Why do most phono preamps lack XLR input even thought cartridges are naturally balanced?

@kijanki

luisma31, If it is not grounded at either end, then capacitance to what? To electrically floating object?

honestly I don't know, I'm not an EE, but the effect of the hum is similar to what high capacitance cables will do, and since capacitors are isolated (just like this cable) I think HIGH CAPACITANCE is right on target

luisma31, It might be true, but I've never heard of hum caused by high capacitance of the cable.  I've heard of output oscillations and frequency roll-offs, but not hum.

Just be aware in my case, with balanced interconnects, the hum was present ONLY when unplugging the connector from one side as I described, when both ends were plugged there was no hum. Replacing the interconnects with no shield cables no hum no matter what.

luisma31, Unplugging connector?  You probably mean - disconnecting shield?  If you had no hum with shield connected at both ends, then why to change it?  I would guess that disconnecting shield at the Phono side only left TT ungrounded with floating antena (shield), while unplugging on TT side or both sides should have less of an effect.  How is your TT grounded? 

Please read my initial post again, I have described my digital rig not TT connected (yet)

I described hum with a shielded balanced cable when unplugged from the pre side, when an unshielded cable was used there was no hum, my understanding is the shield adds capacitance and IMO is not needed and undesirable.