[sdiy] Linear Analog Synth Portamento

[Harry Bissell]

I'd recommend Jurgen Haible's HADSR core for the intergator. Normal OTA have too much offset
voltage to be practical. This is less of an issue in a linear portamento but is trouble
in the RC type where there is little of no feedback (uhhh ... to linearize it :^)

H^) harry


----- Original Message -----
From: David G Dixon <dixon at mail.ubc.ca>
To: 'mark verbos' <mverbos at earthlink.net>
Cc: synth-diy at dropmix.xs4all.nl
Sent: Tue, 03 Apr 2012 15:34:52 -0400 (EDT)
Subject: Re: [sdiy] Linear Analog Synth Portamento

> 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.

Egads!  I've got a simpler idea, but still reasonably complicated.  Start
with a Bissell MorphLag in linear mode, replace the pot with an OTA or a
linearized 2164 VCA, generate a start-of-attack pulse from the comparator,
use that to trigger a sample-and-hold sensing the output voltage, then take
this stored output voltage and the input voltage to a full-wave rectified
differential amp, and use the output of that to control the CV of the
OTA/VCA.  For added complexity and better performance, replace the single
S&H on the output with a two-step analog shift register on the input.

Thoughts?

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-- 
Harry Bissell & Nora Abdullah 4eva