[sdiy] EMS Synthi A

[gavin]

Hey all, 
got two here, first are there any EMS SYNTHI wizards out there.  A friend
has done some work on stabilizing the power supply on one.  Apparently it
takes in +18V DC and divides it down to +12 and -9 rails.  The transformer
was putting out up to 52V!  His solution was to put in a 314 (317?) reg to
drop the voltage to +18V.  He also recapped the entire thing.  Now there is
a strange bleed through of the Gate and Envelope into the CV's for all
oscillators and the filter.  When the envelope is manually triggered, the
oscillator pitch or the filter cutoff rises with the envelope shape.  As if
they were patched together, but there not.  Here's the real weird thing, 
when the envelope is set to 0 it's the gate that bleeds through, you hear a
very clear 5V jump in the pitch or cutoff and then back down when the
trigger's released.  Also, it seems that the waveforms on the oscillators
are not quite stable when the trigger's not pressed, then they stabilize
when the trigger's pressed and they jump pitch.  Whe the trigger's not
pressed they sound "weak" and the waveforms on the scope are shaky.  Any
takers?
Now over here I've been looking through the Old Crow's Yamaha CS-80
resource.  I have a CS-60 that has a massive pitch stability problem.  I
plan to do the temperature compensation diode repositioning mod, and give it
a tune but it's REAL wacked out.  The pitch response on any key varies
constantly and sometimes appears to be modulated in an LFO vibrato type way.
 This seems akin to some of the pitch stability problems he cured by
replacing the 4000 series CMOS chips.  Anyone worked on these?  and by the
way does anyone know any method of giving them a MIDI retrofit?
Thanks to all for any help you can throw this way,
Gavin