Phaser effects pedal originally from MXR but now manufactured by Dunlop. Tone geeks will argue that Dunlop let the quality slide and there are significant differences in tone between newer and older models. A popular mod for people unsatisfied with the newer ones involves clipping out the r28 resistor inside the pedal which is the cause for some unwanted clipping. Its an easy mod, but I recommend you do some research before fiddiling around inside any of your expensive toys.

Dunlop recently released an Eddie van Halen model due to its use on Eruption. This version has a switch which is basically the same as the mod people have been doing with it.

The wonderful thing about the phase 90 is its simplicity, its already dialed in to a lovely, watery sound (Somewhat more subtle than the Small Stone) All it needs is one knob for speed.

As used by (Info taken from guitargeek.com):

john frusciante-red hot chili peppers
eddie van halen-van halen
dave grohl-foo fighters
matthew bellamy-muse
mike mccready-pearl jam
wes borland-limp bizkit
mike einziger-incubus
david gilmour-pink floyd