Zonk II, anyone?…

Coda

Well-known member
Would anyone like to talk about the Zonk II fuzz? Not the Zonk Machine (dark MKI TB), nor the rare two transistor Ge version of the II. I am interested in the Si (pnp) version. It’s very simple, seemingly…a Fuzz Face with one less resistor (and also one more resistor). However, I have not been able to build a satisfying version…

I have been working on the breadboard with this schematic:

zonkIIschem.gif


There’s no way that 2M2 at the end is correct, right? That’s gonna let NOTHING through!…

Meanwhile, I haven’t found a satisfactory transistor for this circuit, either. I started with 3906, but could get nothing through the 2M2. I tried a few other PNP, as well as some NPN. BC109C gave me a somewhat usable fuzz. I started adjusting the bias resistors, and it’s starting to dial in, but I’m about to the limit…

Has anyone ever messed around with the Zonk II? The demos I’ve found are pretty good…

 
No pulldown resistor on the input...


Edit: Sorry..half a thought from a half-wit.. what if you added a 1M pulldown, dumped the 2M2, and changed the volume pot to 25k?
 
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The 2m2 resistor is vintage correct despite being a seemingly odd choice. You can see it included in this vintage reproduction layout by Amplified Parts:


As well as very clearly in the gutshots of original Zonk II and Shatterbox (which was a zonk II and a treble booster in one box)

1689519509012.jpeg


The original transistors were 2n4061, which I’ve read are usually 250-350hfe, just to give you a ballpark range
 
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Recently built one. No issue with the output volume at all, but it was sort of picky about transistors. I built it silicon NPN with an old 2N3500 and a BC109C, also dropped the input cap value A LOT because else it's dark and muffled AF. Low hfe first and high hfe second transistor makes for a good choice in my very limited experience with this circuit.

Check whether your PNP/NPN conversion is correct. Definitely would not bother with a silicon PNP version.

EDIT: Picky with transistors I don't mean in the sense that it wouldn't work or sound like total garbage depending on the transistor but with some models for Q1 especially it just sounded too gated/starved. Reeves Electro makes a fancy Zonk 2, maybe check the demos of that for inspiration too. But trust me, you won't want that 10uF input cap. Hell, 10nF is enough probably.
 
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Recently built one. No issue with the output volume at all, but it was sort of picky about transistors. I built it silicon NPN with an old 2N3500 and a BC109C, also dropped the input cap value A LOT because else it's dark and muffled AF. Low hfe first and high hfe second transistor makes for a good choice in my very limited experience with this circuit.

Check whether your PNP/NPN conversion is correct. Definitely would not bother with a silicon PNP version.

EDIT: Picky with transistors I don't mean in the sense that it wouldn't work or sound like total garbage depending on the transistor but with some models for Q1 especially it just sounded too gated/starved. Reeves Electro makes a fancy Zonk 2, maybe check the demos of that for inspiration too. But trust me, you won't want that 10uF input cap. Hell, 10nF is enough probably.

Lots to consider here, thanks a lot. I’ve noticed the Q1 issue. Reeves is beast, so I’ll definitely look at that…
 
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Recently built one. No issue with the output volume at all, but it was sort of picky about transistors. I built it silicon NPN with an old 2N3500 and a BC109C, also dropped the input cap value A LOT because else it's dark and muffled AF. Low hfe first and high hfe second transistor makes for a good choice in my very limited experience with this circuit.

Check whether your PNP/NPN conversion is correct. Definitely would not bother with a silicon PNP version.

EDIT: Picky with transistors I don't mean in the sense that it wouldn't work or sound like total garbage depending on the transistor but with some models for Q1 especially it just sounded too gated/starved. Reeves Electro makes a fancy Zonk 2, maybe check the demos of that for inspiration too. But trust me, you won't want that 10uF input cap. Hell, 10nF is enough probably.

Looking at the Reeves build, it looks like he uses a 220k at the end instead of 2M2, though his also has a tone control…

backopen3908Zo.jpg
 
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Looking at the Reeves build, it looks like he uses a 220k at the end instead of 2M2, though his also has a tone control…

backopen3908Zo.jpg
I’ve seen some builds where people put a switch to bypass the 2M2 resistor for a supposedly “wilder” fuzz tone. Might be worthwhile replacing it with a 2M pot on the breadboard and seeing how you like that.
 
Note that although the circuit looks like a FF at first glance, the fact that it's lacking the global feedback (through the 100K resistor in the FF) is noteworthy. Q1 is biased with local collector feedback instead. Also, there is typically a pulldown resistor (470k) at the input although schematics often do not show it (the one in OP's post does not), and it's often hidden fairly well in gut pics. You can see it coming off of the same footswitch lug as the 10u input electrolytic in the pic @Bricksnbeatles posted. It just goes from there to GND.

The optional 3k9 resistor will change the bias of Q2, so you may try temporarily jumping one in when you swap out Q2 to see how it sounds with and without.

The 2M2 resistor definitely is odd - it's also in the Mk1 and Zonk Machine (original). The 2M2 resistor with 500K divider reduces the max output to a little less than 20% of what it would be without the divider. It does quiet the output, but IME it should be capable of getting plenty loud still. But yes, people do remove it or lower its value fairly often in modern builds. As far as why it's there - just speculation, but I have two theories:

1) The Mk1 is a modified FZ-1, and the Zonk Machine (original) is nearly identical to the Mk1. The FZ-1 does not have the 2M2 resistor, so it may have been added to the Mk1 in an effort to keep the output more in line with what you'd get from the 3V-powered FZ-1, and it was either just left in or similar logic was used for the Zonk/Zonk II.

2) It's easy to miss, but the volume pot is wired strangely (lugs 2 and 3 reversed from what is normal) in both the Zonk Machine and Zonk II, and the early Tonebender Mk1(s) (stripboard version) supposedly had this same wiring. My guess is that the odd pot wiring is done to limit the effects of the volume knob when bypassed, and the 2M2 resistor is there to limit the loading of the circuit when bypassed, as the Zonks were NOT true bypass (I'm unsure if the early Mk1s were, later ones with standard volume pot wiring DID use true bypass). The Zonk's footswitch basically connects the input jack to either the actual input jack location drawn in OP's schematic or lug 3 of the volume pot (common with the output) depending on footswitch position. With the effect bypassed, lug 3 of the volume pot is still connected to the signal path. The 2M2 resistor limits the loading effect of the rest of the circuit, while the unusual pot wiring ensures that there is always ~500kΩ to GND from the pot which will have minor loading effects.

However, if the pot was wired normally, there would be a variable resistance to GND (the resistance between vol pot lugs 1 & 2) depending on the volume knob's rotation. With the volume knob turned all the way down, the signal would be shunted to GND even when the effect is bypassed. This is less-than-ideal on its own, but it was compounded in the original Zonk Machine by the fact that it has a battery disconnect on the volume knob, so having the volume turned all the way down when disengaged may be fairly common with these pedals.

Lastly, I've heard anecdotally that removing/lowering it can add some brightness. I'm guessing that's from its interaction with parasitic capacitance of cabling etc. forming a subtle low pass filter. Probably not a design intention, but maybe something to keep in mind.
 
Note that although the circuit looks like a FF at first glance, the fact that it's lacking the global feedback (through the 100K resistor in the FF) is noteworthy. Q1 is biased with local collector feedback instead. Also, there is typically a pulldown resistor (470k) at the input although schematics often do not show it (the one in OP's post does not), and it's often hidden fairly well in gut pics. You can see it coming off of the same footswitch lug as the 10u input electrolytic in the pic @Bricksnbeatles posted. It just goes from there to GND.

The optional 3k9 resistor will change the bias of Q2, so you may try temporarily jumping one in when you swap out Q2 to see how it sounds with and without.

The 2M2 resistor definitely is odd - it's also in the Mk1 and Zonk Machine (original). The 2M2 resistor with 500K divider reduces the max output to a little less than 20% of what it would be without the divider. It does quiet the output, but IME it should be capable of getting plenty loud still. But yes, people do remove it or lower its value fairly often in modern builds. As far as why it's there - just speculation, but I have two theories:

1) The Mk1 is a modified FZ-1, and the Zonk Machine (original) is nearly identical to the Mk1. The FZ-1 does not have the 2M2 resistor, so it may have been added to the Mk1 in an effort to keep the output more in line with what you'd get from the 3V-powered FZ-1, and it was either just left in or similar logic was used for the Zonk/Zonk II.

2) It's easy to miss, but the volume pot is wired strangely (lugs 2 and 3 reversed from what is normal) in both the Zonk Machine and Zonk II, and the early Tonebender Mk1(s) (stripboard version) supposedly had this same wiring. My guess is that the odd pot wiring is done to limit the effects of the volume knob when bypassed, and the 2M2 resistor is there to limit the loading of the circuit when bypassed, as the Zonks were NOT true bypass (I'm unsure if the early Mk1s were, later ones with standard volume pot wiring DID use true bypass). The Zonk's footswitch basically connects the input jack to either the actual input jack location drawn in OP's schematic or lug 3 of the volume pot (common with the output) depending on footswitch position. With the effect bypassed, lug 3 of the volume pot is still connected to the signal path. The 2M2 resistor limits the loading effect of the rest of the circuit, while the unusual pot wiring ensures that there is always ~500kΩ to GND from the pot which will have minor loading effects.

However, if the pot was wired normally, there would be a variable resistance to GND (the resistance between vol pot lugs 1 & 2) depending on the volume knob's rotation. With the volume knob turned all the way down, the signal would be shunted to GND even when the effect is bypassed. This is less-than-ideal on its own, but it was compounded in the original Zonk Machine by the fact that it has a battery disconnect on the volume knob, so having the volume turned all the way down when disengaged may be fairly common with these pedals.

Lastly, I've heard anecdotally that removing/lowering it can add some brightness. I'm guessing that's from its interaction with parasitic capacitance of cabling etc. forming a subtle low pass filter. Probably not a design intention, but maybe something to keep in mind.

Thank you for that detailed description. It’s definitely not just another Fuzz Face. I look forward to building a replica…
 
No problem! Also FYI - 2N4061s (used in originals) had a datasheet hfe range from 90-450 hfe from what I can tell, whereas the BC109C starts at 450 hfe minimum (450-900). The 2N3906s (2N3904 if NPN) have a lot more crossover with 2N4061s (100-300). I'd think you should be able to get those sounding nice if it's wired up correctly.

Also, you should be free to wire the vol pot up as you normally would (rather than with lugs 2/3 swapped from what's normal) if you're using true bypass. The first Zonk I built was intended to be the exact Zonk circuit (except with true bypass), but I used standard volume pot wiring simply because I didn't catch that it was different in the schematic I was using. Either way works, and I don't think you'd really notice anything odd about the pot in actual use if you go with the original wiring. The control feels pretty similar to standard wiring to me at least.
 
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I'm planning on building this circuit and have some questions. I found the schematics for the Reeves ZO, and they are different compared to the schematics linked at the original post here. The "Fuzz" pot is not there, instead there is a fixed resistor and cap, and there is a pot at the input, working almost like a guitar volume knob, to adjust input impedance? Also, there is a pot going between the collector of Q2 and 9V, instead of the fixed resistor seen here.

I'd like to have a dedicated "Fuzz" or "Gain" knob, could I use the solution seen in the original post here?

The ZO schematics are here: Dirtbox Layouts: Reeves Electro Zo:
 
Hopefully you saw the comment on Dirtbox Layouts: "*Update 240203* Reeves Electro got in touch with Gray Bench since two of the pot values was incorrect in the trace. Layout and schematic is updated." There had been an error previously.

Same thing happened for this post as well:
In this post above, Andrew compares the Electro Zo circuit schematic to that of the original Zonk II - which may help you with your knob question.

[Edit: I built mine from Andrew's Vero, and it sounds great.]
 
Hopefully you saw the comment on Dirtbox Layouts: "*Update 240203* Reeves Electro got in touch with Gray Bench since two of the pot values was incorrect in the trace. Layout and schematic is updated." There had been an error previously.

Same thing happened for this post as well:
In this post above, Andrew compares the Electro Zo circuit schematic to that of the original Zonk II - which may help you with your knob question.

[Edit: I built mine from Andrew's Vero, and it sounds great.]
Thanks! I saw that the pot values were incorrect, but I have not seen the link you posted, so thanks a lot, very helpful! I constructed the circuit on breadboard today, with the "fuzz" pot, and it seems to work pretty good! However, I found that the 10nF cap at the output removed too much bass for me, so right now I use a 0.1uF instead. My plan is to use the Zonk, into a Fender Princeton tone stack, into a VCF, so right now I'm thinking about if I need to use buffers between each stage to isolate the circuits. I've removed the "Drift" pot and used a 250k resistor to get a bit of input impedance and load, and I removed the "Swell" knob, since I want the volume control to be in the tone (Fender Princeton) part of the circuit.

Does anyone have any input on whether buffers are needed between the different sections?
 
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