EH Big Muff Pi electric guitar circuit effect diagram

The picture below is a schematic diagram of the electric guitar effect: Electro-Harmonix (EH) Big Muff Pi.

The EH Big Muff Pi effects circuit will probably work better with a modern input jack power supply and a ? DPDT bypass switch. The transistor and diode types are unknown. Any high gain NPN transistor and diode 1N914 will probably work. It has been reported to work best if the coupling capacitors marked with * are changed to 0.1uF and the capacitors marked with ** are changed to 1.0uF. The original transistors are marked SPT 87-103 and the original diodes are marked 525GY or 523GY (difficult to read.)

The Big Muff Pi is a fuzzbox produced in New York City by Electro-Harmonix and its Russian sister company Sovtek, primarily for electric guitar. Due to the Big Muff's low frequency response, it is also used by bassists.

The Big Muff Pi was the first overwhelming success of the Electro-Harmonix pedal line. Due to its reliability, low price, and unique sound, the Big Muff remained a bestseller through the 1970s and is in the pedal collections of countless guitarists. For example, David Gilmour and Carlos Santana (although CS owned one he reportedly didn't use it) are some of the famous users of the pedal. David Gilmour used the Big Muff on Pink Floyd's albums Animals and The Wall, and more recently on their 2006 On An Island tour. Other artists who used the Big Muff in the 1970s included Thin Lizzy, Kiss, Frank Zappa (who FZ modified to produce a very atypical BMP distortion), and Ronnie Montrose. Metallica bassist Cliff Burton frequently used the Big Muff for lead bass and solos.