[sdiy] linear vactrol driver circuits

[Tom Wiltshire]

On 27 Jul 2009, at 20:56, Aaron Lanterman wrote:

>
> On Jul 27, 2009, at 12:06 PM, Tom Wiltshire wrote:
>
>> 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.
>
> I wonder if that idea could be used to good effect in a  
> microcontroller-controlled version of, say, a Buchla lowpass gate  
> or 259-style. It would save the cost of specific D/A converters.

What exactly do you have in mind, Aaron? Using the uP to derive an  
envelope-follower signal, which is then fed as a PWM pulse train to  
the vactrol element in the LP gate? That sounds do-able to me.
The AD inputs on a PIC or similar might not be fast enough (or have  
enough resolution) for decent audio quality, but that doesn't mean  
that they can't at least get some general features of the audio. If  
all you're trying to do is get the overall amplitude, as an envelope  
follower, you've probably got more than enough to work with. From  
there, it's pretty straightforward to output that as PWM.

Next question: Why?

T.