Transformer Output Grounding

[little eddy]

For my DAC, I am going to try a transformer output option, and as per the attached Jenson application notes, will include a ground lift switch:

My question is why have a ground connection at all? Why not just let the output float, or more precisely be grounded by the input to my pre-amp in order to eliminate the risk of earth loops (which I guess is one of the benefits of a transformer output)?

[Mike H]

Because if you don't you could get a high Voltage charge develop for the ground on the secondary side due to electrostatic action from primary to secondary of the transformer (capacitive coupling, I think). I've actually 'blown up' stuff like this by plugging one thing into another while one of them is still plugged into live mains and there's no earth lead. ('Cause that's how it comes out the box, twin core flex only)

If it's earthed through the thing connected via the balanced output socket then switch could be opened, but only if.

Instead of the switch you might be able to use a resistor.

[little eddy]

OK so I can use a resistor with a shorting switch around it.

Looking around, I have seen earth lift resistors between 100R an 1M0 - any thoughts? I'm guessing the larger resistor, the lower the rating so maybe a 1M0 0.5W metal film would be appropriate.

I have also seen them with parallel caps of say 0.1 or 0.01uF. Again comments please.

[Mike H]

Not heard of that TBH (caps), I tend to use something like 100R 2W.

Could have the switch across it as well, sounds like a plan to me.