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Modulation1968· Shin-ei (Japan)

Shin-ei Uni-Vibe

Four-stage photocell phaser pretending to be a Leslie — Hendrix's 'Machine Gun' shimmer.

⏳
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 4-stage all-pass phase shifter where the phase-shift element is a photoresistor (LDR) optically coupled to a small incandescent lamp driven by a low-frequency triangle/sine LFO. Because each LDR has slightly different response, the four stages aren't matched — that mismatch is what gives the Uni-Vibe its characteristic 'throbbing, asymmetric' character versus a regular phaser.

Signal chain preview

6 stages
Input
Input buffer (BJT)
4× cascaded all-pass stages, each with LDR in the phase-shift R position
Lamp driven by triangle LFO (Speed pot sets rate)
Wet / dry mix (Intensity pot = depth)
Chorus / Vibrato switch (chorus = mix wet+dry, vibrato = wet only)
Output buffer
Output

Quick facts

  • Jimi Hendrix's 'Machine Gun' and 'Star Spangled Banner' both feature the Uni-Vibe heavily.
  • Originally designed to emulate a Leslie rotating speaker, but the asymmetric photocell response makes it sound nothing like a Leslie — better.
  • The lamp/LDR optoisolator is the heart of the circuit; modern reissues use VTL5C3 vactrols or matched LED/LDR pairs.

Controls

  • Speed (foot pedal or pot)
  • Intensity (depth)
  • Chorus / Vibrato switch

Mod recipes Pro

3 mods
  • Volume recovery

    The original loses 4-6 dB through the wet path.

    How: Add a unity-gain JFET buffer at the output and shift the Volume pot to that stage.

  • Speed expander

    Slower slow speeds for ballad use.

    How: Replace the Speed pot's series timing resistor with a switched 470k / 1M arrangement; the higher value halves the LFO frequency.

  • True bypass

    Remove tone-loading in bypass mode.

    How: Rewire jacks through a 3PDT footswitch and lift the original passive bypass.

References