In 1974, a small company called MXR released its very first guitar pedal. They didn’t try to do everything at once. They didn’t cram in multiple knobs, tone controls, or preset banks. They built a single orange box with a single knob labeled Speed, and they charged $45 for it. That box — the MXR Phase 90 — went on to appear on some of the most recognizable recordings in rock history, became the definitive sound of a generation’s lead guitar tone, and remains in continuous production over fifty years later with essentially the same circuit. No guitar pedal tells a simpler story, and very few have left a deeper mark.
The M101 Phase 90 is not a complex piece of technology. It does one thing: it shifts the phase of your guitar signal through four stages of all-pass filtering, creating a sweeping, swirling effect that sits somewhere between a rotating speaker and a gentle Uni-Vibe. But within that single parameter — the rate of the sweep — lies an enormous range of musical territory. Set it slow and it adds subtle, living movement to a clean tone. Push it faster and it enters psychedelic rotary-speaker territory. Overdrive the input and the phase effect becomes thick, vocal, and aggressive. The fact that generations of players keep coming back to this design is not nostalgia. It is a testament to how precisely right MXR got it on the first attempt.
Where It Came From: MXR and the Birth of the Compact Phaser
MXR was founded in Rochester, New York, in the early 1970s by Keith Barr and Terry Sherwood, two young engineers who recognized that the market for guitar effects was wide open but poorly served. The existing phase-shifting units of the era — the Uni-Vibe, the Maestro PS-1A, the Mu-Tron Bi-Phase — were large, expensive, and often temperamental. Barr and Sherwood saw an opportunity: a compact, rugged phaser that any gigging guitarist could afford, fit in a gig bag, and stomp on nightly without worrying about it breaking.
The Phase 90, introduced in 1974, was their answer. It was housed in a small die-cast Bud box — the same industrial aluminum enclosure used in electronics hobbyist projects — and fitted with a single die-cast footswitch that could survive nightly punishment without complaint. The circuit inside was an elegant four-stage design using operational transconductance amplifiers (OTAs) to shift the phase of the incoming signal at four different points in the audio spectrum simultaneously. The result was a smooth, musical sweep with a characteristic “whoosh” that added movement and life to single notes and chords alike.
The original Phase 90s featured what collectors now call the “script logo” — the MXR name written in flowing cursive on the face of the pedal. That detail matters, because the script-logo units have a specific circuit character that makes them different from the later “block logo” versions released from 1977 onwards. The script-logo circuit runs without feedback — the four stages shift signal without any signal being fed back into the chain — producing a subtler, more musical effect that guitar players describe as a smooth “swoosh.” When MXR redesigned the pedal in 1977, they added a feedback resistor (R28 in the schematic) that creates a resonance peak in the phase shift, giving the block-logo versions a slightly more pronounced, aggressive character. Both are excellent. They are not identical.
MXR went bankrupt in 1984 and production stopped. Jim Dunlop eventually acquired the brand and resumed manufacturing, and the M101 Phase 90 has been in continuous production since. Today’s M101 uses a block-logo circuit with an added input buffer to prevent tone-sucking — a practical improvement over the original that makes it more compatible with a wider range of pedalboards.
Inside the Circuit: What Phasing Actually Does
A phaser works by splitting the audio signal, shifting the phase of one copy at multiple frequencies, then recombining both copies. Where the two signals are out of phase, they partially cancel, creating notches in the frequency response. As the rate control sweeps these notches up and down the spectrum, you hear the characteristic swooping movement. More stages of phase shifting means more notches, and a richer, more complex effect — the Phase 90 uses four stages, which produces two notches moving through the audible range simultaneously.
What makes the Phase 90 distinctive among four-stage phasers is the quality of those notches. The OTA-based design produces a particularly musical interaction between the notches and the audio peaks between them, and the circuit is tuned so that the sweep range falls precisely in the most musically useful part of the guitar’s frequency spectrum. This is why the pedal sounds so different from a generic phaser even when set at the same rate — the character of the sweep is baked into the component selection, not just the speed setting.
The single Speed control runs from an extremely slow sweep — barely perceptible movement, more of a tonal shimmer — through medium rates that suggest a Leslie cabinet at conversational speed, to fast rates where the effect becomes pronounced and almost vibrato-like at its extreme. The most interesting ground lies between 7 o’clock (nearly stopped) and 2 o’clock, where the Phase 90 has the most expressive range.
Specifications
| Specification | MXR M101 Phase 90 | ’74 Vintage Phase 90 (M132) | EVH Phase 90 |
|---|---|---|---|
| Type | 4-stage OTA phaser | 4-stage OTA phaser (script circuit) | 4-stage OTA phaser (switchable) |
| Logo/Circuit | Block logo + buffer | Script logo, hand-wired | Script/Block switchable |
| Controls | Speed | Speed | Speed + Script/Block switch |
| LED | Yes | No | Yes |
| Power | 9V DC or battery | Battery only (no AC jack) | 9V DC or battery |
| Current draw | ~5 mA | ~5 mA | ~5 mA |
| Bypass | Buffered | Non-true bypass (original spec) | Buffered |
| Price new | ~$99.99 USD | ~$179.99 USD | ~$149.99 USD |
| Price used (excellent) | ~$50–75 USD | ~$100–130 USD | ~$80–110 USD |
| Vintage script original | — | — | — |
| Vintage block original | ~$80–200 USD used | — | — |
| Equipboard pro users | 1,000+ | N/A | Separate listing |
Famous Players
Eddie Van Halen
No guitarist is more associated with the Phase 90 than Eddie Van Halen, and his connection to it is thoroughly documented. He first encountered the pedal in the mid-1970s while playing with a friend named Terry Kilgore, who had a Phase 90 on his own board. Eddie was immediately taken by what it did to his tone and acquired one of his own — a script-logo unit — almost immediately. From that point forward, the Phase 90 became one of the very few effects pedals he used consistently throughout his career.
The evidence is all over the first Van Halen album (1978): “Eruption” carries the pedal’s swooping sweep through its cascade of tapped harmonics; “Ain’t Talkin’ ‘Bout Love” features the Phase 90 adding slow movement to the chords; “Atomic Punk” opens with a distinctive phase-shifted guitar sound that listeners have been trying to replicate for decades. Van Halen’s rate setting was famously consistent: between 9 and 10 o’clock on the Speed control, barely above the pedal’s slowest setting. In a Guitar World interview, he described his approach in characteristically direct terms: “I was into Robin Trower too, but we didn’t play any of his songs, so I used it with the control set between 9 and 10 o’clock. I still use it the same way today. I just locked into that one setting, and I’ve used it ever since.”
That single setting — barely moving, creating a subtle shimmer rather than an obvious swoosh — is one of the most instructive things about how great players use phasers. The Phase 90 at 9 o’clock is an almost subliminal effect. It adds space and movement to a tone without announcing itself. The listener feels it more than they hear it. Combined with the script-logo circuit’s subtler character, it was the perfect tool for a guitarist whose playing was already so dramatic that the phaser needed to add texture, not compete with his technique.
Eddie later worked with MXR/Dunlop to develop the EVH Phase 90 signature pedal, which includes a Script/Block mode switch specifically to allow players to access his preferred original-circuit character in a current-production pedal. That collaboration is perhaps the clearest endorsement MXR ever received: the man who put the Phase 90 on the map came back to refine it.
David Gilmour
David Gilmour’s phaser use in Pink Floyd is a study in restraint and precision. Gilmour replaced his aging Uni-Vibe with an MXR Phase 90 around 1974, and the new pedal appeared prominently on Wish You Were Here (1975) — one of Pink Floyd’s most celebrated albums. The Phase 90’s contribution is most clearly audible on “Shine On You Crazy Diamond,” where Gilmour uses it to add sweeping movement to sustained notes, either alongside a rotating speaker effect or in isolation. “Have a Cigar” also carries the pedal’s character throughout.
Gilmour’s approach to the Phase 90 was typically methodical. He used it as a color rather than a centrepiece effect — the pedal provided atmospheric movement to his singing Stratocaster lines without overwhelming the harmonic content of his phrasing. During The Wall era, the Phase 90 appeared in the Pete Cornish custom effects board that formed the backbone of Pink Floyd’s live and studio rig, occupying a specific position in a carefully ordered signal chain designed by Cornish to preserve Gilmour’s clean tone even through layers of effects processing.
Understanding Gilmour’s use of the Phase 90 requires understanding his broader approach to tone: every effect in his signal chain serves the note, not the other way around. The phaser is on when the music benefits from movement; when a passage calls for clarity, it’s off. His Phase 90 settings tend toward the slower end of the range, consistent with his preference for effects that add depth without drawing attention to themselves.
Billy Corgan
Billy Corgan’s relationship with the Phase 90 spans the Smashing Pumpkins’ entire career. He’s described using “MXR Phase 90s for years to kind of get more movement during solos,” and the pedal appears in documented rigs from the Mellon Collie era through current touring. In a particularly revealing interview, Corgan described his application: “On the ‘Oceania’ solo, I use the Phase 90 and the Fulltone Catalyst, so you get some movement in the lead.” He typically runs two Phase 90s simultaneously for his solo sounds, which gives the effect additional depth and complexity.
Corgan’s use of the pedal stands in interesting contrast to Van Halen’s. Where EVH used the Phase 90 as a constant, always-present shimmer on his entire signal, Corgan engages it specifically for lead moments — a deliberate contrast between the dense, layered Smashing Pumpkins rhythm sound and the more fluid, animated solo tone. The dual-Phase 90 approach creates a subtly chorused quality when two slightly different sweep rates interact, which fits the dreamy, psychedelic edge that characterizes the band’s more expansive moments.
Waylon Jennings
The Phase 90 found its most unlikely home in outlaw country, where Waylon Jennings made phased guitar a signature element of his sound throughout the 1970s and 1980s. Jennings used various phaser pedals across his career — the Maestro PS-1A, the Electro-Harmonix Small Stone, and multiple MXR units including the Phase 90 and Phase 100 — and the sweeping, slowly evolving quality of that effect became so associated with his style that Fender eventually released a Waylon Jennings Phaser signature pedal specifically designed to recreate those tones.
The country phaser application is worth understanding as distinct from the rock context. Where rock players tend to use phasing for drama — the slow sweep adding tension to a sustained bend — Jennings used it as a textural element in a looser, more open arrangement. His Telecaster playing through a slow phaser created a quality that has been described as “the sound of the highway,” an apt metaphor for music that was about movement, freedom, and open space. Not every Phase 90 use is about Eruption. Jennings reminds us that the pedal works just as well in a Telecaster/amp-direct context as it does in a Marshall stack configuration. Since no confirmed specifics distinguish Jennings’s Phase 90 use from his Phase 100 use in available primary sources, the attribution is accurate but carries the same caveat: Jennings was a phaser player, and the MXR Phase 90 was definitely in his collection, but the specific recordings it appears on are less thoroughly documented than the Van Halen or Gilmour connections.
Other Documented Users
The Phase 90’s user list is extensive. Steve Hackett was among the earliest adopters, using the pedal on mid-1970s Genesis albums when most of the world hadn’t heard of the MXR brand. Robin Trower used a Phase 90 on stage for a period as a replacement for his aging Uni-Vibe, leaning on its Uni-Vibe-adjacent character at faster speeds. Steve Jones of the Sex Pistols recorded tandem rhythm tracks for “Anarchy in the UK” with both copies processed through Phase 90, creating the snarling, snotty power chord texture that defines that recording.
More recent confirmed users (via Guitar World, Premier Guitar, and Equipboard documentation) include John Frusciante, Dave Grohl, Josh Homme, Matt Bellamy, and John Petrucci — a list that spans hard rock, progressive metal, alternative, and arena rock. The breadth of the user base reflects the pedal’s fundamental versatility: any guitarist who wants subtle movement without the complexity of a multi-parameter effect eventually ends up reaching for the Phase 90.
Signal Chain Placement and Strategy
The Phase 90 is typically placed after drive pedals and before delay and reverb in a standard signal chain. This is the arrangement used by most professional players and produces the most natural result: the phasing effect sweeps through the entire signal including its harmonic distortion content, giving the drive a more animated, living quality without the phase effect becoming smeared by reverb tails.
Reversing this — placing a phaser before an overdrive — creates a different but equally valid effect. When a phase shifter’s notches run through an overdrive’s input stage, the drive responds differently to the notched frequencies and the full-spectrum frequencies, creating a more complex, almost formant-like quality in the overdrive’s harmonic content. Guitar World notes that placing an overdrive in front of the Phase 90 makes the phasing effect more pronounced, particularly useful for Hendrix or Trower-style Uni-Vibe simulation.
The M101’s buffered bypass is worth noting. Unlike a true-bypass pedal that completely disconnects the circuit when switched off, the Phase 90 maintains a buffer stage in bypass mode. This is generally beneficial for pedalboard integrity — the buffer drives the downstream cable and pedals without the capacitance-related treble loss that true-bypass pedals can create in long chains. The one exception is germanium fuzz pedals, which require a high-impedance input to function correctly. If you run a germanium Fuzz Face or similar before the Phase 90, the buffer can affect the fuzz’s character. Solution: place the germanium fuzz after the Phase 90, or use a loop switcher to route around the buffer when needed.
Tone Recipes and Settings
The EVH Signature Shimmer
Speed: 9 o’clock. Script mode if using an EVH Phase 90. Clean amp, single-coil or humbucker direct into Phase 90. The effect is barely perceptible as an independent layer — it adds three-dimensionality and slight movement to a tone without being identifiable as “phaser.” This is the setting on Eruption, Ain’t Talkin’ ‘Bout Love, and dozens of other Van Halen tracks. Slower than this and the effect disappears; faster and it starts to announce itself. The precision of EVH’s rate choice is evident when you try to find it: it’s a very specific notch in the Speed knob’s travel.
Robin Trower / Uni-Vibe Simulation
Speed: 2 o’clock (or 7 on a 1–10 scale). Drive pedal or mild amp breakup before the Phase 90. Block logo version preferred for the more pronounced, resonant effect. The phase effect at this rate mimics the slow pulse of a real Uni-Vibe or Leslie cabinet, creating a “woozy,” pitch-adjacent movement that works particularly well with sustained chords or slow, singing lead lines. This setting also works for Cream-era Clapton tones and late-1960s psychedelic rock applications.
Country Phaser (Jennings-Style)
Speed: 8 o’clock. Clean Telecaster into mild amp breakup. The Phase 90 at this nearly-stopped setting creates a barely-moving shimmer that adds interest to country-style picking without distracting from note clarity. This is the “highway” setting — present enough to feel but not dramatic enough to be noticed on a casual listen. Works particularly well with single-coil pickups and American clean amp tones (Fender Deluxe Reverb is the natural pairing).
Psychedelic Spin
Speed: 3 o’clock. Any amp setting with some harmonic content. At this rate the Phase 90 creates a fast, swirling effect that suggests a Leslie speaker at high speed, complete with the pitch-adjacent wobble that makes rotating-speaker simulation so compelling. Particularly effective on chords rather than single notes — the multiple harmonics interact with the phaser’s notches in complex, unpredictable ways that produce a genuinely psychedelic texture.
Slow Ballad Sweep
Speed: 8:30–9 o’clock. Clean amp, neck pickup. The Phase 90 at this setting adds a slow, meditative quality to sustained chords and arpeggiated passages. It’s not immediately identifiable as phaser — it reads more as a characteristic of the guitar’s natural acoustic bloom. This is the setting that makes a clean tone sound like it’s breathing. Combined with reverb placed after the Phase 90 in the chain, it creates the kind of atmospheric, open-space quality associated with 1970s studio guitar work.
The Script vs. Block Debate: What Actually Matters
The Phase 90’s script-vs-block discussion has generated more forum arguments than almost any other topic in vintage pedal collecting. Here is what the circuit differences actually produce: the script-logo version, without feedback, generates a smoother, more subtly sweeping phase effect — what players describe as a “swoosh” — while the block-logo version’s feedback resistor adds resonance at the phase-notch frequencies, creating a slightly more pronounced, “pulsing” effect. The difference is real, but it is not enormous. Both are excellent phasers. Both will produce Van Halen and Gilmour tones at appropriate settings.
For practical purposes: if you want the most historically accurate EVH Phase 90 sound, the M132 ’74 Vintage Phase 90 ($179.99 new, battery only, no LED) or the EVH Phase 90 with the Script switch engaged ($149.99 new) is the correct choice. If you want a workhorse phaser that covers all the Phase 90 ground with modern conveniences — LED, AC power jack, polarity protection, input buffer — the M101 at $99.99 is the right answer. The block-logo M101 is not a lesser pedal. It is a different character of the same underlying design, and for many applications — faster speeds, playing before a drive pedal, high-gain contexts — it is actually the more appropriate choice.
One practical note: vintage script-logo Phase 90s from 1974-1977 trade between $120 and $350 depending on condition and provenance. Given that the M132 reissue captures the circuit character at $179.99 and is a new, warranted pedal, the vintage premium on script units is difficult to justify for players rather than collectors. Buy the vintage unit if you want a piece of history; buy the M132 if you want the script-circuit sound to use.
Comparisons With Similar Pedals
The Electro-Harmonix Small Stone is the Phase 90’s oldest rival and closest sonic cousin — both are four-stage phasers from the same mid-1970s era, and both remain in production today. The Small Stone adds a Color switch that engages feedback for a more pronounced effect (similar to the script-to-block difference in Phase 90 terms), and it has a somewhat wider sweep range. The Phase 90 generally wins on consistency and build quality; the Small Stone wins on character range and is often described as slightly “warmer” in its phasing. Current Small Stone: $89.99.
The MXR Phase 100 (M107) is the Phase 90’s more complex sibling, adding a four-position waveform selector (10, 22, 44, 100) and an Intensity control alongside the Speed knob. The Phase 100 offers a wider range of phasing textures but also requires more setup time to dial in; the Phase 90’s single-knob approach is a feature, not a limitation. If you use phasing for one or two specific sounds, the Phase 90’s simplicity is an asset. If you need to dial between very different phase characters for different musical contexts, the Phase 100 is worth the additional investment at around $149.99 new.
The Ibanez TS9 Tube Screamer is the Phase 90’s natural pedalboard companion rather than a competitor — the combination of Tube Screamer overdrive followed by Phase 90 for lead sounds is documented on numerous professional boards, including various configurations in the Van Halen and Corgan traditions. The two pedals occupy completely different positions in the signal chain and different sonic roles; owning both makes more sense than choosing between them.
For players considering a Uni-Vibe as an alternative, the comparison is genuinely meaningful. A Uni-Vibe (or any of its emulations, from the Dunlop MXR Uni-Vibe to the Fulltone Deja Vibe) produces a chorus-plus-vibrato effect rather than pure phase shifting — the two circuits create related but distinct effects. A Uni-Vibe at slow speeds sounds similar to a Phase 90 at moderate speeds, but the Uni-Vibe has more “wobble” and a more pronounced pitch-variation character. Van Halen could have used a Uni-Vibe; he chose the Phase 90, and that choice is part of what makes his tone specifically his rather than Jimi Hendrix’s.
Buying Guide
The M101 Phase 90 at $99.99 new is one of the best-value modulation pedals in existence. There is no vintage premium on the current-production unit — all M101s built since Dunlop resumed production use the same circuit and are sonically consistent. Buy the cheapest new or used M101 you can find in good condition and use the savings elsewhere in your rig.
Used M101 units sell for $50–75 in excellent condition — a reasonable saving over new that involves no meaningful risk, as the Phase 90 circuit is robust and simple. There are essentially no fragile components in the design, and the most common failure mode (worn footswitch) is inexpensive to repair.
The EVH Phase 90 at $149.99 is worth the premium specifically if you want the Script mode switch — it lets you access the subtler original character in a current-production unit without paying vintage prices. If you don’t specifically want the script sound, the M101 covers the same ground at $50 less.
The M132 ’74 Vintage Phase 90 at $179.99 is for players who want the purest script-circuit experience with modern build quality. The battery-only operation and no-LED design are authentic to the original; whether these limitations bother you depends on your pedalboard setup. For studio use or for guitarists who run simple, battery-powered setups, the M132 is a genuine pleasure. For touring pedalboards with multiple power supplies and DC daisy chains, the M101’s AC input jack is more practical.
Vintage original script-logo Phase 90s (pre-1977): authentic pieces of guitar history, sought by collectors, and genuinely good-sounding phasers. Expect to pay $150–350 depending on cosmetic condition. Not recommended over the M132 reissue for playing purposes unless you specifically want the original hardware. The Dunlop-era reissues are well-made instruments, not budget compromises.
Living With the Phase 90
The Phase 90 earns its pedalboard real estate through unobtrusiveness. At 5mA current draw it is one of the most power-efficient pedals in production — it can run at the end of a daisy chain without affecting neighboring pedals. The small enclosure fits in the corner of a pedalboard where other modulation effects couldn’t. And the single knob means you can make live adjustments without fumbling through a menu — though most Phase 90 users set it once and leave it.
The one operational note worth considering is bypass behavior. The M101’s buffered bypass keeps the circuit active as a buffer even when the phase effect is engaged off. This is generally beneficial (see the signal chain section above) but means the Phase 90 does affect your dry tone slightly even when bypassed. For most players and most applications, this impact is negligible. For extremely picky about buffer/no-buffer arrangements, the EVH Phase 90 allows true bypass operation as an option.
The Phase 90 pairs naturally with delay placed after it in the chain — the phased signal enters the delay’s input, and the repeats carry the same phased character as the original, creating a cohesive, evolving texture. With reverb after the Phase 90, the phased signal blooms into the reverb space, which produces a very specific kind of atmospheric depth associated with 1970s record production. Try the MXR M169 Carbon Copy Analog Delay after the Phase 90 for a full-vintage MXR signal chain that covers enormous ground with minimal footprint.
Stacking a Phase 90 with an overdrive is one of the great underexplored combinations in guitar tone. Place the Phase 90 before a Tube Screamer or a DS-1 and the phased signal’s notches run through the drive’s clipping stage, creating a more complex, harmonically shifting overdrive character. Place the drive before the Phase 90 and the distorted signal’s harmonics get swept through the phaser’s notches, producing a more pronounced, aggressive phase effect on a compressed signal. Both approaches are legitimate; try both and decide based on what you hear.
Frequently Asked Questions
What is the difference between the MXR Phase 90 script logo and block logo?
The script logo (pre-1977 originals and M132 ’74 Vintage reissue) runs without feedback, producing a smoother, subtler phase sweep. The block logo (1977 onwards, including current M101) adds a feedback resistor (R28) that creates a resonance peak at the phase-notch frequencies, giving a slightly more pronounced, “pulsing” character. The difference is real but not enormous — both make excellent phasers. EVH used a script-logo original; the M101 block-logo is the standard current-production unit.
What is Eddie Van Halen’s exact Phase 90 setting?
Rate/Speed at 9 to 10 o’clock — barely above the slowest setting. In Van Halen’s own words: “I just locked into that one setting, and I’ve used it ever since.” He used a script-logo original from the mid-1970s. On the EVH Phase 90 signature pedal, engage the Script switch and set Rate to that 9-10 o’clock range.
Should the Phase 90 go before or after overdrive pedals?
After overdrive is the most common and generally recommended placement — the phaser sweeps through the distorted signal, giving the drive a more animated character. Before overdrive creates a different effect where the drive responds differently to the phased and un-phased frequency content. Both are valid; the conventional chain is overdrive → Phase 90 → delay → reverb.
Does the Phase 90 work with bass?
Yes, with some caveats. The Phase 90’s sweep is tuned for guitar frequency content, so it may not be as pronounced in the low end of a bass signal. It works best for high-register bass playing or for creating atmospheric movement in a bass tone — it is less effective for the deep, slow-sweep bass phaser sound associated with some funk and soul production, which typically uses dedicated bass phaser circuits like the MXR Phase 90 Bass (M290N) or similar.
What songs specifically feature the MXR Phase 90?
Van Halen: “Eruption,” “Ain’t Talkin’ ‘Bout Love,” “Atomic Punk” (Van Halen, 1978); “Everybody Wants Some!!” (Women and Children First, 1980). David Gilmour/Pink Floyd: “Shine On You Crazy Diamond,” “Have a Cigar” (Wish You Were Here, 1975). Steve Jones/Sex Pistols: “Anarchy in the UK” (Never Mind the Bollocks, 1977). Steve Hackett/Genesis: mid-1970s albums including A Trick of the Tail (1976).
Is the current MXR M101 Phase 90 the same as the vintage original?
Not identical. The current M101 uses the block-logo circuit with an added input buffer and DC power jack. The vintage script-logo originals used a different circuit without feedback and without a buffer. The M132 ’74 Vintage Phase 90 reissue captures the script-circuit character, while the M101 is the modern block-logo version. Both are excellent; they have different characters.
How does the Phase 90 compare to a Uni-Vibe?
A Uni-Vibe creates a chorus-plus-vibrato effect (originally designed to simulate a rotating speaker) with more pitch variation and “wobble” than a pure phase shifter. The Phase 90 creates pure phase shifting without pitch modulation. At slow speeds the two effects converge in character; at moderate and fast speeds they diverge significantly. Uni-Vibe is associated with Hendrix; Phase 90 is associated with Van Halen, Gilmour, and Hackett. Robin Trower used a Phase 90 specifically as a Uni-Vibe substitute when his original unit became unreliable — the overlap is real, though they are not identical effects.
Can I modify a block-logo Phase 90 to sound like a script-logo?
Yes. Removing or bypassing the R28 feedback resistor on a block-logo Phase 90 or M101 converts it to script-circuit behavior. This is a straightforward modification that many guitar technicians can perform, and the result closely approximates the script-logo character. The mod is reversible. If you want the script sound without modification, the M132 reissue or the EVH Phase 90’s Script mode are the recommended paths.