MXR Phase 90 — Complete Guide
The MXR Phase 90 is the most famous phaser pedal in guitar history. Introduced in 1974, it has been used by Eddie Van Halen, David Gilmour, Brian May, Robin Trower, Carlos Santana, and generations of guitarists seeking the hypnotic, revolving sound of analog phasing.
The Phase 90's simplicity is its greatest strength: one knob (Speed), one switch (on/off), and an iconic orange enclosure. Despite — or because of — this simplicity, it produces one of the most musical and versatile modulation effects available.
What Phasing Does
A phaser creates its effect by splitting the guitar signal into two paths, shifting the phase of one path using a series of all-pass filters, and then recombining the two signals. Where the phase-shifted and original signals are out of phase with each other, some frequencies cancel; where they are in phase, some frequencies reinforce. The result is a series of "notches" in the frequency response that sweep up and down as the LFO (internal oscillator) modulates the all-pass filters.
The sound: a rhythmic, swooping "whoosh" that cycles at the speed determined by the Speed control. At slow speeds, the effect is subtle and atmospheric. At fast speeds, it becomes a more dramatic, vibrato-like movement.
The Phase 90 uses four all-pass filter stages (a "4-stage phaser"). More stages (6, 8, 12) produce more complex, deeper phasing with more notches. The 4-stage Phase 90 character is simpler and more musical for rock/blues applications; deeper phasers can sound more extreme or "sci-fi."
The Speed Control: What Each Position Does
The Phase 90 has one control: Speed. Here's what each position actually produces:
7–8 o'clock (slowest): A very long, slow sweep — the phase cycle takes several seconds to complete. Almost inaudible as motion; creates a gentle shimmer on sustained notes. Useful for subtle chord work in clean, ambient contexts.
9–10 o'clock (slow): The Eddie Van Halen position. The sweep is clearly audible on each note but not rhythmically obtrusive. Creates a sense of motion without dominating the sound. This is the most used range for classic rock.
12 o'clock (medium): Balanced between subtle and dramatic. The sweep is clearly rhythmic at medium tempos. Works well with strummed chord progressions where you want the phasing to create rhythmic movement.
2–3 o'clock (fast): Faster sweep creates a more vibrato-like effect. At this speed, individual chord hits will have a rapid oscillation. Works for funk rhythms or dramatic leads.
4–5 o'clock (fastest): Maximum speed creates an almost vibrato effect (pitch variation rather than just tone variation). Extreme — rarely used for whole songs, more often for brief dramatic effects.
Famous Phase 90 Users and Settings
Eddie Van Halen
Eddie Van Halen made the Phase 90 famous through its use on Van Halen I, II, and beyond. His specific tool was the "Script Logo" version (see below) with Speed set around 9–10 o'clock — slow enough to be atmospheric and not rhythmically intrusive.
The Phase 90 is audible on "Eruption," "Runnin' with the Devil," "Ain't Talkin' 'Bout Love," and many other VH tracks. EVH ran it in his effects loop (after the amp), which produces a different character than running it in front of the amp (before the input) — the phasing modulates the amp's output signal rather than the input.
EVH setting: Speed at approximately 9–10 o'clock. Clean to lightly overdriven amp.
David Gilmour (Pink Floyd)
Gilmour used the Phase 90 on various Pink Floyd recordings, most notably for the gentle sweep on "Breathe" (Dark Side of the Moon). His Speed setting was similarly slow — 9 o'clock range — creating a barely-there atmospheric movement on the clean Stratocaster tone.
Gilmour setting: Speed at 9 o'clock. Clean Fender or Hiwatt amp.
Robin Trower
Trower's entire sonic identity is built on the Phase 90 (or similar phaser) — his Stratocaster tone is rarely heard without the phasing. He uses medium-to-slow Speed settings (10–11 o'clock) through a cranked Marshall, creating the distinctive "Bridge of Sighs" sound.
Trower setting: Speed at 10–11 o'clock. Marshall at moderate gain.
Brian May (Queen)
May used phase shifting (including the Phase 90) on various Queen recordings, often combined with his unique multiple-amp delay technique. The phasing adds a dimension to his already complex signal chain.
Where to Put the Phase 90 in Your Signal Chain
Before the amp (standard): Guitar → Phase 90 → amp. The phasing occurs in the front end of the signal chain. The amp then amplifies and distorts the phased signal. This produces a "contained" phasing effect where the amp's tone colors the phased signal.
After the amp (in the effects loop): Guitar → amp preamp → Phase 90 → amp power amp. This is Eddie Van Halen's approach. The phasing modulates the amp's distorted output, creating a "swirling distortion" effect rather than "distorted phase." The character is significantly different — the phasing feels more like it's moving the overall sound.
After dirt pedals, before time effects (reverb/delay): Guitar → overdrive → Phase 90 → delay → reverb. Standard stompbox order for most players. The Phase 90 modulates the overdrive's output, then the delay/reverb smooths and extends the result.
Before dirt pedals: Guitar → Phase 90 → overdrive → amp. Less common — the phaser's notch filtering modulates the input to the overdrive, creating a more subtle, "inside the distortion" quality.
Script Logo vs. Block Logo: The Great Debate
The MXR Phase 90 has appeared with two different logo styles:
Script Logo: The original 1974–1984 versions had cursive "MXR" script text on the enclosure. The script logo units used a specific op-amp arrangement and circuit layout that many players consider to sound "warmer" and "more organic" than later versions.
Block Logo: From the mid-1980s onward, the Phase 90 used block letter "MXR" text. Component changes (including different op-amp types) changed the sound character slightly — generally considered slightly brighter or more aggressive than the vintage Script versions.
The practical difference: Experienced players in controlled tests can tell the two apart; in a live mix, the difference is negligible. Original script logo Phase 90s sell for $150–300+ in the used market. MXR offers the Phase 90 Script Logo Reissue at approximately $75–90 that uses the vintage circuit components — this is the recommended purchase for players who want the vintage character without the vintage price.
Current standard Phase 90: The current black-switch version (block logo) is an excellent pedal at $80 new. The Script Reissue is worth the extra $10–15 for the vintage circuit character.
Phase 90 for Different Instruments
Electric guitar (single-coils): The Phase 90 pairs particularly well with Stratocaster and Telecaster single-coil pickups. The phaser's movement creates a richer, more complex tone from pickups that might otherwise sound thin. The Phase 90 adds width and depth that single-coils naturally lack.
Electric guitar (humbuckers): Works well but the effect is slightly less dramatic because humbuckers already have more frequency content. The Phase 90 adds movement but the individual notch sweeps are less audible. Lower Speed settings work better with humbuckers.
Bass guitar: Phase shifters work beautifully on bass — the sweeping notch filters create harmonic movement that is musical and useful in funk, jazz, and electronic music contexts. The Phase 90's four-stage circuit works well on bass.
Keys: Less common application but phase shifting on electric piano (Rhodes) creates the classic "70s electric piano" sound used extensively in jazz fusion and funk of the era.
Phase 90 vs. Alternatives
MXR Phase 90 vs. Boss PH-3 Phase Shifter
The PH-3 is a digital phaser with multiple modes (4-stage, 8-stage, 10-stage, and rise/fall modes). More flexibility than the Phase 90; less "organic" analog character. For players who want variety and precise repeatable settings, the PH-3. For players who want the classic analog sound with maximum simplicity, the Phase 90.
MXR Phase 90 vs. EHX Small Stone
The Small Stone is another classic analog 4-stage phaser with a Color switch that changes the depth of the effect. The Small Stone has a slightly different character than the Phase 90 — some players prefer it for its "thicker," more resonant quality. Both are excellent; choose by ear if possible.
MXR Phase 90 vs. MXR Phase 45
The Phase 45 is a 2-stage phaser — fewer filter stages produce a subtler, gentler effect. Less dramatic than the Phase 90. Useful for players who find the Phase 90 too prominent and want the phasing to blend into the background without being noticed as an effect.
Frequently Asked Questions
What is the best Phase 90 setting for rock guitar? Speed at 9–10 o'clock (slow sweep). This produces the classic rock phaser sound that blends with the guitar without dominating it. For more dramatic movement, increase to 12 o'clock.
What's Eddie Van Halen's Phase 90 setting? EVH used the Phase 90 at approximately 9–10 o'clock Speed, placed after his amp in the effects loop. He used the vintage Script Logo version. The MXR Script Logo Reissue captures this setting closely.
Does the Phase 90 need to be true bypass? The standard Phase 90 uses buffered bypass. For players with long cable runs or many pedals, the buffer actually helps maintain high-frequency clarity. True bypass Phase 90 versions exist (some modded units); for most players, buffered bypass is fine.
Can you use the Phase 90 at the beginning of your signal chain? Yes — standard placement is between guitar and amp (or before your drive pedals). Running it first in the chain produces the most natural, transparent phasing character.
How do I make the Phase 90 stop being too obvious? Turn the Speed down (counterclockwise toward 7–8 o'clock). Very slow sweep settings make the Phase 90 nearly imperceptible as an "effect" while still adding movement and depth to the tone.
Is the Phase 90 Script Reissue worth the extra money over the standard? Yes — the MXR Script Logo Reissue costs approximately $10–15 more than the standard Phase 90 and uses the original vintage circuit topology. For players who care about the classic EVH/Gilmour character, the reissue is the better purchase.