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

[Antonio Tuzzi]

for the archives...

that was easier than expected...

the lm7915 was giving  -25volts...

with all the consequences (retriggering and portamento bad behaviour...)

thank you
at



On Fri, Mar 7, 2008 at 10:25 AM, Antonio Tuzzi <antoniotuzzi at gmail.com> wrote:
> 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/
>