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

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.

luisma31, sorry, I got confused with initial post about TT problems.  You keep saying "unplugged from pre side" but you probably mean that shield was disconnected, otherwise what are you listening to if nothing is connected to pre?  I suspect that cable might create ground loop.  Lifting shield on pre side might still produce buzz if shield touches connector shell.  Anyway, there is very little chance that anybody can help you if Ralph couldn't.  I use XLR cable grounded at both ends between DAC and power amp and it is dead quiet.  

@kijanki I'm fine, buzz and hum are gone, the point I was making is that shield although indeed blocks RFI / EMI could create other problems which balanced lines really don't need.

There is little, if any, advantage to XLR on short runs.