This is one more module for my quad system. It contains four VCA with normalized input, so you can distribute one input signal to four output channels. With each channel under voltage control you can move the input signal through the room dependent on the control voltages. I have two versions build one AC and the other DC coupled. Beside using this VCA’s for signal distribution you can use every VCA independently. The gain to voltage ratio is linear. This is done because it is easier to predict the performance. The distribution of the signal must be steered through the control voltages. The implementation follows the recommendations from an article at Open Music Labs from October 3, 2015 (Minimizing distortion in OTA’s)
Specs and features
- Four VCA with normalized input
- Usable as four independent VCA as well
- Linear gain to voltage response
- Individual Volume, CV and Bias controls
- Low distortion implementation
- Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
- Power consumption around 35mA each rail
The documentation and the Gerber files for download can be found in my website.
The linear controlled current source for Iabc is straight forward and implemented as usual. An elaborate description for the VCA part is given here.
On the left side are the potentiometers for volume control followed by the input buffers. The only difference between AC and DC coupling are the capacitors. On the right side are the CV input potentiometers and the bias potentiometers followed by the voltage adder.
