This pedal is the classic ratty fuzz/distortion. This is a sound of the '80s and '90s, with some Dazatronyx tweaks. This is achieved by a two-stage distortion of first overdriving the metal can 308 amplifier into fuzz, and then recovering some shape by further compressing the signal using hard-clipping silicon diodes.
The HAIR control dials the mid/high drive saturation. Turning this completely to the right achieves the classic metallic ratty distortion. Turning this left achieves a full, flattened response. This is a variable version of the reutz mod.
Please note: the germanium mode switch shown in demos is no longer included on this model as standard. The "XL" model is available in a Hammond 1590N1 (125B) size case.