Voltage Controlled Amplifier with Balanced Input

  • Rajkumar Sharma
  • 40 Views
  • moderate
  • Tested
  • SKU: EL150155
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The project presented here is a Voltage Controlled Amplifier (VCA). A VCA board helps users control the audio level from a remote potentiometer. This board requires a balanced audio signal. Gain control voltage can be adjusted through potentiometer R13. The project works with a dual (±15V) power supply. Screw terminal connectors are provided for signal input and signal output. The project is built using THAT2181LA chip which is a VCA, designed for high performance in audio-frequency applications requiring exponential gain control, low distortion, wide dynamic range, and low control-voltage feedthrough. This chip controls the gain by converting an input current signal to a bipolar logged voltage, adding a DC control voltage, and re-converting the summed voltage back to a current through a bipolar antilog circuit. Stereo control of VCA with a single potentiometer is possible.

THAT2181series trimmable Blackmer voltage-controlled amplifier (VCA) ICs are very high-performance current-in/current-out devices with two opposing-polarity, voltage-sensitive control ports. They offer wide-range exponential control of gain and attenuation with low signal distortion.

Trimming

The trim should be adjusted for minimum harmonic distortion using PR1. This is usually done by applying a middle-level, middle-frequency signal (e.g. 1 kHz at 1 V) to the audio input, setting the VCA to 0 dB gain, and adjusting the SYM trim while observing THD at the output. In 2181, this adjustment coincides closely with the setting which produces minimum control-voltage feedthrough, though the two settings are not always identical.

Features

  • Power Supply +/-15V DC @ 40mA
  • Total Harmonic Distortion 1V 0dB Gain 0.0025%
  • Screw Terminal for Balanced Audio Input
  • Header Connector for Power Input
  • Screw Terminal for Audio Output
  • On Board Power LED
  • 5mm Mounting Holes
  • PCB Dimensions 53.34 x 25.72mm

Connections

  • CN1: Balance Audio Signal Input, Pin 1 = Audio-Hot, Pin 2 = GND, Pin 3 = Audio Cold
  • CN2: Pin 1 = Audio Output, Pin 2 = GND
  • CN3: Pin 1 = 15V DC, Pin 2 = GND, Pin 3 = -15V
  • D1: Power LED
  • R13: Gain Adjust Potentiometer
  • PR1: Symmetry Adjust

Schematic

Parts List

Connections

Gerber View

Photos

Video


THAT2181 Datasheet

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