Tonebender Mk I Transistor Specifications

[benny_profane]

The Tonebender Mk II and III transistor specifications (i.e., hFE and leakage) are pretty well-documented, but I can't find ranges for the Mk I. Is there a list of nominal values for this circuit anywhere? Or, what values have people found to work with this circuit?

[sjaustin]

Not sure this is helpful, but a friend and I have been working on a fuzz for him lately, and what he's found is that the TB mk1.5 is basically just a Fuzz Face with a few passive component value changes. So I'm guessing Fuzz Face transistor gain would work with the Mk I. But I'm here to learn, and I bet someone with more knowledge will have something more helpful!

[WormBoy]

The Mk1.5 is very different from the Mk1. The latter is definitely not a fuzz face. This one is on my todo list, so I have also been looking for advice. However, there does not seem to be a generally agreed recipe, and no agreement on how a 'real Mk1' should sound. There is some useful (and useless) discussion on DIY-SB, but it seems the only consensus is that the transistors need be leaky to very leaky, and HFE somewhere between 50 and 150. Beyond that it's a matter of breadboarding and auditioning different transistors in the different positions until you hit something you like.

[danfrank]

Here, read through all the links also, especially the pdf file further down about the Zonk Machine:

http://revolutiondeux.blogspot.com/2012/03/sola-sound-ltd-tonebender-mki-hornby.html?m=1

[benny_profane]

Oh that's great, thank you! So, there's still and amount of mystery around these transistors (the Mk II and III have pretty specific ranges indicated), but this is a great start for sorting / bread boarding.

[danfrank]

What I mainly got out of the site was that Q1 needs to be leaky, like 300-500ua leaky or the circuit won't work, because there's no collector to base resistor to bias Q1. Similar to the TB2.
Take a look at attached pic

[benny_profane]

This is a little interesting. From the geofex Zonk Machine page:

"What you need here is your ordinary gain-of-100 type germanium. Low leakage is a real plus. A transistor otherwise used for a Fuzz Face would work well. However, you can tune in many transistors."

That doesn't seem right. I still haven't gotten around to getting this breadboarded, but I guess I'll try out low- and high-leakage.

[WormBoy]

That doesn't seem right. I still haven't gotten around to getting this breadboarded, but I guess I'll try out low- and high-leakage.

My guess is that the circuit as is won't bias right with low-leakage transistors. As R.G. explains, you can tweak the bias resistors to get it right. Low leakage may translate to low noise and good temperature stability. However, will it still sound like the 'real thing'? Some claim it will not, and advise to swap (leaky) transistors rather than tweak resistors. If you have a broad selection of transistors, breadboarding would be good to see what you like best. And, much appreciated if you report back here afterwards 

[Bret608]

I've built a MkI/Zonk mashup in the past so can weigh in to some extent. Definitely look for Lucifer's Trip's discussion at DIYSB. He explains what different gains/leakages will do in each position. For example, do you want it to sound gated? Go for lower leakage in Q3, Q1, or both. Longer sustain? Use something very leaky in Q3. Q1 is the easiest position to bias. If you use something with moderate leakage (around .200mA), it will sound solid and fuzz and you won't have to worry about using lower-leakage transistors in the other positions. On my build, I did something like 65hfe/.200mA leakage for Q1, 83hfe/.70mA for Q2, and 119hfe/.450mA on Q3. I hope this helps!

[benny_profane]

I've built a MkI/Zonk mashup in the past so can weigh in to some extent. Definitely look for Lucifer's Trip's discussion at DIYSB. He explains what different gains/leakages will do in each position. For example, do you want it to sound gated? Go for lower leakage in Q3, Q1, or both. Longer sustain? Use something very leaky in Q3. Q1 is the easiest position to bias. If you use something with moderate leakage (around .200mA), it will sound solid and fuzz and you won't have to worry about using lower-leakage transistors in the other positions. On my build, I did something like 65hfe/.200mA leakage for Q1, 83hfe/.70mA for Q2, and 119hfe/.450mA on Q3. I hope this helps!

That's great! Thanks! I've got a bunch of <110hFE PNP Ge transistors and not many are terrifically leaky. It's good to hear that lower leakages can produce some good results. Do you have a link handy to the DIYSB thread?

[danfrank]

This one?

https://www.diystompboxes.com/smfforum/index.php?topic=101291.60

[benny_profane]

This one?

https://www.diystompboxes.com/smfforum/index.php?topic=101291.60

Seems like it. Thank you! Man, that thread is quite a mess...there's some good insight there though.

[Bret608]

Yes, that is the one! The tone got a little spicy for sure.