LED/LDR VCF?

[Mikko Helin]

I have schematics of LED/LDR based lp vcf at

  http://www.uta.fi/~helin/sch/ledldrlp.gif

That circuit has no cv-converter, but I'g going to use inverting
summing amp (like Electronotes VCF-option 1) -> NPN -> four PNP-
transistors with 470 ohm resistor limiting the current. 
The 2k feedback resistor must be changed to much bigger, as well 
that 150k from 2N3904 to V- smaller. How much current does a LED stand?

Has anybody ever tried led's and ldr's in vcf? Craig Anderton's
book Electronic projects for musicians contains several
circuits that use Clairex's CLM6000 optoisolator, are they
available these days, or are there other some kind of devices?

Don't tell me this is is a stupid idea because it is. The filter will
not be linear, poles are not placed at the same frequencies, and
it's gonna be very slow. CLM6000's "attack" time is 10ms and
"release" time much, much longer (about 100ms).

Are there any other reasons not to give a try to it? I'd like to know 
if it oscillates or not and how does it sound, maybe that's a good reason 
why to eventually build it?  Next time I'm going to use motorized
potentiometers or thermistors+infrared transmitters, that would NOT
be cool.

-Mikko