Re: LPF question

Posted by induction on Oct 08, 2021; 11:37pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/LPF-question-tp50267p50281.html

You don't have to keep c3 and c4 the same value. They can be different from each other if you like. My corrections are for your math results, not your approach to the modification. Your frequency results do not match what you should get by changing only 1 cap, but do match what you get by changing both caps.

Let me be a little more explicit:

Matches your approach: If you keep both pots at 50k, keep c4 at 10n, and change c3 to 2n2, the corner frequency sweeps from 636.6 Hz to 10.3 kHz.
Matches your results: If you keep both pots at 50k and change both c3 and c4 to 2n2, the corner frequency sweeps from 1.3 kHz to 21.9 kHz.

Matches your approach: If you keep both pots at 50k, keep c3 at 10n and change c4 to 15n, the corner frequency sweeps from 243.8 Hz to 3.9 kHz.
Matches your results: If you keep both pots at 50k and change both c3 and c4 to 15n, the corner frequency sweeps from 199 Hz to 3.2 kHz.

Or maybe you intended this approach: If you keep both pots at 50k, change c3 to 2n2 and change c4 to 15n, the corner frequency sweeps from 519.8 Hz to 8.4 kHz.

I can give you values that will result in a sweep from 250 Hz to  22 kHz if you like. But if you want to figure it out for yourself that's totally understandable. Let me know.

FWIW, 22 kHz is pretty high for a bass (or even a guitar for that matter). Amplified guitars have frequency ranges from about 80 Hz to about 4.5 kHz. Guitar speakers generally can't reproduce frequencies outside this range. I don't know what frequency range bass guitar speakers can reproduce, but a 4 string bass guitar has fundamentals in the range of 40 Hz to 400 Hz, while the overtones go up to about 4 kHz. 6-string basses have overtones up to about 5kHz. So I'm guessing you could set the top of your sweep at about 5 kHz without losing anything. This would spread the useful range of corner frequencies across the full range of the dual-gang pot. Personally, I'd test it on a breadboard before soldering anything.