JH-4 news. VC-ADS

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Wed Aug 28 19:40:00 CEST 1996


Just coming back from Hollidays.
Kreta was fine, and so was the sound of the waves on the
beach, but when I came back my ears were longing for
a pure, unfiltered SAW wave.

Some time ago I have posted about my JH-4 PolySynth project.
As you might have guessed, the final thing will become much
smaller than it was intended to be. The Envelopes will not
be ADSR anymore, but just ADS as in the SEM. This was
not because of the circuit size, but rather because of Front Panel
size and usability.
First, I wanted to use SSM2056's and tie the "R" and "D" pins
together, but then I thought this might be overkill. Also, all the
talk on DIY about avoiding rare chips made me think. So I
decided to build a VC-ADS from standard components.
I used the original SEM circuit (to have exactly the same
asymptodes etc.), and simply replaced the potentiometers
and the buffer with a LM13700 and a FET. It works great.
(You don't have the glitches due to offset currents in the ota
that you find in 13700-based ADSR's.)
So now I have a volage controlled SEM-style ADS with as few
as one LM13700 and a handful of discrete transistors.
If I find the time, I may draw a picture in the next days.


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