This Module is currently available.
Passive Filter / LPG / VCA
Amazing what you can do with a bunch of resistors and an optocoupler - this is a revamped version of the old OptoThing which uses (mostly) surface mount components, meaning it's a little bit cheaper. I have, however, kept the Sharp PC817 optocouplers since I wasn't really happy with the response of the SMD Toshiba optos that I was trying.
Surprisingly versatile - a control voltage is used to trigger an optocoupler which sits between the input and output signals. So far, so boring. However, this is not your typical Vactrol-type application: by fiddling with the potentiometer you can limit the current passing through the optocoupler (think in terms of a current-limiting resistor on a 'regular' LED) which can have quite a profound effect on the final sound - it can be used as a low-pass gate, a resonant quasi-filter or a ghetto-style VCA (the original intended use).
Inputs are DC coupled, although since this module is passive you may wish to buffer any control voltages if you're using the output to drive a VCO or similar.
