Orban 412A User manual

412A/414ACompressoi/Limiter
OPERATING )W\NUAL
ofbon
Orban Associates, 645 Bryant St., San Francisco, CA 94107 [phone]
Telex: 17-1480 FAX [phone]
95042-000-04 1/89-4P Copyright ©1984 by Orban Associates

Table of Contents
About This Manual 21 PART D: MAINTENANCE
Registration Card
Fig. A-1: Registration Card 21 Introduction
Warranty 21 ALIGNMENT AND PERFORMANCE VERIFICATION
21 General
1PART A: INTRODUCTION 21 Power Supply
22 Signal Processing Circuitry
1Performance Highlights 25 MAINTENANCE AND SERVICE
3Front-Panel Description 25 Preventive Maintenance
3Rear-Panel Description 25 Corrective Maintenance
25 Service Access
5PART B: INSTALLATION 26 Lamp Replacement
26 Component Replacement
5Mechanical Installation 26 Replacement Parts
5Installation Of Options 27 Replacement Of Components On Printed Circuit
5Fig. B-1: Wiring Of Optional Connectors Boards
6Electrical Installation 27 Removal
6AC Power 27 Installation
6Fig. B-2: AC Line Cord Color Coding 27 Troubleshooting IC Opamps
6Control Loop Bass Rolloff Jumper 28 Factory Service
7Fig. B-3: Control Loop Bass Rolloff Strapping 29 Shipping Instructions
7Audio Connections 29 CIRCUIT DESCRIPTION
7Input 29 General
7Output 29 Input Buffer
8Preferred Wiring 30 Voltage-Controlled Amplifier (VCA) Operation
8Fig. B-4: Grounding 30 Current-Controlled Gain
8Table 1: General Input/Output Connection Rules 31 Exponential Converter
9Wiring The 414A With Single-Conductor Shielded 31 Compressor/Limiter Circuitry
Cable 31 General
31 Rectifier With Threshold
11 PART C: OPERATING INSTRUCTIONS 33 Timing Module
11 Quick Operating Guide 33 Threshold-Setting Circuitry and RATIO Control
12 Fig. C-1: Output Level As AFunction Of Input 33 Gain Reduction Meter
Level For Various Settings Of The RATIO Control 34 Line Amplifier
15 Description and Function of Front-Panel Features 34 Power Supply
17 Using The Compressor/Limiter
17 Some Specific Applications 35 APPENDIX A: INTERCONNECTIDNS AND
17 Sidechain Processing GRDUNDING
17 De-Essing 35 Driving The Input From High-Impedance And/Or
18 Frequency-Selective Limiting High-Level Sources
18 Stereo And Multichannel Operation 35 Grounding
18 Speech-Activated Ducking Of Music 37 APPENDIX B: SPECIFICATIDNS
39 PARTS LIST
44 Vendor Codes
45 ASSEMBLY DRAWING
46 SCHEMATIC DIAGRAM

PART A;
Introduction
The Orban Model 412A/414A Compressor/Limiter is ageneral-purpose AGC device
of highest professional quality. It can perform compression and peak limiting
simultaneously with unusual freedom from side-effects.
The flexibility and natural sound of the 412A/414A make it applicable in virtually
all areas of professional audio: recording studios, broadcasting, sound reinforcement,
public address, motion picture sound, etc. However, it is not optimized for
overmodulation protection of broadcast transmitters; the Orban OPTIMOD-AM, -FM,
or -TV should be used in such applications.
The product is available in both single- (412A) and dual- (414A) channel versions.
(For clarity, only the 414A 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. (If they are set non-identically ,the gain of both
channels will still be equal, tracking the channel demanding the highest amount of
G/R. However, the control circuitry will respond differently to material in the two
channels even if amono feed is used. This might be useful for special effects.)
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 414A Compressor/Limiter is equipped with electronically-balanced input and
output, 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.
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 414A, and that the time you take reading the manual will be
well-rewarded by agreater understanding of the unit's potential.
1

PERFORA/IAIMCE
HIGHLIGHTS
-streamlined, straightforward front panel offers the most-demanded user
controls, including ATTACK TIME, RELEASE TIME, RATIO, and THRESHOLD.
The wide range of these controls permits extremely natural sound or special
effects.
-Uses exclusive Orban feedback control circuitry adapted from our popular 424A
Gated Compressor/Limiter/De-Esser to achieve remarkably natural sound.
-User controls interact intelligently to simplify and speed setup, and to prevent
errors.
-Peak limiting and compressor functions are crosscoupled to eliminate potential
pumping and modulation effects.
-THRESHOLD control with 20dB range allows user to determine the level at
which gain reduction first occurs, without changing below-threshold gain. Ideal
for sound reinforcement applications.
-Proprietary circuitry achieves optimum headroom and signal-to-noise regardless
of THRESHOLD control setting.
-Front-panel OUTPUT ATTENUATOR control with OUTPUT CLIP LED to
indicate line amplifier clipping.
-Illuminated, true peak-reading GAIN REDUCTION meter is more accurate and
readable than LED displays.
-GAIN REDUCTION OVERLOAD lamp warns of control circuit overload due to a
demand for G/R which exceeds the range of the VCA.
-Hard-wired system bypass switch for fail-safe protection.
-Side-chain externally accessible for special effects such as frequency-selective
limiting.
-Active-balanced, floating input interfaces easily to any system.
-Active-balanced, floating output stage can be operated unbalanced simply by
grounding one side.
-Proprietary Class-A Orban VCA features very low distortion and noise.
-Stereo 414A has STEREO COUPLING switch to permit either stereo or dual-
mono operation; an unlimited number of units can be wire-coupled to track
+0.5dB.
.. All-metal chassis with RFI suppression on input, output, and AC leads.
2

PROMT PAMEL
DESCRIPTIOM
REAR PAMEL
DESCRIPTIOM
The Front-Panel Photograph at the beginning of this Manual shows the various
operating controls. These controls and their operation are fully described in
Description and Function of Front Panel Features in Part C(OPERATING
INSTRUCTIONS) below.
The FUSE used In both the 412A and the 414A is a1/4A (115 volt operation) or
1/8A (230 volt operation) 3AG 250V SLO-BLO type. Replace with the same type
only. (An adapter is available from the factory to accommodate aEuropean-style
5x20mm fuse.)
The INPUT and OUTPUT connections are located on abarrier strip (#5 screw).
Holes are provided for installation of "XLR"-type connectors; aretrofit kit is
available from your dealer.
Please refer to the Electrical Installation section for connection instructions.
The SIDECHAIN IN and SIDECHAIN OUT connectors are 1/4" 2-conductor
(tip/sleeve) normalling phone jacks. These Jacks let you insert additional signal
processing (such as an egualizer) into the compressor control sldechain to achieve
frequency-dependent compression, de-essing, or other such functions. This is further
described below in Sidechain Processing in Part C(OPERATING INSTRUCTIONS.)
3

PART B;
Installation
MECHANICAL
INSTALLATION
INSTALLATION
OF OPTIONS
|— COWMECTOR'a 1
UME oik \M
Vertical space of one standard rack unit (1 3/4"/4.5cm) is required for the 412A;
two rack units (3 l/2"/8.9cm) are required for the 414A.
Mounting the unit directly over large heat-producing devices like avacuum-tube
power amplifier may shorten component life and is not recommended. Ambient
temperature should not exceed 113°F (45°C) when equipment is powered.
XLR Connector Installation: To install the optional XLR connectors, obtain (2 ea.)
Switchcraft D3M and (2 ea.) Switchcraft D3F (or equivalent) connectors from a
local supplier. These connectors are also available directly from Orban as retrofit
kit RET-28.
Remove the cover plate from the rear chassis apron and install each connector
with apair of #4-40-1/4" flat-head screws, nuts, and lockwashers. On each channel
in turn, connect jumper wires from the barrier strip to the XLR's as shown in Fig.
B-1.
FROIA OF CHAS>S>S
RETZa.VdlRE UST
(XER CONMECrOK-El
XUR C0^4^VeCT0R KLR. CO^^^ieCTOR L\»^e COT
TO FROIA TO COLOR
LOO flSQlii JW-v (Ar) LOO BLR
(lo) BUJ'I JU-E (ui) Tft-i-S oot(-) )tw\5T
Jvo-E (hO TB5-1 W(+) JU-3 (Wh T6'5-‘V 00T(+)
-TABV-t SUOViJVi FOR CWAV\ViE.\. A, R.E.PU\CATe FOR CRAMMEU E
Fig. B-1: WIRING OF OPTIONAL CONNECTORS
5

ELECTRICAL
IIMSTALLATIOIM AC Power
The power transformer can be connected for 115 volt or 230 volt 50 or 60Hz AC
operation. If the unit was ordered for 230 volts, atag on the power cord warns of
the modification.
The two primary windings of the power transformer are connected in parallel for
115 volt operation and in series for 230 volt operation. (See the Schematic
Diagram in the back of this manual.)
To strap the power transformer for adifferent voltage, remove the top cover
(412A) or bottom cover (414A). Strapping instructions are found on the insulating
fishpaper around the power transformer. It is not necessary to rearrange the heavy
insulated wiring; all strapping can be performed with bare jumper wire. Take care
not to burn the insulation.
The power cord is terminated in a"U-Ground" plug to USA standards. The
green/ yellow wire (which is connected to the long prong) is connected directly to
the 414A chassis. If it becomes necessary to lift this ground to suppress ground
loops, this should be done with athree-prong to two-prong adapter plug, rather
than by damaging the power plug. It is not recommended that this ground be
defeated unless absolutely necessary because it eliminates the intrinsic safety
feature of the three-wire system.
CONDUCTOR WIRE COLOR
Normal Alt
LLINE BROWN BLACK
NNEUTRAL BLUE WHITE
EEARTH GND GREEN-YELLOW 'GREEN
Fig. B-2: AC MAINS LINE CORD DETAIL
WARNING!
If the ground is defeated, certain fault conditions in the unit or the
system to which it is connected can result in appearance of full line
voltage between chassis and earth ground. Such voltage is capable of
causing electrical shock, possibly resulting in severe injury or death!
Control Loop Bass Rolloff Jumper
The compressor/limiter control loop is ordinarily operated with abass rolloff
which simulates the response of the ear and results in amore natural sound.
However, certain applications demand that the 414A perform an accurate peak
limiting function. This requires a"flat" response from the control loop.
The bass rolloff network can be jumpered out on the circuit board(s) inside the
414A. Each unit is shipped with the jumpers in the "rolloff" position. To restrap to
the "flat" position, move the jumpers according to Fig. B-3, following the User
Access instructions in Part D. (The jumper is on the bottom side of the board on
Channel Bof the 414A.)
6

SCH <e001^
Fig. B-3: Control Loop Bass Rolloff Strapping
Audio Connections
Connecting the 414A Connpressor/Limiter to other equipment is quite
straightforward. Relatively uncomplicated systems (such as home playback systems,
"semi-pro" recording studios, electronic music studios, dance bars, etc.) tend to
come together without serious grounding problems even if the wiring practices are
somewhat casual, provided that high RF fields are not present. Unusual situations
can be analyzed if you are familiar with the standard rules governing grounding and
interfacing between balanced and unbalanced systems.
The instructions below will apply to the majority of cases. Acomprehensive
discussion of interconnections and grounding can be found in Appendix A.
Input: The cable should be connected to the 414A input according to Table 1
below.
The electronically-balanced input of each channel of the 414A Compressor is
compatible with most professional and semi-professional sound equipment, balanced
or unbalanced, whose source impedance is 6D0 ohms or less. If it is greater (as in
some vacuum-tube audiophile preamps), aminor modification may be made to the
input to accomodate the situation. Please refer to Appendix Afor further details.
Nominal input level is between -10 and +4dBm. The absolute overload point is
+20dBm.
Output: The two outputs of each channel of the 414A are electronically-balanced
and floating. The source impedance of each leg is less than 100 ohms in parallel
with lOOOpF to the chassis (for RFl suppression). The output is capable of driving
loads of 600 ohms or higher.
Both balanced and unbalanced outputs can be taken between the (+) and (-) output
terminals. In the unbalanced case, the output amplifier is designed to operate
correctly if its (-) output is grounded, and no special precautions need be taken.
7

Preferred Wiring: We recommend wiring with 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. The following table and diagram
are applicable to agreat majority of installations.
If you wish to use single-conductor shielded cable, see the section immediately
below.
0»T~l
fBAtANCCO) I
OUT <
I(UN8A1.ANCED)|
Him Mm
IORBAN
UM\T
—
i
1
»
\\ A» J
11
37? o
1
1
DRIVEN EQUIPMENT
^IF ORftAM UMVt (S COUIPPED WITH OPtlONAL OUTPUT TPANSTORMCR, TWIN INSTALL THIS JUMPSR.
Fig. B-4: GROUNDING
TABLE 1:
GENERAL INPUT/OUTPUT CONNECTION RULES
INPUT
1) Always use (+) and (-) as the two input terminals to the 414A.
2) When the 414A is driven from an unbalanced source, connect the shield to
circuit ground at the source and to chassis ground at the 414A. Connect
the (-) input to chassis ground as well.
3) When the 414A is driven from abalanced source, connect shield at the
source end to chassis ground. Do not connect shield at 414A end.
OUTPUT
1) At the 414A output, connect the shield at the 414A end to chassis ground
(whether driving balanced or unbalanced loads). Do not connect the shield
at the other end.
2) When driving an unbalanced load, connect the circuit ground of the driven
equipment to the 414A's (-) output. Connect the hot side of the driven
equipment's input to the 414A's (+) output.
3) When driving abalanced load, jumper the circuit ground to the chassis
ground on the 414A (on rear panel). When driving an unbalanced load, do
not use this jumper.
R

GENERAL
1) The 414A chassis should always be earth-grounded (through the third wire
in the power cord or through the rack) for maximum protection from
shock. Float this ground (to reduce hum) only as alast resort.
Because it is not always possible to determine if the equipment driving or being
driven by the 414A has its circuit ground internally connected to its chassis ground
(which is always connected to the ground prong of the AC line cord, if present),
and because the use of the AC power line ground often introduces noise or other
imperfections such as RFI, hum, clicks, and buzzes, the wiring techniques in the
diagram are not universally applicable.
If you follow the diagram and hum or noise appears, don't be afraid to
experiment. If the noise sounds like alow-level crackling buzz, then there probably
isn't enough grounding. Try connecting the (-) input of the 414A to achassis ground
terminal on the barrier strip and see if the buzz goes away. You can also try
strapping the 414A's chassis and circuit grounds together (on the barrier strip) to
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 414A'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 the 414A
dual-channel unit are connected together internally, and could conceivably introduce
aground loop if you do not take this connection into account in planning your
wiring.)
Wiring The 414A With Single-Conductor Shielded Cable: Sometimes, particularly if
you are using the 414A with musical instruments or home-type equipment, single-
conductor shielded cable may be the only type immediately available (as opposed to
the preferred two-conductor cable). In this case, connect the inner conductors of
the shielded cables to the (+) sides of the 414A inputs and outputs. Connect the
shield of the 414A input cable to the (-) input, and connect the shield of the 414A
output cable to the (-) output on the rear-panel barrier strip.
The shield will ordinarily receive chassis ground from the external equipment
which it is connecting to the output of the 414A. The chassis ground/circuit ground
jumper on the rear barrier strip of the 414A 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. Because use of single-
conductor cables virtually eliminates any possibility of carefully controlling the
system grounding scheme, it is NOT RECOMMENDED! Even so, it often does work
adequately.
9

PARTC;
Operating Instructions
QUICK This section is designed to help you get started using your 412A/414A. While the
OPERATING unit is easy and "friendly" to use, it does contain many sophisticated and powerful
features. Later parts of this C3PERATING MANUAL describe these features in
more detail, and can help you get the most from your 414A after you have become
familiar with the basics.
Since the 412A is asingle-channel version of the 414A, we will refer only to the
414A in the text unless the context demands otherwise.
The 414A is acompressor, alimiter, or both, depending primarily upon the setting
of the ATTACK time and RELEASE time controls. This is explained below under
ATTACK TIME.
Referring to the instructions in Part B, install the unit.
To activate the circuitry, the SYSTEM OPERATE/BYPASS button must be IN
(white dot showing).
The INPUT ATTENuator, THRESHOLD, RATIO, ATTACK TIME, and RELEASE
TIME controls are adjusted by ear to obtain the desired sound. If you have used
any common professional compressor or limiter before, these controls should be
familiar.
1) INPUT ATTENuator AND THRESHOLD: Both of these controls affect the
amount of gain reduction (G/R) produced by the unit, but in different ways.
(The amount of G/R is indicated by the illuminated G/R METER.)
The INPUT ATTENuator is located before the main part of the
compressor/limiter circuitry, and consequently adjusts the audio level presented
to this circuitry.
The THRESHOLD control affects the compressor/limiter control circuitry,
determining the audio level (as seen after the INPUT ATTENuator) that first
begins to cause G/R.
For most applications, the amount of G/R is determined by adjusting the
INPUT ATTENuator (thus changing the drive to the main compressor/limiter
circuitry), while leaving the THRESHOLD control at Its center detent ("0").
Unless the RATIO control (explained below) is adjusted for low ratios,
determining the amount of G/R in this way produces arelatively constant level
at the output of the compressor/limiter regardless of the amount of G/R.
Therefore, using the INPUT ATTENuator to adjust the amount of G/R is most
appropriate when the device driven by the compressor/limiter (such as atape
recorder) has afixed overload level, beyond which distortion or other problems
occur.
Determining the amount of G/R by means of the THRESHOLD control is most
useful in sound reinforcement. Here, the system gain must be constrained to a
maximum value or feedback can occur. Adjusting the G/R with the INPUT
ATTENuator would also change the overall gain (even with no G/R occurring),
and might therefore cause the system to feed back. By using the THRESHOLD
control to adjust the amount of G/R, there Is no danger of Introducing
feedback.
11

Provided that the compressor/limiter is into G/R, its average output level will
change in proportion to the setting of the THRESHOLD control. (Lowering the
threshold, for example, causes more G/R, thus reducing the output level.)
Determining G/R by adjusting this control Is therefore inconvenient if your
primary goal is to protect afollowing piece of equipment from overload, since
every change in the THRESHOLD control will require acompensating adjustment
of the OUTPUT ATTENuator control to readjust the output level of the
compressor/li miter to the desired value.
The available range of the THRESHOLD control is only +10dB, so even if you
wish to determine G/R with the THRESHOLD control, you may have to first
adjust the INPUT ATTENuator to bring the THRESHOLD control within range.
Ordinarily, you will determine the desired amount of G/R by ear: simply adjust
the INPUT ATTENuator and/or THRESHOLD controls until the desired
subjective effect is obtained.
If the G/R OVERLOAD LED comes on, you must reduce the setting of the
INPUT ATTENUATOR. (G/R overloads cannot be cleared with the THRESHOLD
control.)
2) RATIO: This control determines if compression will be "tight" or "loose".
"Tight" means that a large change in input level will produce asmall change in
output level. As the ratio becomes "looser", the output level will change more
for agiven change in input level. 2:1 is the "loosest" ratio; oo:l is the
"tightest".
"Looser" ratios tend to give more natural, dynamic sound at the expense of
lower average loudness and less consistent levels. "Tighter" ratios produce
maximum loudness and density, but may tend to sound less natural than looser
ratios. By comparison to conventional compressors and limiters, the 414A's
program-controlled attack and release time constants minimize these less natural
effects.
0
U
T
P
U
T
1
N
d
(Adjusting the RATIO control to "looser" settings automatically lowers the
compression threshold to prevent peak overload of the 414A circuitry or that of
the device being driven by the 414A when high amounts of gain reduction are
Fig. C-1: OUTPUT LEVEL AS AFUNCTION OF INPUT LEVEL
FOR VARIOUS SETTINGS OF THE RATIO CONTROL
12

3) ATTACK TIME: Traditionally, acompressor is considered to be an automatic
gain control device which controls the average (or RMS) level of an audio
signal, and which operates with relatively slow attack and release times.
Conversely, alimiter controls peak levels, and operates much more guickly.
The 414A can operate as acompressor, as a limiter, or as acombination of
both depending on the setting of its ATTACK TIME control. The ATTACK TIME
control determines how quickly the 414A responds to an input level increase.
When the ATTACK TIME is operated towards the fast part of the scale, the
414A behaves like alimiter if only asmall amount of G/R is used. As the
amount of G/R is increased, the unit begins to behave more and more like a
compressor cascaded with alimiter.
When the ATTACK TIME control is set towards the slow part of the scale, the
amount of limiting is progressively reduced, while the amount of compression
stays essentially the same: The unit behaves more and more like apure
compressor.
Fast attack times produce the most consistent control of peak levels (and
therefore produce highest average loudness). However, fast attack times tend to
produce more audible side effects than slow attack times. Slow attack times
permit transient material to pass through the 414A unaffected, so that transient
definition is retained at the cost of peak control.
(To prevent any transient overshoots permitted by slow attack times from
overloading either the 414A circuitry or subsequent devices, the threshold of
compression is automatically 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 (0 to 10)
because the actual attack time varies automatically according to the nature of
the program material. This minimizes audible side-effects.
Because the range of the ATTACK TIME control has purposely been made very
wide, certain sounds can cause the 414A 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 eliminated by operating with slower attack times —usually between "5"
and "SLOW" on the dial
RELEASE TIME: This control determines how fast the 414A gain recovers
toward maximum (OdB G/R) 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 which can hide any side-effects.
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
actual release time varies automatically according to the nature of the program
material. This minimizes audible side-effects.
5) OUTPUT ATTEN: This control can be adjusted to achieve the desired level at
the 41ZA's output. If the CLIP lamp lights, reduce the setting of the control
until it goes out.
13

14
FRONT
AND
REAR
PANEL
FEATURES

DESCRIPTION
AND FUNCTION
OF FRONT PANEL
FEATURES
I
i
While the following control descriptions might seem unnecessarily complex on first
reading, they have been crafted to answer any reasonable question either the
novice or the experienced user might ask. The effects of, and interactions between,
the controls have been designed to promote ease of use, facilitating good results
with minimum effort. Some of these interactions and effects are subtle, and are
much more easily appreciated by actual practice than by reading.
Refer to the Quick Operating Guide above for an overview, and to the Front
Panel Photograph at the front of this Manual.
The INPUT ATTENuator adjusts the drive level to the compressor/limiter,
thus determining the amount of gain reduction for agiven setting of the
THRESHOLD control.
In most cases (such as recording studios) where arelatively constant level at
the 414A output is desired, this control is used (instead of the THRESHOLD
control) to determine the amount of G/R, since there is no need to readjust
the OUTPUT ATTENuator to compensate for INPUT ATTENuator adjustments
(except when very low ratios are used). In addition, adjusting either the
ATTACK TIME or RATIO controls also adjusts the threshold to keep the peak
output level approximately constant. However, this automatic threshold
adjustment does not affect the amount of G/R available.
The GAIN REDUCTION meter is electronically conditioned to show the true
peak gain reduction of the VCA (Voltage-Controlled Amplifier) in dB.
The G/R OVERLOAD lamp lights when no further G/R is available. When this
lamp is lit, the gain of the VCA is "stuck" at its lowest available value.
Further increases in input level will cause proportional increases in output
level, rapidly driving the VCA into clipping.
The amount of available gain reduction changes with the setting of the
THRESHOLD control: When the control is set to "+1D", 15dB of G/R is
available. This increases to 35dB when the control is set to "-10". Therefore,
G/R overloads cannot be cleared with the THRESHOLD control, because the
available gain reduction is reduced in exact proportion to the increase in
threshold. G/R overloads must be cleared by turning down the INPUT
ATTENuator.
The THRESHOLD control determines the threshold of compression (and thus
the amount of gain reduction) without changing the below-threshold gain. It is
mostly useful in sound reinforcement applications where the system gain must
be constrained to amaximum value (to avoid feedback), while control over the
amount of gain reduction is retained. Adjusting the control will proportionally
change the nominal compressor output level.
This control has been carefully implemented to avoid compromising the signal-
to-noise ratio of the compressor regardless of the setting of the control.
Accordingly, the amount of available gain reduction available from the
compressor varies in direct proportion to the setting of the THRESHOLD
control: there is less G/R available at high thresholds (where less G/R will be
produced) than at low thresholds (where more G/R will be produced).
Best VCA distortion and signal-to-noise performance are achieved with the
control at its detented "0" setting. However, performance compromises are
extremely small over the range of the control, and it can be used freely to
achieve your goals.
15

The RATIO control adjusts the compression ratio (i.e., the dB change in input
level divided by the resultant dB change in output level). The calibrations are
only valid at the threshold of gain reduction. As more gain reduction is used,
the compression ratio increases, yielding a"soft knee" curve when the RATIO
control is adjusted for lower ratios.
The ATTACK TIME control scales the program-controlled attack characteristic
faster or slower, and simultaneously adjusts the compression threshold. (The
attack time is not constant: it varies according to the recent history of the
program dynamics.)
At faster ATTACK TIME settings, substantial peak limiting action is produced
with typical program material. As the ATTACK TIME is slowed, the 414A acts
more and more like apure compressor, and fast peaks are permitted to
overshoot more and more.
Because of these overshoots, the compression threshold is automatically
lowered as the attack time is slowed to avoid clipping the VCA used as the
gain-control element. At the very slowest attack times, the release time is
also lengthened by afactor of approximately 4:1 to assure that the 414A is
working in atruly "averaging" mode at these very slow attack times, and that
the attack time does not get slower than the release time.
The RELEASE TIME control scales the program-controlled release
characteristic faster and slower. (The release time is not constant; it varies
according to the recent history of the program dynamics.)
To avoid having fast transients punch "holes" in the program material, the
release rate is automatically speeded up after alarge change in gain reduction.
This creates afast "peak limiting" function which rides on top of amuch
slower "compression" function. It is the recovery rate of the "compression"
function which is affected by the RELEASE TIME control.
The OUTPUT ATTENuator control adjusts the gain of the balanced line
amplifier in the 414A. Under certain conditions, enough gain is available to clip
the line amplifier. Such clipping is indicated by illumination of the CLIP lamp.
To clear this clipping, turn the OUTPUT ATTENuator down.
The SYSTEM OPERATE/BYPASS switch is ahard-wired bypass switch; its
principal use is to keep asound system functioning in an emergency mode
despite a failure in the 414A. Because it bypasses all 414A circuitry, it is
ordinarily not used as an in/out switch since it tends to produce clicks and
level changes when operated.
The COUPLED/INDEPENDENT switch (414A only) permits the use of the two-
channel unit either as two independent compressor/li miters, or as a coupled
stereo unit. In the COUPLED mode, the gain reduction in both channels tracks
that channel calling for the most gain reduction at any given instant.
Therefore, stereo imaging is always preserved even if operating controls are
adjusted differently on the two channels. (Ordinarily, they would be adjusted
identically.)
The POWER ON/OFF switch is self-explanatory.
16

Using The Compressor/Limiter
*
SPECIFIC
APPLICATIONS
To use the Compressor/Limiter, apply signal to the unit and adjust the operatinq
controls by ear to achieve the sound desired. (An explanation of the operatinq
controls is found above.) ^
Adjust the INPUT ATTENuator control until the desired amount of gain reduction
IS indicated on the G/R meter. You may now further adjust the amount of gain
reduction over a+10dB range by means of the THRESHOLD control. Be careful not
to over-compress such that the G/R OVERLOAD lamp comes on. You may wish to
readjust the ATTACK, RELEASE, and RATIO controls to "fine-tune" the sound to
your taste. This will often result in achange in the amount of gain reduction, and
you may wish to readjust the INPUT ATTENuator or THRESHOLD controls to
compensate.
If you hear a"hashy" distortion on voice, or on instruments like electric bass
synthesizer, or Hammond organ, this can be completely eliminated by slowing down
the attack time. (The "hash" is caused by the very fast release-time peak limiting
function modulating the instrument waveforms. By slowing the attack time, you
produce less peak limiting, forcing the 414A to behave more like apure
If you hear unnatural "pumping" or "breathing", this can usually be eliminated by
slowing the release time and/or by using less gain reduction.
In general, the peak level at the 414A output will remain relatively constant
regardless of the adjustment of the ATTACK and RELEASE TIME controls. If you
choose arelatively low RATIO, the peak level will decrease at gain reductions less
than 25dB. This prevents VCA clipping if the input level rises sufficiently to cause
afull 25dB of gam reduction, since the output level will, in this case, increase
significantly due to the low compression ratio.
Because peak output levels are held relatively constant, you can readily hear the
effect of adjusting any control upon the relative loudness achieved by the
processing. Fast attack and release times and high ratios result in maximum
loudness (low peak-to-average ratios), but introduce the greatest risk of audible
side-effects. In the 414A, special circuitry minimizes these effects when compared
to conventional limiters and compressors.
Sidechain Processing
External signal processors can be inserted in the control sidechain of the 414A by
use of the normalling SIDECHAIN jacks on the rear panel. These outputs and inputs
are line-level, unbalanced, and require tip/sleeve (2-conductor) phone jacks. The
output impedance is 100 ohms, and the input impedance is greater than lOK. Any
signal processor inserted in the sidechain should be capable of +20dBm peak
headroom.
De-Essing: If ahighpass filter or bandpass filter tuned to approximately 6kHz is
inserted in the sidechain, the 414A can be used as ade-esser. Adjust the ATTACK
TIME control to "2" and the RELEASE TIME control to "0" for smoothest sound. If
you insert an external compressor (you can use the other channel of the 414A) in
constant de-essing over arange of input levels equal to
the amount of gain reduction used in the external compressor can be achieved. In
this mode of operation, gain reduction is desired only on the "esses", and the 414A
cannot be used simultaneously as avocal compressor.
17

If you want to use the 414A to compress and de-ess simultaneously, use an
equalizer instead of afilter in the sidechain, and boost the 6kHz region. This is a
compromise mode, because the optimum time constants for vocal compression and
de-essing are very different. It is necessary to set attack and release times very
carefully to avoid punching "holes" in the audio when de-essing occurs.
The Orban 536A Dynamic Sibilance Controller is an economicai two-channei de-
esser which has been specifically optimized for no-compromise de-essing. Because
the 536A is extremely easy-to-use and performs better than the 414A with
sidechain processing in this application, we recommend use of the 536A if you
require high-precision de-essing.
Frequency-Selective Limiting: The de-essing application is one example of
frequency-selective limiting. If you insert an equalizer or filter into the sidechain,
then compression and limiting action will be increased when program material
containing large amounts of energy in the boosted frequency range is applied to the
compressor. Conversely, if acertain frequency range is suppressed by the equalizer,
then program material rich in energy in the suppressed frequency range will not
produce as much gain reduction as it otherwise Would.
This principle can be used for awide variety of special effects, or to increase
naturalness when processing some types of program material. For example, the
414A already contains afrequency-selective element in the side-chain: the LF
rolloff network reduces the sensitivity of the compressor to low frequency material,
reducing the normal tendency of bass to audibly modulate midrange loudness in
wideband compressors such as the 414A.
The gain of the external sidechain processor must be adjusted to optimize the
signal-to-noise ratio in the 414A's VCA. Too much gain will cause excessive gain
reduction, resulting in poor noise performance (due to under-utilization of VCA
headroom), while too little gain will cause insufficient gain reduction, leading to
VCA clipping. Because there is no VCA clipping indicator (the 414A control
circuitry without external sidechain processing has been carefully designed to
automatically optimize VCA signal-to-noise while avoiding clipping), you must use
your ears to determine if the VCA is producing audible distortion. Certainly, if
temporarily pulling out the plugs from the 414A's SIDECHAIN jacks (thus bypassing
your sidechain processing) causes substantial increases in gain reduction, there is
danger of VCA clipping, and you should increase the gain of your sidechain
processing until at least as much G/R occurs with the processing as without.
Stereo And Multichannel Operation
The two channels of the 414A may be strapped by means of the
INDEPendent/COUPLED switch to assure stereo tracking and stable imaging. In
addition, any reasonable number of 412A's or 414A's can be tracked by paralleling
their rear-panel STEREO CPL terminals. All compressor/limiter VCA's will then
track the channel requiring the highest amount of gain reduction. All operating
controls are usually set identically.
Speech-Activated Ducking of Music
Speech-activated ducking of music is one unusual capability which requires the use
of two (or more) channels with the controls set in aunique way. In this broadcast-
oriented application, the level of the music in the on-air mix is automatically
reduced whenever speech is present.
A414A or two 412A's, in COUPLED or strapped mode, must be used. Channel "A"
is used for the speech, and Channel "B" for the music.
18

Apply the speech to Channel "A", and adjust the "A" operating controls to produce
fast attack and release times.
Apply the music to Channel "B", Adjust the "B" INPUT ATTENuator so that the
music never causes gain reduction to occur in channel "B" even on the highest
peaks.
Speech appearing at the Ch. "A" input at alevel high enough to cause gain
reduction in Ch. "A" will cause equivalent gain reduction in Ch. "B", thus ducking
the music automatically during speech. The RATIO control determines if the music
level is reduced in direct proportion to the speech level (high RATIO), or less than
proportionately (low RATIO). The setting of the INPUT ATTENuator and/or
THRESHOLD primarily determines the depth to which the music is ducked (the
more gain reduction, the more ducking).
The outputs of the "A" and "B" channels (speech and music) may be mixed in an
external mixer in any proportion desired. The original speech source may even be
processed by another 414A with different settings, processed by other equipment, or
left unprocessed.
By analogy, asimilar setup can be used to modulate any signal by the envelope of
any other signal. The range of the ATTACK and RELEASE TIME controls define
the ability of this setup to track rapidly-varying envelopes.

1: ALIGIMMEIMT AND
PERFORMANCE
EVALUATION
PART D:
Maintenance
Introduction: This part of the manual provides instructions on how to maintain the
414A, how to make sure that it is working according to specifications, and how to
repair it if something goes wrong.
Factory service is available throughout the life of the 414A. Please refer to
Factory Service subsection of MAINTENANCE AND SERVICE below for further
information.
CAUTION
Service instructions are included for use by qualified personnel only. To
avoid electrical shock, do not perform servicing other than that
described within Operating Instructions unless you are qualified to do so.
Refer all such servicing to qualified service personnel.
General:
This procedure refers to the 414A (dual-channel version), but is equally applicable
to the 412A (single-channel version). This section provides aseries of thorough
bench tests which will usually verify whether or not the 414A is operating
normally. Certain subtle failures in the dynamic control circuitry cannot be
detected by these tests, since special factory test procedures and equipment are
necessary to fully characterize the dynamic operation of the 414A. Such subtle
failures are usually detected by ear in the field, and factory service is
recommended.
In the case of the dual-channel 414A, the completely redundant channels make "by
ear" trouble diagnosis easier, as the bad channel can be directly compared with the
good one.
The 414A is aligned as these tests are performed. The 414A has five trimmers per
channel (which standardize VGA gain, calibrate the meter, and which null DC
offset, thump and distortion). Alignment is ordinarily required only when 1C3, 1C13,
or 1C14 is replaced.
Power Supply:
Equipment Required;
1) VTVM or DVM
2) Oscilloscope
The following tests will verify correct operation of the Power Supply:
1) Using the DC voltmeter, measure the voltage from circuit ground to both
positive and negative unregulated supplies. This can be readily measured across
the two large filter capacitors. This voltage may be expected to vary widely
depending on line voltage; it should measure between +18 and +26 volts DC.
2) Measure the voltage between circuit ground and the outputs of the positive
and negative voltage regulators, IC13 and IC12. The supplies should deliver
between +14.25 and +15.75 VDC. If either suppiy exceeds 15.75 VDC, it
implies that its associated IC regulator is defective. If either supply is lower
than 14.25 VDC, refer to the Power Supply portion of Part 3in this section
for troubleshooting hints.
3) Using the oscilloscope, measure the ripple and noise on the regulated positive
and negative power busses. Ripple and noise should be less than 2mV peak on
each bus.
21