[sdiy] linearize OTA for VCF?

[jh.]

> Looking through my vcf schematic collection, I notice that none of the
> designs use the linearizing diodes on the OTA inputs. Does anyone have any
> comments on the pros and cons of using these, and has anyone actually
> incorporated them in a design?

The CEM3320 has kind of linearized OTAs (ok, there are other tricks inside
a 3320, too), so one can state that there are many synths with linearized
filters out there. I also remember application circuits for SSM VCAs
in filter configuration, and the SSM2000 and SSM2020 are OTAs with
Gilbert input. (Of the filter chips, the 2040 and 2044 are not).
Normally, the soft clipping of non-linearized OTAs is considered
a good thing for LP filters. OTOH there are filter designs with resistor
dividers that prevent the (non linearized) OTA from any serious clipping.
Here, SNR can be improoved without sacrificing too much of the "sound".
Also see the recent discussion about using the CEM 3320 - HPF's are
a different story.

JH.