Voltage Controlled Amplifier with Balanced Input
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.
THAT2181–series 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
Share
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.
THAT2181–series 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
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