are some phono stages more resistant to hum?

Lloydc:
I am wrestling with a similar condition after replacing my ss pre with a tube unit. Are you sure that your problem is a 'hum' and not a 'buzz'? Mine is definitely a buzz (heard only in the tweeter), and my current thinking is that it relates to external circuit noise which is induced into the system and picked up by the tubes and sent through the rest of the system. I must admit that I am early in my process of diagnosis, but nearby lighting dimmers cause similar a similar buzz when activated. Anybody else have comments on that line of thinking?

Rtilden, Check to see whether any of your ICs, particularly the one from tonearm to preamp, are running parallel to or anywhere near an AC cord or a PS umbilical. I had an identical buzz that drove me a bit nuts until I noticed that my phono cable was running near to BOTH the AC cord from the turntable AND the PS umbilical from the phono stage PS. Re-routing it made a huge difference. Sometimes we lose track of what's going on with all the spaghetti hanging down at the rear of our system shelves.

Thanks, Lewm. I will check out that possibility in my next step.

Rtilden, just FWIW, tubes are no more prone to picking up noise from lighting than transistors. That is a power supply problem, not a tube/transistor problem.

Lewm:

The cartrigde may be connected in "balanced mode", but when you connect the shield to the minus input, you convert it to single ended. You have to reference the input voltage to somewhere, and for phono inputs its the shield (-). If you could get a cartridge with a true balance output (like a center tapped transformer), with the split (or center tap) connected to the analog ground/shield, then you can have a true balanced input. Some microphones are wired this way. But phono cartriges are not.

For example, I have a PS Audio GCPH that uses a "differential" input pre-amp. The input RCAs are ground referenced via a 100 ohm resistor to analog chassis ground. The two phono inputs (V+) and (V-) are twisted pair from the tonearm/cart with a separate isolated shield. Shield is connected to chassis ground. Is this balanced? NO!!! Because the potential between the shield/chassis ground and the (V-) input is essentially zero, because no current flows in that 100 ohm reference resistor. In a true balanced system, V- and V+ would be the same, only opposite in polarity. In this phono setup, V- is 0.
So while this system may give you some CMR, it will not be anywhere nearly effective as a true balanced system.