Which RCA cables do I use?

[Brian617]

I have an Eclipse avn6620 that tech support identifies as having single ended RCA outputs. My amps are an older RF P8004 and Orion xtr15001. Both amps seem to have balanced inputs from the info I can find on the net. I watched the following video:

http://www.youtube.com/watch?v=QOagVDZLQnA

that states with balanced amp inputs and se head unit outputs I should still go with twisted instead of coax RCA cables. I don't understand the thinking. If the negative rca wire is grounded, even if only at the head unit, it should still ground the noise, or at least greatly reduce it. Differential inputs cancel noise under the assumption that the same type and amplitude noise exists on both + and - signal wires. The only way the - signal wire grounded at the head unit would carry ambient introduced noise to the amp with the output grounded would be if there was a resistance in the length of the wire high enough to develop the voltage of the noise. Even then the noise on that lead should be greatly reduced compared to the floating + wire. So shouldn't I go with coax over twisted if either the amp input or head output is single ended?

[Wicks]

Its mostly obvious that using a twisted pair cable in a total SE system would be the worst case scenario.

Noise could easily get induced into the positive conductor with nothing to filter it out.

The best case scenario would be a twisted pair cable in a differential system as Tony showed in the video.

Sure you could use a coax cable with an amplifier that has differential inputs and the HU grounding will probably help a bit with the noise, but you wouldn't be letting the amplifier's differential inputs do their job to their full capacity.

Its best if a coax cable is grounded at both ends for general noise immunity.

Like Tony mentioned, the center conductor may get a small amount of noise induced on it in which the amp's differential inputs now can't filter it out properly.

By using a twisted pair cable, sure the "negative" wire will be held around zero volts by the HU, but noise will still be induced commonly on both wires.

Therefore the differential inputs can properly filter out the noise. As far was the actual signal goes, 0 (neg wire) gets subtracted from the actual signal and you still get the signal (as opposed to 2x the signal in a differential output).

As you could imagine, this is all theoretical and could depend on on a lot of variables.

The difference in noise might be negligible?

Sounds like a good opportunity to put this to a test and see how they actually compare.

Another very important thing to keep in mind as well:

If you use a different cabling system, it doesn't mean you instantly get noise.

There has to be noise already present in your system for it to get induced into other areas.

It is nice though to understand the differences in the cables though and where each one should be used for noise immunity (in the event that noise is present).

[Brian617]

I believe that as soon as an RCA plug from a SE head unit is plugged into a differential amp input, the amp input behaves like a SE input (one side grounded). If the shield is grounded at the head unit, it can't carry a signal at the same amplitude as the other wire, so the cancelation effect of the amp's differential input won't cancel any noise. I was asking a question, but I'm pretty sure I need coax if either side is single ended.