Loud hum when connecting Receiver


I have a NAC 152XS set up with the unit gain feature. I have connected an older Yamaha receiver and it has been going just fine.

I recent got my CD3 back from being serviced (needed a new dac) and after setting it up I now get a loud hum when the AV input is selected. No hum with any of the other inputs are selected.

If I disconnect the CD3 from the nac that hum goes. It also goes if I disconnect the pre out from the Yamaha from the nac.

I discovered that the Yamaha does not even have an earth, the plug does not even have the pin for it, but it does have a phono stage earth. I was wondering if earthing it might make a difference here?

I have a flatcap and a nap150x too.

Any other thoughts?

From your description above, it sounds like re-introducing the CD3 into the system has made a ground loop. The CD3 has a signal ground to mains Earth connection so it sounds like you also have another one elsewhere in your setup via the Yamaha. Although the Yamaha receiver has no mains earth connection itself, it’s probably connected to other items that could provide this connection - what else is connected to this ?

If it is a ground loop then the simplest fix is to add a ground loop isolator between the Yamaha receiver and 152

Hi James, oh yes that is interesting.

Other things connected to the Yamaha are an Apple TV (not earthed) and a Panasonic Plasma TV bth via HDMI, I’m guessing the earth loop could be via the TV aerial as the TV itself does not have an earth either.

I’ll try disconnecting that. I can’t remember the last time I watch terrestrial TV, lol.


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