curious as to why more TT/tonearms would not have balance outputs and
equipment inputs for these in various equipment be the xlr balanced
inputs
The idea of the cartridge being a balanced source was introduced to home audio in 1989 by Atma-Sphere (the MP-1 was the first balanced line preamp for home use). Before that it just wasn't around. To this day, I still occasionally run into tone arm manufacturers that don't realize that the cartridge (and thus the tone arm) is a balanced source. If we're talking about inexpensive gear that uses OPamps, its almost the same cost to run balanced as it is single-ended. But the industry relies heavily on tradition- meaning that it will try to do the same thing the same way decades on after its been shown that there is a better way. In that regard audio is like a host of other industries- and maybe that's just a human nature thing.
I am instead asking you how RCA outputs from a typical modern table can be used in balanced form as you clearly stated.
This is sort of a cringe-worthy thing that you sometimes run across. The idea is that the RCA connection is not tied to ground- usually they 'float' and if tied to ground, are done so by a wire. But you could use the ground side as the minus output of the cartridge, and so- you could then have the input circuit be a differential amplifier and *if* the ground wire is tied to chassis it would work. Sort of- you do have this little problem that the '+' output of the cartridge is likely going to be shielded by the '-' output of the cartridge (by the single-ended tone arm cable), and this is where the cringe-worthy issue comes up- this leaves the system highly vulnerable to hum. Now if the cable was built balanced, and the shield was actually the ground wire, then the only area where the system is hum susceptible is the RCA connector itself.
I think this idea got going so that the preamp would be instantly compatible with any turntable interconnect, but in reality it isn't. On top of that, as soon as the minus output is acting as a shield for the plus output, the construction of the cable is going to have an effect on the sound, so you just lost an important aspect of balanced operation, which is cable artifact immunity. IOW it really should be done with an XLR.
