this is a DOD effect that started up in the early 80s with the metal footswitch series like the OD250 but carried on into the chitty plastic switch line unchanged other then the box and switch. Get the odler version, these switches stink. As the name suggests this is a couple of cascaded fets. I think its similar to that boss preamp pedal the Edge uses. This can add clean or hairy gain to any signal. Its a fantastic boost. I suspect it was actually meant to be a preamp for piezo pickups, but it really excels as a booster/light dirtbox. Really good inf ront of a DI in the studio. Imaprts some interesting color to a guitar signal.