Buzzaround hfe/leakage ranges

[nieradka]

Hey, search is failing me, so i was wondering if anyone knows off hand the answer. I have a bag of 50 IT308v ge trannies I brought on a whim, and never did anything with, so I figured i should build a ge fuzz pedal. I never built one (not counting harmonic percolators). I like the sounds I hear from videos of a buzzaround, would these trannies likely work there? and if so what hfes/leakages am I looking for for q1,q2,q3 etc?

[nieradka]

Ok after a some research there seems to be alot of conflicting info. But the best at a consensus im seeing is q1,q2 low leakage around 60hfe q3 higher hfe and leaky. Does this seem right? (yes, ill breadboard and test a bunch, but its nice to have a starting point, and know if i need to buy some leakier trannys.)

[twin1965]

I built mine with the following values: Q1 EFT83 Hfe=74, Q2 GT308 Hfe=75 and Q3 AC128 Hfe=114. Can't remember the exact leakage values but the AC128 was definitely very leaky!

Built this on tagboard using mojo components. Makes no difference to the sound but it sure looks cool 

Also, this thing is loud! Had to add a volume control.

Best thing is to breadboard it and use whatever sounds good to you.

Its a very good sounding fuzz.

[nieradka]

Thanks that confirms what im finding, ill start there. (it depends, of course, or what my bag of 50 contains, i havent tested them yet.) Thanks!

[midwayfair]

Worry about voltages in a good sounding unit, not gains. You might be able to find them in someone's build, or possibly on DIYSB or FSB. If Luciferstrip on DIYSB ever built it, he would have good voltages (he's good about posting that stuff, and the guy knows his fuzz). Getting a Tonebender set is by far your best option overall.

A few more thoughts:

Q1 and Q2 form something very similar to a Darlington. This means the gain is multiplicative; that gain is then used to overdrive Q3. (This is part of the reason the pedal is so loud.) You also multiply leakage in this arrangement. So you want low leakage in Q1 and Q2, and you honestly don't need nearly as much gain as 60hfe x 60hfe would get you. I actually had the best results in mine with a silicon transistor in Q2 with really, really low hfe (25). You can probably also use silicon in Q1, but I didn't bother swapping it out. It was far less noisy than trying to build with all germanium, and using silicon has no effect on the overall sound because neither Q1 nor Q2 is significantly distorted (and anything they're doing is completely obliterated by Q3).

Q3 is a different beast. Take a peak at the schematic and you'll see that there's no positive bias feedback resistor. So the biasing is accomplished solely by leakage (well, and the 1N34A helps a little, and you'll notice that flipping it changes the sound), so this means you actually need some leakage to get a functioning pedal. It doesn't have to be a ton (100uA is probably enough), but it shouldn't be a pristine, perfect transistor. This is actually one of my favorite things about this circuit -- that you don't need a really "good" transistor like you do in the Fuzz Face. The Percollator also has this benefit.

[nieradka]

Thanks, that makes a lot of sense. Thanks for the advice. Luciferstrip did build one, http://www.luciferstrip.com/fuzz/buzzaround-final.jpg.

As the goal of the project is more to start using the russian germaniums I brought on impulse, Ill go the hard route instead of buying a tonebender set, the main problem it seems is going to be finding one with enough leakage, the first ten or so I tested all didnt have nearly enough.

[twin1965]

You might find it hard to find Russian transistors with high leakage. I've got some GT108's and leakage is very low on all of them.

Hopefully you'll get a 'good' one!