A-101-6 is a filter module that uses so-called opto FETs to control the filter frequency. Opto FETs are very similar to Vactrols but use light depending field effect transistors (FETs) instead of light depending resistors (LDRs). A opto FET is a combination of a light depending FET and a LED (light emitting diode) both put into a small light-proof case. The advantage compared to vactrols is the much faster response of opto FETs compared to LDRs. This allows much faster attack/decay times and even FM effects. The disadvantage compared to vactrols is that the FET behaves as a normal Ohm resistor only for small levels. 

Module A-101-6 is made of six serial 6dB filter stages. Each stage can work as lowpass, highpass or one of two allpass types. 
The brightness of the Opto FET LEDs and consequently the filter frequency can be adjusted manually (Frequ. control) and controlled by means of an external control voltage (CV) with attenuator.

technical details

Width: 8HP 

Connections: 
Audio input 
FB input 
FB output 
CV input 
Audio output