EarthQuaker Devices Dirt Transmitter Fuzzdriver Effects Pedal Bias control - allows you to control the voltage being sent to the transistors. This allows for everything from gated, 60s fuzz tones all the way through, heavy thundering fuzz snarl with a simple twist of the dial. The fuzz control can produce tones from overdrive like break up to all out thick ripping fuzz tones while never getting flabby. Excessive amounts of volume and virtually no extraneous noise. Works great with both single coils and humbuckers, excellent clean up with the guitar volume.