Originally Posted by ereed
Yes, XLR is just balanced and you use one cable vs 2 rca unbalanced cables. Sound is the same. But for very long runs such as 30+ feet xlr would be best if you had xlr connection option. If not, good quality rca is just fine. Nothing to stress over. Usually very high end equipment will have both xlr and rca options to give you more flexibility with connections, but the sound is pretty much par.
With only one XLR (balanced) cable you will only get one channel. In your example above: if the one XLR cable you mentioned is used in a stereo system for only one channel and the 2 RCA cables are used one for the left and one for the right channel, the sound will certainly be different. Do you actually believe the two options will sound the same?
XLR cables have many advantages:
They help to prevent hum in a system. In an RCA cable one wire also carries the ground which often causes hum. RCA cables of any length can cause hum due to ground loops. This forum and others sees lots of posts that mention hum problems. Pro's use balanced cables to avoid dealing with this problem. .
XLR cables are twisted-pair cables with a shield. This helps to reduce induced noise; both the twisting and the shield. This video gives a demonstration of how noise is induced. It also shows the advantages of star quad cable construction for balanced cables. Even without the star quad construction, balanced cables are to be preferred.
An XLR cable has a male connector on one end and a female on the other. This allows the cables to be connected in series when longer lengths or exact lengths are required.
Of often XLR cables have latching connectors which prevents accidental disconnects that are common with RCA cable.
Monoprice sells acceptable balanced cables. Companies such as Have, Inc. and Markertek will make up any lengths of XLR cable desired using whatever wire (manufacturer, color, construction) and connector (Neutrik XX connectors are nice and only cost a few dollars) are desired. The cables they produce are very high quality and the prices are less than from Blue Jeans. Blue Jeans XLR cables are well made, but their prices for XLR cables are much higher than for similar quality cables, that are also assembled in the U.S., from other sources.
This Monoprice cable is excellent for connecting RCA sources to XLR inputs. The cable has a male RCA on one end to connected to the source, and a male XLR on one end to connect to the input.
Connecting an XLR source to an RCA input isn't a good idea. One of the single lines from the XLR side (usually pin 3, the (-) pin) will likely be connected to ground which will over stress the electronics in the XLR output with little or nothing gained.
This piece, written by Bill Whitlock of Jensen Transformers, shows the circuitry for the XLR-RCA connection noted above. See figure 2.1. The piece also has a lot of good information on balanced connections. Mr. Whitlock is an expert in this field. You can often find his presentations on YouTube.