RDL STGCA3 Specifications

STICK-ON® SERIES

Model ST-GCA3
Audio Gain Control Amplifier

ANYWHERE YOU NEED...

 Automatic Gain Control
 Wide Dynamic Range AGC
 Slow or Fast Gain Adjustment
 Low Noise, Low Distortion AGC
 RDL SupplyFlex™ Power Input

You Need The ST-GCA3!

The ST-GCA3 Gain Control Amplifier is part of the group of STICK-ON products from Radio Design Labs. The
durable adhesives provided with the ST-GCA3 permit permanent or removable mounting. Numerous available
mounting accessories, brackets and rack-mount chassis are optionally available to facilitate any system design. The
ST-GCA3 is a unique, high-performance electronic module offering constant, automatic level control of audio signals.

APPLICATION: The ST-GCA3 is a high performance automatic gain control amplifier designed to maintain a
constant average output level over a wide range of input levels. It automatically adjusts for changes in input levels,
bringing up low levels and reducing high levels. The adjustment rate is switch-selectable to either SLOW or FAST.
The SLOW setting on the ST-GCA3 is the ideal choice anywhere slowly varying audio levels such as music need to
be maintained at a constant level. The slow gain-riding maintains the desired average operating levels without
introducing any audible compression artifacts. The FAST setting of the ST-GCA3 makes it ideal for use in systems
prone to loud bursts of audio, and inconsistent levels which must be constantly and quickly corrected, such as voice.
The gain of the ST-GCA3 automatically adjusts to deliver a nominal +4 dBu line level output. The MIC level output is
50 dB below the line output. The regular AGC action is supplemented by a circuit which detects the amount of peak
material present and speeds up the AGC correspondingly. When audio is not present on the input, AGC searching is
limited to about 5 seconds. During a sustained period without audio input, the ST-GCA3 outputs fade to a muted
condition. When audio is next applied, the output instantly ramps up to the correct level.

Two LED indicators are provided to make setup accurate and simple. A green LED varies in intensity to show the
amount of expansion. An adjacent yellow LED varies in intensity indicating gain reduction. For most installations, a
normal audio level is applied and the gain trimmer is adjusted for minimum indication on both LEDs, producing equal
available expansion and gain reduction.

The ST-GCA3 features RDL SupplyFlex. The power supply input may be fed from a floating (not ground-referenced)
24 Vdc power source, from a bipolar power supply (+/-12 Vdc or +/-15 Vdc), or from a ground-referenced 24 Vdc
power supply. A jumper on the terminal block is used to select the ground-referenced power configuration.

Some examples where levels are not consistent, but often need to be:

 Production studio outputs feeding recording machines
 Mic mixer output where people speak at inconsistent levels
 Audio feeds from telephone systems
 Line-level feeds in an audio system where users can set controls too high or too low
 Pre-conditioning levels into an audio limiter
 Paging, intercom, and interconnect systems

Making audio levels uniform and consistent improves the performance of nearly any type of audio system in
broadcast, paging, or sound reinforcement. With its unique combination of features, exceptional audio performance,
and convenient installation, the ST-GCA3 provides the solution! Use the ST-GCA3 with other RDL RACK-UP®,
STICK-ON, TX™, or FLAT-PAK™ series products as part of a complete audio/video system.

RDL  659 N. 6th St.  Prescott, AZ., USA 86301  [phone]  FAX [phone]  www.rdlnet.com

STICK-ON® SERIES

Model ST-GCA3
Audio Gain Control Amplifier

A
C

G

T

LINE LEVEL

A

I

I

O

INPUT

N

N

SIGNAL

FROM

BALANCED

LINE-LEVEL

SOURCE

A
C

G

T

LINE LEVEL

A

I

O

I

INPUT

N

N

OPTIONAL JUMPER

(WHEN USING GROUND-REFERENCED
POWER SUPPLY)

GAIN CONTROL AMPLIFIER

GATED OUTPUTS

MIC LEVEL

OUTPUT

SIGNAL

FEEDING
BALANCED
MIC-LEVEL

EQUIPMENT

LINE LEVEL

OUTPUT

SIGNAL

FEEDING
BALANCED
LINE-LEVEL

EQUIPMENT

GAIN REDUCTION
GAIN EXPANSION

GAIN CONTROL AMPLIFIER

GATED OUTPUTS

MIC LEVEL

OUTPUT

RDL PS-24

TYPE

SUPPLY

LINE LEVEL

OUTPUT

GAIN REDUCTION
GAIN EXPANSION

24 Vdc

POWER

SOURCE

PWR

SLOW FAST

U

MODULE

AGC

ACTION

Set slide switch to
either the S (SLOW)
or F (FAST) position.
This determines the
speed of gain control
action the module
applies to the signal.

PWR

SLOW FAST

U

A
C
T

I
O
N

FS

A
C
T

I
O
N

FS

AUDIO

WIRING

25 TURN

GAIN SET

ADJUSTMENT

For most installations, adjust
gain with a "normal" input level
applied. The LEDs show the
amount of expansion (green
LED) or gain reduction (yellow
LED). Turn up the gain until
the green LED becomes
dimmer and the yellow LED is
not flashing frequently. This
setting provides equal available
gain reduction and expansion.
If less gain reduction and more
expansion is desired, then
adjust for greater activity of the
yellow LED. If less expansion
is desired, adjust for a brighter
green LED and no yellow
flashing. The intensity of each
LED indicates approximately
18 dB of activity (expansion or
gain reduction).

SUPPLY

WIRING

DO NOT

GROUND

NEGATIVE

FOR FLOATING

OR BIPOLAR

POWER

INSTALLATION

OR

ADD GROUND

JUMPER TO

SUPPLY "-"

FOR GROUND-

REFERENCED

POWER

INSTALLATION

A
C

G

T

LINE LEVEL

A

I

I

O

INPUT

N

N

SIGNAL

FROM

UNBALANCED

LINE-LEVEL

SOURCE

A
C

G

T

LINE LEVEL

A

I

O

I

INPUT

N

N

AUXILIARY

BIPOLAR

SUPPLY

Installation/Operation

EN55103-1 E1-E5; EN55103-2 E1-E4

Typical Performance reflects product at publication time
exclusive of EMC data, if any, supplied with product.
Specifications are subject to change without notice.

GAIN CONTROL AMPLIFIER

GATED OUTPUTS

OUTPUT

FEEDING

UNBALANCED

LINE-LEVEL

EQUIPMENT

LINE LEVEL

SIGNAL

MIC LEVEL

GAIN CONTROL AMPLIFIER

GATED OUTPUTS

OUTPUT

LINE LEVEL

MIC LEVEL

GAIN REDUCTION
GAIN EXPANSION

OUTPUT

GAIN REDUCTION
GAIN EXPANSION

OUTPUT

-

12

G

OR

N

15

D

Vdc

BIPOLAR SUPPLY

PWR

SLOW FAST

U

FS

NOTE: If this ST-GCA3 is
replacing an RDL ST-GCA1
in a system, set the
ACTION switch to SLOW.
If this ST-GCA3 is replacing
an RDL ST-GCA2 in a
system, set the ACTION
switch to FAST.

PWR

SLOW FAST

U

FS

+

12

OR

15

Vdc

A
C
T

I
O
N

A
C
T

I
O
N

TYPICAL PERFORMANCE

Input: +4 dBu balanced (nominal); -45 dBu to +20 dBu for rated output
Maximum Input Level: +26 dBu
Outputs (2): +4 dBu, 150 balanced LINE (nominal, +0/-3 dB); -45 dBu balanced MIC into 150 
AGC Range: >40 dB (Input signal range for which output level is maintained within 3 dB)
Frequency Response: 10 Hz to 20 kHz (+/- 0.75 dB)
Noise:

No input signal, output un-muted: <-70 dB
No input signal, output muted: <-80 dB

Input signal present, output muted: <-50 dB
THD + N: <0.3% (50 Hz to 20 kHz; Typ. 0.05% @ 1 kHz)
Mute Threshold: -46 dB below maximum input; -28 dB below normal input
Muting Response: 15 sec. for 50 dB

SLOW AGC response: 8 sec. for 20 dB average level adjustment
FAST AGC response: 3 sec. for 20 dB average level adjustment

On Delay: 50 ms to ramp from muted to fully on condition
Indicators (2): LED, green variable intensity to indicate audio expansion

LED, yellow variable intensity to indicate audio gain reduction

Note: Both LEDs display equal intensity for normal input level (equal available expansion and gain reduction).

Power Requirement: 24 to 33 Vdc @ 40 mA, Ground-referenced or Floating

Radio Design Labs Technical Support Centers

U.S.A. [phone], [phone]; Fax: [phone]

891-1125C

Europe [NH Amsterdam] (++31) 20-6238 983; Fax: (++31) 20-6225-287