Hum in a phono cartridge?

A phono cartridge ground loop could come into existence if the cartridge body is not electrically isolated from the headshell / tonearm assembly, _AND_ one of the negative polarity right or left cartridge terminals is bonded to the cartridge body. 

erik_squires

If you mean AC, then no.

Otherwise, are you calling ground the preamp shield conductor and neutral the catridge

No, we're not talking about AC here. We're talking about phono cartridges.

When you unbalance the phono cartridge, you connect ground to neutral.

If you mean AC, then no.

Otherwise, are you calling ground the preamp shield conductor and neutral the catridge (-) ??

When you unbalance the phono cartridge, you connect ground to neutral. The difference in electrical potential is between whatever minute voltage is on the ground and 0V, which is where the neutral should be, no?

@cleeds

OK ... help me out a little here. But even if it gets grounded at the phono input, that is a single ground reference. Where's' the competing ground that the phono catridge attaches to?

I'm not trying to be difficult here... I'm just genuinely not seeing the whole picture.

Of course, YES, phono cartridges are notoriously susceptible to ground loops. My own mental model just doesn't explain it yet.

erik_squires

So, my statement was "Balanced and isolated"
Where is the ground contact happening at the cartridge side?

The phono cartridge is only "balanced and isolated" if it's fed into a balanced phono preamp. But very few phono preamps are balanced. (Of those that are, not all meet the AES balanced spec, an issue Ralph frequently points out here.) 

Once a phono cartridge is connected to an unbalanced input, the cartridge is no longer "balanced and isolated."

If the phono cartridge - which as you note in inherently balanced - is connected to a truly balanced phono input, there should be no ground loop or hum problem. If there is, it suggests an issue with the cartridge itself or the pickup arm wiring that results in unbalancing the phono circuit.

So, my statement was "Balanced and isolated"
Where is the ground contact happening at the cartridge side?

I'm honestly curious, as I've not touched a turntable in decades.

A ground loop is the result of multiple paths to ground that are of different electrical potential. That can happen whether the circuits are balanced, or not. If the phono cartridge ground is of different potential than the phono preamp ground, you’ll have a ground loop.