Voltage Controlled Amplifier – VCA

  • Rajkumar Sharma
  • 58 Views
  • easy
  • Tested
  • SKU: EL148503
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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. It requires a single-ended audio signal in the input. Gain control voltage can be adjusted through an on-board potentiometer or use an external potentiometer connected to CN4. 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, a VCA that is designed for high-performance audio-frequency applications requiring exponential gain control, low distortion, wide dynamic range, and low control-voltage feedthrough. These parts control 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.

THAT 2181-series trimmable Blackmer voltage-controlled amplifier (VCAs) 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 THAT2181LA, 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
  • Gain Range -100dB Min-+20dB Maximum
  • Total Harmonic Distortion 1V 0dB Gain 0.0025%
  • Screw Terminal for Single-Ended Audio Input
  • Input Impedance, Audio 20K Ohms
  • Screw Terminal for Audio Output
  • On Board Power LED
  • 5mm Mounting Holes
  • PCB Dimensions 60.96 x 23.50 mm

Connection

  • CN1: Pin 1 = Audio Signal Input, Pin 2 = GND
  • CN2: Pin 1 = Audio Output, Pin 2 = GND
  • CN1: Pin 1 = +15V DC, Pin 2 = GND, Pin 3 = -15V DC
  • R9: Gain Adjust Potentiometer
  • CN4: Optional External Gain Adjust Potentiometer
  • D1: Power LED

Schematic

Parts List

NO.QNTY.REF.DESC.MANUFACTURERSUPPLIERSUPPLIER PART NO
12CN1,CN22 PIN SCREW TERMINAL PITCH 5.08MMPHOENIXDIGIKEY277-1247-ND
21CN33 MALE HEADER PITCH 2.54MMWURTHDIGIKEY732-5316-ND
31CN43 PIN MALE HEADER - OPTIONALWURTHDIGIKEY732-5316-ND
43C1,C4,C1047uF/35V ELECTROLYTIC SMD 6.6MMWURTHDIGIKEY732-8508-6-ND
51C222PF/50V CERAMIC SMD SIZE 0805YAGEO/MURATADIGIKEY
64C3,C5,C7,C8100nF/50V CERAMIC SMD SIZE 0805YAGEO/MURATADIGIKEY
72C6,C910uF/16V CERAMIC SMD SIZE 0805YAGEO/MURATADIGIKEY
81D1LED RED SMD SIZE 0805OSRAMDIGIKEY475-1278-1-ND
91PR150K TRIMMER POTBOURNS INCDIGIKEY3296W-503LF-ND
101R12.2K 5% SMD SIZE 0805YAGEO/MURATADIGIKEY
111R2100E 5% SMD SIZE 0805YAGEO/MURATADIGIKEY
122R3,R420K 1% SMD SIZE 0805YAGEO/MURATADIGIKEY
131R55.1K 1% SMD SIZE 0805YAGEO/MURATADIGIKEY
141R651E 0.1% SMD SIZE 0805YAGEO/MURATADIGIKEY
151R74.12K 1% SMD SIZE 0805YAGEO/MURATADIGIKEY
161R8680K 1% SMD SIZE 0805YAGEO/MURATADIGIKEY
171R910K POTENTIOMETERBOURNS INCDIGIKEYPDB181-K420K-103B-ND
181U1NE5532 SOIC8ONSEMIDIGIKEYNE5532D8R2GOSCT-ND
191U2THAT2181LA SIP8THAT CORPMOUSER887-2181AL08-U

Connections

Gain vs Control Voltage

Gerber View

Photos

Video

THAT2181LA Datasheet

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