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Interconnects, speaker wire, power cords. Ask the Cable Guys.

RE: unshielded digital interconnector

It is unlikely you will find a true 75 Ohm cable that doesn't have the outer jacket.

The main difference between that and an analog interconnect is the 75 Ohms are defined by the ratio of diameter of the central wire, and the diameter of the outer meta jacket ("shield") with adjustment made for the type of dielectric. And since both the source and the destination of the SPDIF signal are both 75 Ohms, this is really important to avoid jitter.

Analog interconnect have a low source impedance (typ ~20 Ohms or so) and high terminating impedance (say, 1000 Ohms) so you have a lot of flexibility in the cable as a "tone control" and a shield in that case may be changing the way power couples slightly causing a tonal difference.

All you get with diverging form 75 Ohms in a SPDIF system is increasing jitter.

Having said that - the RCA connector isn't a 75 Ohm termination as it was based upon the analog interconnect scheme where it doesn't matter very much. You could have it replaced on your equipment by a 75 Ohm BNC and use 75 Ohm BNC cable - will make a big improvement provided you have true 75 Ohm SPDIF cable terminated in 75 Ohm BNC's.

There are "true 75 Ohm" RCA's out there, but they don't make a huge difference unless the mating connector is also "true 75 Ohm RCA" ... but worth a try.

I'd recommend getting a 75 Ohm BNC terminated 75 Ohm cable, and use a BNC to RCA adapter (the adapter makes a big difference - so make sure that that is 75 Ohms, too).

"We have met the enemy and he is us" - Pogo

Edits: 03/19/12 03/19/12 03/19/12

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