I bought an MCRU Ultimate in line DC blocker to deal with a similar issue on a 250.2 and it worked for me
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All food disappears at an unbelievable speed here 
Cheese seems to be the patch for teenagers arriving home after a day on school.
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DC Blocker is what everyone with hum needs. Supra DC Blocker I use myself with great result.
Hi, before you spend lots, I have tried all the obvious DC blockers, from the cheap to the eye watering and all killed the music to a greater or lesser extent. In the end, I just live with the hum when it happens. We are rural (farmers) and SP Energy Networks are forever turning something off/on/switching over. You get used to it!
. . . same here
Accepting we are all different I have to say that I don’t mind the occasional hum from our Naim. The intensity varies from hour to hour from nil to clearly audible although seldom intrusive. Spending serious money on addressing it would never occur to me 
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Isol-8 is returnable if not impressed.
G
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Ditto anything from MCRU within 30 days - nothing to lose in giving these things a try
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All back in place now. If nothing else it gave me a chance to re arrange the rats nest, sorry, carry out some cable dressing.
+1 I have the same, and it stopped humming in our old house. Before buying, I had a demo unit for one week to make sure it would help…
A humming transformer is a not fully performing transformer. Removing the DC will make it perform as intended. In my system a DC Blocker showed this very well.
According to the Naim manual, transformer hum has no effect on SQ. This is stated explicitly
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My Lotus top speed or handling on track isn’t affected by a scratch in the paintwork, but I’ll still have it removed.
Hearing it upsets my perception of sq even when the music is not on. A quiet room isn’t quiet if there’s a buzz or hum.
I will try a dc blocker.
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Maybe some naim magic hidden somewhere. But there’s a lot on transformer saturation effects due to DC components. I trust my ears on this.
For example
- Most transformers do not tolerate DC - even a very small amount will cause premature saturation and distortion at low frequencies
If you have a multi meter, check your voltage, and ensure its within tolerance of 230V +10% -6%. If its above 253, log it with your provider, as its their responsibility. If its within tolerance, but still on the high side, then look at Balanced Power Supplies.
Some Naim users have used Balanced Power Supplies from Airlink Transformers (just search the name on this forum). They can resolve DC offset and over voltage issues. I’ve not tried one (yet) but people have had some success. Remember though the BPS may also hum, so you may be just moving the volume. You can return them if they dont work. Also if you have a separate HIFI circuit, you can fit them by the CU.
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Just pointing out that the Naim manual always has this:
Transformer hum is not transmitted through the speakers and has no effect on the performance of the system; however, a separate mains circuit may reduce it. Such a circuit (ideally with a 30 or 45 Amp rating) will also generally improve system performance. (…)
They may be right or wrong, I like to think they know what they are doing
Certainly a good idea, and a possible cheaper upgrade that buying more HiFi units, although it may not solve over voltage or dc offset issues
Update on this, and without any spending!
We had a power cut overnight which isn’t unusual here. Power came back on and the hum was loud enough to annoy the dogs. Second power cut a few hours later and the hum is almost gone, only heard it getting close and listening for it.
Thanks to those that suggested it was likely power supply. It was obviously an unbalanced supply somewhere locally that the transformer was picking up. I may even offer an early warning service to EDF
Meanwhile I may conduct an experiment sometime by swapping my own 3 phases around. ie. Instead of 1,2,3 incoming connecting to a,b.c outgoing I’ll reconnect to b,c,a, and note if there’s a change.
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I turn mine off from time to time. It may take a little while for the system to come back sounding refreshed.
Mostly the loud hum from the 500 lasts only a short time. Before the 550/552 (18 months since purchased preloved and serviced) the 555DR was the offender. Just goes to show it’s more complicated than one transformer but a system balance issue. The MusicWorks Ultra G3 with sparkly base made a significant difference to SQ and hum.
Phil
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