Why so few balanced phono inputs?

The thing you have to be careful about with this statement is the cable used. If a shield is involved and it is tied to pin 3 while pin 2 has the inside connection, its not going to work regardless of the impedance to ground.

Ralph, if you would note my earlier post on 5/08 I already mentioned that a coaxial cable would make for a very poor balanced line. I was trying to make the point that just because some piece of equipment has an XLR jack on its panel, that doesn't necessarily mean it's truly balanced. The definition of a balanced output or input is equal impedance from the two signal lines to ground. As an example, with some OP amp based balanced to single-ended conversion circuits the impedances do not exactly match and are off by a few ohms. Doesn't sound like much but it can seriously degrade the CMRR.

^^ got it John!

Thekong, you hit the nail on the head- dealers don't like to change cables- removing a tone arm cable from its connector under the 'table can be a bit of a pain. Anytime you see an XLR connection but the circuit is single-ended, its likely that the connector is just there for show, unless it is connected to an input transformer, in which case the connection might be entirely legit, as transformers can have excellent CMRR numbers.

Building a balanced phono stage itself is another matter. There are a lot of ways to do it, some overly complex (feeding into that notion that all balanced circuits have to have twice as many components, which is otherwise not true). You do have to have matched parts and I think the one that stymies many designers is how to do the EQ. That can be quite tricky if you don't know what you are doing!! But overall one of the nice benefits is lower noise per given stage of gain, which might mean that you don't have to have as much gain to make it work (we have two stages in our phono section for example)...

You do have to have matched parts and I think the one that stymies many designers is how to do the EQ. That can be quite tricky if you don't know what you are doing!!

Ralph, thanks for the reply! When I discussed the issue with some local DIYers, they did mention having difficulities in doing the EQ in balanced mode !

I run balanced all the way to the pre amp. Balanced cables from the tt-Trans Fi, to the phono pre-BAT, to the pre-Zesto. Balanced for the CD Player-NAD M5 to the Pre-Zesto.
Got hum in the phono chain. Dead quiet in the CD chain.
Bought a Buss bar and tried every kind of ground. Amps are Mac 60s across the room single ended. High efficiency ZU speakers.
Bought a BPT 3.5 with all sources into it. Still got hum.
Suggestions or just wish me luck?

If you have hum in the phono its because its not wired correctly or the interconnect is not built correctly.

We built the world's first balanced line phono preamps; whenever we ran into a hum problem it was because of either a wring error or a cable simply was not built correctly.

If you remove the tone arm interconnect from the phono input, does the hum go away?