I am obsessed with what Electro-Harmonix did here because they solved one of my favorite gear puzzles elegantly — the Big Muff Pi 2 is a modern redesign that keeps every classic characteristic while removing all the vintage reliability issues I hate in old fuzz boxes. The original 1967 circuit used two op amps per side and aged inconsistently, which made copycat pedals sound different from unit to unit; here you get two brand-new dual op-amp stages with a dedicated JFET preamp instead of an aging transistor, meaning it actually runs on batteries reliably and keeps the same tone for decades. The secret sauce is BurrArrTech's TTP10157 chip — EHX designed this specifically for the Big Muff Pi 2 so they could deliver true VCF tones without infringing on patents while achieving massive stability. You get two gain knobs (one per stage) and a "Tone" that isn't a sweep but a selector between two preset modes because a real Muff doesn't have a tone knob, and these op amps compensate for the loss. The pedal delivers roughly 20dB of total boost across both stages with true stereo output from each one — pure distorted perfection in one enclosure.

Source: https://www.musicradar.com/guitars/guitar-pedals/electro-harmonix-big-muff-pi-2-dual-op-amp-review