Author Topic: help me understand this circuit / take the farts out of a peach(y) fuzz  (Read 585 times)

mwnovak

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Hi all.

Full disclosure: this is built on a "Peachy Fuzz" PCB from pedalparts.co.uk, but I'm not troubleshooting a build problem so much as wanting to better understand the circuit.  The pedal is built and boxed, and the fuzz, volume, and tone controls all behave as expected.  Schematic and parts list attached.

So . . . this fuzz farts a lot.  Lower notes fart more than higher notes.  Decay farts more than attack.  Dialing back the fuzz makes the farting less obvious, but the same basic (farty) behavior is always there.  I want to make this fuzz less farty.

Looking at the schematic, I see the following (any/all of which may be incorrect . . . I'm learning):

  • C1 (0.1uf), R1 (33k), and the guitar pickup form a high-pass filter at the input
  • IC1 (TLC2262) acts as a preamp and just boosts the signal (maybe?)
  • fuzz pot (a10k) determines how much signal gets into IC2
  • IC2 (LM386N-1) is running at its preset gain of 20
  • R8 (120k) and C4 (18p) form a low-pass filters with a very high cutoff, maybe filtering out noise before the signal hits IC3?
  • IC3 (another LM386N-1) is also running at its preset gain of 20
  • R10 (10k) and C6 (0.47u) (low-pass) with C5 (0.01u) and the tone pot (b10k) (high-pass) create something like a variable band-pass filter?
  • finally the volume pot (b100k) controls how much signal gets out of the pedal


That's more-or-less everything I (think I) understand about the circuit.  I would love to know what I've gotten wrong and more about what I've left out (e.g. what are C2 and R3 doing?).

Now, about that farting . . .

I've ignored the tone circuit because it's at the end of the chain and the signal is what it is at that point: I can tweak values to roll off more highs or more lows, but the farts are already baked into the signal.  Is that a reasonable conclusion? 

Instead, I started playing with C1 and the input filter.  Dropping C1 to 0.01u rolled off more bass and successfully cleaned up the farts, but it left an overall thinner and more sterile fuzz effect.  0.022u (humbuckers) or 0.033 (p-90s) brought back some of the body without the farts . . . so that's something.

But I'm wondering where else I could play with values in the circuit?  Working with that input cap feels like a blunt instrument: it seems to do the trick by keeping bass out of the amplification chain, but it also changes the overall character of the fuzz.  Makes it less . . . full. 

Anyway, feedback and discussion are appreciated.  This is the first build where I'm really trying to understand the circuit well enough to manipulate it for a specific outcome (rather than just plugging in modded values suggested elsewhere), and it feels like a steep learning curve.

Thanks for any help,

--Matt
« Last Edit: April 10, 2019, 11:41:45 PM by mwnovak »