[sdiy] Re: A new Korg ms20 (or ms10...) riddle for you: ADSR retriggering
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
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
> thank you
> 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
>> 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
>> 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
>> better visibility here (ms10 eg is the same!) but with ic
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