Zeugma (Zonk Machine MKI)

Guilherme Collateral

Guilherme Collateral

Well-known member
What a finicky circuit to build, I hate every second of testing transistors for Zonks and MKI. There is no magic formula to follow, gotta socket and try infinite combos to find the sweetspot between gain, sustain and gate. But when it sounds good, oh boy, does it sound good! Went full mojo on this one, 0.15” pitch Vero, carbon comp (for the values I had on Stock), Philips capacitors and Mullard OC44/71 and GET873. Got weird noises on the decay but got rid of it with a 1nf cap between input and ground. Very inspiring Fuzz, I even recorded a little video of it!

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Guilherme Collateral said:
What a finicky circuit to build, I hate every second of testing transistors for Zonks and MKI. There is no magic formula to follow, gotta socket and try infinite combos to find the sweetspot between gain, sustain and gate. But when it sounds good, oh boy, does it sound good! Went full mojo on this one, 0.15” pitch Vero, carbon comp (for the values I had on Stock), Philips capacitors and Mullard OC44/71 and GET873. Got weird noises on the decay but got rid of it with a 1nf cap between input and ground. Very inspiring Fuzz, I even recorded a little video of it!

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Great looking build. How did you do the graphics and where did you get the enclosure?

I’m wondering how you chose the transistors.
As far as I can tell Q1 has to have a gain of 60-80 with relatively high leakage such as 200uA. Transistor Q2 has a bias network so it doesn’t have to be leaky to bias. The gain/attack control sets the bias of the second stage. I’m not sure was is an ideal gain for the transistor or what the collector voltage should be.
Q3 needs to be a leaky transistor as it is bias by its leakage. I believe the collector voltage should be quite high for this stage in order get it to clip.

Regards

Mark
 
Hey @Mark, the enclosure is from @mwpedalparts-maggie, really great stuff. The artwork is silk screened to the enclosure. As for the transistors, it doesn’t really exist a formula (as you can see from the wide range of gain/hFE used on originals). You need to have the sound on your head and swap lots and lots of transistors ‘till it sounds good. I start with a ~80hfe medium leakage for q1, 120+ high leakage (up to 0.8uA) for q2 and for q3 it’s a low gainer; you need to know what do you want, if you want more gate, you need leakage, if you want more sustain, the less leakage, the better (but the pedal will sound noisier).
 
There is a LOT of info about this circuit condensed here, https://vero-p2p.blogspot.com/2022/12/zonk-machine-component-values-table.html

And this is a rare case of a pedal which isn’t really “paint by numbers”. I tried to make one using different brand transistors with the same hFE/leakage for each transistor and the second one sounded nothing like the first, on a side by side test. This and the MKI are, IMHO, the hardest pedals to make with the right tone; sustain and noise ratio, you need to have a good stash of transistors, lots of patience and be prepared to deal with really esoteric nonsense, some units will have a lot of noise and fizzy decay, which you can almost always solve with a 1-10nf cap from the input to ground.
 
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