The Cusack Music Project 34 is a preamp/overdrive pedal based on an old component that, as often happens with vintage technology applied to audio, is finding a renaissance for the character it imparts to the signal. Enter the Selenium rectifier.
Used between the ’30s and ’50s in older amps such as the early tweeds, they were later replaced by solid-state silicon components. Cusack had already experimented with them in the Screamer Fuzz Selenium pedal.
Rather expensive and rare, these rectifiers, when embedded in an overdrive circuit, have a sound of their own reminiscent of a a small tube amp.
You can hear it in the videos below.