Around the same time that the EHX Big Muff was first released in 1969, Mike Matthews also released the Muff Fuzz. It was unrelated to the BMP other than the name, and came in the same small enclosure as the LPB-1 that plugged straight into the guitar. Later it was re-released in a floor pedal as the Little Muff Pi and more recently as the Muff Overdrive. In the mid-70s, the circuit was updated, moving away from the Fuzz Face based transistor circuit to a design based around the popular JRC4558 op-amp. I’ve laid out both versions below and both should fit in a 1590a.
