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

Dave Kendall davekendall at ntlworld.com
Sat Mar 15 18:54:38 CET 2008


out of curiosity, was it an ST micro part?
IIRC, there was a thread somewhere about a bad batch of 7912s from ST 
(-21V!  .....)

cheers,
Dave

On Mar 15, 2008, at 16:42, Antonio Tuzzi wrote:

> 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/
>>
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