Maestro Phaser

The Maestro Phaser is the circuit that started the phaser pedal as a product category. Released by Maestro in the early 1970s as the PS-1 Phase Shifter, it was the first phaser pedal ever sold, and Delicious Audio credits it as "the device that launched this effect's long and successful existence"¹². Maestro, the effects brand of Gibson, is better known to some players for the Maestro Fuzz-Tone, but its 1970s range also included the PS-1 Phase-Shifter, the BG-1 Boomerang Wah and the Echoplex tape echo³¹².

The original was a fixed-recipe machine: six phase stages, three speed switches, and no other adjustments¹. Everything a modern player expects from a phaser, the Rate knob, the depth control, the feedback switch, traces back to circuits built to add flexibility the PS-1 never offered. Gibson's current Maestro Orbit Phaser is a direct descendent of the PS-1, and a string of independent builders have made pedals based on, or in homage to, the same circuit.

Where the Maestro Phaser came from

The PS-1 arrived in 1971 as a three-speed phase shifter⁴⁵. Maestro produced three versions of the Phase Shifter over its run: the PS-1, the PS-1A and the PS-1B⁶. The PS-1A carried three paddle rocker knobs as its speed controls⁷, a control scheme that tells you how little there was to adjust: you picked a speed and played.

The design goal was not originally a "phaser sound" at all. The pedal was released intending to replicate the sound of a Leslie rotary speaker⁸, the rotating-speaker cabinet long associated with organs and, in guitar circles, with players running amps through cabs like the Leslie model 16, which was virtually identical in design to the Fender Vibratone⁹. EarthQuaker Devices' beginner guide puts the effect in that context: phasing was one of the earliest guitar effects, and the intention was to imitate a Leslie rotating speaker¹⁰. The circuit did not literally simulate a spinning speaker; instead it became a sweeping filter effect that players adopted for its own sound, and Mojo Hand FX notes that "the phase shifter turned into" a widely popular effect in its own right¹¹⁸.

The Leslie connection is worth keeping straight because it separates the Maestro circuit from its closest ancestor. The Uni-Vibe, the other early rotating-speaker-inspired effect, is a variation of a four-stage phase shifter, as Voodoo Lab describes for its Micro Vibe¹². The Maestro circuit went bigger: six stages, which gives a deeper, more pronounced sweep than a four-stage design.

Six phase stages and three speeds: how it works

A phaser works by splitting the signal, shifting the phase of one copy through a chain of all-pass filters, and recombining the two. Where the shifted and unshifted signals cancel, notches appear in the frequency response, and sweeping the filters moves those notches up and down. The number of stages sets the number of notches: Vintage Synth Explorer's page on the Moog MF-103 explains that a 6-stage mode has three dips in its frequency response while a 12-stage mode has six¹³, and the same arithmetic applies to any phaser.

The Maestro PS-1 is a six-stage circuit where six JFETs provide a cascading all-pass filter network⁶. Those JFETs are the variable element: their resistance changes with a control signal, which sweeps the filter notches. Premier Guitar's review of the Heptode Virtuoso, a re-creation of the '70s Maestro PS-1A, puts the stage count in perspective: "It's a six-stage phaser (the Uni-Vibe and Phase 90 employ four stages)"¹⁴¹⁵. More stages means more notches and a more complex, deeper sweep.

The original's control surface was minimal:

That simplicity is exactly what later builders reacted against. Pedal of the Day, reviewing the Mojo Hand FX Mister-O recreation, noted that "since the original had just three speed switches, this one has extra flexibility"¹⁶.

Gibson's modern Maestro Orbit Phaser keeps the lineage but expands the control set. It is an all-analog phaser pedal with a 4-stage and 6-stage mode and a three-control layout³. Its two-position Mode switch gives a choice of 4 or 6-stage phasing³, which Guitar World's Alex Lynham describes as "a choice of two different phasing sounds: a six-stage phaser, as found in the PS-1 series, and a four-stage phaser"²¹⁷. The three knobs are Width, Rate and Feedback, with the Feedback knob offering "an extra layer of subtlety in shaping the sound"¹⁷. Gibson describes the pedal's character as warm and smooth, with the versatility needed to dial in phaser effects³.

The Orbit is mono, fully analog, and built as a 3-knob plus 1-switch pedal⁵. Power comes from a 9V battery or a regulated 9V DC supply with a 5.5 x 2.1 mm center-negative plug, drawing 27.5 mA³.

A smaller sibling also existed in the original range: the Maestro MPS-2 Mini Phase. A DIY stripboard layout of it on Guitar FX Layouts notes that the effect is slightly different from similar phasers in that it has no resistors between the drain and source of the JFETs, and that the original used 2N4303 JFETs¹⁸. An owner's SoundCloud demo of the original pedal, linked from that page, walks through the speed control from 0 through 3, 6 and 9 o'clock to full speed, with each pause between riffs marking a change¹⁸.

The Maestro Parametric Filter (MPF-1) and its controls

The Maestro range of the 1970s also included a pedal that shares this circuit family's DNA but does something entirely different: the Maestro Parametric Filter, or MPF-1. It was designed by Bob Moog for Gibson in the 1970s¹⁹, a rare Bob Moog-designed '70s effect²⁰, and it is a parametric filter with overdrive²¹. MusicRadar describes it as having had "a hugely expressive, wheel-driven EQ"¹⁹.

Its three controls, as listed by Godlyke:

Premier Guitar, reviewing the Stone Deaf FX PDF-1, characterized the original Maestro as "a clever, clunky filter pedal that a resourceful player could use for everything from simple EQ to total fuzzification of the signal". The overdrive side is not the point on its own: builders on Guitar FX Layouts report that it is not supposed to be a strong overdrive, but meant to be used after a fuzz or an overdrive²¹. One builder's verdict on pairing it: "It really takes my Fuzz Factory to a new level"²¹.

The players associated with it are a big part of its reputation. Premier Guitar notes that "6-string adventurers, including Alex Lifeson and Josh Homme, have used the Maestro to sculpt their tones", and Delicious Audio names the hard rock bands Rush and Queens of the Stone Age as users²³. MusicRadar calls it "a favourite of Josh Homme"¹⁹.

The MPF-1 has also become a DIY project. Guitar FX Layouts published a stripboard layout for it in October 2015, verified after two component value changes and a switch to a CD4007UBE IC, the modern equivalent of the CD4007AE in the original schematic²¹. Builders there also found that the original schematic called for an S-taper pot on the height control where a 10k linear pot works differently, and that a 20k pot in series with a low-ohm resistor to ground can serve as a usable gain control for the overdrive side²¹.

The MPF-1's control names outlived the pedal. Stone Deaf FX's PDF-1 is described in Premier Guitar as "a sturdier and more versatile evolution of the Maestro circuit," with each of its curious control names identical to those on the Maestro MPF that inspired it: Height, Freq and Bandwidth²³.

Pedals based on the Maestro Phaser

The PS-1's status as the first commercially available phase pedal²⁴ has made it a recurring reference point for builders. Some copied the circuit, some re-created it, and some built homages from scratch.

• Mojo Hand FX Mister-O: a six-stage phaser released in 2021 "to nail the dreamy '70s tones of the original Maestro units"⁴. It stays true to the original's six phase stages¹⁶, but Mojo Hand FX states that "not one single trace of the original circuit of the Maestro phaser from 50 years ago was copied, we only used our ears" and programming skills²⁵. It draws about 70 mA¹.
• Heptode Virtuoso Phase Shifter: a re-creation of the '70s Maestro PS-1A Phase Shifter¹⁵, a six-stage phaser reviewed by Premier Guitar¹⁴.
• Maestro Orbit Phaser: Gibson's own descendent of the PS-1, re-engineered for current players³⁵²⁴.
• Function f(x) Parallax: its phaser section credits "the old Maestro Phase Shifter, which we updated with modern components and modified for inclusion in this pedal"²⁶.
• Spaceman Explorer: a small form factor reissue of the original Explorer phaser, a classic circuit with the deluxe features of the original²⁷.

The Mister-O's approach is the interesting counterpoint: rather than cloning, Mojo Hand FX gave it Speed, Depth and Color controls to add the flexibility the three-speed original lacked¹¹⁶. Where the original had three speed switches and no other adjustments, the Mister-O's extra controls let a player shape depth and character, not just speed¹.

A cousin in the family tree is worth knowing about: the Roland AP-7 Jet Phaser, whose manual describes it as achieving "thick swirling phase and faux Leslie rotary speaker effects"²⁸, the same Leslie goal the Maestro circuit started from. And on the four-stage side of the family, the Uni-Vibe remains the other main branch of early phaser design¹².

Pedals on this page

Maestro Echoplex EP-3

Maestro · Delay

Maestro Phase Shifter

Maestro · Phaser

Maestro Orbit

Maestro · Phaser

$149 list price

Fender Vibratone

Fender · Speaker simulation

Voodoo Lab Micro Vibe

Voodoo Labs · Vibrato

$299.99 list price

Dunlop Uni-Vibe

MXR · Chorus

Heptode Virtuoso

Heptode · Phaser

MXR Phase 90

MXR · Phaser

$99.99 list price

Maestro MPS-2 Mini Phase

Maestro · Phaser

Maestro MPF-1

Maestro · Filter

Heptode Virtuoso Phase Shifter

Heptode · Phaser

Spaceman Effects Explorer

Spaceman Effects · Phaser

$279 list price

Roland AP-7 Jet Phaser

Roland · Fuzz

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