[sdiy] Linear Analog Synth Portamento

[mark verbos]

On Apr 3, 2012, at 2:41 PM, David G Dixon wrote:
> 
> It is possible to have constant-time linear portamento, but (AFAIK) this
> requires storing the voltage difference and using it to program a
> variable-current source to the Miller integrator.  This would be a very cool
> effect, and it is something I'd like to try to build in the near future
> (probably with linearized 2164s).  (Consider: three VCOs in tune playing
> random 3-note chords, and each time the chord changes, all three notes snap
> (not in an asymptotic manner, but abruptly) to their destinations at exactly
> the same time, no matter how big their individual intervallic jumps are.
> That would be awesome!)  If someone here is sitting on such a circuit, I'd
> love to see the schematic!


The Buchla MARF does that. The length of the stage is voltage controlled. The clock is a ramp. There's a sample and hold that grabs the starting voltage and then it crossfades from the S&H output to the destination voltage. It's an extraordinarily complicated circuit compared to a pot and cap.

Mark