AW: AW: RE: [AH] Korg MS-20

[Haible Juergen]

	>Von: 	Glenn Gregory[SMTP:filmshark at yahoo.com]
	>> (1) The MS-20's VCOs tend to interlock, i.e. they
	>> have a tiny amount of soft
	>> sync
	>> that cannot be switched off. Very slow VCO beating ?
	>> - not on the original.
	>
	>Maybe this is a characteristic of particular instruments. I get
really
	>amazing, very slow VCO beating on my MS-20 all the time -- in fact,
I
	>wish that it had some sort of (switchable) soft sync, because if
you
	>don't want that VCO beating, it can be a real pain in the ass to
sync
	>the oscillators.

This is interesting. The MS-20 I used to own had severe interlock, and I've
heard about this problem from many other people, so I asumed all MS-20's
have it.
So maybe there was an improovement on later models ? This would especially
be interesting for owners of original MS-20's, but you have caught my
curiosity
as well. In the schemos, there are two capacitors in parallel to the
thyristor
part of the VCOs, which was obviously intended to prevent interlock. As I
saw this in the schemos, and noticed interlock on my MS-20, my conclusion
was these two caps were not enough. (Mind you, the EDP wasp uses RC
filters in both, VCC and GND connection of the 555 chips in its VCOs, for
the very same reason, so there is a good argument that parallel C's are not
enough !)
It *may* be that my MS-20 (and others with the Sync problem) dont have these
caps, and the schemos show a later, improoved version. I do not know - it's
just speculation. Anybody want to check this ?
And are there more MS-20's without VCO interlock ?
(Just for the record, I'm speaking of the (un)ability to have beat rates way
below
1Hz, more like 1/10 Hz.)

	>This is kind of intersting. Just out of curiosity, what is a "track
&
	>hold"? 

Well, just what the word says. Output tracks input when Gate input is high,
and holds the last value when Gate is low.
S&H would only track input during a very short time after a *change* of Gate
input from high to low, and then hold the last value.

	>BTW, the number one thing I would change about the MS-20 would be
to
	>make the output of the two VCO's available on the patch panel to FM
the filter(s).

Right. Forgot this one. OTOH, if it had this possibility, we might have
never discovered
the trick to modulate stuff from the HP output in a feedback configuration
(;->).

JH.