Zonk Machine - middle transistor is silicon ??? trim pot

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...

Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby Manfred » 24 Jun 2019, 09:15

Q2: B -.643V -.672V
C -7.16V -3.632V
E -0.1mV -0.1mV


I assume that the collector voltage was notet on the left and right stop of the "Bias" potentiometer,
which value was finally set?
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby acidfuzz » 25 Jun 2019, 15:00

Manfred, No. The internal trimmer was adjusted to ~152K. Voltages were then measured with the external "FUZZ" control set at 1/2 (12 Noon) and at full clockwise rotation at room temperature (~70°F). Like in the Maestro Fuzz Tone and the MKI Tone Bender, the "FUZZ" control is essentially an external bias control for Q2.

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Manfred (25 Jun 2019, 22:22)
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby Manfred » 25 Jun 2019, 22:24

acidfuzz, thank you for your clarification.

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acidfuzz (28 Jun 2019, 21:40)
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby EmmG » 26 Jun 2019, 05:41

Cool stuff, acidfuzz. I just built a clone drawn by a friend who's been following this thread and posted to his new layout blog.
https://dirtboxlayouts.blogspot.com/2019/06/hornby-skewes-zonk-machine-mk-i-sige.html

Here's a hissy audio clip verifying it, even though I don't have the "right" parts yet.
https://soundcloud.com/user-562468024/alexs-zonk-hybrid-01
Russian germs and a BC558 will do for now. I look forward to hearing what works for other builders.

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acidfuzz (28 Jun 2019, 21:40)
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby acidfuzz » 28 Jun 2019, 21:55

Nice! Cool to see clones coming to life. If it helps, the 2N4061 hFE was 110, obviously with zero leakage (Si). You could easily use a Ge tranny in there, but the Si does make it more temperature stable. Here's the corrected schematic with the 2.2M output resistor:

ImageZonk Hybrid Schematic Correct by Jonathan Curl, on Flickr

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Ocular Dawn (24 Jul 2019, 18:06)
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby EmmG » 29 Jun 2019, 22:01

Yes, putting a lower gain one in Q2 got rid of all the hiss. I also tried a germ. and it sounded fantastic.
How different, if at all, did this sound and feel for you compared to the all germanium models?
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby Electric Warrior » 30 Jun 2019, 12:07

acidfuzz wrote:There's a fun article on the Zonk here: https://www.vintageguitar.com/23068/hor ... -machines/

"Skewes translated that cultural shift into a business; with his wife, Madge, he founded his own musical-instrument company in ’65, from his home in Garforth, in West Yorkshire – far from swinging London. Among his first products was a fuzz pedal." I think it's cute that JHS started out just his wife and him working from home. Reminds me of the Acid Fuzz thing.

"To design and build his stompboxes, Skewes commissioned a small firm called Wilsic Electronics, in the village of the same name near Doncaster. Owner Charlie Ramskirr set to work."

“Charlie designed the pedals, and I guess he cribbed circuit ideas from others, though I do not know whether from the Tone Bender,” Skewes remembers.


I'm gonna take a wild guess and assume that whoever was building the Zonks got fed up with tuning the all germanium transistor set and the hybrids were an in between stage before the Zonk II? I pulled the pots, but no date codes. If there are photos of others with pots dating to 1968, I assume these were the final version of the Zonk before they moved on to the Zonk II?


Isn't the "D8" on the fuzz pot a date code? I've seen several with this code, but many germanium ones have it as well.
The hybrid version being the last of the Zonk Is makes sense and sounds perfectly logical, but it's only an assumption. I don't think we can say for sure.

According to the article and catalog pages picutured, the Zonk Machine and Zonk II were being sold concurrently at first, with the Zonk II being a much cheaper pedal. I guess at one point they simply discontinued the Zonk Machine? From what I understand they made the Zonk II well into the 70's. I've seen some with 1972 date codes on the electrolytics and pots.
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby nightraven » 30 Jun 2019, 13:54

Electric Warrior wrote:According to the article and catalog pages picutured, the Zonk Machine and Zonk II were being sold concurrently at first, with the Zonk II being a much cheaper pedal. I guess at one point they simply discontinued the Zonk Machine? From what I understand they made the Zonk II well into the 70's. I've seen some with 1972 date codes on the electrolytics and pots.

The earliest silicon Zonk II's look pretty similar in parts selection and construction to the vero Zonk I's. It is possible (but never certain!) that Wilsic(?) stopped making the I and started their version of the Zonk II in its place, and that the Zonk II in the product catalogue, advertised alongside the Zonk I etc was the Sola Sound version instead.
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby acidfuzz » 16 Aug 2019, 06:21

Electric Warrior: "Isn't the "D8" on the fuzz pot a date code? I've seen several with this code, but many germanium ones have it as well.
The hybrid version being the last of the Zonk Is makes sense and sounds perfectly logical, but it's only an assumption. I don't think we can say for sure."

Yes sir, exactly. There is a "D8" code on the "Fuzz" pot. RS (Radio Spares) UK potentiometers use only two digits. The first digit is a letter from A to L representing one of the twelve months of the year. The second digit is the last digit of the year of production. So, the “D8” on the RS pot in this Zonk tells us that at least the pot was made in April of 1968. Incidentally WIMA capacitors also use this same code. The hybrid being the last version of the Zonk is totally a guess on my part.
Electric Warrior, while we're on the subject of JHS, I had someone offer me a JHS T.B. 2 Selectatone a couple of years ago and I wasn't interested. I told them to contact you on FSB to see if you would/could trace it for the community before he sells it. Did that ever happen? If you can PM or quick reply here that would be cool.

EmmG: "Yes, putting a lower gain one in Q2 got rid of all the hiss. I also tried a germ. and it sounded fantastic." Cool. I agree, a germanium Q2 does sound fantastic in this circuit.

"How different, if at all, did this sound and feel for you compared to the all germanium models?" The sound is very similar when you dial in the "Fuzz" to the sweet spot. Nothing drastically different in terms of the sound. It's ~the typical Ge/Si difference you'd expect, though somewhat watered down because of the hybrid situation. The clipping is harder, so not as smooth (less sensitivity/higher threshold voltage) as the all Ge, with more artifacts at higher fuzz settings (probably due mostly to the slightly higher frequency and gain of the 2N4061). The real difference is in the overall feel and performance in various temperatures, which is a mixed blessing. There's a very noticeable difference between the two when changing the "Fuzz" control settings and with ambient temperature changes. The Fuzz control on the hybrid has a narrow range of usefulness and effectiveness, making it harder to dial in a useable bias for Q2 with the "fuzz" control even with an audio taper pot. The good news, or mixed blessing, is that once you do dial in the "fuzz" it doesn't tend to drift all over with ambient temperature changes the way the all Ge Zonks do. It's a more stable control in that sense.

No Zonk cleans up with your guitar volume like a Fuzz Face/YAFF type of fuzz, but this Zonk did not clean up as well as the all Ge. This isn't entirely due to it having a Si Q2 as such. Even a poorly biased all Ge Zonk will ~perform the same way in terms of clean up. It's due to the circuit not being re-designed enough for a silicon Q2. IMO this hybrid schematic isn't tweaked enough as is for a silicon Q2 to sound and perform as good as the all germanium version. "Good" is a subjective term. Maybe I should say "as similar" or as expected instead? The most obvious area needing help is the voltage divider bias of Q2. The negative side of the rail already has the 500K trimmer which is a fine and can be adjusted as needed for whatever Q2 you're using as long as the specs aren't too wacky. It's the string of fixed 2.2K, 33K, and variable B50K (Fuzz) from Q2's base to ground that need attention. Silicon transistors leak MUCH less than germanium. I'd increase the value of the fixed 2.2K and 33K about ten times.

Long answer short, there are noticeable differences in the hybrid in terms of sound and feel/performance. The differences in sound are subjective. The performance of the FUZZ control can be improved. The added temperature stability of the hybrid I can only see as a bonus.
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby Electric Warrior » 17 Aug 2019, 23:42

acidfuzz wrote:
Yes sir, exactly. There is a "D8" code on the "Fuzz" pot. RS (Radio Spares) UK potentiometers use only two digits. The first digit is a letter from A to L representing one of the twelve months of the year. The second digit is the last digit of the year of production. So, the “D8” on the RS pot in this Zonk tells us that at least the pot was made in April of 1968. Incidentally WIMA capacitors also use this same code. The hybrid being the last version of the Zonk is totally a guess on my part.
Electric Warrior, while we're on the subject of JHS, I had someone offer me a JHS T.B. 2 Selectatone a couple of years ago and I wasn't interested. I told them to contact you on FSB to see if you would/could trace it for the community before he sells it. Did that ever happen? If you can PM or quick reply here that would be cool.


Ha, thanks for sending him my way. :) I don't think I've ever been contacted by someone with a Selectatone. I may have seen it when it was for sale, though. Was it one with a silicon transistor? I've seen two of those in the last couple of years and they confirmed the suspicion that the missing cap values in my schematic were 0.1µF.
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Re: Zonk Machine - middle transistor is silicon ??? trim pot

Postby acidfuzz » 22 Aug 2019, 04:49

Yes, it was a 2N4061 silicon. This was about ~3 years ago. Glad you found the correct cap values :) . I remember the owner did send me a pic (guts), but don't remember if the 0.1uf caps were visible.
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