Instead of tolerating something so annoying, why not consider installing a balanced power supply on your dedicated radial? If you are in the UK, a call to Airlink Transformers should sort you out. Many owners of Naim systems have done the same.
Best regards, BF
This suggestion seems to indicate that the dealer doesn’t understand that a loudly buzxung transformer is a saturated transformer and the ill effects it has on the performance of other units goes beyond a humming noise and into EMI.
Just get your sparky to tell you what your mains abnormalities are and tackle just that problem.
Worth noting, before I joined the forum, I’d never heard of a humming Naim transformer. Certainly never had it on any of my 8 boxes that use toroids.
Hi @Bluesfan, I appreciate your comments and this may be what has to happen. I’m just wondering how far we have to go to get something to work. As not all power supplies hum on the same spur should this be considered a fault in those that do?
Hi @feeling_zen, this is the point really, not all power supplies experience this issue, we have three, one is very noisy.
I started a long thread all about our experience of hum, mains conditioners and the BPS. Search for “Suffering from those transformer hum blues?” And you should find your answers there.
Best, BF
No, likely not a fault. Every transformer will react slightly differently to whatever it is on the mains that is causing the hum; some will be quiet (but may be noisy with different artefacts on a different supply), some will hum. On a perfectly clean supply, with no DC or other artefacts, you would expect no hum from any toroidal transformer.
As for Naim, the transformers are tested by the maker (currently Nuvotem) and then again by Naim at the factory. Naim have a device that will replicate many different types of noise that may be found on a mains supply. Any transformer that exceeds a set limit is rejected. Of course, the test cannot replicate everything. Certain devices can dump DC locally onto the mains. Just try running a hairdryer or anything that uses a simple heated element in the house and see what happens. Also things like fridges can be notorious culprits if they’re not in good health.
Hi @Richard.Dane, thank you for stepping in. The culprit in this instance is a 2018 power supply for our NAC552 which is on a dedicated mains supply and probably not being affected by other household electrical items. I’m interested to find out what level of hum is deemed acceptable by Naim before “fault” is declared?
Having now double checked the serial number of the NAPS 552 DR power supply is 3883** looks like 2015 not 2018 and out of warranty 
Regrettably, just because the former is the case does not make the latter true. Having a 555PS, Supercap and NAP135s on a dedicated radial did not insulate them from the asymmetric mains that was being caused elsewhere for us. A DC blocker (I think @Mike-B may be knowledgeable here) or BPS may be helpful for you. If the 552PS is 6 years old and historically has not hummed badly, then this would point towards your mains supply as being the issue, rather than the 552PS.
Hope this helps, BF
Not being electrically minded I wonder if I shut off all household electrical items at the fuse box except the dedicated circuit for the Naim items if the hum would stop? Is there some period over which this should happen, ie desaturation of the toroidal transformers ?
I can’t recall the details (Naim would know, of course), but, IIRC, in recent years each transformer usually has a test number on a little sticker. It’s critical that no transformers that exceed limits accidentally make it into the kit. Instead they join the pile of ones that failed and await scrapping.
You could try that, certainly. However, it wouldn’t prevent the possibility of an issue being caused locally by a neighbour who’s supplied off the same transformer.
By all means try this to identify the source. If the source is in your home, then this should work and the transformer should stop humming instantly. If the source is coming from a neighbour (as in our case), then the transformer will continue to hum and you may have to revert to a DC blocker or BPS.
Best regards, BF
The household mains has been switched off and only the dedicated supply to the Naim items left on for 5 minutes and sadly as before there is still very noticeable hum audible from the door to our lounge never mind the listening position.
Suggest you have an external problem, then. Perhaps try contacting your Electricity supplier - ???
Saturation of transformers is something that only occurs when the power is on, power off & it’s gone.
It seems to me that you have naturally noisy transformer(s), the main indicator is if one is less or more noisy than another.
I had the same problem, compounded with some day/evening periods of DC offset. I designed a DC filter, that fixed the variations in tone & volume, but the transformers noise, now less but a steady noise remained.
That has recently been fixed by the power supply voltage being reduced from 248/250v down to 238/240v, this is being done nationally I believe. The hum is still there, but no longer audible in the room.
What is your voltage ? something to consider, but whatever I would suspect that a balanced power transformer is something that might be the answer.
Just to confirm the sound I am hearing phases in and out. Over a period of 15 seconds loud then a bit quieter for the same period and repeats. This is quite noticeable from a distance of 6 meters away and very distracting when just sitting in the room. I’m surprised that this is only happening on the one power supply considering they all go through the same testing procedures by two separate companies as mentioned above by @Richard.Dane before reaching the end user.
Great post!
Allthough i understand that sound quality is the prime reason why Naim designs their gear how they do it should be noted that our homes are much more prone to interferences nowadays. We have so much more things hooked up to our mains than 20 years ago. Any current hi-fi gear must take that into consideration.
Without having any technical knowledge i think we could assume that basically Naim has done nothing to tackle this problem.
I think it is time for Naim to see how they can design more silent units. There are other high end manufactures who are able to do so! And not at the detriment of sound quality.
Every transformer is an individual, which is why they have to be tested individually. But of course artefacts can all be slightly different too and effect each transformer differently.
What you describe is exactly what used to happen with one of my power supplies when an electric blanket was switched on upstairs.
@0.0 - Can you tell us which other Naim units you have, with transformers…?
I would suggest that units with larger transformers, might be more susceptible to humming…?
To show the other side of the coin, I have 2 HiCaps, and XPS (likely biggest transformer…? ) and a 140 - and none of them hum or buzz. I have heard buzzing in the distant past (in different house to my present one), but it has always been a short term thing - caused by something being used which generated noise on the mains (believe Hairdryers have been cited…?) .
Another trick is to see if the hum or buzz is less, very late at night - when less electrical items will be in use.