Pro Co RAT
Op-amp distortion with hard clipping to ground — gritty, percussive, iconic.
About
A high-gain LM308 op-amp stage drives a pair of 1N914 diodes clipping to ground (hard clipping). A passive low-pass 'Filter' control rolls off treble after clipping for the RAT's signature dark fizz. Capable of overdrive to full-on distortion to fuzz-ish territory.
Signal chain preview
5 stagesInput
Input pulldown + DC blocking
LM308 inverting op-amp gain stage (gain up to ~60 dB via 100k Distortion pot)
Output
Quick facts
- Hard clipping (diodes to ground) produces a more aggressive, square-wave-like distortion than the TS808.
- Original LM308 op-amp has a low slew rate that limits fizz on transients — part of the sound.
- The 'Filter' knob is wired backwards: clockwise = darker.
- Used by Jeff Beck, Thurston Moore, and Kurt Cobain (notably on In Utero).
Controls
- Distortion (100k log)
- Filter (100k linear, reverse-wired)
- Volume (100k log)