There is a big difference between XLR and RCA interconnections if the system components are truely of a balanced design. First, the third wire, in the XLR is a case ground which ties all the components chasis ground togethers, hence no hum due to stay voltage potentials, just like the ground line from turntable. Second, the neutal line is isolated from chasis ground in balanced designs so it is not subject to any voltage influences via the chasis where as in an RCA set-up, neutral and chasis ground are one in the same. Third, the polarities of the plus and neutral are reversed in the left versus right channels so that your signals are out of phase initially. This reduces the output load on your power transformer by almost half thus providing a much higher gain signal. About a 6db difference in most cases. The out of phase signal also help cancel any line noise. The signal is reinverted at the other end and thus in phase at your speakers. The reason that this circuit topology is not more common is that it is expensive to implement correctly. Every switch in the preamp grows by a magnitude of four, as well as added isolation of signals and provisions for RCA connections still need to be supplied in order to satisfy market compatibility. In almost all cases balanced versus SE RCA is superior. Problem is that if you mix RCA and balanced at any point in the system you lose much of its benefits but still may gain some reductions in noise levels. Regards.
