Korg MS-20 Clones anyone?

[Haible Juergen]

	>Has anybody attempted to clone the Korg MS-20 VCO?  We seem to have
more
	>or less just about every element of it cloned (the LFO, EG, and
VCF) and
	>it seems only the VCO and VCA are left.  

I've built the VCO, sort of. That is, the cco core with original
transistors, including
the FET cascode and the npn pair exponential modulation input. So I can
confirm
it works. (It obviously does in thousands of MS-20's (;->) - what I mean is
that you
can just directly clone it, there are no hidden secrets.)
I have not built the waveshapers, though, because I liked the Minikorg's VCO
back end better.
I've also built the keyboard interface. Again, it's a actually a mix of
Minikorg and MS-20,
because I wanted the Minikorg's glide circuit. But I've powered it from
+/-15V (like
MS-20; the Minikorg uses +20V / -10V). When you compare the circuits, they
are
very similar. Nice circuit to derive expo CV and gate / Sample&Hold signals
from
a single contact keyboard. It's single-trigger only. If you want a optional
multi trigger
feature, look at the Korg Sigma circuit. Again the same basic circuit, plus
some additions.
(I have not built this version, though.)
VCA: I once made simulations of both, the 1-transistor and the 2-transistor
version.
And in one Mono/Poly I replaced it with a SSM2020. But I haven't built the
Korg VCA
from scratch yet. Should be very easy.

JH.