When switches make a difference it can’t be the bits (i.e., a 0 coming through erroneously as a 1, or vice versa) or the Internet wouldn’t work. So it has to be electrical noise introduced into the audio device(s) and that can in theory make its way through either data wires or shielding. An optical data link eliminates electrical noise howsoever it could have got through: only the bits are transmitted!
Of course there’s then the issue of noise introduced by the fibre media converter (FMC) itself at the audio device end of the optical link, plus anything picked up by the ethernet patch cable between the FMC and the audio device. My approach is to have my FMC very close to my streamer’s RJ45 socket¹ and to have a very short (6 inch) patch cable between them. The FMC has an Uptone Audio LPS DC power supply. This is he best I can think of to get the bits into my Directstream Junior whilst keeping out electrical noise as best I can.
Perhaps PS Audio will one day make a streamer that incorporates an FMC within it (ideally with a choice of optical Ethernet sockets on the back). Then we could optically feed the bits and only the bits of music data files into the streamer.
Perhaps this will be a feature of the new, very high end PS Audio DAC.
BTW I’m grateful to James for educating me in the matter of transformer coupling of Ethernet. There’s always something new to learn.
Peter
¹ Actually the network socket that goes to the Bridge II built in to my Directstream Junior