MXR M-103

Ok, Jimmy Page used it once, but it's got much more going for it than that. Leave the Output knob up ay full - it's useless anywhere else. With the Blend knob at full, it's a gnarly fuzz. With it rolled back, it's a fuzzy minus 2 octave glitch monster. And I mean that in a good way! So pick your spot between the two, and go mad. You'll need to experiment with which pickup and guitar tome setting to use to get the most out of the -2 octave.
If you're even just a bit handy with a soldering iron, I'd recommend putting a sqitch on the C11 capacitor, which brightens the sound up a bit. Also, a switch to flip between -1 and -2 octaves is a good and easy mod to do. i've done both (first modded pedal I've done), and it improves the pedal 100%. There's a bit of bleed-through on the dry signal. At the moment I'm just yanking out the power cable to remedy it, but I might buy/build a bypass looper to solve it. Modding it for true bypass might me a little more than I can handle. It benefits from an overdrive in front of it. Or be The Melvins, and just use it and a Rat (or Moorer Black Secret) and fuzz out!

The MXR M-103 Blue Box is a combination of a Fuzz- and Octavepedal.
This pedal takes your guitar signal and duplicates it 2 octaves down.
The tone is modulated by an output and a blend control knob to mix the fuzz tone with the octave signal
The result of the Blue Box is a crazy effect that can be heard in Jimmy Pages solo in "Fool in the Rain" by Led Zeppelin.
Because of its unique sound, the Blue Box turned to one of my favorites and became a standard pedal on my Pedalboard.
Like every MXR pedal with its massive casing it is perfect for the use on the road and on stage.