AW: Re: AW,2:Re: AW: Another VCF Finished

[Haible_Juergen#Tel2743]

> SSM-2040 filter uses 100k/200 at input stage for attenuation with 10k 
feedback
> from first buffer output to (-) input of gm stage, rest of stages use only
> 10k/200 attenuation with 10k feedback resistor, and last output summing
> inverter stage has 10k/100k resistor divisor (10X amplification), maybe
> this is way to go (or not).

The original reason for this was to prevent the OTA *outputs* from
clipping in the 2040.
Anyway, using 18k/200 in the input stage gives *wonderful* overdrive
capabillities with the SSM2040. I use this approach in my Modular
(I have a 10Vpp standard for VCO signals, btw.).

JH.

PS.: Speaking of input overdrive: For a given input spectrum you get
increasing distortion with decreasing cutoff frequency. Think about
what happens during a filter sweep: Clean and smooth when the filter
is open (i.e. no nasty intermodulation at high frequencies), but fat
with lots of plesant slow intermodulation when the filter is closed.