The Plasma Vintage Drive is a clone of the Colorsound Overdriver, a transistor-based boost/drive pedal with 2-band tonestack that was first sold in 1972.
The Overdriver was an updated version of the Power Booster from 1970. The Power Booster ran at 18V using two batteries in series. The Overdriver dropped the requirement of the second battery and ran on a normal 9V supply. There were a few other very minor tweaks to component values, but it’s the same basic circuit.
The Plasma project is a direct clone of the Overdriver, but with one modification: it adds an output volume control. This way you can set the gain according to the tone you want without being tied to the volume that is produced along with it.
Note that the Overdriver can be “splatty” at medium gain levels as the notes decay. It works best at low gain as a clean boost with tone-shaping capabilities, or at high gain where it’s not unlike a Big Muff. If you hear this splattiness, know that it’s a byproduct of transistor-based distortion and it’s working correctly!
The 125B version of the Plasma is different from the first version in that it drops the Power Booster compatibility. The Power Booster is instead available as another circuit, the Nucleus, which has an on-board charge pump for 18V operation. In addition, in this revised version, the transistor bias trimmers have been removed. It’s not necessary to bias the transistors in the Overdriver circuit for correct operation.