I started copying the original layout for veroboard and gave up toward the end as it was a cramped mess - this is a similar but more practical version.
The germanium John Hornby Skewes Zonk II is similar to a Fuzz Face but without the 100k feedback resistor, and note that the output cap is taken directly from the collector of Q2, and there's a resistor in series with the cap to take a bit of edge off the output level. There's also a 680k resistor to help bias the base of Q1, probably due to the missing 100k feedback resistor.
It appears to be a progression from the original Zonk Machine (like a MK1 Tone Bender), before the all-silicon model, which also has two transistors. To make things even more confusing, a hybrid silicon germanium version was thrown in for good measure.
I’ve read that these were made by Sola Sound for JHS in approx 1966-67. Check the thread on the D*A*M forum for photos, as this is slightly different from one of the schematics.
JHS ZONK II - 0.15” VERO LAYOUT
I used a 20k trimmer instead of the 8.2k resistor to bias the collector of Q2. Do you think using a 1M trimmer for the 680k resistor might be the better way?
ReplyDeleteDo you have a breadboard? OC75s can bias quite differently to other transistors, as they're usually pretty leaky. I'd try the 47k
DeleteI am actually Russian transistors for this build. Sounds great so far, but I was wondering what it could sound like with a bit of tweaking.
ReplyDeleteGreat - I'm yet to try this one. I like the look of it
DeleteI got a step further: I installed two trimmers (20k instead of 8.2k resistor & 100k instead of 47k resistor). Now it’s easy to bias. I started with FuzzFace values and am now trying to find my own sound. 🙂
DeleteCool - should be able to dial in something nice with that.
DeleteI was just wondering how and if it were possible to include a sundial (like in Analogmans Sunface and Sunbender) to this layout?
DeleteA sun face is basically a trimmer in series with a fixed resistor on the collector of Q2. Since you already have a 20k trimmer in this position, you are well on the way to this.
Delete1. Turn the trimmer down to a point where you don't like the sound (low resistance). Measure the trimmer resistance, and note the value.
2. Same again, but turn it up this time, just to the point where no further change happens with the sound / you don't like it anymore. Now measure the resistance again and note it.
3. Put the nearest value fixed resistor on to the collector of Q2 for the low point reading of the trimmer (step 1), and then add a pot in series with this, that takes the value up to, or maybe a bit past the high point (step 2).
You should now have a useful bias control. Ideally you don't want the pot value to be too big, as it will have too much range where nothing happens. You want it to sweep through a useful range.
If you are doing this, you might also want to replace the Fuzz pot with a fixed 1k resistor. Sometimes the fuzz pot doesn't do that much, compared to the range of sounds you get from an external bias control.
Hope this helps
Thank you! That is very kind and helpful. :-)
DeleteI just read the article about the Zonk II on fuzzboxes again (https://fuzzboxes.org/zonkii), and there seems to be another version of this very rare pedal:
ReplyDeletehttps://fuzzboxes.org/wp-content/uploads/2021/05/germanium-Zonk-II-PCB-version.jpg
I am not very good with this, but what kind of circuit is this?
I know that later versions were TB MKII, but the two earlier versions are two and three transistors circuits that are not related to the MKII.
It looks like what is considered to be the classic Zonk Machine circuit. I can’t see all of the components, but the only difference I can see is a 1m2 on the base of Q1 instead of a 1m. The rest looks about the same.
DeleteThey used a lot of different construction methods.
Coming back to this, what transistor setup would you suggest: Vox Tone Bender or MK1.5?
ReplyDeleteAnd if 1.5, that basically means Fuzz Face transistor with way more leakage, right?
Hello - I'd try more like a MK1.5 as they both used OC75s.
ReplyDelete