Quick gyrator question for EQ

[Fancy Lime]

Hi there,

I'm planning a simple tone stack: Lo, Mid, Hi. Wherein the mids shall be semi-parametric. The Hi band will be a shelve filter, the others will be bands. Just like in the Boss 7-band Eq but with only three bands. the bass band will be low Q, the mid band somewhat higher Q. Needs experimentation.

Anyway: I'm wondering if I should use discrete transistors or opamps for the gyrators. Squeezing out the maximum Q is not a factor in this design, so decently high-gain transistors should be OK on that front. But what about noise and other factors I'm not thinking of? I'm not opposed to using opamps. Just wondering if there are any benefits to going discreet here, since there are many designs out there that opt for discreet instead of opamp. Layout and saving board space may explain some cases but probably not all.

Thanks,
Andy

[antonis]

Squeezing out the maximum Q is not a factor in this design, so decently high-gain transistors should be OK on that front.

IMHO, it should depend on your particular Q needs, Andy..

http://www.guitarscience.net/papers/namu.pdf, pages 5 - 8

[Fancy Lime]

Hi Antonis,

thanks, that's a nice paper. Very useful.

The Q is not decided yet. As I said: quite wide for the bass band and narrower for the mid band. Possibly somewhere between 1/3 and 1 octave bandwidth but I will have to experiment with that.

Andy

[antonis]

For 1/3 octave Q I should only use op-amp..

In general, I prefer discrete BJT buffers for graphic & semi-parametric EQs where for fully parametrics the use of op-amps is one way..

I've (still..  ) on breadbord the following EQ with 2N5089s without experiencing any noise or other kind of issues..



P.S.
Sorry for the messy schematic but you probably get into the point..