I've constructed a circuit to cancel out LED emitter noise with a feedback control circuit. PDref monitors just the emitter, while PDsig carries the sensor signal + emitter noise. Feedback consists of integrator -> JFET VCR -> current divider. Please see attached circuit. LT Spice simulation works well, but in real-world implementation I don't see the JFET resistance changing. Any suggestions on what I could be missing from moving from the simulation to prototype?