Voltage Controlled Wah Wah for Modular Synths

YouTube via thecmpguru — April 27, 2010 — "This is a circuit I designed, based off of a multiple feedback active filter described by R.G. Keen (http://www.geofex.com/article_folders/wahpedl/wahped.htm).

The effect is a band-pass like response with a movable center frequency. Unlike Keen's circuit, however, the frequency of this circuit is voltage controllable (instead of manually using a pot). Also, I have increased the input impedance and made it non-inverting overall.

The circuit takes an input signal (typically, 5 Vp-p audio) and an input control voltage (tested ranges of -5V to 5V). It outputs the filtered audio with a potentiometer for controlling volume.

This demo shows a MOTM synth generating the input signal (a sawtooth wave) and the control voltage signal (from the LFO). The control voltage sweeping up and down is akin to a guitarist rocking a wah-wah pedal back and forth. But instead of guitars, here we're dealing with a modular synth.

Next steps..... make a prototype board of this sucker!"