[sdiy] Minimoog EGs?

[Gene Stopp]

I've never really done an analysis of the Minimoog EG. I've looked it over
and said things like "there's the attack flip-flop" because of the
cross-coupled transistors, and "there's the attack transistor" and "there's
the sustain voltage buffer transistor" but I've never done any math in
there. Can somebody comment on why the peak would climb as more triggers
come in? Some kind of charge pump action? Also please note that this does
not happen when Attack is something higher than the minimum setting.

One thing I did do one time was build up a clone VCF from the schematic onto
a piece of vectorboard, which was pretty cool. There have been many times
that I've looked at the circuits in the Mini and realized that it would be
pretty darn easy to clone the VCF/VCA/EG sections. The parts count really
isn't that high. The biggest problem would be finding those low-ohms
wirewound trimmers! For VCO's one could probably use something more modern
(like Terry Michaels core).

Best Regards,

- Gene


-----Original Message-----
From: Michael Ruberto [mailto:frankentron at hotmail.com]
Sent: Thursday, February 06, 2003 1:20 PM
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Minimoog EGs?




This is very interesting! I dug it up doing some research http://analog.no/
on the envelopes page is some very interesting EG perfomance data! good job 
to the author! it would seem that the Minimoog's EG design is very fast 
which I knew already (secondhand) but also has some added sustain time 
contributing to a punchier sound.
now looking back at the circuit I was wondering if this added sustain time 
is coming from C959 (I think), the .1uf on the keyboard trigger input. I 
imagine it's job is to debounce the trigger signal but is it's value large 
enough to also noticably extend a short trigger?

if this is the case it should be easily tested by comparing the EGs while 
triggering from the keyboard and triggering from the external trigger input 
which bypasses that cap.


Mike



_________________________________________________________________
Protect your PC - get McAfee.com VirusScan Online  
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963