Author Topic: Tone Bender MK1 (with russian transistors)  (Read 467 times)

pietro_moog

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Tone Bender MK1 (with russian transistors)
« on: December 16, 2019, 01:27:55 PM »
Hi guys.
Recently i was really into Doyle Bramhall II, and in his Reverb interview he talked about the Zonk Machine as a secret weapon.
So i decided to build a Tone Bender MK1 just to see what it is.
I didn't have fancy 60s transistors, so i used some russian ones. They say you need leakage for MK1, but these are very low.

pietro_moog

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Re: Tone Bender MK1 (with russian transistors)
« Reply #1 on: December 16, 2019, 01:29:34 PM »
I adjusted a few resistors and caps, and the Q3c voltage is like -8.05v
I don't what to make of Q2C: it really depends from the voltage divider, so i tried 180k (-1,2v) and 430k (-5v); i don't know what i like more, i can't decide.

Q1 is the strange one: it has very low hfe and leakage, but everything works. i tried to reach the suggested voltage (around -1v) changing the bias resistor, but i only get to -0,4v with a 4,7M resistor. There is a noticeable effect though, it doesn't SAG anymore.
With 1M on Q1B i had a HUUUUGE Sag, i wasn't expecting this (but i like it).
Is this suppose to happen?

my transistors are

Q1 = MP40B, 30hfe, 20mA L

Q2 = gt308b, 64hfe, 5mA L

Q3 = MP42 , 52hfe, 50mA L

Bret608

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Re: Tone Bender MK1 (with russian transistors)
« Reply #2 on: December 16, 2019, 03:23:20 PM »
Do you have anything in more like a Rangemaster gain range to use for Q1? Around 60-70 hfe with under 200mA leakage should work well with the stock resistors. I think you had the sag with 1m because the hfe is a little low. But if you like it, no problem!  :)

For Q2, measure your collector voltage at max and minimum fuzz. For a starting point, it should sweep between about 9-7.5v at minimum and maybe 4-2v at maximum with your current transistor, if you have a 470k resistor with a 50k pot. A 180k pot would probably need a 25k pot (like some Zonks) to work like the vintage units. See if you can get usable sounds from most of the pot. Some gating in some spots will be normal--the fuzz control is really just variable Q2 bias. This one might not need to be leaky.

For Q3, this might effect sustain--more leakage will sustain more, and Q3c will be closer to 9v; less will have more gating (which you might like) and come down to 8v or less. You could try switching your Q2 and Q3 and see what happens!

pietro_moog

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Re: Tone Bender MK1 (with russian transistors)
« Reply #3 on: December 16, 2019, 04:00:51 PM »
Thanks.
Q3 is fine, with the original value it was closer to -9v. It was fine, i just read around that it has to be close to -8v, that's way i changed things.
Regarding Q1 I don't have transistors with that leakage, so i tried that. It sounds good to me, i wanna try 2.2m to se if a get just some sag (it is a beautiful sound!)