Korg MS20 filters

[Martin Czech]

Thanx for your repsonse.


> 	I don't know what's inside the Korg-35. It looks like a hybrid, and
> my
> 	guess would be that they use a diode ring, similar to the MS-50
> 	filter.



This is likely, it would explain the bad S/N, same series of products. Why
invent something new. Indeed, after doing my analysis of the MS50
filter it is quite clear that a diode ring is simply one possibility
for creating a variable resistance. I'd also like to see what really is
inside a Korg35 module. Perhaps the changed later on to the 13700, because
of production troubles with the diodes (matching, no more available etc.).


> 
> 	Building a 13700 version is high on my priority list. It's hard to
> believe
> 	that old and new MS-20 sound the same, though that is often claimed.

Yes, I found this claim in the archive. When you do it, we'll know.
I suspect you have an old MS20 in your studio ?

> 	I'd say this cannot be true, just because the VCA has changed as
> well.
> 	But maybe in the mere filter the main influence on sound is not the
> 	variable R or gm part in the first place. I guess the typical
> behaviour
> 	at overdrive and / or self oscillation is because of the special
> clipping
> 	in the feedback loop. But these are all just guesses.

The filter topology is also an influence. Very strange Sallen-Key.

> 
> 	I'd love to see the internal diagram of the Korg-35.
> 	One thing I'd even love more to see is the internal circuit of the 
> 	old Keio ICs. Wasn't there someone on the list who said he had
> 	an unpotted filter pedal from the Minikorg aera ??
> 	Any news in reverse-engineering ?
> 
 Me too, please!

m.c.