The BIG MUFF Pi Harmonic Distortion-Sustain Fuzz Pedal from Electro-Harmonix is designed for the electric guitar player. It has three controls that let you dial in fine harmonic distortion/sustain. The Volume control adjusts the output level. The Sustain control optimizes the long sustain, and the Tone control provides a range of sounds, from warm bass to crisp treble.

Power from the internal 9-volt battery or external battery eliminator is activated by plugging into the input. To achieve its long sustain, the Big Muff Pi has a high maximum gain. The small jack on the back of the Big Muff Pi is for a 9V battery eliminator capable of delivering 100 mA of current. The unit's battery may be left in or taken out when the eliminator is in use.