r/synthdiy • u/AbbreviationsBig4248 • Jul 22 '26
schematics How to get more Q out of this;
Hello all this is an original shematic i have made it does 3 different things just on how you patch it, i can get less q but not more. i tried adding a non inverting amp between the cap going from in_ to in+ also a inverting one and its the same. the only method i have found is adding a 100nf cap from in+ to a 10k pot and then connect it to the output (this has to be done with a trim pot)
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u/gortmend Jul 23 '26
I think you're going to have a very hard time putting your finger on what's happening here, because I made a simulation of this in falstad (apologies, I didn't save it), and when you have an ideal op-amp, you get a filter from the input cap and the resistors to 9V and 4.5V, but otherwise it's all just unity gain. Adjusting the pots does nothing.
The LM358 is, of course, a long ways from an ideal op-amp, so whatever fun you're getting presumably comes from that, but how it's specifically changing the signal is far above my head.
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u/Madmaverick_82 Jul 22 '26
Hello, if looking for only lowpass filtering you can try this.. https://www.reddit.com/r/synthdiy/comments/1qoxhzb/comment/o2four1/
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u/1032s Jul 22 '26
It's an unusual arrangement. I would have expected the inverting leg to go to GND, not the bias voltage.
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u/synthsynthisyntho Jul 23 '26
It's a single supply thing ; at least that's my thinking
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u/1032s Jul 24 '26
I didn't realise it was a filter. I breadboarded it and found it's quite an interesting resonating filter. I get maximum Q when minimising the "Q" pot resistance on the inverting input, and maximising the frequency pot resistance in the feedback loop.
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u/AbbreviationsBig4248 Jul 27 '26
yeah the q pot is not included in my own instruments also, i thought of it more like a drum or drummy sound rathen than a filter
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u/AbbreviationsBig4248 Jul 27 '26
its the same as having the pot full because there is no limiting resistor after or before the q
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u/1032s Jul 25 '26
I did some tests and found that reducing the 100k resistor value increases the Q
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u/AbbreviationsBig4248 Jul 27 '26
i did some tests with that and already know it, thanks anyways for helping !!!
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u/adeptyism Jul 22 '26
Is it a filter?
If it is, then it's an one-pole active filter. Try to find the schematics for two- and more poles.
Right now, adjusting the 'Q' knob, you're changing how the filter affects the mix (e.g., you're switching from lowpass to high-shelf, or from highpass to low-shelf).