The Electro-Harmonix Tube Zipper is a legendary, now-discontinued "Classics" series pedal that combines a high-voltage vacuum tube distortion with a sophisticated envelope filter.It is notorious for its "wild" character, capable of everything from warm overdrive to self-oscillating, synth-like chaos.
The Core Circuit
Dual 12AX7 Tubes: Unlike many "tube" pedals that run on low voltage, the Tube Zipper runs its two 12AX7EH tubes at a high internal voltage. This provides authentic tube compression, harmonic richness, and a tactile response that reacts heavily to your picking dynamics.
Hybrid Design: The tubes primarily drive the distortion stage, while the "patented moving filter" section handles the envelope-following duties.