[sdiy] linear vactrol driver circuits

[HARRY BISSELL]

PWM must be high enough in frequency not to introduce any noise...
vactrols are slow but even if a high frequency is MANY dB down, you
may hear it...

H^) harry 

----- Original Message -----
From: Tom Wiltshire <tom at electricdruid.net>
To: Julian <julian at port23.co.uk>
Cc: synthdiy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 27 Jul 2009 12:06:54 -0400 (EDT)
Subject: Re: [sdiy] linear vactrol driver circuits 


On 27 Jul 2009, at 15:56, Julian wrote:

>
> Ive been considering using vactrols to add CV control, but am  
> wondering what my best approach is for driving them.
>
> Im thinking along the lines of a CV input jack, and a front panel  
> pot, and an opamp mixer / driver for the led, but am wondering as  
> to the best way to get away from the log response of the vactrol.
>
> Im sure this must be a common issue when using vactrols, so im  
> wondering what other people do?

I don't know what other people do, but I've been experimenting with  
driving the LED in a vactrol with a PWM signal. This is supposed to  
give a more linear relationship between the driving signal and the  
LED brightness. I was using a microcontroller, but you could easily  
use a ramp or triangle wave oscillator and a comparator for an analog  
PWM solution.

T.


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