UhClem
Senior Member

That 8 Ohm load on your output can't be making that opamp happy. If all you want to do is reduce the amplitude to drive a low level input then all you need are some resistors. But make sure that you don't have a...

Since you only need to sink current a simple NPN transistor driver is sufficient and robust enough so that the Zener isn't required.

You didn't fix it. The only way that can have any hope of working is if there is a connection between the opamp ground and the ground of whatever is driving J1. Which defeats the purpose of the optocoupler.

I am wondering how that circuit is supposed to work. The the opamp has no explicit reference for the signal it gets from J1 (MIDI-in). It might be getting it via its output which manages to have a route back to the...

When I look for a data sheet on the AD8225 IA, what I find looks nothing like your schematic. The AD8225 is a single device in an 8 pin package with fixed gain and no Rg. What are you really using?