Couldn't resist to draw a schematic and a layout for this interesting mutant of a circuit that just got traced.
First two gain stages is almost identical to a Jumbo Tonebender (except for one cap and one resistor value), the third gain stage is almost identical to the saturation stage in a Tonebender Mk. 3. Transistor bias is quite different with the zener diode, though. Tonestack is Big Muff style followed by a Volume control.
Note that earlier versions had 100nF or 470nF instead of 10nF so it might be worth socketing that cap.
Cool! Any word on HFE or leakage?
ReplyDeleteThe schematic shows C3 as 100nf but says that earlier schematics show 100nf or 470nf. C5 on schematic in 10nf. Based on your notes above, do you mean to socket C5 and test different values or socket C3?
ReplyDeleteOops. A typo. It is C5 that had different values. Sorry, a bit rusty.:-/
DeleteI've got it working and getting a heavy saturated fuzz.
ReplyDeleteI had to add a cut at K-7 and experiment with flipping the diodes as some of mine are Russian. At the moment we don't know the value of the Zener, but I put a 4.7v to get it going.
Thanks Alex. Cut added.
DeleteSo, what do you have for Q3? Leakage and Hfe?
I don't know what the original was like. So far, any NPN I put in there "works". The MK3's aren't that picky, right?
DeleteI know what I’ll be doing this weekend. Thanks for sharing the schematic
ReplyDeleteYou're welcome.:-)
DeleteNote that the tracer discovered that the tone control is actually a 20kW pot with center detent. So both layout and schematic is updated.
I don't have any experience with OC140 transistors so I wonder if you don't know typical Hfe and leakage for those? I've heard that they are popular in NPN Rangemasters so I assume the leakage should be pretty low?
Ok, thanks for the update. I don’t have any OC140, I was planning on using an AC127 which is supposed to be the equivalent. Can’t recall the leakage on the AC, but from memory they probably leak a decent amount. I’ll find out soon enough...
DeleteFWIW, the OC140 is the non-military version of the CV7112 and has a specified gain range of ~50 to ~150. OCxxx and Cvxxxx (Mullard) devices tend to remain low leakage devices. And most NOS NPN germanium transistors with a gain of around ~100 and low leakage should do the trick. Bias resistor values may need to be adjusted to tweak for different transistor part numbers.
DeleteThanks for the info. Now I know what to aim at for Q3....
DeleteJust a +1 to those OC140 numbers - the ones I have are all around 70 or 80hfe with almost no leakage. So russian NPNs will probably work pretty well? I think those tend to have very little leakage as well.
DeleteYeah, I was thinking about using a russian MP38A for this.
DeleteHead's up - I think D1 in your schematic is flipped. It should be anode to ground. There's a PNP and an NPN version of the pedal and photos / values of both were floating around in the thread. Thanks so much for putting the layout together - I'll A/B it with the OG pedal as so soon as I can grab some zeners.
ReplyDeleteAlso, the 4,7V is kind of a best guess as the value isn't visible on any of the actual pedals we looked at; the Q3 collector should be at around 2.5/2.6V so maybe just try a few different zeners until you're in the ballpark.
ReplyDeleteI really love this fuzz, hopefully you'll enjoy it too!
Thanks for the headsup!
DeleteI'll flip the ge diode ASAP and add info about the zener.
I think enjoy this one already, only by looking at the schematic.:-)
Thanks for tracing this oddball, it has been on my radar for a couple of years now...
Happy to contribute - i've definitely built plenty of your layouts, so I'm glad to be able to share something back.
DeleteI built one today using my own layout and it works just fone, sounds a lot like the demos, and has that velcro sound. I made a few subs due to lack of parts. 5.1V zener, AC127 and a slightly random old transistor for Q1.
ReplyDeleteOh and I used 100n instead of 10n, as I like a bit more bass. Never made a comparison to 10n.
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