Since plugging in my new (2nd hand XPS DR) - i get a low hum .
It’s not so bad that i can hear it when music is playing , even at low volumes , and the XPS has certainly made an improvement to over sound howwever would like to fix it.
This never happened when I had my 272 plugged in.
Both were plugged into an MCRU extension hub.
Not knowing too much about this topic i have also found there is a “polarity error” where the devices are connected which i suspect I will have to get an electrician to look into - but can this hum be fixed - what are potential causes?
XPSDR seems more prone to hum for some reason. I had one that hummed a lot and a DC blocker did not help. Updated to a 555PSDR which is dead silent. Everything else in my setup is the same.
Don’t think it relates to size of transformer. It’s a wild spread between Naim boxes on what hums and not with no relation to transformer size. I’d say it’s related to design and tolerances.
I had an XPS non-DR together with SCDR, 555DR, and 300PS. My mains is ok and most of the time all are silent (except with the ear right next to them). But occasionally, usually late in the evening, they hum (not badly but audible from 2 meters) for an hour or two. And when they do, it is either all of them, one of them (or at least more than the others), or any combination of them, and the XPS not being more frequent. Beats me but possibly any particular kind of mains pollution may affect some units more.
My understanding is that Naim themselves have tried very hard, over many years, to get to the bottom of the hum or buzz problem - without success. The only ‘fix’ - which is applied - is to test all transformers on receipt - see Post below from @Richard.Dane.
Yeah, might be better to keep it to the Starting Guide thread. I wanted to say it should be in the manual but it is. (I do believe though that Naim dealers should point it out to new owners, nobody should leave the shop without knowing)
I have a HiCapDR and XPSDR.
The HiCap used to hum, the level of hum would change at different times of day, and when The Home Secretary was using her hair dryer.
The XPSDR was always quiet though.
I purchased a DC blocker and the HiCap is now silent, unless I put my ear to the case.
One of life’s mysteries
but possibly any particular kind of mains pollution may affect some units more.
hear we go again another post regarding humming toroidal transformers 
but it is. (I do believe though that Naim dealers should point it out to new owners, nobody should leave the shop without knowing)
