Naim earthing update please clarify

I’ve just reassembled my Naim setup - NAC252 Supercap, CDX/XPS & serviced NAP250 after some decorating and now have what appears to be a very low frequency earth loop that I had mistaken for quite some time prior to dismantling the system as the odd lorry grinding its way up the hill at the end of the garden.

My speakers are quite efficient Yamaha NS1000M’s and go really quite low and now reveal a definite very low frequency earth loop or maybe some weird electromagnetic pickup in the myriad cables connecting the system together. I disconnected all input cables apart from the AV input and the hum is still present. It disappears completely when I select AV or press mute so what does that say earth loop or Electromagnetic pickup ?

Now I know that once upon a time all Naim kit was designed such that the CD player provided a single point connection of signal and chassis mains earth. I checked my CDX and indeed the earth link is present via a small resistor. With the XPS and Supercap in the system I’m not clear which acts as the common signal earth.

My kit is all fed from a Grahams 6 headed hydra fed from a single wall socket. Is this not sufficient to ground the system properly and elliminate earth loops. ?

To try and get rid of my earth loop i made up a cable connecting just the earth pin on an MK mains plug to the earth shied on an RCA phono plug. When I use this cable to connect one of the aux1 phono inputs to a wall socket my low frequency hum is drastically reduced to a very acceptable level. So what gives with the current Naim earth system.
I noticed that there is a signal ground connection on the back of the NAC252 yet no mention in the manual as to what it is for, Any ideas?

I should add that I am not cloth eared and more often than not and these days listen to the system with TV or Squeezebox digital stream sources via a TAG AV32Rdp dac/processor via the NAC 252 AV line level input which has an absolutely silent background.
Any suggestions greatly appreciated

An earth loop will always be at 50Hz. The signal earth in your system is via the CD player. The connection on the 252 is for a turntable. Maybe if the cables are a mess, it’s worth sorting them out.

Eddie - you’re right about the Naim CD player providing the signal ground to mains earth (effectively chassis / safety ground) connection.

In your case the CDX is connecting signal ground to mains earth via the XPS. This should happen at one place in the system.

If you just connect the CDX/XPS to the 252/SC/250 (don’t connect the AV kit or anything else to the 252 ) do you still get the hum ?

Hi, @eddie.pugh.
I had a similar issue. I found I could eliminate the hum by either disconnecting my CD5X from the NAC112, or disconnecting the AV amp from the NAC. Further tests found disconnecting my house from CATV service also eliminated the hum.

In the end, I replaced the interconnect cables between the AV pre and NAC with ground-loop-isolator cables at $17 per pair, I think Solved.

I see Amazon has some RCA extensions for $7-10 that look similar to mine — you add them to your existing interconnects.


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Decorating ? on the fsh site, you have just fitted different boards in your 250 and maybe its down to them ?

Tried disconnecting my TAG AV32r and earthloop did not reduce one bit. The TAG is double insulated and has no earth connection on the mains lead

Tried connecting signal earth on the back of the 252 to MK plug mains earth and now earth loop gone.

Well spotted. I also have an unadulterated NAP250 Olive and substituting this does not change the earth loop annoyance one bit


O right, its just that you state, you have been using a modified 250 for 10 years and just changed the boards to a new spec modified boards. I just thought this could have been the issue

I have had a modified NAP250 serving front L & R channels a NAP 140 biamping a KEF centre speaker and a second NAP 250 driving L&R rears for years

When I noticed the earth loop just recently I tried the unmodified rear 250 on front duties with no noticeable difference on the earth hum Incidentally the rear 250 is fed directly from the AV32r with no hum issues albeit the speakers are a bit smaller

I’m trying to gather the energy to swap out the 250 altogether for the AV32r as a pre but its just too many boxes and cables to swap at the moment . I have tried playing some CDs via the DVD32r
AV32rdp combo into the 252 AV input and the result when compared with the CDX XPS combo can not be reported on this forum Mind you my CDX is over 20 yrs old

Ok - it’s not an earth loop if not there with only the CD player connected. If it wasn’t there before then it’s worth checking through the whole system to make sure all the connections are good. If the hum goes when you connect the Mains earth to the 252 earth post (which is signal ground) then I suspect the signal ground to mains earth connection isn’t being made at the CDX/XPS where it should be. What resistance value did you measure here between signal ground on the CDX DIN socket and the earth pin on the XPS mains plug ?


Sadly it is there with only the CDX connected. I checked to see if the little connection cable between signal earth and chassis was ther in the CDX box and it was all present and correct. I even polished it up but no improvement. That would suggest the XPS / Burndy might be the problem I will have to google which pin in the Burndy is the earth but I hope you will forgive me if I close this down for now as I am sitting here with the system turned on with nothing playing and it is absolute silence. My boxes are shoehorned into some wall shelves and getting at the back to connect or disconnect anything let alone a Burndy is a serious operation and requires serious time

It being Sunday morning there are virtually no lorries or Park and Ride buses grinding their way up the hill at the bottom of the garden and I am not hearing any from the Yamahas either so for now problem solved and I’m back to enjoying the peace or should I say the music


The NAC is always the signal ground star reference, specifically it’s PSU. So if 252 it will be the SuperCap.
The Naim CD player typically is the link to mains Earth. However if there is no Naim CDP, most Naim sources have a float/ground switch so they can act as an Earth grounding point. Switch to ground/chassis for this to happen.
There should be such one and only one connection in a system, so all other sources if they have this capability should be set to float.
If you have a CDP then all other sources should be set to float, otherwise there may be an earth loop.
Non Naim sources should be examined to see how they operate with Naim.

BTW don’t assume there are no potential ground loops with double insulated in all circumstances … the earth loop can still exist in some scenarios through capacitively coupling to mains earth… and may depend on wiring and other external factors and a slightly loose signal connection.

Now I’m confused I can understand the NAC252 being the star reference signal 0v but my understanding is that the route to common chassis / power ground is via the CDX and onward via the XPS to mains earth .

Ther is no float / ground switch on my 252 which admittedly is proably aout 15 yrs old
Is this a modification to the newer versions.

All I know is connecting the signal ground point on the 252 to mains earth solves the problem in my case


There have been no modifications to the 252 in this regard as far as I am aware. It acts as the ground star point for inputs and it uses the CDP or other input as discussed to act as the path to mains earth. So for what ever reason it sounds like your CDP is not acting as a mains earth path, if you need to manually set that path.
The PSU is the common power Ov point the NAC and NAP. Hence why the signal burndy passes to PSU and then the power amp.
BTW I will check my Naim CDP but I don’t believe there is any small resistor in its earth path… which I can’t see how that would provide an accurate mains ground reference … ie it will start to rise above ground with any earth current present which sounds like what might be happening here.
At least you have working,

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Ok that’s good. Were the earthing tags present and correct next to where the Burndy sockets is too ?

It’s certainly worth checking the Burndy, XPS and XPS mains cable for continuity all the way through to the XPS mains plug earth pin as it does look like something maybe amiss if all the earth tags are correct in the CDX. With this sorted you can get rid of your additional earth wire. I’ll be interested in what you find,



Without dismantling anything now that it is almost all back in the rack I can easily measure the resistance from CDX signal lead Preh connector outer casing to Graham’s Hydra mains plug earth pin
It’s a fairly tortuous route
cdx Preh – casing — Burndy — XPS — Hydra — Hydra lump connector — Mains plug earth pin
With my trusty Fluke 189 which is pretty accurate I get 0.7 ohms only
I don’t think there’s much wrong continuity wise. What do you think


That’s sounds good. I’ll be interested in what you get from the CDX signal ground on the DIN socket to the outer casing.


More worrying I measured the resistance of the outer shield from CDX end to NAC52 end all while both ends connected and got a worrying 27 ohms
I disconnected the interconnect and measuring resistance across the plug outer casings gives infinite so the outer casings are not connected via the interconnect so the resistance I measured must be somehow internal to the system probably in the 252 Does that make any sense
I also checked the resistance between the earth pin on the Hydra and the earth pin on the cable I made to eliminate the hum also 27 ohms

Hi Eddie - what you should have is :-

CDX DIN socket signal ground pin to XPS mains plug earth pin - close to zero ohms. This is assuming CDX connected to XPS via the Burndy cable. This is where your signal ground to main earth connects.

With the CDX / XPS now connected to the 252 via a DIN cable, you should be able to measure between the ground post (signal ground) on the 252 and the XPS mains plug earth pin you should get a reading very similar to what you got measuring between CDX DIN signal ground pin and XPS mains plug earth pin.

Edit - just re-reading your post when you got 0.7ohms - was this between the outer case of the DIN socket (rather than the signal ground pin of the DIN socket) and the XPS mains plug earth (or Hydra mains plug earth) ?

Yes that was measuring outer case of DIN to Hydra earth It’s not possible for me to measure the signal earth pin but I think it will be the same reading