Whisker Biscuit tone stack/volume question

[midwayfair]

EDIT: Brian at ROG e-mailed me with an explanation.
"here's my take on your Whisker Biscuit tonestack question.  First off, the circuit is just plain loud.  Secondly, the 220n cap completely removes the BMP scoop and replaces it with a mid hump.   The Tone control still rolls off treble and bass, though not as much as the stock version.

I've attached a screenshot of the stock response with the Tone at 50% and your humpy version at the same setting.  A lot more signal there, no?"

I'll leave up the original post in case anyone else is ever curious ... or wants to know how they can make the stock pedal louder.

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I built a whisker biscuit not too long back, and I ended up, heaven knows why at this point, using a 220nF cap in place of a the 4n7 listed in the schematic:



This seems to have resulted in an absurdly loud pedal.*

But what I'd like to know is ... why, when it looks to me like it's just part of the tone stack, does this seem to have affected the volume, but not so much the tone sweep (despite being 50x the proper value), so drastically?

Anyway, I had originally planned on just swapping out the volume pot for a 25K or even 10K to "fix" the "problem", but now that I found the wrong cap and know that I built it wrong, I'm curious what's going on.


*It's so loud that I think it's actually boosting my signal when it's in a box in another room not even plugged in. Which, don't get me wrong, is actually kind of cool. I used it on a recording because it creates feedback simply by existing.

[R O Tiree]

I'd first try to prove that it is the cap that's caused this. Swap it for the right one and see what happens. If it's still insanely loud, then something else is going on.

[midwayfair]

I'd first try to prove that it is the cap that's caused this. Swap it for the right one and see what happens. If it's still insanely loud, then something else is going on.

The cap was definitely part of it. After removing the volume pot, I discovered just how loud this pedal was ... it actually passes signal (I expect through the ground) without the volume pot connected. I had to double check that there wasn't a wiring issue. Nope. Holy crap!

Here's what I ended up doing:

1) Volume pot change. Ended up with 20K. This only dropped the volume a little.
2) Settled on a 8n2. Sounds a bit closer to a Green Russian, which is sort of my goal (even though that Muff gets its mids elsewhere ... I can do that on future builds, but I'm kind of limited on this one).
3) Swapped out the MPSA13 for an MPSA18 and rebiased it all the way up to 100K (tested with a 500K pot). WAY over the suggested values for that transistor, but in the end it's what gave me the best decay on sustained notes with the volume knob rolled down.

I've got a ton of boards from CultureJam's/Effdub's licensed run from not too long ago, so I can experiment more and build it stock on those. I did test dropping the output buffer, but that just sounded thin and horrible.