[sdiy] A new Korg ms20 (or ms10...) riddle for you: ADSR retriggering

Antonio Tuzzi antoniotuzzi at gmail.com
Fri Mar 7 10:25:56 CET 2008


Hi friends.

I have a KORG ms20 from a friend suffering for a strange EG2 behavior.

the EG2 is an HADSR envelope generator, where the HOLD parameter
simulate a sustained key

the HOLD is working...
the ATTACK seems to respect timing and so the RELEASE
when the key is released, the RELEASE is working

the problem is the SUSTAIN: when the level is lower than 3 the EG2
automatically retrigger (that is not a bad at all: similar to the
retrigger of the trapezoid in the EMS Synthis, but should be
controlled by a switch at least...)  and redo the ATTACK and DECAY
phases, so the sound never reach the SUSTAIN level but is doing
ADADADADAD and so on...

If the SUSTAIN value is bigger than 3 the behavior is more erratical

seems a comparator problem...

examining the schematics for the EG2
http://www.flickr.com/photos/49813884@N00/2316397180/sizes/l/

the IC20 (a 4558) pin 3 is the comparator involved, but I can't the
see the connection to the retrigger that should come out from
IC23 (4069) pin 10 (top right): the only connection is coming from
IC21 (tl081) pin 6

but ic21 seems to work as the A and D and R are working...

I'll change as number one the IC20 and after the IC23..

what is your guess ?

thank you
Antonio

ps
better visibility here (ms10 eg is the same!) but with ic numberdifferent
http://www.flickr.com/photos/49813884@N00/2315589139/sizes/o/



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