Dunlop Univibe

The Uni-Vibe is a modulation effect that, despite its name, is really a phaser: a four-stage optical phase shifter originally built to imitate the Doppler effect of a Leslie rotating speaker cabinet¹². It was designed in Japan in the late 1960s and became famous through Jimi Hendrix, who used a vintage Shin-ei unit from 1969 to 1970³⁴. Today the Uni-Vibe name belongs to Dunlop, which sells current versions under the Dunlop and MXR names⁵.

What sets the circuit apart from a standard phaser is how it shifts phase. Each of the four stages has its own unique corner frequencies, thanks to uneven capacitor values, and the sweep is driven optically, by a light bulb and photoresistors, giving a unique LFO curve¹²⁶. The result is the throbbing, hypnotic pulse players associate with the effect⁷.

What a Uni-Vibe does

The Uni-Vibe was conceived as a pedal alternative to a Leslie speaker: an electronic attempt to simulate the way a spinning horn shifts pitch and volume as it rotates⁹⁴. Instead of moving air, the circuit shifts the phase of the guitar signal in four staggered stages, each with its own corner frequency, and sweeps those stages with an LFO¹².

Unlike most commercially produced phase shifters, the Uni-Vibe does not use op-amps; it is built from discrete components, which is part of why players describe its sweep as lo-fi and organic compared with a modern phaser⁹. Function f(x) puts it bluntly: the Dunlop Univibe "is a vibe pedal, but it's really an optical phaser with no dry signal" in vibrato operation¹². In its simplest form it is a staggered phase shifter known for its throbbing, hypnotic pulse and lo-fi sweep⁷.

The controls

The original pedal kept its control set small, and most versions since have kept it that way:

The original also shipped with a foot treadle for rotational speed and a rocker switch for the two modes². Dunlop's current pedals follow the same layout: the Authentic Hendrix '68 Shrine Series Uni-Vibe has three knobs for Speed, Level and Depth plus a Vibe button¹⁵, and Dunlop sells a separate Uni-Vibe Foot Control that manipulates the Speed and effect/bypass functions of the Uni-Vibe Chorus/Vibrato by foot¹⁶.

One detail worth knowing: the volume control is not transparent. The pedal contains a transistor-based preamp circuit, so even the dry input signal is colored and amplified⁹.

Chorus mode and vibrato mode

The Chorus/Vibrato switch is where the two personalities of the circuit live, and the difference is simple:

• Chorus mode: the dry signal is mixed with the phase-shifted signal, producing the unique asymmetrical phase shifting that is the classic Uni-Vibe sound⁴¹⁴.
• Vibrato mode: only the pitch-shifted signal is heard, with the dry signal taken out of the path¹⁴¹³. MusicRadar describes it as thinner and quieter, with a more pronounced pitch warble⁹.

Dunlop's own description of the MXR Uni-Vibe Chorus/Vibrato is the same: the VIBE switch selects either Chorus Mode, "dry signal mixed with pitch-shifted signal," or Vibrato Mode, "only pitch-shifted signal"¹⁴. On the JHMS3 Shrine Series pedal, the switch out is chorus and pushing it in engages vibrato mode, indicated by an LED³.

The naming is a piece of history in itself. Tru-Fi notes the original makers found the phase sound so distinctive that "they actually labeled Chorus" what was really phase shifting¹⁷. Reviewing the Authentic Hendrix '69 Uni-Vibe for Guitar.com, Richard Purvis called the chorus mode the Uni-Vibe sound: "an insistently pulsing, not-quite-whining throb that sounds almost like a phaser but with a dash of Leslie and harmonic" character¹⁸.

History: Shin-ei, Fumio Mieda and Univox

The story starts in 1967, when a Japanese company called Honey, later known as Shin-ei, designed the first Univibe⁸. The engineer behind it was Fumio Mieda, a Japanese designer also known for other legendary products¹⁹¹¹. According to Shin-ei designer Fumio Mieda, his inspiration came from the sound of shortwave radio signals, powerful signals that bounced off the ionosphere²⁰⁴.

The unit was originally manufactured as a stand-alone effect with no footswitch, by Shin-ei²¹. From 1968 onwards it was manufactured and distributed in North America by Univox⁹, which is why vintage units are usually called the Univox Uni-Vibe⁹.

Its fame came fast. Jimi Hendrix used the effect on his Band of Gypsys record and in his landmark Woodstock performance of "The Star Spangled Banner," on songs such as Machine Gun²²¹. David Gilmour then grew fond of it and used it live and on records, as did Robin Trower²¹¹¹.

Original versions and later clones

There were two main versions of the original unit⁹:

• The first version has a gray power cord and hand-painted "Uni-Vibe" on the front; this is the true "Jimi" version⁹.
• The later version has a stencilled logo that is more silver in color⁹.

Original Univibe pedals are highly sought after today for their vintage sound and character²³. The clone tradition goes back decades: Dave Fox of Foxrox was the first person to come out with a clone of the Univibe, reverse engineering one²⁴. Modern Univibe pedals come in compact, pedalboard-friendly enclosures with true bypass switching, and many offer compatibility with expression pedals for real-time control of speed or depth²³.

Dunlop's current range carries the circuit forward under the trademark it owns⁵:

• MXR Uni-Vibe Chorus/Vibrato: a compact chorus/vibrato pedal with Chorus and Vibrato modes and true bypass¹³.
• Authentic Hendrix '68 Shrine Series Uni-Vibe Chorus/Vibrato: three knobs (Speed, Level, Depth) and a Vibe button toggling chorus and vibrato modes¹⁵³.
• Uni-Vibe Stereo Chorus (UV1SC): a stereo chorus pedal inspired by the original classic Uni-Vibe, with left and right outputs and a variable mix from spatially wide to classic mono²⁵.

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