Beavis Audio Research FKR - Four Knob Rat

Beavis Audio Research

The Proco Rat is probably one of my all-time favorite pedals. Nothing comes close, as far as I'm concerned, to the raunchy irreverent growl that comes out of that box. A few months ago I built a Rat clone and started studying the circuit. What I discovered is that the Rat topology is an ideal laboratory for mods. It uses a cheap nasty LM308 opamp with a pathetic slew rate, and bog-standard 1n914 diodes that clip the output. So why does it sound so good? I think a combination of things like the interesting feedback loop to ground and the fact that the LM308 adds a lot of its own clipping.

I've long wanted to try and create a sort of distortion pedal “synthesizer.” No single pedal meets all of my needs. Wouldn't it be swell if I had a distortion stompbox that I could flip switches and turn knobs so as to create a whole array of sounds. And if the Rat is a great lab for mods, maybe that's a good place to start? Indeed! That how the Four Knob Rat (FKR) started.