relatively high RFI fields such as those common in
broadcasting.
The controls and features of the 424A Compressor are fully described in this
manual. It will familiarize you with the unit's potential and enable you to
imaginatively use the 424A for your specific installation and application.
Because the front-panel controls are marked in afamiliar way, you may be
tempted to jump right in without reading the manual. However, if you take the
time to review the Description And Function Of Front-Panel Controls and
Operating Instructions in Part C, you will find that there is "more than meets the
eye" inside the 424A, and that the time you take reading the manual will be well-
rewarded by agreater understanding of the unit's potential.
Production AGC function using circuitry adapted from industry-standard
OPTIMOD-FM Model 8I00A broadcast signal processor
De-esser characteristics similar to highly-accepted Orban dedicated de-essers
Independent compressor/limiter and de-esser control loops with optimized,
program-controlled parameters for each
Unbeatable ability to increase average loudness of program material or
individual tracks without introducing unnatural sound quality or artifacts
Defeatable gain-freezing gate with user-adjustable threshold to prevent
pumping and breathing during pauses
5

Wide-range attack time,release time,and ratio controls permit device to
sound extremely natural or to create special effects
Extremely easy to use because attack and release time controls interact and
also change the compression threshold, assuring consistent peak output levels
and minimizing need for manual readjustment of the output attenuator
Operation is intuitive and natural -- you don't need achart or an advanced
degree to figure out what's happening
Low-distortion operation teams clean class-A VCA with all-important dynamic
distortion reduction in the control circuitry
—25dB gain reduction range with constant 90dB (typical) clip-to-noise ratio
regardless of amount of gain reduction
Better than 25dB de-ess gain reduction available in addition to the 25db
compressor/limiter gain reduction
—True peak-reading output level meter allows operator to positively prevent
VCA clipping —or to use acontrolled amount of clipping to limit peak levels
—True peak-reading gain reduction meter
—Choice of general-purpose linear or special-purpose exponential release
characteristics
—Strong all-metal 19" rack mount package for ruggedness, roadworthiness, RFI
shielding, and ease of mounting
—Lighted meters with long-life lamps
Input, output, and AC power RFI suppression make the unit ideal for difficult
environments like broadcast stations, areas near mobile communications
transmitters, etc.
—Balanced inputs and outputs
—II5/230V 50/60Hz power supply standard
—Industrial-grade parts and construction
—Highly cost-effective
FRONT PANEL The Front-Panel Photograph at the beginning of this Manual shows the various
DESCRIPTION operating controls. These controls and their operation are fully described in
Description and Function of Front Panel Features in Part C(Operating
Instructions) below.
REAR PANEL The FUSE used in both the 422A and the 424A is aI/4A (115 volt operation) or
DESCRIPTION I/8A (230 volt operation) 3AG 250V SLO-BLO type. Replace with the same type
only.
The OUTPUT ATTENUATOR is fully described in Description and Function of
Front Panel Features in Part C(Operating Instructions) below.
The INPUT and OUTPUT connectors provided allow connection via barrier strip (#5
screw). Holes are provided for installation of "XLR"-type connectors, and aretrofit
kit is available from your dealer.
Please refer to the Electrical Installation section for connection instructions.
6