[sdiy] Filter strangeness.

[Scott Gravenhorst]

<synth at oldmail.charlielamm.com> wrote:
>> If you wanted a photo resistor to vary cutoff, how
>> would you setup the input
>> stage?
>
>You can use opamp, with a transistor to up the current it can
>source...examples on my site.  Look at the circuit fragment surrounding 
>IC1D.
>
>http://www.charlielamm.com/synth/vactrolvcfsch2.pdf

No disrespect intended here, but wouldn't it be better to have the LEDs in
series?  Series forces the current to be identical in both LEDs and both
are guaranteed to light up, whereas parallel means you could have more
current through one than the other, and you could even have one LED that
doesn't allow the other one to turn on at all when they are in parallel. 
It looks like you could have current sharing problems.


>Vactrol filter page is here.
>http://www.charlielamm.com/synth/vactrolvcf.php3
>
>There are other ways to do this...eg, check out some of the buchla clones
>for instance on Verbos site, buchla is the grand master of using
>photoresistors to do clever things.
>
>http://www.simple-answer.com/DIY.html
>
>

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