The History of the MXR Phase 90

The MXR Phase 90 was introduced in 1974, by MXR co-founders Keith Barr and Terry Sherwood in Rochester, NY. While the MXR brand is commonly attributed to these two founders, Michael Laiacona—though involved in the early distribution—was not an official co-founder of MXR. The Phase 90 quickly became a go-to phaser effects pedal for electric guitarists and bassists alike.

A Bit About Phasers

Phasers produce a sweeping, swirling modulation effect by altering the phase of an audio signal. Guitarists have embraced phasers for:

• Subtle modulation for clean tones
• More aggressive sweeps for solos or psychedelic textures
• Unique textures on both rhythm and lead guitar

Why Was the MXR Phase 90 Designed?

Keith and Terry operated an audio repair shop and noticed many commercial pedals were unreliable. Motivated to produce better gear, they created MXR to build durable, tone-focused effects pedals. The Phase 90 was their first commercial success.

MXR Phase 90: The First MXR Pedal

The Phase 90 was the first pedal released by MXR in 1974. The “90” in the name references the 90-degree phase shift in its four-stage phasing circuit.
Eddie Van Halen famously used the Phase 90 on the first Van Halen album, contributing to its legendary status. The original version—called the Script Logo Phase 90—featured a bright orange enclosure and a cursive “MXR” script logo.

Expansion of the MXR Line

Following the success of the Phase 90, MXR launched:

• Distortion+: A gritty, saturated distortion pedal
• Blue Box: An octave fuzz with glitchy, synth-like textures
• Dyna Comp: A compressor pedal known for its squashed, clean tone

In 1977, the Script logo was replaced by a block-style logo. MXR continued producing pedals until it declared bankruptcy in 1984.

Takeover by Dunlop

Jim Dunlop acquired the MXR brand and resumed production of its most iconic pedals. Dunlop reissued the Phase 90 with added features such as:

• LED power indicator
• 9V power supply jack
• Modern internal circuitry (though some purists prefer vintage specs)

A Summary of MXR Phase 90 Versions

• Script Logo Phase 90: The original design, battery-powered, no LED or power jack. Known for its smoother, vintage tone.
• Block Logo Phase 90: Introduced around 1977. Slightly different circuit voicing—more pronounced midrange and sweep.
• Phase 45: A two-stage phaser with a subtler sweep. Preferred for cleaner, subtler textures.
• Reissue Phase 90: Standard model offered by Dunlop. Based on the Block Logo version, widely used for its reliability and tone.
• Phase 100: Offers more control with an intensity knob to select among four phasing modes. Four-stage design with added flexibility.
• EVH90 Phase 90: Eddie Van Halen signature model. Includes a switch to toggle between Script and Block voicings. Features his iconic red, white, and black “Frankenstein” paint job.
• CSP026 ’74 Vintage Phase 90 Reissue: Hand-wired version without LED or power jack. Built to replicate the exact specs of the original Script Logo version.
• CSP101SL Script Phase 90: Vintage tone with modern conveniences such as an LED and AC jack. Ideal for players who want vintage sound with modern reliability.
• CSP105 ’75 Vintage Phase 45: Reissue of the Phase 45, offering smoother, less intense phasing with modern build quality.
• Phase 99: A dual Phase 90 pedal in one unit. Allows you to run the circuits in series or parallel with independent speed controls and sync toggle.

Legacy and Enduring Popularity

The MXR Phase 90 remains a staple in the world of guitar effects. Its simplicity—a single speed knob—and sonic versatility have kept it relevant for decades. Suitable not just for electric guitars, it’s also used with:

• Keyboards
• Bass guitars
• Vocals and studio effects chains

From vintage classics to modern reissues, the Phase 90 offers something for every tone-chaser.