Robert Keeley retained the Differential Pair transistor setup at the heart of the design that is unique to the Fuzz Head. Keeley added a JFET tube-amp simulator on the front end followed by a germanium transistor gain stage. They vastly improved the Tone Control and moved it to the outside of the pedal. Diode clipping can be completely removed for a brutal overdrive sound. This does Fuzz to the extreme and Overdrive supreme. Want to own a truly unique Keeley design? This is it. It combines the best elements of all out raging fuzz and overdrive. The key elements to that design remain intact.