[sdiy] more sh-101 mods?

[john mahoney]

----- Original Message ----- 
From: "NATE!" <timexheater at comcast.net>


> ok i have been starting to plan on modding my sh-101... [snip]
>
> now i was wondering about some other mods that i haven't seen done
> anywhere...
> what i'd really like is CV in for the decay stage of the ADSR, and CV in
for
> resonance on the filter...
>
> i don't see why they would be much different than doing the CV in mod [but
> of course i'm probably wrong :P]... shouldn't a basic CV mixer after the
> sliders do the trick?

Ah, but they *are* different. EGs (ADSRs) are rarely voltage controlled on
non-programmable analog synths. VC filter resonance is also fairly uncommon.

Modding the ADSR is probably asking too much. However, there are VC Slew
Limiters. You could insert one of them at the ADSR's output, then you'd have
VC decay/release; it would affect both decay and release times. Thing is,
you need voltage control *and* independent up/down lag times (you only want
down, actually), and only MOTM seems to have that feature set. (Someone
prove me wrong, please.)

The MOTM also has VC Bypass. You can run an inverted Gate signal into that,
so the lag is bypassed on "note off", thus the Release will not be
affected -- only the Decay will. Tricky, eh? ;-) One more reason to like the
MOTM: it allows VC of Attack time, too.

So, how do you make a voltage controlled slew limiter? I really want Harry's
Morph Lag
(http://www.wiseguysynth.com/larry/schematics/Morph-Lag/Morph-Lag.gif) with
voltage control.


As for the filter, I believe that you can add VC resonance with a VCA.
That's probably why it's not found on a lot of synths, because it's not
considered worth the cost of another VCA. Some filters require an inverted
signal to be fed back, so you may need an inverting op amp, too.
--
john