[sdiy] PWM gain control

[Ken Stone]

Look up the ETI 4600 synth circuits. Particularly the filter. They did a lot
of PWM gain control using 4016 or 4066 in this synth.


>On Friday 25 August 2006 01:09 pm, Thomas Hudson wrote:
>> I've ordered an Arduino board (http://www.arduino.cc/) to experiment
>> with a microprocessor side chain controlling an all analog signal
>> path for  gain manipulation (compressor, expander, guitar sustainer,
>> etc).
>>
>> The processor can output an analog value as a varying duty cycle PWM
>> (frequency 30769 Hz). I had originally intended to use an LED/LDR to
>> convert this to a resistance for controlling gain in an op amp, but
>> came across an article about the Crane Song Trakker, which uses PWM/
>> FETs.
>
>Is this article online someplace?  Got a URL?
>
>> Just wondering if anyone had experience with either approach (or any
>> others)? Also any suggestions on selection of FETs for this application.
>
>I thought about doing something like this one time,  with a 4016 or 4066,  and 
>actually started to breadboard the idea.  The immediate result was truly 
>horrible distortion,  but a lot of that was because,  as I realized at the 
>time,  I wasn't keeping the signals in the proper framework of being between 
>the supply rails -- what I _should've_ done was perhaps use a couple of 7.5V 
>split supplies,  or something of the sort.  At that time what had started out 
>as simply idle curiosity turned into something that was looking like more 
>trouble than it was worth and I never did anything further with it.  But 
>maybe one of these days I'll pursue it a bit further...
>
>-- 
>Member of the toughest, meanest, deadliest, most unrelenting -- and
>ablest -- form of life in this section of space,  a critter that can
>be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
>-
>Information is more dangerous than cannon to a society ruled by lies. --James 
>M Dakin
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
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