CT phono power supply

[modder]

I have a center-tap +v15 and -v15 power supply driving a phono preamp. I am trying to sort out earthing.

1. What happens to a CT power supply if the CT is connected to true earth ?
Does it blow up ?!
2. If the CT it is not connected to true earth is this what is called a "floating earth" ?

I've done the following so far - most beneficial:
1. reduce ripple to the voltage regs
2. use Rubycon ZA caps after the regs
3. use Eichmann interconnects - this has been the most striking improvement. Total removal of a deep roar when preamp (not phono) is turned up to full volume.

[modder]

To answer my question ........
I noticed the CT is connected to true earth through 2 zener diodes, back-to-back, presumably to keep out RF (and a small ceramic cap).