Also a guitar effect pedal first popularized by Jimi Hendrix.

It can most clearly be heard on the guitar solo to "Purple Haze," on the LP "Are You Experienced?"

Its characteristic sound is not unlike a fuzz box, with the addition of a note an octave above the original note added to the signal. The octave effect is more pronounced when playing through a guitar's neck pickup, with the tone control rolled back to de-emphasize the treble.

Construction-wise, the pedal differs little from a distortion or fuzz unit, with the addition of a step-up transformer that causes the frequency doubling. There is usually a series of diodes between the transformer and the output jack, which serve to clip the waveform and distort it.