I'd like to make a single band peaking filter using only discrete components. I don't need to be able to sweep the frequency, my design calls for a specific frequency (2kHz) and a single Q (0.70). On the treble side, actually, I'd like to add a treble shelf, but that can be done quite easily. Anyway, all the designs I've seen call for opamps (and they're much too powerful, I don't need all those features). I'd like to implement it with BJTs or FETs. Any ideas?
For example, I found this design:
https://qph.fs.quoracdn.net/main-qimg-39a1f20c8f373c9a1660d1bd0c816556-pjlq
which gives basically the kind of response I want, an octave lower, but are there any alternatives (maybe which employs BJTs instead of FETs)?
Those FETs are running as source followers (no voltage gain). They could be replaced by BJTs as emitter followers but you'll have to provide a DC bias current to the base. You may also have to adjust component values to operate at a lower impedance while keeping the frequencies the same.
It's at this point where I get off the bus and let someone with better analog skillz take over.
After simulating that circuit, I decided it's no good for audio purposes. It doesn't work as is (you have to add a coupling capacitor between the two FETs). And weirdly, it only provides the stated response (although with a very "linear" shape) if you feedback the output to the input, and accept -20dB attenuation, otherwise it's steep on the bass side and shallow on the treble side (which could work as a bell filter, mixing it with the clean sound, if the phase shift weren't too high and all over the place).
it needs 4.5v bias, and the other things like power supply decoupling to work well, just like an opamp needs.
(https://i.postimg.cc/MMnx3VpJ/2283-Hz-boost.jpg) (https://postimg.cc/MMnx3VpJ)
this has a Q of 0.74
cheers
Great, thanks!
In the meantime I was fooling around with this bandpass filter:
(https://i.postimg.cc/yJMPWMRX/bandpass.png) (https://postimg.cc/yJMPWMRX)
and by varying R28 (the resistor in series with the bypass capacitor on the first transistor) you can effectively vary the filter's Q (the smaller the sharper, because of course, there's more gain and more feedback)... but I can't figure out how to mix it with the clean signal.