What phono preamps are balanced

How does a balanced phono input work? Don't you need sum and difference from the tonearm/cartridge with some sort of differential driver interface for each channel at each end of the cable?

It is my limited understanding (correct me, someone if I'm wrong) that the signal from any MC cartridge (along with microphones) is already fully balanced. It's also my understanding that most tonearm wires (in the tonearm itself-not external phono cables connecting the arm to a phono pre) have the ground floated, so if you want to connect a MC cartridge/tonearm to a balanced phono input it is simply a matter of having the phono cable properly terminated with the appropriate balanced/XLR connectors. It was that way for me anyway, recently, when I bought an Aqvox 2CI. I'm running fully balanced from turntable right through to my integrated amp through the Aqvox, and in my opinion, it's performance in the balanced mode is superb, and quite a bit better than running it single ended. The Aqvox literature expresses some surprise that balanced configuration is not used more frequently in phono preamps; I think the combination of balanced input/output along with the current mode really provides outstanding performance at a reasonable price.

Which phono preamps have balanced in?

Hdm, you got it spot on. In fact almost all cartridges are balanced sources, not just MC. I think the old Decca that had 3 leads was the only one that was not balanced- even ceramic cartridges can be run balanced, and most of the BSRs, Garrards , Duals and other inexpensive older turntables had 5 connections (the 5th being ground) as to connect the 5th wire to the same point as the negative output of the cartridge creates a ground loop.

What dop you wan to spend?And you can get XLR terminated phono cables run into balanced Phono (if it has in's many like like the PS GCPH are out only so balanced cicutry isn't thier just ability to run long distance to amp.The thing that you don't want to do is go (according to Holt or whoever wrote the Stereophile Guide To Hi-End) is go from unbalanced to banced to un to balanced.Once say from your pre to amp is ok just you are ebtter off with RCA's only instead of converting it to many times.But with some company's like BAT (BALANCED Audio Technology) and some others everything is true balanced all the way though.When I had a Nelson Pass designed Adcom all XLR and balanced rig (CD/Pre/AMP) I thought about converting my phono cable and looking for a balanced circut phono but that limits you,costs and I sold Adcom rig before it became issue.If I had speakers far off I'd keep everything un-balanced and just get true balanced pre and amp or intgerated or just go unbalnced all the way.yes theoretically it's better and on some equipemnt l;ike krell it's all balanced but it's not necessary given how ling most IC to amp connections are.Phone company and others use because for extremely l;ong runs you must.Go for better gear and don't obsesse on balanced if it's not the sound you want or causes you to deny kids college.
Chazz