PEDAL BENCH
by Stompbox Labs
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EQ/Filter1982· Dunlop Manufacturing (USA, originally Thomas Organ 1966)

Dunlop Cry Baby GCB-95 Wah

The world's most-used wah — inductor-based bandpass filter swept by your foot.

⏳
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 single-transistor (originally 2N3565, now BC109C) gain stage with a resonant LC bandpass filter in its feedback path. Rocking the treadle changes a 100k pot connected to the inductor's resonant network, sweeping the peak frequency from ~400 Hz to ~2.2 kHz.

Signal chain preview

4 stages
Input
Input buffer (single BJT, common emitter, low gain)
Resonant LC filter (Halo/Fasel inductor + 100k sweep pot + capacitor network) in collector load
Output cap to next stage
True bypass switch (later revisions; original was hardwire bypass)
Output

Quick facts

  • Vox originally invented the wah in 1966; Thomas Organ in the US licensed it and it became the Cry Baby line.
  • Jimi Hendrix, Eric Clapton ('White Room'), and Slash all built signature tones on the GCB-95 circuit.
  • The Fasel red inductor (the original Italian-made part) is prized for a slightly warmer voicing; modern Halo / Yellow Fasel are the standard substitutes.

Controls

  • Treadle (100k linear sweep pot)

Mod recipes Pro

4 mods
  • True bypass

    Eliminates the bypassed wah's tone-loading.

    How: Replace the DPDT switch with a 3PDT and rewire input/output directly through it; lift the bypassed signal path from the buffer.

  • Sweep range mod

    Shifts the bandpass peak lower for a vocal/bassier wah.

    How: Increase C5 (the filter cap across the inductor) from 0.01 µF to 0.022 µF for a Hendrix-style bassier sweep, or 0.0047 µF for a sharper, more cocked-wah top end.

  • Q / vocal mod

    Sharper, more resonant peak.

    How: Reduce R8 (4.7k from emitter to the filter network) to 2.2k. Beware: too low becomes self-oscillating.

  • True input buffer

    Stops the wah from loading vintage-style fuzzes upstream.

    How: Add a JFET buffer (2N5457) ahead of the wah circuit; switch it out of the path with the bypass switch.

References