Electro-Harmonix Nano Bass Big Muff Pi Distortion/Sustainer for bass The new Nano Bass Big Muff is the latest EHX bass guitar, effect pedal. It delivers that huge Bass Big Muff sound in a nano-sized package. With voicing inspired by the battle-tank green, Russian Big Muff and a classic Big Muff Pi layout of Sustain, Tone and Volume controls, it provides sounds ranging from a slight but satisfying grit to an over-the-top wall of bass fuzz.