ldr vactrol - getting a useful range

[Dj Task Manager]

Hi all, I am puzzling through making a rather thorough LFO to affect various parameters on my filtery delayey SK5.  The LDRs will be able to be switched in to take the place of the potentiometers that control a filter and a Delay (and possibly a second LFO), or if i can manage it, work with the pots to give depth control.  The issues im facing are as follows:

1) LDRs dont give a linear response to decrease in light intensity (http://www.kitronik.co.uk/resources/understanding-electronics/how-a-ldr-light-dependent-resistor-works)

2) The pots in question are in range of 10-100k and LDRs are usually 1-2m.  I could put resistors in parallel with the LDRs to get the overall resistance range down, but again this would not give a linear response.

Would it be possible to cleverly pit these non-linear responses against each other to sort of cancel each other into something more linearish?! or will it result in devilish double tapered response?!

anyone SHED ANY LIGHT (groan) on this quandary?

Oh and this is a likely candidate for the LFO I'll build... (using the output to as a CV in for the res of my Q&D filter and everything else with vatrols off the LED (if, that is, the LED light is influenced by the shape knob, it sort of looks like it might not be)) : http://www.casperelectronics.com/images/finishedpieces/speak-n-spell/Speak-n-Xbending/LFO%20schematic2.jpg

[Dj Task Manager]

this is interesting...: http://www.diystompboxes.com/analogalchemy/emh/emh.html

[Gordonjcp]

There's a reason why you don't see vactrols used anywhere...

[Circuitbenders]

Don't you? There was definitely one in the compressor section of the Focusrite channel strip i was working on the other day...............

[Dj Task Manager]

for most of the functions I want the vactrol to perform the response from the instrument diminishes as it hits and exceeds the top resistance of the pot it is replacing, therefore if I put a trim in parallel to the LDR to bring the top resistance down to perhaps 1.5 - 2 X the pot value it should curve off at the top resistance rather than spike.  It will by no means be linear, but hopefully perhaps a misshapen sort of sine  .  Like I say sometimes this wont work, such as rate on a pt2399 delay where it will continue to plunge into the casams of slow-doom as the resistance increases...
...having said that spikes of slow-doom dont sound so bad now that I think about it!

[wax+wire]

Have you built the casper electronics LFO?

I hav built some to control (not Vactrol, but CV-In) my Atari Punk Console synth and found the 'depth' and 'shape' don't work for me.  could be my fault, but I don't seem to get it.

I'm keen to use my LFOs with a vactrol also to control non-cv-in situationsm so keen to hear how you fair.

[Dj Task Manager]

Hi wax and wire, ive been doing some research into getting responses out of LED LDR pairing, its going well, im just waiting for a heck load of LDRs from china so I can work out exact values for things.  Its involving using a complex equations a spreadsheet and drawing graphs.  Bloomin love having an excuse to draw a load of graphs!  I will post my findings In a couple of weeks...

[wax+wire]

Finally got my Casper LFO circuit working well (not sure what I'd been doing)

I'm keen to build now some LFO VACTROLs into a Commodore 64 filter cuttoff as well as have them working better in my Atari Punk Console, and hopefully start to incorporate LFOs either as CVs or VACTROL in some circuit bent goodies