Using an /|\ ST as a...

[Ingo Debus]

Mikko Helin wrote:
> > 2. Also, I would like the Atari to control several envelopes by software.
> > and I figured I only need a DAC  as a programmable currentsource for
> > each ADSR, charching a cap . Am I right?
> 
> Yes, a standard unbuffered multiplying DAC is indeed a currect source,
> but then you need one DAC for each CV output.

But doesn't the output of such an unbuffered DAC has to be connected to
virtual ground (opamp summing junction)? Since the voltage difference
between reference input and output affects the current?

But perhaps it's possible to connect the DAC output to the inverting
input of an opamp with a cap in the feedback path. This could be viewed
as a "digital input" integrator. For an envelope generator, the output
of the opamp integrator has also to go down sometimes, but this could be
accomplished with another resistor from a negative reference voltage to
the summing junction. And to keep the output at zero after the release
phase has expired, a switch might be needed.

Should be possible, but makes an envelope generator with linear slopes.
For expo slopes I'd use Juergen's 4-tranny VCADSR core, and regular
voltage output DACs.

Ingo