[sdiy] Simple bell-EQ

[Eric Schlappi]

I've been looking at gyrator based EQ circuits lately, basically replacing
an inductor in a passive filter with an active circuit (transistor or op
amp). The transistor based ones show up as the EQ in a bunch of DOD pedals
which got me interested in it.

There are some suitable op amp based circuits and theory in this article:
https://sound-au.com/articles/gyrator-filters.htm

On Mon, Jul 6, 2020 at 12:10 PM Rutger Vlek <rutgervlek at gmail.com> wrote:

> Hi list,
>
> I’m hoping for some collective wisdom on the following issue. I’m trying
> to make myself a fancy (analog) guitar buffer with some basic tone
> controls. I already implemented a switchable high shelf filter (bright
> switch), and an adjustable 1-pole HPF for cutting bass. Now i would also
> like to implement a switchable mid-frequency scoop. With a VST parametric
> equalizer I found a bell-shaped curve with a certain Q and frequency I
> liked, and would like to implement this with a switch to select a few
> preset gains (boost/scoop). But I struggle to find a good analog circuit
> topology that fits my (simple) needs. Google turns up a lot of digital
> implementations, or way too complex equalizer circuits where every aspect
> can be controlled, but of which I don’t understand how to set gain, Q and
> frequency. Any suggestions for a simple bell-shaped EQ for which Q, gain
> and frequency can be set (and forget)?
>
> Many thanks!
>
> Rutger
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