Driving Vactrols - off a cliff

[BananaPlug]

I'm not getting anywhere with this so after a some fruitless experimentation and web trawling it's time to ask the gurus.

I'm building the Ian Fritz ADAR envelope generator which has 1M pots for the attack and decay timings.
Here it is: http://bridechamber.com/bridechamber.com/IF_EG_PCB.html

I'd like to replace the decay pot with a Vactrol and drive the LED in the Vactrol with current derived from a panel knob and a CV input, which would sum with each other.

I got it to more or less work but the problem with it is the wildly non-linear response of the Vactrol as the LED gets dim. The curve is so steep that as I turn the knob I'm well beyond the midpoint before I get 1K and near the very end it ramps up quickly. If I carefully get it to about 500K and just touch it it can easily move by a few hundred K.

Common practice seems to be to drive the Vactrol LED with a transistor or opamp or sometimes put the Vactrol LED in the feedback loop of an opamp. I get similar falling-off-a-cliff results from everything I've tried.

So what are people doing? Are they biasing things so as to only use a small part of the range? I just don't get it. Is there a way to linearize the response so that a panel pot driving the Vactrol performs similarly to a 1Meg pot?

[BananaPlug]

Nobody?

[diablojoy]

i don,t recall ever seeing any vactrol ccts that would acheive what you want however you could look at PWM ccts to gain better control over the LED intensity of the vactrol, varying the pulse width may hold the key
just an idea , haven't tried it myself .

[BananaPlug]

[BananaPlug]

Well, although I had a Vactrol burning a hole in my pocket cooler heads prevailed and I came up with a better solution using just a few resistors and a transistor.

If anybody has a nice way to tame that Vactrol response curve I'm still curious but probably won't be attempting it myself.