ST-GCA3 Line-Level Automatic Gain Control Amplifier
The automatic gain control unit shall be an RDL ST-GCA3. The unit shall provide one balanced line-level audio input. The unit shall automatically adjust the gain applied to the input signal to drive two separate balanced outputs, one at line level and the other at microphone level.  A user gain control shall be provided to set the amount of expansion or gain reduction for normal input levels. Adjustment of the unit shall be possible using provided LEDs that indicate the amount of expansion or gain reduction.  The unit shall be capable of both slow and fast operation according to a switch setting.

The nominal line input level shall be +4 dBu.  The combined gain of the installer input gain trimmer working with the AGC circuitry shall be capable of producing an output level of +4 dBu for an input signal range from -45 dBu to +20 dBu.  The maximum allowable signal input to the unit shall be +26 dBu.

A continuously adjustable multi-turn trimming control shall be provided to set the fixed gain of the input stage. Two LEDs shall be provided to set the input gain.  A green LED shall vary in intensity in proportion to a nominal range of 18 dB of audio level expansion.  A yellow LED shall vary in intensity in proportion to a nominal range of 18 dB of audio gain reduction.  

The unit shall maintain an average output level within 3 dB over input signal level variations of more than 40 dB. In the absence of a valid input signal, the unit shall slowly mute the output.  Input signal validity shall be determined by a mute threshold which shall be nominally 46 dB below maximum input level or 28 dB below normal input level.  The nominal muting response shall be 15 seconds for 50 dB of output attenuation.

The unit shall provide audio frequency response of 10 Hz to 20 kHz (± 0.75 dB) with total harmonic distortion and noise <0.3% (50 Hz to 20 kHz) and a noise floor exceeding 70 dB below an output level of +4 dBu with the unit output active and less than 80 dB below an output level of +4 dBu with no input signal and the unit output muted.

The unit shall provide a switch to set the AGC action to SLOW or FAST.  Slow AGC shall require 8 seconds for a nominal 20 dB of gain adjustment.  Fast AGC shall require 3 sec for a nominal 20 dB of gain adjustment.

From a fully muted condition, the unit shall ramp to an output active condition within 50 milliseconds nominal.

The unit shall provide one line-level balanced audio output at a nominal rated output level of +4 dBu with an output impedance of 150 O. The unit shall provide one mic-level balanced audio output at a nominal rated output level of -45 dBu into an output impedance of 150 O. Each output circuit shall be configured to produce an unbalanced output of proper phase between the positive output leg and ground. 

The unit shall be constructed in an electrically non-conductive, thermally conductive enclosure. Internal circuitry shall be protected from moisture and vibration using a thermally conductive compound that permanently secures the circuitry within the enclosure.

The face of the unit shall provide graphical labels identifying wiring connections and operating controls. Indicators and controls shall be oriented toward the front edge of the unit.

Connection to external wiring shall be provided using a fixed terminal block on the edge of the unit. The terminal block shall accept wiring gauges from 14 to 22 and shall include a positive electrically conductive mechanism to prevent wire abrasion by the terminal screws.

The unit shall measure 3” (7.6 cm) x 1.6” (4 cm) x 0.7” (1.7 cm) and be compatible with all RDL STICK-ON mounting accessories. The unit shall be supplied with a two part re-closable polypropylene fastener system equipped with a rubber adhesive that bonds to low surface energy materials.

The unit shall be equipped to operate from either 24 Vdc ground-referenced power or from bipolar ± 12 Vdc or ± 15 Vdc power with a maximum current not exceeding 40 mA. The unit shall utilize an external power supply. The unit shall be engineered, assembled and tested in the U.S.A. and be specified for continuous duty in professional installed systems. The unit shall be specified for operation in an ambient temperature between 0 and 55 degrees C. The unit shall comply with relevant EMC requirements and shall bear the CE marking.

The unit shall be an RDL ST-GCA3.