Author Topic: AC128s for ZVex Fuzz Factory?  (Read 2560 times)

Philtre

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AC128s for ZVex Fuzz Factory?
« on: February 13, 2018, 04:52:54 PM »
I'm going to build a ZVex Fuzz Factory from this layout - http://tagboardeffects.blogspot.co.uk/2012/10/zvex-fuzz-factory-compact-layout.html but it requires 2 AC128 transistors. Are these readily available (in the UK)?

I found that Fuzzdog sells them here - https://shop.pedalparts.co.uk/AC128_Germanium_Transistors/p847124_15540300.aspx - but I have no idea what the hFE ranges mean (61-70, 71-80, 81-90, 91-100).

Any advice on the mysterious AC128 readily accepted!

somnif

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Re: AC128s for ZVex Fuzz Factory?
« Reply #1 on: February 13, 2018, 04:58:18 PM »
Old school Fuzz's (like those the fuzz factory is based on) care about the specific gain of each transistor to get the "best" sound out of them. Most of the time, a DIY seller will tell you the ranges that work best.

The fuzz factory is basically a modified fuzz face, and it likes a gain of about ~80 for transistor 1, and ~100-120 for transistor 2.

Note that these are the "gospel" ranges, but its always down to opinion. Folks like the way those settings sound. If you get something outside those ranges and you like it, run with them.

I know there used to be a Slovakian fellow on Ebay who sold matched sets for the pedal, but it appears he has disappeared.

cresconio

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Re: AC128s for ZVex Fuzz Factory?
« Reply #2 on: February 14, 2018, 04:57:27 AM »
I know there used to be a Slovakian fellow on Ebay who sold matched sets for the pedal, but it appears he has disappeared.

Yup, just checked my order history and indeed that user (eleb.cz) disappeared...

Philtre

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Re: AC128s for ZVex Fuzz Factory?
« Reply #3 on: February 14, 2018, 05:02:21 AM »
I've ordered a couple from Fuzzdog. Pricey but the rest of the parts cost little.

somnif

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Re: AC128s for ZVex Fuzz Factory?
« Reply #4 on: February 14, 2018, 09:58:37 AM »
I think I paid ~11$ US for my set. I ended up going with AC125's just because they were cheaper and available in the US. Smallbear also offers a ton of different options for those stateside. Unfortunately I haven't spent much time digging through euro supply chains, though.

The fact is most germanium transistors (of the same hfe range) will sound pretty similar in a fuzz factory with some wiggling of the settings. Maybe not similar enough to satisfy the cork sniffer fuzz snobs, but close enough for my ears.

Then again, I actually liked the way mine sounded with silicon trannys in it, so perhaps I'm just a weirdo to begin with. (for reference I have the Aion 8-knob version of the circuit)

bsoncini

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Re: AC128s for ZVex Fuzz Factory?
« Reply #5 on: February 14, 2018, 01:07:38 PM »
I have built at least 5 fuzz factories for friends.  Every time |I used different transistors in them, ac125, ac128, mp16b, mp20b, basically whatever I had on hand.  Also with differing hfe's.  50 and 70 or 110 and 140.  They all sounded like fuzz factories to me.  I never compared them next to each other though.  As Somnif said, changing up hfe's might just result in the pot levels being slightly different.

If you planning on building more germanium fuzzes, check out the russian mp16b and mp20b. With shipping you can get a lot of 25 for about 10 euros on ebay.  Really low leakage
« Last Edit: February 14, 2018, 01:09:36 PM by bsoncini »

Philtre

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Re: AC128s for ZVex Fuzz Factory?
« Reply #6 on: February 16, 2018, 10:04:01 AM »
I built the Fuzz Factory and wired it up to my testing harness on a breadboard. I then spent over an hour debugging it trying to figure out why this thing was oscillating and giving out so much spurious noise. Then I watched a YouTube demo of one, and realised that there was nothing wrong with it, that's how it's supposed to be.  ;D  :o

thesmokingman

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Re: AC128s for ZVex Fuzz Factory?
« Reply #7 on: February 16, 2018, 12:30:58 PM »
if it makes you feel any better, zvex didn't exclusively use ac128s either ... I've got zvex branded 2n404s
once upon a time I was Tornado Alley FX

somnif

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Re: AC128s for ZVex Fuzz Factory?
« Reply #8 on: February 16, 2018, 02:22:47 PM »
I built the Fuzz Factory and wired it up to my testing harness on a breadboard. I then spent over an hour debugging it trying to figure out why this thing was oscillating and giving out so much spurious noise. Then I watched a YouTube demo of one, and realised that there was nothing wrong with it, that's how it's supposed to be.  ;D  :o

Oh yeah, 90% of knob-position combinations sound like utter garbage on the thing. Its trying to hunt down (and remember...) the remaining 10% that gets interesting.