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Fuzz1969· Electro-Harmonix (USA)

Electro-Harmonix Big Muff Pi

Four-stage transistor fuzz with diode clipping in two stages — walls of sustain.

⏳
Schematic pending verification

We don't ship reference schematics until they've been hand-authored against authoritative sources (manufacturer service docs, ElectroSmash analyses, GEOFEX writeups) and reviewed in the simulator. Until then, the BOM, signal chain, controls and mod notes below are accurate, and you can still add this pedal to a project — it just won't include a circuit yet.

About

A four-stage circuit: input booster, two cascaded clipping stages (each with diodes across the feedback resistor), a scooped passive tone stack, and an output recovery amp. Produces enormous sustain and a deeply scooped midrange.

Signal chain preview

6 stages
Input
Q1: input common-emitter booster
Q2: 1st clipping stage with anti-parallel diodes in feedback
Q3: 2nd clipping stage with anti-parallel diodes in feedback
Passive scooped tone stack (Tone pot between low-pass and high-pass)
Q4: output recovery amplifier
Volume pot at output
Output

Quick facts

  • The 'scooped' tone stack is what gives the Muff its signature 'recessed' midrange.
  • Cascading two soft-clipping stages produces extreme sustain without losing note pitch.
  • Variants are legion: Triangle (1969), Ram's Head ('73), Op-Amp (~'78), Russian Sovtek ('90s).
  • Used by David Gilmour, Billy Corgan, and Jack White, among many others.

Controls

  • Sustain (100k log)
  • Tone (100k linear)
  • Volume (100k log)

Mod recipes Pro

4 mods
  • Mids Switch

    Restore the scooped mids that the stock tone stack notches out.

    How: Add an SPDT center-off switch wiring a 0.022 µF cap from the tone pot wiper to ground (up = scoop, middle = stock, down = mid boost via 4.7nF).

  • Civil War tone (Sovtek '91)

    Smoother, darker low-end variant favoured by Gilmour-era leads.

    How: Replace tone-stack low-pass cap with 0.01 µF and high-pass with 0.001 µF. Use 2N5089 transistors throughout for slightly higher gain.

  • Clipping diode swap

    Change the clipping character per stage.

    How: Stages 2 & 3 each have a pair of clipping diodes (typically 1N914). Try: BAT41 (softer, more open), 1N34A germanium (compressed), 3 mm red LED (loud, edgy). Mix-and-match between stages for asymmetry.

  • Input cap upgrade

    Tighten the bass response and reduce farty low-end.

    How: Replace C1 (input cap, 0.1 µF on most versions) with 0.047 µF for tighter low end, or 0.01 µF for a treble-boost flavor.

References

Community-sourced (ElectroSmash, Kit Rae's Big Muff history). Targets the 1973 Ram's Head spec.