ND555 ground switch - again

My question is simple and it seems people say opposite things.

If I have two sources in my system:

  1. ND555
  2. Superline+Supercap

Should the ND555 ground switch set to Floating or Default?

It looks like the supercap does “send” grounding to the preamp (-ve?) via DIN 4-5 so it should be set to Floating, but I’m not sure.
I don’t get hum either way, I just don’t want to get a compromised SQ.


It should be set to default (chassis) as the ND555 is providing the single mains earth to signal ground connection. The Superline doesn’t provide this so you’re fine leaving the ND555 at default.

If you had a Naim CD player in the system too, then this would also provide a mains earth to signal ground connection and so you’d set the ND555 ground switch to float to prevent a ground loop and possible hum issues.

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Thanks James, but I don’t understand another thing.
You said the superline doesn’t provide earth, so if someone has a system with one source: superline, this system is not ground connected?
If someone has a system with superline and a CD player for instance, the superline on that system sounds different to the one-source system above because the whole system is grounded?

Naim digital sources have always connected signal ground to mains earth. It’s the Naim preferred way of doing things. There doesn’t have to be a mains earth to signal ground connection (all the mains powered items have mains earth connected to chassis for safety) and it would appear that with a single vinyl source (if the TT doesn’t provide this connection) and a Superline, this would be the case.

In Martin Colloms’ review of the ND555 he mentions that he set it to floating and when he realized his superline is not connected he then moved the switch to Default, so it looks Martin set the ND555 to floating when the superline is connected. Seems rather strange to me that he’s wrong and also writes about that.

“ At this point we noticed that the signal grounding switch on the back panel of the 555 was set to the left (when viewed from the front) noting at this point that my system didn’t have the otherwise grounded Naim Phono Superline amplifier connected. As such the correct setting for the ND555 was for a ‘to the right’ position. ”

Look here:

Yes I’ve seen that review - Maybe MC’s turntable is providing this connection ?

Why not try both settings to find out which sounds best? I’ve always found that it’s easy to hear when the right setting is selected as the image tends to open up (widen out), high frequencies have more sparkle and the bass sounds a little deeper. Neither setting can harm anything.


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