Pre-distortion Diodes for Moog Ladder Filter

[Michael B. Irwin]

Tony,
Thanks for the info gleaned from  your first-hand experience with
building Moog VCF's. I agree with you that the distortion from these
filters is not unpleasant and in reality is probably an essential
component of the overall sound of the filter. Software synths that
attempt to emulate the Moog filter need to consider the distortion
characteristics as well. The distortion I can live with; it's the
background hiss that is annoying. On your VCF schematic I see that you
have used some very low-noise, well-matched components. In OTA filters,
the linearizing diodes are effective in improving the S/N, but when
distortion occurs it happens very suddenly, which is not a desirable
characteristic. Does good matching of the top and bottom pairs
significantly reduce the noise ( I can see that it is essential for
minimizing CV feedthrough) or is the noise reduction mainly a
consequence of the LM394 being a very low-noise part?