[sdiy] Ladder filters and gain drop, that old chestnut

Mattias Rickardsson mr at analogue.org
Thu Aug 27 11:04:01 CEST 2015

Hi Andrew et al.,

On 27 August 2015 at 10:24, Andrew Simper <andy at cytomic.com> wrote:
> If you check the 303 schematic you will see gain compensation at the
> output, there is a boost in the output signal level with increased
> resonance to make it not as quiet. You can do this boost anywhere you
> want, at the input, at the output, or a bit of both.

the nice thing with doing it the 303 way is that the resonance pot (or
VCA) is doing both jobs; providing resonance feedback as well as
boosting the output of the filter. No extra boost pot (or VCA) is
needed before the filter. On the other hand, it might end up less
"fat" than when adding the boost before the filter, as Richie just
mentioned before.

When it comes to the gain drop, shouldn't it be possible to add more
poles & phase shifts somewhere else in the frequency range in order to
avoid some of the cancellations?


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