A 3rd version of MS-20 ?

[Haible Juergen]

As you surely know, there are two different versions of 
the Korg MS-20, the most prominent (but not only)
difference being the filters (Special Korg-35 IC vs.
LM13600 OTAs).
A few weeks ago, a friend called me and said he had
two MS-20's which both have a little add-on pcb,
(like the later OTA version), but *no* LM13600's.
He found a lot of diodes instead ...

This makes me think - was there actually a 3rd
MS-20 version with a diode ring filter like the
MS-50 had ?

I haven't seen it with my own eyes, but this friend
is very trustworthy, so I take it that there is a 3rd version.

Remaining question: Is it the same filter as in the MS-50,
or another variety of the basic concept ?

Anybody got more info ? Schematics even ?

JH.