[sdiy] SSM2040 filter question

[Antti Huovilainen]

Hi

I've been doing some simulations of analog filters lately
(http://www.hut.fi/~ajhuovil/asynth).
I remember hearing something about SSM2040 having asymmetric distortion.
Taking a look at the schematic this seems to not be the case as long as
the signal is not running too close to supply rails.
As far as I can see, the circuit should behave exactly same as 4 OTA
sections in series. Yet many people claim that it's the best sounding
filter there is, so there must be something wrong with my analysis.
Any suggestions?

I've used Rene Schmitz's version of the circuit as a basis for the
simulation: http://www.uni-bonn.de/~uzs159/rs2040.html

4poletest.mp3 and drone4.mp3 use that filter in the normal two sawtooth
oscillators + VCF + VCA configuration.

Antti

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