[sdiy] Simple bell-EQ

[Kylee Kennedy]

Thank you for responding with your analysis and updates. Love this list for
info like this.
I might attempt a SDIY build of that Crest circuit later tonight.

Kylee

On Sat, Jul 11, 2020 at 12:45 AM Rutger Vlek <rutgervlek at gmail.com> wrote:

> Hi everyone,
>
> Thanks so much for the suggestions! From the thread Neil suggested, I ran
> both the Crest and ASP versions of the parametric EQ circuit in Spice and
> simplified it to my needs. Fixed frequency, fixed Q and two predefined
> amounts of gain turn it into a really simple circuit! It turns out the
> Crest outperforms the ASP version in terms of THD+N performance. It seems
> to me the ASP was a “designed for manufacturing” version of the original
> Crest idea, with 10K pots (cheaper/simpler to find) instead of the various
> higher values used by Crest. As I don’t need pots anyway, I went for best
> performance.
>
> Rutger
>
> On 06 Jul 2020, at 21:33, Eric Schlappi <eric.schlappi at gmail.com> wrote:
>
> 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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>
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