Japanese and Korg35

[tomg]

> This whole thumping only becomes unpleasant when the cutoff frequency
> is modulated way below, or way above the audio range. On the bottom end,
> a resistor across the capacitor at the opamp input is crucial. But Tom,
> your
> 100k across 1nF would kill the bass range wouldn't it ? 10Meg seem about
> right,

You are probably right. I can't seem to get good hi-pass response out of it
the way it is. No problem with lo-pass though. Did you leave the diode
pair as it was? If so is the distortion a quality of the ms35? Am I missing
something by trying to make it sound like the ota version? 

> As I said, I don't know how close I am to the real Korg-35, but I am
really
> fond of this filter.

It sounds good! It's really pretty cool JH. Once assembled and functioning
I don't think it will be so hum sensitive. Fet opamps should take care of
the noise the original generated. I'm sure this had something to do with
the later change to otas . It does suffer the same flaw's as it's little
brother the emitter pass vca. However like the vca it's small, it's simple
and it works!

> I still have one big question. When Korg already had Diode Ring filters
> (in the MS-50 for sure, and probably in some of the Traveller filters
> as well), why would the go back to an asymmetrical filter for the
> custom chip they were going to use in so many products ??
> The diode ring should have much less CV feedthru even with
> unselected diodes, wouldn't it ?

Nah .. the ms50 clone I built has the "thump" syndrome and it's tricky to
set it up too. If you were only going to build one sk type filter the
13600/700 ota version would probably be the best choice it's a lot easier
to deal with and it really does work and sound better MO, but if you like
neet stuff, this is fun! 

BTW the ms50 diode ring must be matched or it doesn't work well at all.
Thats why I used the 3046. It probably should have the limiting diodes too.
When it breaks into oscillation it just kills me the way it is. I'm glad I
built it but I like the ms20 much better...... maybe most of all.

-tg