[Re: S&H]

[Gene Zumchak]

    This looks like a description of the Moog keyboard.  He actually used a 1.0 mfd cap and a large pot in
series.  The knob on the keyboard he called portamento.  He didn't have the luxary of a fet op amp in the late
sixties, but he used a fet source follower.  I think Tom was looking for something for saving a pot voltage.

Gene



Harry Bissell wrote:

> This might be ok, but the inrush current to the cap will depend on the
> resistor matrix on the keyboard. The charging time might depend on which key
> you press, and the cap will try to draw INFINITE current when confronted with
> a step voltage change. This might fry the gold off the contacts.... Otherwise,
> the switch is a good idea. Air is an excellent insulator.  :-) Harry
>
> Mike I <mirwin1 at istar.ca> wrote:
> Hello,
> Why not disconnect the keyboard CV bus from everything else, connect a
> 0.1 - 0.2  microfarad polystyrene cap between ground and the CV bus, and
> buffer the cap voltage with a BIFET op amp voltage follower. The op amp
> output  becomes the keyboard CV output. The keyswitches act as the S/H
> switches now, and leakage is kept at a minimum, plus the CV is
> continuously measured for as long as the key is held down, helping to
> reduce the effects of external noise. Just make sure the cap is not too
> large in order to avoid an unwanted CV "glide" between notes.
>
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