Radio Design Labs ST-VCA3
Voltage-Controlled Amplifier


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Radio Design Labs' ST-VCA3 is used in applications requiring smooth audio level control from a remote control panel, potentiometer or dc voltage (0 to 10 V). Installation in series with the audio input of a power amplifier allows remote control of that amplifier’s level. For installations where it is preferred to keep the audio localized in the rack, audio controls are extended outside the rack from the ST-VCA3.

Many installations benefit from avoiding long-term potentiometer wear from audio running through the potentiometer. An ST-VCA3 with external dc control provides virtual immunity from scratchy audio. Audio/video system control units often provide 0 to 10 Vdc control outputs that can directly control audio levels using an ST-VCA3.

The ST-VCA3 is primarily intended for line-level attenuation; a high quality utility microphone preamplifier is included in the module. If remote control of a microphone preamplifier is desired, such as a wall mounted level control for a microphone jack, the ST-VCA3 may serve as a remote controlled microphone preamplifier.

NOTE: Radio Design Labs' PS-24AS power supply is NOT included but is required in order to power this product.  Please see the "Accessories" tab or click here for more information on the PS-24AS power supply.


  • Audio Level Remote Control
  • Audio Level Control from a DC Voltage
  • VCA with Microphone or Line Level Input
  • VCA with Line-Level Output
  • VCA with LED Metering of Operating Level
  • Two Wire with Shield or Three Wire Control


  • Inputs (2):
    - Mic: 200 Ohms balanced; 5 k Ohms unbalanced
    - Line: 30 k Ohms bal. bridging or unbalanced
  • Input Levels (for +4 dBu output):
    - Mic: –44 dBu to –60 dBu (150 Ohms source)
    - Line: -18 dBu (-20 dBV) to +4 dBu
  • Output Signal (normal rated): +4 dBu, 150 Ohms balanced
  • Headroom: 18 dB
  • THD+N:
    - Mic: < 0.05%
    - Line: <0.025% (unity gain)
    0.025% typical at 15 dB attenuation
  • Frequency Response:
    - Mic: 30 Hz to 20 kHz (±1 dB)
    - Line: 10 Hz to 20 kHz (±0.1 dB)
  • Noise:
    - Mic: < -71 dB below +4 dBu output (150 Ohms source; 50 dB gain)
    - Line: <-78 dB below +4 dBu output (maximum gain)
  • CMRR:
    - Mic: > 60 dB
    - Line: > 60 dB, (50 Hz to 120 Hz)
  • Control Input: 0 to 10 Vdc or 0 to 10 k Ohms Linear
  • Attenuation Range: 0 to 90 dB (>90 dB at 0 Vdc control)
  • Power Requirement: GROUND-REFERENCED, 24 to 33 Vdc @ 50 mA
  • Dimensions: 0.7" H x 3" W x 1.6" D (1.7 x 7.6 x 3.9 cm)
24 VDC 500mA Switching Power SupplyRadio Design Labs PS-24AS 24 VDC 500mA Switching Power Supply

Radio Design Labs' PS-24AS is a 24 Vdc switching power supply with a North American AC plug.  500 mA, dc plug.Specifications: Input: 100 to 240 VACOutput: 24 Vdc, 500 mA (UL, CSA)Dimensions: 1.65" x 2.75" x 1.45" (4.2 x 7 x 3.7 ...

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