Eml synthesizers

Interesting.  I've heard about these things, but this is the first time
I've ever actually seen any.  I'm guessing that the four pots on the
keyboard interface module are perhaps coarse tune, fine tune,
scale, and glide, based on the interface in the EML 101.
(However, the 101 doesn't have a coarse tune in the keyboard
interface.)  If it's the same basic circuit as the 101, then it 
interfaces
to an EML duophonic keyboard with Pratt-Read mechanicals.
The circuit is rather trick and you have to know what you're doing
to interface a non-EML keyboard to it.  Also, if it's like most EML 
stuff,
the output is scaled normally to 1.2 V/octave.

The VCO is interesting to me because of the two DIP ICs (741s probably).
My 101 was built without any DIP-packaged ICs -- all the ICs in it are
in metal cans.  I'm a bit curious as to what all those switches are for 
--
waveform selection?  One of those metal can ICs is likely to be a uA726,
which is a very valuable part.

The ADSR caught my attention too.  It must have been a more recent
design, because the 101 doesn't have ADSR envelopes -- only ADS
or ASR, depending on a switch selection.  Incidentally, those pots
aren't particularly rare or valuable, nor can they be easily fitted to a
101, because all of the 101's pots are panel mount.

And finally, my guess is that the mystery boards are VCAs.  The one
with the gray caps looks to be a later revision.  It would be great if
they were copies of the fancy VCA from the 101, which has both
two-quadrant and four-quadrant inputs, but they don't look "busy"
enough to be that.