![]() ![]() There are even 'dual receiver' optoisolators for just this purpose. While a single optocoupler is rarely linear enough for audio signals, a pair run under the same conditions, one used as feedback for the driving signal, can track well enough to reduce the distortion to useable levels. ![]() There is a way to use optocouplers to give a DC coupled, truly isolated, reasonable distortion analogue link between equipments. This is not isolation in the true sense, especially with the protection diodes which will allow a fault in one to blow a fuse in the other, but it does break ground loops, reject inter-ground noise, and allow a ground lift functionality. The reversed biassed diodes are for protection, in case the cable is unplugged and the shield subject to a large signal, they would not normally conduct up to a few hundred mV of ground offset. The normal differential amplifier rules apply to the R1/2/3/4 values. ![]() Simulate this circuit – Schematic created using CircuitLab The amplifier senses the voltage of the remote ground, and adds it to the signal being transmitted. The actual circuit is identical to a differential amplifier, with the connections taken to slightly different places. However, the existing receiver, which I couldn't modify, had a solid, ground referenced, single-ended input, and all I could play with was the transmitter. Normally, I would use a differential signal, with a differential receiver. I had two pieces of equipment with slightly different ground environment, and wanted to pass a high fidelity signal between them. This is a circuit I designed several decades ago to do just what you want. ![]()
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