Fiber Optic isolation causing listening fatigue

Maybe I missed it, but are you using a LPS on the second FMC?

I’ve found that the cheaper FMCs can do more harm than good, especially if using their generic power switching wall-wart (especially on the last FMC prior to the streamer).

The “detail” and listener fatigue could be jitter. 

The quality of FMC matters. The opticalModule Deluxe with LPS can re-clock the signal better, which should reduce the jitter, and subsequently avoid that listener fatigue (which I also experienced when experimenting with generic FMCs). AudiophileStyle has a pretty good 10-year thread about FMCs

For context I currently run oModule Deluxe and oRendu.

I cannot stand Ethernet streaming and only do fibre. Yesterday at show I was helping out at I had 2 Sonore OpticalRendu’s connected to a Meitner MA3i and the Allnic D-15000 Signature OTL.OCL. Two of the best DACs around. The Meitner also has direct Ethernet streaming, the OpticalRendu’s went into USB. 

I used a Unifi network switch that I got for $150 to convert my Ethernet to fibre. Now this same switch goes for $400 to $600 after people like me hyped it up a few years ago for audio. In reality my $45 dollar network switch with the same Ethernet and fibre conversion is as good.

I never liked the separate convertors because they were so unreliable. I like the network switches with built-in fibre outputs. I have 3, they cost $45, $75 and $150. They all sound the same.

I compared the Meithner MA3i with Ethernet versus fibre into USB and USB was so much better. I was actually hoping to show the difference at the Denver show that I wrote up about in another thread, but we got lost in other more fun stuff.

Now why was the OP’s irritating. That is tough to say, and we all hear differently. The level of differences you will hear with Ethernet vs fibre will depend a lot on the quality of your Ethernet chain and also the implementation of the Ethernet stream on the DAC. With fibre what is in the chain before the fibre and hopefully next into the DAC does not really matter.

Maybe I missed it, but are you using a LPS on the second FMC? 

Yes, I did replace the switching power supply, but I replaced it with a very inexpensive "Linear regulated wall adapter" that was recommended in this article . 

I imagine the issues I'm having are due to using cheaper (non-reclocking) converters, as you pointed out. It's been an interesting experiement. I'll need to decide where to go next. 

yyzsantabarbara, what Denver show? I live 3 hours west of Denver. 

Fiber is dead now....did the TP WR920 as a client. Now I have removed my Sonore Optical Deluxe V2 and the sound is fantastic.

https://www.whatsbestforum.com/threads/review-the-best-yet-most-affordable-network-switch-tplink-wr902ac.41708/