The MXR CSP001 Variphase is a phaser pedal with a rocker pedal instead of knobs and a footswitch. MXR built the classic Phase 90 phasing circuit into a Crybaby-style treadle housing, so instead of setting a speed knob and leaving it, you control the speed of the phasing with your foot in real time1.
RockBoard describes it as "a killer twist on the classic Phase 90 phaser pedal," with the same warm and thick analog phasing as the original, but now adjustable on the fly2. MusicRadar put it more plainly: "the pedal is, in a nutshell, a Phase 90 placed inside a Crybaby's chassis"1.
A Phase 90 circuit with a rocker pedal
The Variphase takes the Phase 90 circuit, the classic rock phaser pedal, and puts it under a treadle. The Phase 90 itself has been reissued by MXR in many forms over the years, from the Script Phase 90 to the EVH Phase 90 and the Phase 95, but all of those are conventional stompboxes with a speed knob. The Variphase is the one version where your foot does the work13.
What that means in practice:
- Speed is foot-controlled: the treadle lets you alter the speed of the phasing in real time1.
- The range is wide: you can vary the speed from a subtle, long cycle to a fast, watery warble2.
- The sound is the familiar Phase 90 character: warm and thick analog phasing2.
Controls and bypass
The treadle alters the speed of the phasing in real time, and when you take your foot from the pedal, it springs back into its full-back position, bypassing the effect1.
- Treadle: rocks forward and back to change phasing speed while you play1.
- Side-mounted volume control: at its minimum, it sets the wet signal to the same volume as the dry signal; higher settings make the wet sound significantly louder1.
- Bypass: when you take your foot off the pedal, the treadle springs back to its full-back position, bypassing the effect1.
Because the effect engages only when your foot is on the treadle, the Variphase cannot sit on a board and be tapped on and off like a normal stompbox. MusicRadar's reviewers called this its main drawback: "It's a shame that you can't use this as a more conventional stompbox, but at least you can have both this and your favourite phaser on your board at the same time"1.
Power
The Variphase runs on a 9V DC center negative supply and draws 20mA2, the same standard power arrangement as most compact MXR pedals, so it works with a typical pedalboard power supply.
Availability
The Variphase comes from the MXR Custom Shop and was made in limited quantities2. MusicRadar noted it is "sadly only available in limited numbers"1, so it is not a standard catalog item and may take some searching to find.
What reviewers said
MusicRadar's review team found the pedal works well overall, with the practical caveat that the volume control needed to be at minimum to keep the wet and dry signals at the same level1. Their verdict:
"It's a shame that you can't use this as a more conventional stompbox, but at least you can have both this and your fabled script Phase 90 on your pedalboard."
Videos
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Questions
What power does the MXR Variphase need?
It runs on 9V DC from a center negative power supply and draws about 20mA. That is the same standard supply used by most MXR compact pedals, so it fits a normal pedalboard power brick.
What does the rocker pedal control on the Variphase?
The treadle controls the speed of the phasing in real time. Rocking your foot forward or back speeds the sweep up or slows it down, moving from a subtle, long cycle to a fast, watery warble while you play.
Can you still buy the MXR Variphase?
It was made in limited quantities by the MXR Custom Shop, and reviewers noted it is available only in limited numbers. Finding one new may take some searching, since it was never a standard production model.
What does the side-mounted control do?
The side control is a volume control for the wet signal. At its minimum it sets the wet signal to the same volume as the dry signal; higher settings make the wet sound significantly louder.
What circuit is the MXR Variphase based on?
It is based on the classic MXR Phase 90 phaser circuit. MusicRadar described it as a Phase 90 placed inside a Crybaby chassis, with the same warm and thick analog phasing as the original.
How do you turn the MXR Variphase on and off?
There is no footswitch. The treadle springs back to its full-back position when you take your foot off, which bypasses the effect. You engage the phasing by putting your foot on the treadle and rocking it forward.
Sources (3)
- MXR Variphase CSP001 review, MusicRadar, 2008-02-05
- CSP001 Variphase by MXR, RockBoard (rockboard.de PedalPedia), 2026
- MXR Phase 95 Mini Phaser - Squeezing more orange into less, gearnews.com, 2016-09-21
