This pedal is a vintage Musicman HD-130 master volume amp's preamp mounted in a pedal running on 9 volts (it draws 19 ma). It has an internal charge pump that converts 9 volts into a bi-polar 9 volt power supply for the circuit. It sounds great with guitar or bass and can be used as a clean boost, or a mild to heavy overdrive. It comes in a polished and etched 125B enclosure with all top jacks. If you're a fan of the vintage HD amps (like I am), you'll love this pedal.