AW: env shapes

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Fri Oct 25 20:01:00 CEST 1996


>  How would this apply your linear 13600 AR circuit? Could you run the
>  output straight to the (-) inputs on the OTAs and get RC curves (instead
>  of connecting the - inputs to ground)? The current out of the OTA is
>  based on the difference of the inputs, so this would make sense - bigger
>  difference = more current = faster change...

Don't have the thing you refer to in front of me, but I always use a 
feedback
on my OTA-based envelopes. It's the resistor ratio that makes slopes 
different.
For linear slopes, theoretically you could connect the buffer output
directly to the negative OTA input, but you have to make sure that
you don't destroy the OTA when the differential voltage exceeds 5V.
So I usually take a 1/3 or  1/5 divider to be on the save side with 15V 
supplies,
and the OTA input still acts as a comparator (i.e. hard stopping to charge
when the output equals the input).
For RC-slopes, I use something close to the ususal 100k/200R divider.

I have a completely designed ADS circuit that is built around the Oberheim
SEM-envelopes and uses a single LM13600 chip (Dual-OTA) for voltage
control, and it works absolutely superb.
I think I will give it to Kevin to include it into my now evolving WWW-page
(Kevin is doing great work !!!), but I will have to redraw it first.

JH.





More information about the Synth-diy mailing list