All Silicon Zonk Machine

[gregtoolson]

I'm new to the forum, but have been using DIYstomp for a couple years now as an invaluable resource for my pedal building hobby. I've built quite a few transistor fuzzes and boosters, and several IC based ODs(Rat, 250+, etc.). Anyway, I just built an all silicon Zonk Machine which works alright considering I don't really know what I'm doing. At least it sounds Zonk-ish, like the Ge Zonk I built a while back. The only problem is that the fuzz pot doesn't do anything. The attack sounds like it's full up no matter where I turn it. Anyone have any ideas?

Below is the schematic I came up with based on the Hornby Skewes schematic that I tweaked using ideas from the Marcelo Tripodi's Si Tone Bender MKI(https://www.diystompboxes.com/smfforum/index.php?PHPSESSID=r5f66sj6rh4gjc15a84n0n1qo1&topic=101610.0)

[Dormammu]

With a such screwed circuit like that, it's amazing that it works.
Simple way:
You can move the knob in base of 2nd or 3rd transistor, like voltage divider (aka volume).

Not so simple:
Modify the gain knob to the type of original fuzzface and put it in the emitter of the 2nd transistor. This will allow you to adjust the actual gain.
It would also be nice to return the resistor of negative feedback to the circuit.(not nessesary)

[Steben]

original sketch technique! 

You could omit the 33K resistor. If that does not do anything, the pot is wired incorrectly I guess.

[antonis]

Just Welcome...

[mac]

The attack sounds like it's full up no matter where I turn it. Anyone have any ideas?

Read the voltage at Q2 collector as you vary the pot:
- if no change then the pot is not wired correctly.
- if for example the voltage goes from 6v to 3v then Q2 is fuzzing hard. Ideally Q2 should go from 9v to Gnd to cover all the bases. You could try removing those 22k, 33k and 50k pot and use just a 50k-100k pot at the emitter and write down at what resistances you get almost 9v and gnd. Say at near 2k2 you get 9v then your "22k" is now 2k2, and if at 33k you read almost Gnd then those "33k//50k pot" are 100k//50k pot.
I bet a 2k2 and a 25k pot in series will do it.
If you have already soldered, try smaller resistors across the 22k until you find the one that works fine.

- you can do the same at Q3 emitter, this way you can adjust collector voltages to have a wide range of fuzzy tones.

https://www.diystompboxes.com/smfforum/index.php?topic=122631
https://www.diystompboxes.com/smfforum/index.php?topic=101610.0

mac

[gregtoolson]

I bet a 2k2 and a 25k pot in series will do it.

Thanks Mac, that did the trick. And I ditched the 33k for a more effective pot; though it still only effects 5/8 of the sweep (but that's much better than nothing).