Good morning everyone, sorry to revisit such an old thread but it's very close to what I'm on the hunt for today. Unfortunately electronics isn't my first or even second language, so although the answer is probably already clearly stated I'm just not picking it up.
I also am looking for an audio bandpass circuit that has fixed gain but variable Fo and Q. It seems like it should be possible with some version of a state variable filter, but each that I've tried allows the gain to vary with Q. Ultimately I'm wanting to build a 2nd order all-pass filter with adjustable Fo and Q, but to do that using a 1-2BP method the BP has to be very consistent. I've built fixed Q and Fo versions of the all-pass already with great results, but would like the ability to tune by ear.
The only version I found that did come close was altering the gain on the first op-amp to compensate for the gain change with Q, but I can't come up with any way to do that with a ganged pot, and I don't know if digital pots would maintain the high level of sound quality that I'm looking for. I just don't know enough about them and what they can do. Here's that circuit (courtesy of www.next.gr):
Does anyone have some circuits they can point me to that might be able to do this? Or if it's already been solved in this thread maybe you could push me a little in the right direction. Thanks in advance,
Chris
Kansas City