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

roberttdid, Of course.  I posted only to state that shield, IMHO, plays important role in defense against electrical noise (when connected properly).  I also strongly agree with you that shorting open ends of the shield with wire creates large loop that picks-up electrical noise.  Noise currents in such loop produce magnetic field that will "transform" noise into signal wire.    

I was not saying that shorting the shield with a loop will pick up noise kijanki. It will act as a shorted turn and will direct an external magnetic field away from inside conductors to a degree. However, it will also act as a shorted turn to the current carried by the internal conductor, which could seriously impact it's performance.

roberttdid, Sorry I read it wrong and I understand argument about shorted turn, but transformer works both directions. Any closed loop will pick-up ambient electrical noise.  Induced electric charge will flow in this loop thru/along the shield producing magnetic field around signal wire, that will induce electric noise current in it.

In the experiment presented, and the "concept" for shielding presented, their is an external magnetic field noise source. As the shorted loop is passive, and it's current is only due to the external magnetic noise field, the field it would create cannot be larger than the field already created by the magnetic noise source. It cannot effect the other wire more than the noise field would have already. It would direct the field away from the wire.

Perhaps it works, but I would think that it can do more harm than good in comparison to plain grounded shield.  High frequency noise currents induced in the signal wire flows on the surface (skin effect) - shield to ground.  I'm not sure replacing it with shorted turn will be better, but who knows.  I'm just skeptical, but if it works it works.