DIY Breakthrough and Fuzz Face noise question

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MrShake
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DIY Breakthrough and Fuzz Face noise question

Post by MrShake » Sun May 15, 2022 5:09 pm

I'll keep it as brief as I can. I come to the Fuzz Face experts with my hat in hand.

Last week, I was watching a video on circuits and something clicked. For the first time in my life, I could read a basic schematic. I kinda understood the schematics for a Bazz Fuss and a Fuzz Face and see what they were doing. I'd failed a few kits ten years ago and stuck to modding from then on.

I went on a tear through some online vero layouts. A green LED Bazz Fuss variant I'd promised my wife last year. One with switchable diodes to mail to an old bandmate. The LPB-2 that had crushed my dreams years ago. A really sick octave fuzz.

And a Fuzz Face.

Image

They all worked first crack except the fuzz Face, but something was wrong with the board, I whipped up a new one and dropped it in and it works basically as expected.

Image

I socketed everything as a learning process. It's my "Training Fuzz Face". I used the "Silicon Fuzz Face" layout with the dramatic pink and purple fonts I couldn't find an author for, maybe Aron Nelson?

The character of the fuzz sounds like it should, so I know it "works".

Here's my issue:

When I turn the fuzz knob up over 9, it roars into a noisy mess. Pull it back a bit and it's just like a Fuzz Face should be. If I lower the volume knob on the guitar at that point, there's faint oscillation that changes in pitch as I roll it down.

All this suggests to my freshman ass that there's a component whose value could be tweaked to account for this, but I don't know which one to raise or lower. The Fuzz pot is a B1K (linear), volume is 500K log. I've seen so many pot values thrown around I don't know what to believe, and the sound this thing makes above 9 isn't something I've heard most Fuzz Faces do, so I don't know if it's just a matter of a linear/log sweep.

Transistors are currently standard 3904s. I plan to get a matched pair of BC108s or 109s, but for the time being, I just kinda want to assemble and understand the basics of the build, I can custom-tune the tone later.

I don't need this to be THE Fuzz Face, just understand how to make one behave somewhat properly. Having some idea which component(s) are responsible for the fuzz pot having some extra unwieldy at the end will help me learn what does what to what in an overall sense.

Can anyone tell me which component moved up or down might remedy the noise and shriek above 9 on the Fuzz Knob in my "basic parts" beginner Fuzz Face build?

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Re: DIY Breakthrough and Fuzz Face noise question

Post by MrShake » Mon May 16, 2022 2:36 am

More reading shows me people get squeal from just about every component one way or another.

I woke up early today and started tinkering before coffee. Dropping the 8k2 bias resistor down one step at a time (i.e going through my resistors and lining up values), I hit upon a 5K1 resistor as the first where the noise was gone enough. Still some crackle when I brush the strings lightly, but pretty quickly gated out. I like it. Spitty but without losing the Fuzz Face character. And I like my fuzzes silicon anyway, for the most part.

Doing this is definitely teaching me the effects of parts on parts. And now I see why other middle-aged players go down the Fuzz Face circuitry rabbit hole.

Next time... trimpots! Everywhere!

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Re: DIY Breakthrough and Fuzz Face noise question

Post by MrShake » Mon May 16, 2022 8:36 am

Conclusion:

I wasn't totally satisfied. I got out the multmeter and my pack of resistors and went to town. New to the DMM, but I figured it out and I looked up what numbers I should be reading on the transistor collectors. Seems like in general, Q1=1.4 and Q2=4.5 made for a good middle of the road.

It was biased way off, so I picked through value by value until I landed on some that hit the numbers. It took changing R2 from 33K to 10K and changed R3 from 8K2 to 3K3, but I ended up getting 1.47 and 4.6 volts. Once the numbers added up, I plugged it in.

Sounds like a Fuzz Face.

More than last night. Sounds good, a little crispy, but it would pass the muster as a spare parts Fuzz Face. I fully understand the benefits and reason for trimpots in those resistor spots and why it drives some people mad. Other than a 3PDT and maybe a rev log pot for the fuzz, I'm calling it done and successful. So, check your collector voltages with a multimeter and get them right, just like the rest of the internet says.

Maybe now I'm ready for a Fuzz Factory.

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Re: DIY Breakthrough and Fuzz Face noise question

Post by fuzzjunkie » Mon May 16, 2022 5:57 pm

Maybe now I'm ready for a Fuzz Factory.
I was going to say you’re halfway there with the 1st version. Like Zach Vex was there 30 years ago and thought “Hey, I like this!”

Fuzz circuits are very sensitive to parts values as you discovered. I have never built a Fuzz Face, but I think most builders try to match the transistors to reach the working Q1 and Q2 range. They take gain and leakage into account. Some fuzz circuits require leakage to work while others don’t. It sounds like your transistors are too high gain, but that can also be remedied by changing resistance in the circuit, as you did.

Possibly using 109 transistors at a better gain level and you won’t have as many trade offs to get a proper fuzz tone.

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Re: DIY Breakthrough and Fuzz Face noise question

Post by MrShake » Wed May 18, 2022 12:40 pm

Thanks, fuzzjunkie, you've always known what's what.

It's funny how I see longtime builders suggest people build a Fuzz Face as their first homebrew/vero/strip board pedal, but I really think it's a terrible idea until AFTER someone gets that gratification of a successful build/mod.

You're dead-on, these parts are so delicately balanced it's like a floating trem. Change the bias of one thing, adjust another part. If one just wants to learn how to solder on a $50 kit and get a fun noisebox that they made, it's a lot to have to learn to read collector voltages, understand what the biasing is, and how to do it, and how the bias of Q1 affects Q2, and how resistance and signal are somewhat like valves and water pressure, and that if you want one that sounds like a vintage one you'll probably need to get special transistors and then bias again... it might be a lot to ask.

But on the flip side, for my intermediate/"advanced beginner" level, having to understand all that to make it work and learn what I needed to do to get that balance and "intonation", it was invaluable. I mean, with a bunch of online reading available, I learned how to diagnose symptoms (high setting misbias squeal), where to adjust the bias, how to do it, how to read it with multimeter, what people advise for original spec sounds, it was all a huge step in the learning process, and seeing how it applies to the schematic and the signal flow was eye-opening.

Oh, and I went in and converted the Fuzz pot to a reverse log one for a better sweep than any Fuzz Face I've yet played.

... and this morning I built that Fuzzrite I was posting about. All further steps from the Fuzz Face lesson

So I take back the things I said about Fuzz Face obsessives over the years.

Some of it

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