Replacing an optoisolator with transistor?

[charmonder]

I'm planning on building up a 4ms Stereo Panneur (schematic http://commonsound.org/panneur/pcb2.4.1/schematic.pdf),

I like the design, controls and features, BUT, I have a feeling the LFO waveshaper controls could be a lot more eventful if I could replace the LED/LDR combos with transistors.

I have it on breadboard, so I tried a few shot in the dark attempts, just to see if I could run signal through any transistor and modulate by the voltages that were intended for the LED. A few of them seemed to actually work, (2n3906, and j201), the problem is I couldn't find anything that wouldn't also distort/fuzz up the signal.

I'm willing to do the work to tweak it correctly, I'm just not sure what I need to do though. Can anyone help point me in the right direction? I would appreciate any advice you might have about this! Thanks!

[armdnrdy]

You can get the same type of effect as the vactrols with a JFET.

Take a look at the Ibanez ST810 Stereo Pan for ideas.

It's my opinion that vactrols sound more smooth/liquid in a circuit such as this.