I had to double check these cables were indeed being used for Ethernet as they can also be used for balanced audio circuits; and was a bit surprised this stupidity has carried through to the digital age.
A digital connection either works or it doesn’t.
You should of course use as good copper cable as you can afford (not copper covered aluminium) and shielded cables can have some advantages but if noise is getting in via the DAC (digital to analogue converter) it is most likely there is either a flaw in its design where functional earth (signal ground) and protective earth (earth ground) are connected using a “noisy” parth – they must be at one point if there is any exposed metal on the equipment (it stops the users being electrocuted in case of a fault).
In some cases it is likely there is a wider earth fault in the listening rooms electric wiring such as insufficient protective earth or a diverted neutral on a TN-C-S wiring system (where protective earth and neutral are combined at various points of the network but separated when they enter a building) – most newer electric supplies in Europe and the USA are wired in this fashion. Its often called PME (Protective Multiple Earthing) in the UK.
Earth faults are potentially dangerous and should be checked out by a competent electrical engineer although it can be the case with TN-C-S that there is enough nuisance current leaking in the system to upset audio and computer equipment but not to be a safety hazard and trip the RCD (GFCI) circuit breaker.
I’ve had to research this for a new building at work where we already have a TN-C-S supply; I’m also setting up some sound equipment for a wide area loudspeaker system and have noticed the functional earth for the sound equipment is much noisier than my house where I have a TN-S wiring setup to the house the earth is from the outer metal shield of the electricity cable.
The solution to this (which isn’t immediately apparent) is often to add more earth connections from the main electricity earth (deriving them from anywhere else is dangerous). £300 will buy plenty enough 4mm^2 copper cable to do this and (if the person installing the hifi isn’t confident about their electrical engineering skills) should pay for a registered electrician to do so…
