Earth Sound Research - Graphic Fuzz  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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FiveseveN
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Post by FiveseveN »

Intripped wrote: 21 Jan 2023, 07:28 true and scientifically proved
To what σ?
(That's not how science works)
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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Intripped
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Post by Intripped »

Isn't it?
Oh well, I don't give it a f...
Is it clear now?

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CheapPedalCollector
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Post by CheapPedalCollector »

ESR, phase shift across frequency spectrum, impedance across frequency spectrum, leakage, inductance, ripple, these are all measurable things. The whole "capacitors are all the same" schtick has been beat to death.

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FiveseveN
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Post by FiveseveN »

Yeah but you'd need to understand what those do like a nerd and then do a bunch of math *groan*. The People just want to know which ones have the most tone, goddamit!

Regardless, Intripped's response is technically correct (the best kind of correct) except my minor objection. Since 25% to 50% derating is recommended for ceramics, 10V would for sure be too close.. Green packaging is not as common (unless vintage) for them though nor is such a low breakdown voltage: 50% derating is no issue when even the smallest ones you can buy are 63 or 100V. Maybe they meant the popular polyester greencaps and/or misread the marking.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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CheapPedalCollector
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Post by CheapPedalCollector »

Well yeah understanding it is paramount of course, I just see a lot of bickering about it and it gets kind of old.

Yes he's current, DC rating and AC rating are different too. Lots of old pedals have 10 or 12 volt ceramic caps, and they can fail. Mostly though it's because they've absorbed moisture, same with resistors and other components. Running stuff below rating tends to be fine, but quality of component I guess matters there, especially if it doesn't say that's operating voltage, or max voltage.

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Lukasen
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Post by Lukasen »

I also played around with this really original fuzz/filter. He reminded me a bit of Big Muff on some psychedelics in some settings and I enjoyed that about him at times.
But what I didn't like about it were the oscillations. So I got into modding and playing around with it. I finally managed to remove them by connecting the 220R from the Zobel network to a real ground (not a virtual one as in the original schematic). Oscillations finally appear to a lesser extent only with the volume on the guitar at minimum and the tone control on the guitar at minimum, that's not bad (In the previous modification in the original scheme, I replaced the 220R with 10k in the Zobel network and this also reduced the oscillation, but it did not disappear).
I also tried setting the zero offset of the opamp with the potentiometer and its effect on the sound. Around 50% it seemed to add a clean sound to the distorted one, it did something but it wasn't as pronounced as I expected.
It's a really sensitive high-gain circuit and filter at the same time, so if the components are not well placed, it can cause problems.
And I also remembered: I put a 1k resistor to ground on the output. For a "room volume setting", it's really too loud :-).


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george giblet
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Post by george giblet »

The schematic and an oscillation fix for for this unit was posted on DIYSB some years back.
Earth Sound Research Graphic Fuzz - oscillation fix mod.png

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