Electro-Harmonix Poly Chorus

Originally released in the late seventies and reissued in the 90s, these large box EH pedals are highly sought-after: Kurt Cobain used a Poly Chorus and Echo Flanger as part of his signature guitar sound with Nirvana – his handwritten settings for certain songs are easily found online.

From Tonefrenzy.com:

This is probably the swirlingest analog pedal made. It sounds similar to the “Small Clone” but has another couple of layers that you can set into motion. There are five knobs worth of choices to select from. If you find one of these pedals, dig in. Just keep turning the dials until you find your mix of cycles within cycles. Some of the choices don’t cause much of a change, while others are dramatic; so don’t fire this up on stage without rehearsal, unless you’re a good sport.

Besides sheer volume of choices, it’s the layering that makes this pedal special. It has the ability to colour music with more than one feeling at a time. Most people’s initial take is of a nice chorus sound/feeling, but after a while the tonality takes on a sadness. This is the kind of thing that works wonders in movie scores, and for atmosphere/backgrounds: used with restraint, its subtlety can make you want to hear more: In addition to the composition, one needs to find a setting that embellishes the theme as opposed to drowning it out. Newer players might want to use a phaser, or chorus before moving to this pedal.

Check out this YouTube demo (with thanks to the uploader):