EKI 826 Fuzz Box

The EKI 826 Fuzz Box has an unique spin on the 2TEF topology. Unlike a typical 2TEF, Q2's emitter has a very large emitter resistance (usually R_E ≈ 1k, here R_E > 50k).

The 50k pot, which is the single control provided, isn't even given a definitive label in the EKI manual. From the manual:

C2 and R4 (the 1nF cap and the 50k pot) also provide feedback from the output and at the same time offer a means of tone or fuzz control.

The manual claims this circuit provides a gain of 100. In simulation, there is a large amount of gain seen at Q1's collector, but this is reduced at Q2's collector, and reduced further still by the 68k and 10k voltage divider which is effectively a 100k volume pot in a fixed position. Replacing voltage divider with an "OUTPUT" control is an obvious mod. The stock setup is pretty much just unity at the output.

Viewing the scope with a sine wave input, the output is asymmetrically hard clipped, with a hard top and roundish bottom with the control CCW, and differentiated spikes come in when the control is rotated CW.

As is, this fuzz box has a kind of cool "broken amp" type sound; perhaps even a "slashed speaker" simulator. It does not sound like typical 2TEF at all.

EKI stands for Electronic Kits International of Kyle, Texas. I have no idea when this kit was put out, but it appears to be of either late '70s or '80s vintage.