GHR Audio

Problem with some of the classic opto compressor designs is slow attack and release time. NSL-33-007 optocoupler has fast rise and decay time. With fast optocoupler attack and release can be controlled almost entirely with the sidechain.

https://mm.digikey.com/Volume0/opasdata ... 33-007.pdf

Here's asidechain I came up with RV1 = Threshold
RV2 = Release
RV3 = attack
RV4 = Ratio

Design of the amplifier part should be fairly trivial. Balanced line receiver at the input, series resistor and LDR to ground, make up gain and DRV134 output.

Opto compressor schematic

Found this the other day. Have you ever test-built this?

How does the Auto Attack interact with the variable attack setting?

I have the boards and I'm going to build one soon.

Auto attack bypasses the attack pot for large transients. For smaller signals the attack pot always determines attack time.