LEAMING INDUSTRIES AGC432 User manual

March, 1992 AGC432 PAGE 1
LEAMING INDUSTRIES AGC432
STEREO/DUAL MONO
AUTOMATIC GAIN CONTROL
INSTRUCTION BOOK
IB 173432-21B
ALL ENGINEERING DESIGNS, DRAWINGS AND DATA CONTAINED HEREIN ARE
PROPRIETARY. NO PART OF THIS BOOK MAY BE COPIED OR OTHERWISE USED
WITHOUT WRITTEN AUTHORIZATION
COPYRIGHT MARCH 1992
BY
LEAMING INDUSTRIES
15339 BARRANCA PARKWAY
IRVINE, CALIFORNIA 92718
[phone]

March, 1992 AGC432 PAGE 2
AGC432
TABLE OF CONTENTS
SECTION SUBJECT PAGE
1.0 INTRODUCTION 3
2.0 CONFIGURATION 3
2.1 CONFIG, DUAL MONO 4
2.2 CONFIG, STEREO 4
2.3 CONFIG, SYNTHESIZED STEREO 5
2.4 CONFIG, GAIN CONTROL SLOPE (INTERNAL) 5
2.5 CONFIG, RELEASE TIME (INTERNAL) 5
2.6 CONFIG, OUTPUT LEVEL (INTERNAL) 6
3.0 INSTALLATION 6
3.2 CONNECTORS, SCREW-TERMINAL PLUG BlockS 6
3.2.1 REMOTE CONTROL CONNECTION 7
3.2.2 AUDIO INPUT CONNECTION 7
3.2.3 AUDIO OUTPUT CONNECTION 7
4.0 OPERATION 8
4.1 AUDIO INPUT LEVEL SETTING 8
4.2 AUDIO INPUT SELECTION (AD INSERTION) 9
4.3 TRUE STEREO/SYNTHESIZED SELECT (AD INSERT) 9
4.4 VIDEOCIPHER BACKUP AUDIO WITH STEREO SYNTH 10
4.5 ACTIVATING AUDIO AGC REMOTELY 11
5.0 THEORY OF OPERATION 11
6.0 PERFORMANCE EVALUATION 13
7.0 SPECIFICATIONS 14
APPENDIX
COMPONENT LOCATOR DIAGRAM
WARNING
The AGC432 is powered by 120 volts AC. Contact with 120 volts can cause injury or
death. Disconnect the AGC432 from electric power before opening the cover.
Refer service and internal adjustments to qualified personnel.

March, 1992 AGC432 PAGE 3
AGC432
1.0 INTRODUCTION
The AGC432 is a stereo (or dual mono) automatic audio gain control designed
to maintain average program levels within a reasonable range without
reducing the dynamic range to the extent that quiet passages are no longer
quiet and loud passages are no longer loud.
The AGC432 includes a programmed gain controller. When the audio level
falls over 20 dB below normal, the AGC432 assumes that there is a pause in
the program and holds its gain setting for 10 seconds. This maintains the
ambient background levels in their original perspective during brief program
pauses. If the program level has not returned to normal after that 10 seconds,
the AGC432 resets its gain to the bypass value, in preparation for a new
program.
The AGC432's gain controller responds quickly to reduce higher-than-normal
program levels, which avoids audible distortion. For additional protection
against over-modulation by sudden peaks, a limiter clamps any remaining
spikes. Conversely, the gain controller responds gradually to increase
lower-than-normal program levels.
The AGC432 offers three gain-control mode options: Internal jumpers may be
positioned to provide a 2:1 (dB) output compression ratio (Mode 1), or a
Constant-Level output (Mode 2), or an Adaptive-Slope output (Mode 3).
WARNING: To avoid electric shock hazard, disconnect the AGC432 from
electric power before opening the cover.
Refer internal adjustments to qualified personnel.
With this third method, which is the standard configuration, the control slope
makes a gradual transition from a 2:1 compression ratio at low levels to a
constant-level output at elevated input levels. Therefore, a realistic dynamic
range is preserved at normal program levels while very significantly reducing
excessively high program levels.
Each AGC may be used to independently process two monaural inputs, or it
may be configured to process a stereo (L & R) input. In both cases, alternate
inputs ("A" & "B") are provided for local ad insertion or backup audio.
A stereo synthesizer is built-in. The synthesizer may be used, when in the
stereo mode, for the second program input and/or the main program audio.
2.0 CONFIGURATION

March, 1992 AGC432 PAGE 4
NOTE: The toggle switches used on the AGC432 may have self-locking
levers; to actuate, gently pull out on handle, then move lever to selected
position and release.
The AGC432 is shipped ready-to-run in the dual-mono, adaptive-slope mode.
However, you may wish to configure it differently for your application. If not,
you may skip this section and proceed to the Installation section.
The AGC432 may be configured for either dual mono, or true stereo, or
synthesized stereo. This may be done by connecting jumpers to the control
connector on the rear panel, as detailed below. In addition, internal jumper
jacks permit independent selection of any of three gain control curves, as well
as selecting any of three release times for each channel. If in the dual mono
mode, the control curves and release times may be set differently for each
channel, if desired.
The two channels are totally independent in the dual mono mode; whatever is
done to channel 1 will have no effect on channel 2. However, when
configured for the stereo mode, both the left and the right channels can be
simultaneously switched to either the "A" or the "B" program inputs and to
either the AUTOmatic or BYPass mode. By placing both of the the right-
channel switches in their center REMote positions, the left channel switches
will act as masters, controlling both channels simultaneously.
2.1 CONFIGURATION, DUAL MONO
Configure the AGC432 for dual mono operation by removing all straps from
the 8-pin control connector on the rear panel. (Pins 2 & 3, 5 & 6, and 7 & 8
may have been strapped together for stereo operation, and pin 4 may have
been strapped to pins 2 & 3, or to pins 5 & 6, to enable the stereo synthesizer.
The stereo synthesizer should not be enabled in the dual mono mode; the
result would be crosstalk between channels.)
2.2 CONFIGURATION, STEREO
Configure the AGC432 for stereo by strapping the 8-pin control connector on
the rear panel as follows:
Pins 2 & 3 connected together to enable the stereo mode;
Pins 5 & 6 connected together to select the "B" inputs simultaneously;
Pins 7 & 8 connected together to activate the AGC's simultaneously.
Set the Right/Channel 2 A/REM/B input selector and the Right/Channel 2
AUTO/REM/BYP switches in their center REMote positions.
The right channel will then track the switch settings of the left channel.

March, 1992 AGC432 PAGE 5
NOTE: If a remote control is connected to pins 5 & 6 or 7 & 8, the remote
control may over-ride the tracking of the left channel by the right channel; in
this case, the remote control can be over-ridden by setting the switches for
both the left and the right channels in the desired mode ("A" or "B",
AUTOmatic or BYPass).
2.3 CONFIGURATION, SYNTHESIZED STEREO
Configure as for true stereo, and, on the input connector(s) which are being
fed mono audio, strap the left and right channel program inputs together: pins
1 to 4 and 2 to 5 (Right High to Left High, and Right Low to Left Low).
In addition, enable the stereo synthesizer by either connecting pin 4 to ground
at pin 2 or, to automatically switch from true stereo to synthesized stereo when
the "B" program input is selected, strap pin 4 to pins 5 & 6.
2.4 CONFIGURATION, GAIN CONTROL SLOPE (INTERNAL)
WARNING: To avoid electric shock hazard, disconnect the AGC432 from
electric power before opening the cover.
Refer internal adjustments to qualified personnel.
The AGC432 may be configured to any one of three gain control slopes (2:1,
Constant Output, or Adaptive Slope) by positioning jumper jacks on quads of
pins on the circuit board. The four pins arranged in a quad on the left half of
the board (as you look down from the front) are for the left channel (Channel
1); those in the quad on the right half are for the right channel (Channel 2).
The compression mode is normally factory-set to Adaptive Slope (Mode 3).
This is optimum for most applications.
2.4.1 Mode 1 (2:1) is selected by installing two jumper jacks to connect the front and
rear pins of both sides of the appropriate quad.
2.4.2 Mode 2 (Constant Output) is selected by installing just one jumper jack, to
connect the front and rear pins on the right side of the appropriate quad. Store
the remaining jumper jack on one of the remaining pins.
2.4.3 Mode 3 (Adaptive Slope) is selected by installing just one jumper jack, to
connect the front and rear pins on the left side of the appropriate quad. Store
the remaining jumper jack on one of the remaining pins.
Mode 3 is a combination of the most desirable characteristics of both modes 1
& 2. Mode 3 preserves most of the apparent dynamic range of programs at
normal audio levels by gently increasing the gain when the level drops below
normal. However, if the input level rises above normal, the gain is decreased
by a considerably greater factor. For a more thorough discussion of the gain
control curves, refer to the Theory of Operation section of this manual.
2.5 CONFIGURATION, RELEASE TIME (INTERNAL)

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WARNING: To avoid electric shock hazard, disconnect the AGC432 from
electric power before opening the cover.
Refer internal adjustments to qualified personnel.
The AGC432 may be configured to any one of three release times (10, 15, or
25 seconds). The release time can be set by positioning jumper jacks on a
row of three pins on the circuit board. The three pins arranged in a row on the
left half of the board are for the left channel (Channel 1); those in the row on
the right half are for the right channel (Channel 2).
The selection of release time always involves compromise: A faster release
time may make the operation of the gain control more obvious, and a slower
release time may result in prolonged recovery when a different program
source at substantially lower level is encountered. The factory setting of 10
seconds is optimum for most TV audio programs.
2.5.1 10 seconds is selected by installing a jumper jack to connect the two pins on
the left end of the row.
2.5.2 15 seconds is selected by installing a jumper jack to connect the two pins on
the right end of the row.
2.5.3 25 seconds is selected by not connecting any of the three pins. Store the
jumper jack on one of the pins.
2.6 CONFIGURATION, OUTPUT LEVEL (INTERNAL)
WARNING: To avoid electric shock hazard, disconnect the AGC432 from
electric power before opening the cover.
Refer internal adjustments to qualified personnel.
The peak program output level of the AGC432 may be adjusted from zero up
to greater than +18 dBm. The standard factory setting is +10 dBm.
The level controls are located on the AGC432's circuit board, at the right rear
of the unit as you look down from the front. The control on the left affects the
left channel (channel 1) and the control on the right affects the right channel
(channel 2).
Accurate adjustment requires the use of an external audio generator and
meter. Set the AUTO/REM/BYP switch to BYPass. Connect the generator to
the input of the channel(s) to be re-calibrated and adjust the generator's output
to 1000 Hz at a level which will illuminate the yellow 0 dB LED(s) at approx.
half-intensity. Connect the meter to the output to be calibrated. Adjust the
appropriate level control on the AGC432's circuit board as required.
3.0 INSTALLATION

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3.1 MOUNTING
The AGC432 is intended to be mounted on a Leaming PMU401 Mainframe.
Each unit requires one-third of the PMU401.
To mount the AGC432 in a PMU401, remove the blank front plate (if any) from
the PMU401, place the AGC432 in the selected position, and secure it with the
four #6-32 screws provided.
3.2 CONNECTORS, SCREW-TERMINAL PLUG BLOCKS
The connectors on the AGC432 are a combination plug/screw-terminal type.
To wire the connector, simply pull the body of the connector straight back, off
the plug inside the chassis. Strip the insulation off the wire (approx. 3/16"),
slip the wire into the clamp, and tighten the screw. After each wire has been
secured, push the connector body onto the plug in the chassis.
NOTE: The AGC432 uses four separate connectors. Observe the pin/body
alignment when installing, to avoid possible connector damage. The connector
groups and pin assignments are noted on the chassis. They are as follows, as
observed from the rear of the chassis:
3.2.1 REMOTE CONTROL CONNECTION
The remote control connector uses 8 pins:
Pin 1, Reserved for optional +24 V
Input
Pin 2, Ground
Pin 3, Stereo Mode
Pin 4, Synthesized Stereo
Pin 5, Select "B", Ch. 2
Pin 6, Select "B", Ch. 1
Pin 7, Activate AGC, Ch. 2
Pin 8, Activate AGC, Ch. 1
The remote controls are active-low. Grounding the respective remote control
line selects the alternate mode, such as SYNTHesizer on, and/or Input "B".
To enable each remote control pin, the respective switch on the front panel
must be in the REMote (center) position.
The remote ground may be by hard-contact switch or relay, or by any suitable
solid-state device which can pull a 10 k-ohm line from +5 V to within 1 V of
ground, and release it with over 100 k-ohms.
3.2.2 AUDIO INPUT "A", AND AUDIO INPUT "B" CONNECTION
Each input ("A" & "B") uses a 5-pin connector:
Pin 1, Right/Channel 2 High
Pin 2, Right/Channel 2 Low
Pin 3, Ground
Pin 4, Left/Channel 1 High

March, 1992 AGC432 PAGE 8
Pin 5, Left/Channel 1 Low
Be sure that the chassis of the AGC432 and the source are both grounded.
Usually this is done with the power cord safety ground and/or the mounting
rack frame ground.
For optimum results, use twisted-pair cable with an overall shield. Connect
the Right and Left shields together to the common ground terminal on the
AGC432.
If driving from an unbalanced source, the AGC432's High terminal carries the
signal and the AGC432's Low terminal is to be connected to the shield.
Input "B" can either be used for local ad insertion or for backup audio. The "B"
input is wired in the same procedure as the "A" input, with the exception that it
is plugged into the "B" Input connector on the back of the AGC432 (rather than
Input "A"). See Section 4.2 for information regarding the selection of A/B
inputs and stereo synthesis.
3.2.3 AUDIO OUTPUT CONNECTION
The audio output uses a 4-pin connector with the same sequence as the
inputs, except the center Ground pin has been eliminated:
Pin 1, Right/Channel 2 High
Pin 2, Right/Channel 2 Low
Pin 3, Left/Channel 1 High
Pin 4, Left/Channel 1 Low
Be sure that the chassis of the AGC432 and the load are both grounded.
Usually this is done with the power cord safety ground and/or the mounting
rack frame ground.
If driving to a balanced load, the shield should be connected at one end only,
that being at the load end, in order to minimize ground loops.
If driving to an unbalanced load, the AGC432's High terminal carries the signal
and the AGC432's Low terminal is to be connected to the shield, which should
be grounded at the load end only, in order to minimize ground loops.
4.0 OPERATION NOTE: The toggle switches used on the AGC432 may have
self-locking levers; to actuate, gently pull out on handle, then move lever to
selected position and release.

March, 1992 AGC432 PAGE 9
4.1 AUDIO INPUT LEVEL SETTING
The AGC432 is furnished with two sets of input level controls on the front
panel: LEFT/CH 1 "A" & "B", and RIGHT/CH 2 "A" & "B". Audio program
levels are monitored with peak-reading LED bargraphs, one for LEFT/CH 1
and one for RIGHT/CH 2.
4.1.1 Set the AUTO/REM/BYP switch to the BYPass mode. Before switching the
AGC to the AUTOmatic mode, be sure that the input levels have been set.
4.1.2 Set the A/B Input Selector switch to correspond with the input you are using.
4.1.3 Adjust the appropriate Level control (Left/Channel 1, Input "A" or "B" or
Right/Channel 2, Input "A" or "B") on the AGC432 so the peak-reading VU
meter reads approximately 0 dB (yellow LED) and the red LED flashes only
rarely and only on very loud program material. Be sure that the AGC mode
switch on the front panel is in the "BYP" position when making any level
adjustments.
NOTE: If the AGC was just in the active mode, and if the meter was reading
above mid-scale, wait 10 seconds after switching to "BYP" for the gain to
return to normal before positioning the input level control. This wait may be
shortened to one second by momentarily switching to the other input.
(Whenever the input selector is switched, the release time is momentarily
reduced to permit rapid recovery and accomodation of any program level
change.)
4.1.4 Set the AUTO/REM/BYP switch to AUTO. The green AUTO LED will
illuminate. If your levels were set high, you may notice them drop down;
otherwise, there should be no noticeable level changes. If the program
pauses or the input level drops over 20 dB below normal, the VU meter LED
will extinguish, indicating that the automatic level control is holding the gain at
the last setting. If the program level remains at or below this level for 10
seconds, the AUTO LED will extinguish and the gain setting will change to 0
dB, the same as in the bypass mode. The unit will automatically be re-
activated when the program returns.
NOTE: The operation of the AGC432 is nearly transparent; consequently it is
extremely difficult to detect, as over-modulation is quickly reduced, and low
levels are raised very slowly, in order to retain the apparent dynamic range
and eliminate audible gain changes. To demonstrate that the unit is indeed
functioning, intentionally apply a noticeably stronger-than-normal signal with
the AGC432 in the bypass mode, then switch the AGC432 to the active mode.
There should be a noticeable reduction in the audio level. When the AGC is
switched off, the audio level will gradually recover. It is convenient to use an
input level control of the AGC432 to do this; just re-set this control as outlined
above when the demonstration is completed, in order to set the AGC432 into
its optimum range.

March, 1992 AGC432 PAGE 10
4.2 AUDIO INPUT SELECTION (AD INSERTION)
In the REMote position of the A/REM/B selector switch, when terminal
A/B CH 1 (pin 6) or A/B CH 2 (pin 5) is grounded, the AGC432 switches that
channel from Input "A" to Input "B". The front panel A/REM/B switch will
override any remote control connections on the back panel if placed in either
the "A" or "B" position.
To switch from Input "A" to Input "B" by remote control, such as when using ad
insertion equipment, connect the appropriate A/B terminal(s) on the AGC432
to the relay(s) which you are using to control the audio switch. The relay(s)
must be capable of pulling a 10 k-ohm line normally at +5 volts to within 1 volt
of ground.
4.3 TRUE STEREO/SYNTHESIZED SELECTION (AD INSERTION)
The AGC432 is equipped with a built-in stereo synthesizer, for use whenever
the desired output is stereo but the source programming is mono (e.g. many
local commercials are mono, while the main program audio is stereo). The
AGC432 is normally in true stereo. By simply installing one jumper on the
remote connector, combinations of true and synthesized stereo can be
selected: "A" & "B" true stereo; "A" true & "B" synthesized, or both "A" & "B"
synthesized.
To automatically select synthesized stereo whenever the "B" inputs are
selected (either locally or remotely), connect pin 4 (SYNTH) to pins 5 & 6 (A/B
CH 1 & A/B CH 2) on the Remote Control connector. Then, when pins 5 & 6
are grounded (e.g. by local commercial insertion equipment or VideoCipher
bypass) pin 4 is also grounded, selecting the "B" inputs and stereo synthesis
together.
CAUTION: If the stereo synthesizer is also to be used with both ad insertion
and backup VideoCipher audio (as follows in Section 4.4), replace the wire
between pin 4 and pins 5 & 6 with any standard silicon diode (1N4148 or
1N4001 or similar) to avoid selecting the "B" input when only the stereo
synthesizer is desired; the cathode of the diode must be connected to pins
5 & 6 and the anode must be connected to pin 4 (The diode's arrow should
point toward pins 5 & 6).
OPERATIONAL NOTE: If the program source is mono and the corresponding
AGC432 input is configured for synthesized stereo, the listener will hear an
apparently stereo source with considerable ambience and some (artificial)
directionality.