Author Topic: Zonk Machine/Tonebender MKI sizzle and sustain  (Read 1219 times)

artr

Zonk Machine/Tonebender MKI sizzle and sustain
« on: June 29, 2019, 07:59:14 PM »
Hey guys, I've breadboarded a zonk machine after this schematic
, I have 6 transistors that I've been experimenting with (2 old oc41 and 4 old oc71, gains from 50-100 and all pretty low leakage). Changes in the transistor lineup result in changes in gain/compression, general noise, sustain and amount of "sizzle" on the decay of the note, and my question is: can I do anything else to the circuit to control these things, especially the sizzle and sustain? Also, are any of the things/characteristics specific to Q1, 2, 3?

PRR

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #1 on: June 29, 2019, 09:20:12 PM »
Q1 Q3 "can't work" because they appear to be biased dead-off, stone-cold.

GE always leaks. But this pedal may have used "selected rejects": leaky but not too leaky.

Try trimming the bias like so:

  • SUPPORTER

artr

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #2 on: June 29, 2019, 09:48:23 PM »
Q1 Q3 "can't work" because they appear to be biased dead-off, stone-cold.

GE always leaks. But this pedal may have used "selected rejects": leaky but not too leaky.

Try trimming the bias like so:

Thanks Paul, I'll try it! are the trimming pots connected to ground on one side and -9v on the other?

Harry

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #3 on: June 29, 2019, 11:09:59 PM »
If you turn down the fuzz knob and/or roll the tone knob back on your guitar does the sizzle and noise go away?

On mine the fuzz/attack knob does not function like a normal fuzz gain or drive control. It acts more like a bias and you need to balance it between sustain and noise. There should be a sweet spot somewhere in the midpoint. I believe this was how it was intended to function?
Check out: https://youtu.be/YJFnV3Eqy_s

I ended up selecting my transistors by ear rather than gain and leakage.

There should be some leakage how much Iím not sure of, because my experiments with this circuit gave pretty inconclusive results. However, i do think i ended up with mid to higher leakage germanium.
« Last Edit: June 29, 2019, 11:15:04 PM by Harry »

Electric Warrior

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #4 on: June 30, 2019, 04:59:54 AM »
Q1 Q3 "can't work" because they appear to be biased dead-off, stone-cold.

GE always leaks. But this pedal may have used "selected rejects": leaky but not too leaky.


Acidfuzz posted some measurements over at the other forum:
http://....org/viewtopic.php?f=19&t=16723&hilit=zonk&start=20

Quote
-Q1 TI AO2 650 Hfe= 180, leakage= 0.12mA.

-Q2 Mullard OC75 Hfe= 78, leakage= 0.29mA

-Q3 OC44 Hfe= 58, leakage= 0

Pretty much as expected. OC44s don't leak much, if at all and OC75s are quite leaky in general.

I have 6 transistors that I've been experimenting with (2 old oc41 and 4 old oc71, gains from 50-100 and all pretty low leakage). Changes in the transistor lineup result in changes in gain/compression, general noise, sustain and amount of "sizzle" on the decay of the note, and my question is: can I do anything else to the circuit to control these things, especially the sizzle and sustain? Also, are any of the things/characteristics specific to Q1, 2, 3?

Some Zonks used OC71s for Q2 and Q3, but they have a different bias setup with a 220k on Q1b and a 25k fuzz pot. Chances are this setup will work well for your OC71s.

Q2's collector voltage with the fuzz maxed out should be somewhere between 5 and 7V from what I've seen.
« Last Edit: June 30, 2019, 05:38:25 AM by Electric Warrior »

bms19

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #5 on: September 05, 2020, 03:05:44 PM »
Hello, does anyone knows a good replacement for the impossible to find AO2 650?
Cheers
Benoit

Steben

Re: Zonk Machine/Tonebender MKI sizzle and sustain
« Reply #6 on: September 06, 2020, 02:14:10 AM »
Is it correct to state that high leakage will lead to more bias current and less gating yet less gain and sustain?
Rules apply only for those who are not allowed to break them