The Electro-Harmonix English Muff’n Tube Distortion first appeared on John’s pedalboard around late 2007, seemingly replacing the Big Muff Pi, which he had used since the release of By the Way.
Given that Stadium Arcadium was released on May 9, 2006, it’s likely that John used the Big Muff during the album’s recording sessions. The decision to switch to the English Muff’n toward the end of the Stadium Arcadium World Tour remains unclear. If you come across an interview where John discusses this pedal, feel free to share it in the comments below!
Hey, according to this interview where John goes through each track of Stadium Arcadium, English Muff’n had already been used in the studio while recording the album.
https://invisible-movement.net/press/2006-11-guitarplayer