At what distance are balanced XLR cables needed?

No answer is possible without knowing (1) the output current abilities of your preamp and (2) how much EMI noise there is.

Kal

There are no guarantees. I have heard of people resorting to balanced cables for much shorter lengths because their situations involve lots of EMI. (Do you live near a radio/TV transmitter?) Recording/mastering studios have miles of cables all influencing each other.

So, my cables are no less antennas than anyone else's but, as far as I can tell, they are not picking up any signals inside my apartment. Literally, YMMV.

Kal

I run 10meter interconnects, balanced and unbalanced, in Manhattan and have no noise problems with either. FWIW.

Kal

Mariv26: Anything over 3 meters, but I would still keep the interconnects as short as possible

I don't think you can make such a general recommendation. It really depends on the EMI environment. OTOH, if you believe that there are no potential disadvantages, only potential advantages, to balanced interconnects, you might want to use them regardless of length.

Kal

AFAIK, there are no such standards for unbalanced audio connections.

Kal