Saga of the uP developer

[Fraser, Colin J]

> -----Original Message-----
> From: Paul Maddox [mailto:paul.maddox at ndirect.co.uk]
> Sent: 27 June 2000 14:00
> To: Fraser, Colin J
> Cc: Synth-DIY
> Subject: Re: Saga of the uP developer
> 
> > The CPU sends two voltages to an expo slew circuit, with a 
> comparator
> input
> > back to the CPU to tell it when the peak value is reached 
> (end of the
> attack
> > phase).
> 
> nice trick..
> but how do you get the rate to change?

One cv is the rate, the other is the target. The slew ciruit is based on a
3080.
The rate controls the bias current, the target voltage goes to the positive
input, and the buffered output feeds back to the negative input to give an
expo curve.
The schematics are at http://www.encoreelectronics.com/cont_moogsup.html 
(note that R194 is labelled wrongly in the schema - it's 100R not 100K)
Check out the bottom right corner of Analogue Schematic page 4.

> Im wanting to do a poly synth now and I dont fancy doing 4 
> Egs for each of
> the 8 voices
> in discrete components..

This could be a good choice then. Still a lot of hardware, but less than
discrete EGs.

Colin f