PositronPreamp Drive

From the vendor

The preamp circuit of the Gorilla TC-35 amplifier adapted for use as an overdrive pedal.

The Positron Preamp Drive is an adaptation of the Gorilla TC-35 Tube Cruncher amplifier that first appeared in 1986. The Gorilla amps were solid-state combo amps aimed at the budget market. They were not terribly well-regarded in their day, but they caught the eye of Josh Homme from Queens of the Stone Age who cranked them for their unique overdrive tone.

Interestingly, there are no clipping diodes present, and so all of the overdrive comes from overloading the opamp. Typically this is an undesirable characteristic that is avoided, but in this circuit it works.

The Positron is an adaptation of the TC-35’s preamp section. It’s a direct clone of the circuitry based on factory schematics, running on the same voltage as the original, but meant to be used as a standalone drive pedal instead of a true preamp.

Note: This project uses a type of capacitor that has been temporarily discontinued by WIMA. Please see our news article about the issue and the substitution spreadsheet for project-specific recommendations. We are stocking a limited supply in the mean time. The build document has not yet been updated to reflect this.