Noisy ethernet cables

@erik_squires , sorry that is wrong.

Many shielded ethernet cables ARE shielded on both ends, and that shield connects to case ground on both ends. Audio circuits often have capacitive couping to case ground if not a direct connection from the DC ground to case. Surprisingly many linear supplies use a grounded plug, as do most things with metal cases and integrated AC supplies.

POE, if compliant to the specification is also galvanically isolated.

If you don't know how your shielded cable is built, you are better off in most cases not using a shielded cable because to your point, the data portion of the transmission is galvanically isolated.

Many shielded ethernet cables ARE shielded on both ends, and that shield connects to case ground on both ends

Oh, so wrong. ALL shielded ethernet cables have shields at both ends.

The cable shield is end to end, with the RJ 45 connectors on both sides having a shield connection. That doesn’t mean the equipment maker is forced to use a shielded socket or to ground it. No shield connection on the socket, no ground connection there.

and that shield connects to case ground on both ends.

Only if the equipment designer makes it a choice to do so.

The shield on an Ethernet connection is not carried by the signal wires inside the jack, but on an outer foil like connector. It’s hard to see, but here:

As a streamer maker, you can either ignore that shield, or keep that shield separated from the rest of the system. You are not obligated to connect this shield at all, or to the equipment case.

Don’t confuse the shield on an Ethernet cable with the case and safety ground connection that is made to an AC outlet. They are two different things. There is no safety requirement that a signal cable be case grounded, and in fact lifting or isolating signal grounds whenever possible is good practice.

@erik_squires ,

Except the Ethernet connector, metal shell, where the connector plugs into, is usually connected to the metal enclosure to improve the EMI. Even before shielded Ethernet cables were common, most connector shells were metal to form a seal with the metal enclosure for EMI purposes. I am well aware of Ethernet implementation (hence why I know POE is galvanically isolated if done to the specification).

Signal grounds very commonly have capacitive connections to case grounds where they exist for noise reasons.

In the average home environment, unless you are co-running your Ethernet in long run in parallel with a seriously noisy AC like in industrial/commercial, there really is no need for shielded. There simply are not the noise sources to make a difference. As you noted, it is already galvanically isolated.

Except the Ethernet connector, metal shell, where the connector plugs into, is usually connected to the metal enclosure to improve the EMI.

That is entirely up to the equipment manufacturer.  I have a hard time believing a high end streamer maker would both ground for the sake of better EMI rejection AND leave themselves open to ground loops.  I certainly wouldn't design a mixed digital/analog device like that.

@erik_squires , I would have more faith in a lower cost, higher volume product from a lesser vendor, that has the proper equipment for testing, and probably more experience, that a boutique vendor who in many cases is winging it.

I am not saying that is exclusively the case, but measurements by Stereophile/ASR have shown enough "high end" equipment to have questionable performance, even on the basics, that I have some confidence that is correct. I would expect the larger high end vendors to be designing "properly", at least I would hope that is the case. Fortunately, this is an easy one to test. Measure the resistance/capacitance from the Ethernet jack -shell to the case.