The ARDUINO WAH // JC Maillet (c) 2016

A few years back I went through a brief “mixed-signal” design phase – mainly with the intended purpose of seeing how far I could get using off-the-shelf CMOS analog gates driven digitally. Yes, similar to how Keith Barr did it in the 70’s with his Auto Filter design – except he did it using analog PWM – which is way cooler in a way, but too limited for my purposes. Hence, the ARDUINO (nano) AVR based clock generator – with tune-able end-points, yada yada …

Much of this experimenting came from be-friending TEK456B who is as passionate about coding than I am about circuit design. I took advantage of this opportunity and with his invaluable assistance designed mildly original phasors, compressors, wah’s and a few other nifty contraptions – while, in the process, getting an indirect measure of the gate’s AC equivalent resistance against duty-cycle.

Much of what we did involved a 32khz running clock with an 8-bit PWM resolution – ie., with +/- 0.39% PWM variation per bit. In this particular case the polling that reads the WAH pot voltage is set to a frequency of 20hz, yielding smooth action. Absolutely no aliasing was perceived in the process – yielding surprisingly clean behavior for such a bare signal path.

Using a “threaded” 50kA pot custom custom made Joe Gagan, the pedal provides a good WAH feel and sound character (especially for an inductor-less circuit) along with very good headroom qualities – despite only running at 5vdc …

This as my third “alternate” emulation of the WAH circuit concept – the other two are full-analog hardware simulations of the classic circuit; this one is different … the fact that this simple pseudo-state-variable filter came out sounding this close to the Kushner-Plunkett (two transistor) classic was a bit of a surprise! Not quite the same exactly in AC response, but similar enough …