Voltage/Resistor/Q1/Fuzz Face

Frequently asked question on transistors: types, substitutions, how to test, use and misuse them.
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DrNomis
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Post by DrNomis »

polifemo wrote:Yes I can!

I'm just asking because there's so much talk of the type: "Eric Johnson prefers a 100k volume pot" * when one as well could say that "E.J likes a slight bass cut at the end of the circuit", or is it something about the range/travel of the pot that makes 500k different from 100k, regardless of the cap/cut off frequency?

*which in fact turned out to be 470k reverse log :wink:


I've read alot of that online, I'm thinking that the volume pot resistance in combination with the output cap tends to form a passive high-pass filter, to my ears a 100k pot definitely makes a Fuzz Face sound brighter and less woofy you can also get the same effect just by changing the value of the cap...... :thumbsup
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Post by dwmorrin »

> to my ears a 100k pot definitely makes a Fuzz Face sound brighter and less woofy you can also get the same effect just by changing the value of the cap......
+1

I was fixing a Zvex Wooly Mammoth today, and I would recommend checking out that schematic to get more fuzz face ideas. The "pinch" control is a variable resistor in series with the 100k feedback resistor. It has an effect on the "pulse width" or "mark to space ratio" of the fuzz wave.
Also check out the fuzz factory schematic. The "comp" is like making the 1k fuzz pot variable. The "gate" is making the 33k variable. There is an extra booster transistor stage at the front end, but the last two transistors are fuzz face topology.

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Post by polifemo »

Today I'll hopefully have time to make a new breadboard layout that includes trimmer for both collectors and the feedback loop plus a pre gain trimmer:

- Q1/Collector = 50k trimmer and a 10k resistor in series.
- Q2/Collector = 10k trimmer and a 2.2k resistor in series.
- Feedback loop = 100k trimmer and a 47k resistor in series
- Pre gain = 50k trimmer

:horsey:

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Duckman
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Post by Duckman »

How it ended??

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Post by polifemo »

Well, nowadays I usually go for the "traditional" FF resistor values regarding the collector of Q1 and the feedback loop.
For the collector of Q2 I use whatever is needed to get the bias that I want.

A pre gain pot is nice, and I usually use 100k-250k.

Regarding volume pot I most often use a 100k pot for germanium FF's, and 250k for low/medium gain silicon ones.
For higher gain SI circuits I use 500k.
The reason for this is that it's a good way to control high end.

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Post by Duckman »

Did you check the Bonamassa version?
It has some features (well, similar features) that you were trying to apply, like trimmers in both collectors

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Post by polifemo »

Yes, I've been looking on that one a bit :D

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