Not a lot out there on this one. It's a optical noise gate DOD produced in the late 70s and works best at the beginning of your signal chain. The original had a very strange way of bypass switching, but I've omitted this as your true-bypass method of choice is probably much superior. Originals used a VTL5C2, but experiment with LED and LDR combos, and possibly the value of the resistor feeding the LED (10k right above the LDR and Q1).
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.