z-vex GE transistors

[El Heisenberg]

what GE transistors would you use??? If I got some from small bear, they'd come with a list of resistors values for biasing. How would I bias this circuit??

http://basicaudio.net/Fuzz%20factory%20schem.PNG

[oliphaunt]

I believe Z uses the AC128 in the Fuzz Factory.

As for biasing, the values from Small bear sometimes work, sometimes they don't in my circuits.  You need to measure the bias and adjust the value of that resistor until you find the range you are looking for.  You can replace the resistor with a pot or a trimmer and adjust the pot until it sounds good.  Leave the pot or trimmer in the ciruit in case you need some fine tuning later on, or measure the value of the pot and replace it with a resistor of that value.

[trad3mark]

Could you use different GE's? would it matter what transistor pair you use as long as they're ge with a similar hfe to ac128's?

[oliphaunt]

128s are also PNP, but beyond that I believe you can use any similar gain range PNP transistor.

[slacker]

You probably don't need to worry about changing resistor values to bias the transistors in the fuzz factory. The gate and comp pots change the biasing depending on where they are set so you should be able to find a position of those that gives you whatever fuzz sound you want.

[bumblebee]

Just use trannies with a hFE of around 200+ in Q1, 80 in Q2 and 100 in Q3 and use the values listed in the fuzz factory schematic as like already said, two pots are for variable bias of this pedal so you don't actually bias it like a fuzz face.

[Matt505]

Not to hijack the thread, but I've got some related questions:

After digging thru my stash, I only have 1 Ge PNP (2N404)...I do however, have a bunch of Ge NPN (2N385) and Si PNP (2N2905).
What's most important for Fuzz Factory sound - the Ge or the PNP??

If I use Ge NPN, do I just flip Q2/Q3 top to bottom as in the schem?

One last q - what kind of pots are used? The schem doesn't say log or linear...

Thanks
Matt

[joegagan]

if i understand correctly, zvex built a limited run of 'reverse' fuzz factories sometime back in the 90s. i think they were probably npn, and they definitely had the controls all operating backwards.
so i believe if you build it npn the polarized caps would need to be reversed as well as the pot wiring for it to maintian the mojo.

in my own experiments, the third transistors sounded best when they tested out to the 125-ish gain range using Rg's method. the stock 2000 fuzzfactory i had came stock with a germ for Q3 that measured right in that range as well.

[El Heisenberg]

Thanks

[trad3mark]

if i understand correctly, zvex built a limited run of 'reverse' fuzz factories sometime back in the 90s. i think they were probably npn, and they definitely had the controls all operating backwards.
so i believe if you build it npn the polarized caps would need to be reversed as well as the pot wiring for it to maintian the mojo.

in my own experiments, the third transistors sounded best when they tested out to the 125-ish gain range using Rg's method. the stock 2000 fuzzfactory i had came stock with a germ for Q3 that measured right in that range as well.

WHOOSH!!!


Do want...

[Paul Marossy]

For my clone, I used some old NOS Raytheon Ge PNP transistors that I bought off of ebay. They sound pretty good. Really, there's quite a few Ge transistors that will work in that circuit. To get the right sound, the secret is to get Q2 with an Hfe of around 215 and Q3 with an Hfe of around 280. My clone works exactly the same way and sounds very very close to what you can hear in the Z Vex video.

[joegagan]

paul, what method are you using to measure those germs? in testing around a 1000 ge trannies in 10 years, i have never seen a gain number above 150 using RG's method.

[Paul Marossy]

paul, what method are you using to measure those germs? in testing around a 1000 ge trannies in 10 years, i have never seen a gain number above 150 using RG's method.

I used RGs method. Or at least I think I used it correctly. The transistors I bought were made by Raytheon. IIRC, they were "power transistors" as listed by the seller on ebay. This was a long time ago now, so I can't go back and look at what exactly the auction said. Anyway, they look like the standard 2N2222 metal can types, but are the bigger version of that.

EDIT: They were Raytheon T59247-6416 audio transistors. I've tried to find a data sheet for them, but to no avail.