[sdiy] linear vactrol driver circuits

[Aaron Lanterman]

On Jul 27, 2009, at 12:33 PM, HARRY BISSELL wrote:

> Look at National Semiconductor AN-20, Analog Multiplier.
>
> I'd try to match two vactrols, put the LEDs in series, use one
> cell for feedback, the other for your variable resistance. It would
> not be perfect but would greatly improve the linearity...


Ah! Buchla uses a variation of this idea for Amplitude Modulation in  
the 259. See the middle of this page:

http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2590_4_200.jpg

Funny, if you type "Buchla 259" into google one of my homework  
assignments comes up as the third hit. ;)

- Aaron