I've been trying to get my hands on some Vactrols (opto-variable resistor) for a long time, unsuccessful. Not even digikey has them.
some examples: VTL5C2, VTL5C3, NSL32
Can't see them as "too expensive to manufacture" considering you can improvise one using an LED+LDR+Tape, but it's in no way as "linear" or robust as the actual components.
Anyone knows the story behind it?
Edit: So there are places where you can get them, but at least where I live it's something almost unheard of..
They look usefull in many ways (at least to me), yet I've seen them nowhere except some old audio equipment..
Edit2: Ok, so what could be the alternative to a vactrol if I require exactly that, a significant resistance change controled by voltage, (MOSFET as resistor is not an option for me because of the very low resistance range). Is there such a device/equivalent circuit that allows all this with the simplicity of the vactrol? This is a hypothetical question, based on many compressor units I have seen and seems Hard to achieve such functionality in such a simple way, the closest I've seen are OTA based for closed loop circuit, but they arent nearly as simple as vactrols.
Best Answer
They are not stocked because nobody is using them in large quantities. The kind of designs that can be (kind of) achieved with vactrols can also be done with op amps and LM13700s, and will yield much better results.