[sdiy] Minimoog EGs?

[Michael Ruberto]

hi Gene,


>One thing I can tell you about the EG's in the Minimoog (at least the VCF
>EG) is that when Attack = minimum (10ms) and the Decay = 1-2 seconds, the
>amplitude of the envelope increases the more often it is triggered. It's as
>if the new attack builds on top of the existing charge on the EG cap. I 
>have
>not run into another EG that does this,


you might be suprised but the software EGs on the Prophet 600 actually do 
something quite similar to this. I have found that sending it several short 
note-ons allows me to controllably build the EG level up and have used this 
effect as a sort of replacment for velocity control (which it does not 
have). this little trick also can allow one to get 2 distinctly different 
sounds at the same time if you are careful about how many voices you use ;-)


>Try this:
>
>http://www.fantasyjackpalance.com/fjp/sound/synth/synthdata/16-minimoog/sche
>matics000/minimoog-schematics-01.gif
>
wow! this is great! thanks for the help with this! The design is remarkably 
simple. The various discharge paths from the integrator cap are a bit 
misleading. I see one goes to the switch labeled sustain and I imagine this 
will bypass the decay stage completely for a legato mode is this correct? 
(obviously I have never played this instrument) now the part that is 
confusing is the offboard connection between points 22 and 6 if I am reading 
those correctly. If I follow 22 it goes to a transister who's designation I 
cannot determine for certain but looks like Q803. this transister is 
providing a discharge path as indicated by the diodes from the decay/sustain 
stage. ok I think I get it now. when the signal is positive on that line it 
forces the discharge through the sustain transister and when it's not 
positive provides the decay path. very clever. please tell me if I am 
incorrect in this assesment. well now that I have some understanding of it's 
operation I need to think about what part of it's operation makes it unique 
from other EG designs I have seen. That decay/sustain arrangement is rather 
suspicious so I will start there next time I have the time to think. ;-)

Mike


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