Warm Audio WA-MPH Mutation Phasor II Analog Optical Phaser Pedal

Warm Audio WA-MPH Mutation Phasor II: Deep, Optical, Feedback-Driven Phase

The Warm Audio WA-MPH Mutation Phasor II is a 100 percent analog phaser pedal built around an electro-optical phase-shifting circuit with a feedback control. It recreates the lush, swirling character of a 1970s experimental-era optical phaser, a design prized for its liquid, three-dimensional movement. The feedback knob is the standout feature, adding a resonant, funky intensity that most phasers cannot produce. Housed in an ultra-tough steel enclosure with vintage looks, it is as durable as it is characterful. For players who want more than a gentle, predictable sweep, the Mutation Phasor II delivers phase modulation with real depth and attitude.

How a Phaser Pedal Works

A phaser splits your signal and passes one copy through a series of all-pass filter stages that shift its phase across the frequency spectrum. When that phase-shifted copy is recombined with the original, it creates moving notches in the frequency response, and sweeping those notches produces the familiar whooshing effect. The rate of the sweep sets how fast the swirl moves, and the number of stages sets how thick and complex it sounds. Adding feedback routes the output back into the input, sharpening those notches into resonant peaks for a far more dramatic, vocal effect. This is the mechanism behind decades of funk, psychedelia, and shimmering clean textures. Understanding it helps a player sculpt anything from a subtle shimmer to an aggressive throb.

The Electro-Optical Circuit and Its Sound

Rather than using transistors or digital modeling, the WA-MPH modulates its filters optically, with a light source and light-sensitive resistors controlling the sweep. This electro-optical approach, drawn from a rare experimental phaser of the 1970s, produces a smoother, more organic movement than typical designs. The signal path stays 100 percent analog and is built with classic RC4558P op-amps alongside vintage-style diodes, carbon resistors, and film capacitors. Those component choices give the pedal a warm, musical tone that flatters rather than clinically processes the source. The optical heart is what gives this phaser its liquid, breathing quality. It is a sound that is difficult to fake with modern parts.

The Feedback Control and Deep Modulation

The feedback control is where the Mutation Phasor II separates itself from a standard phaser. Turning it up feeds the phased output back through the circuit, intensifying the resonant peaks until the effect takes on a hollow, throaty, instant-funk swirl. At lower settings the pedal offers classic, gentle phasing suitable for clean rhythm parts and pads. Pushed further, it becomes an expressive, almost synth-like modulation that dominates a part. This range makes it equally useful for subtle motion and for bold, signature textures. Few phasers give a player this much reach from one knob.

Where the WA-MPH Shines

On funk and psych guitar it delivers the swirling, wah-adjacent movement that defines those styles. On keyboards and synths it adds motion and dimension that turns a static patch into something alive. Bass players use it for subtle, sweeping textures that keep a groove interesting without losing low end. In the studio it becomes a sound-design tool for stereo width, evolving pads, and experimental effects. Anywhere a part needs movement with a vintage, organic feel, the optical circuit answers the call.

Who the Mutation Phasor II Is For

Guitarists chasing authentic vintage phase with more depth than a basic pedal get a characterful, road-tough tool. Keyboard and synth players get a lush modulation source that pairs beautifully with electronic sounds. Experimental musicians and producers get the feedback control's extreme, resonant textures for sound design. Its steel enclosure makes it reliable enough for constant gigging and touring. For phase modulation with genuine vintage optical character, the WA-MPH is a distinctive choice on any pedalboard.