[sdiy] Problems with linearized SSI2164 ?

Phillip Gallo philgallo at gmail.com
Fri Feb 15 18:26:54 CET 2019

Keeping in mind that were talking about the Control amp portion of Mike's
VCA technique not the audio path.

100k is, by modular synth tradition, the expected load a driving module
would see.
This is due to the many inputs a control module could commonly be expected
to drive.

The audio path using 30k input is of course not-traditional but might be
excused as the audio input of a VCA is most often a single driving source.

Bandwidth reduction resulting from the 100pF feedback capacitance has no
practical impact for the usual VCA Control sources and stabilizes the loop
(with it's dynamic gain element) across all 3 possible chip alternatives.
Any increased noise level in the control path pales when considered against
the dynamic range of the technique which is restricted by the op-amp


On Fri, Feb 15, 2019 at 4:18 AM Mattias Rickardsson <mr at analogue.org> wrote:

> On Thu, 14 Feb 2019 at 22:10, David G Dixon <dixon at mail.ubc.ca> wrote:
>> Increasing the resistors from 30k to 100k also fixed the problem, with
>> the same 22pF cap in place.
> FWIW, 100k gives higher noise floor than 30k - but improves the THD a bit.
> Depending on the design, the "right" choice could be either one.
> /mr
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