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

[Antonio Tuzzi]

nope...
Texas Instrument

at


On Sat, Mar 15, 2008 at 6:54 PM, Dave Kendall <davekendall at ntlworld.com> wrote:
> 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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