Erica Synths Black Quad VCA2 is a versatile four channel voltage controlled amplifier and mixer module for use in complex modular systems. Each channel has linear/logarithmic response selector and signal level indicator LED. All outputs are sequentially mixed and CV inputs are normalled to each other, so you can use the module in various configurations. If no CV is applied, the Black Quad VCA2 performs as a signal mixer, and the 4th channel is DC coupled for controlling CV sources, as well.