NAP 250-2 transformer

Hi, my NAP250 started produced hum(50Hz all the time) from transformer.
What is the best or not expensive way to replace transformer for quiet one?
Thanks for help.

Is this a mechanical buzz from the amplifier itself, or hum through the speakers? If it’s mechanical buzz, and it’s just started, it is very likely due to something you’ve changed in your house. Turn off every other electrical item and see if the buzz stops. Then you can turn things on one at a time until you identify the culprit. If it’s hum through the speakers it will very likely be an earth loop.

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As HH has said this is likely to be due to interference from the mains supply - the transformer will be affected by this and this doesn’t suggest a fault in the amplifier itself.

Hi boys, this is typical mechanical noise- hum from transformer, 50Hz stable noise all day!
I have to replace transformer or throw amp through the window :smile.
This is normal Naim…

If this hum has suddenly started, it is likely that it is caused by another device in your home, or another location nearby, that is having a detrimental effect on your mains power quality. As HH says above, you should first try to identify this, as you may be able to solve the problem at source.
There is, of course, a possibility that your amp has developed a fault, so you could have it checked by a Naim dealer. How old is the amp?

Calm down, and find a plug-in isolating transformer (sometimes called a balanced transformer) to sit between the wall socket and the 250. If possible a non conditioning one. That will remove DC offset without most of the detrimental effects of a power conditioner.

There are plenty on the market (Equitech have a sterling reputation), many geared towards audio but it just needs to be rated for the current of your mains. Ideally fully 1:1 on whatever your circuit amperage is in your country. Most are standard audio gear width and support several outputs in case you have multiple buzzing boxes.

I know full well that Naim do not recommend power conditioners or similar devices, but that recommendation should be taken in the spirit of which it was given: normal functioning mains. No one is expecting you to rewire your house to resolve the issue.

Of course if the DC offset is really bad, you could actually find that it just moves the hum from the 250 to the balanced transformer. But if that happens, even swapping the 250 would likely not help.

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Franta2, I am sorry to read of your problem. One of the best things about Naim beyond its products is its dealers. Using social media may not solve your problem. What does your dealer say?

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I had a washing machine that interfered with mine, But it
was only during the wash cycle not the spin cycle.

Franta, if the NAP250 has just started to do this then it probably indicates that something on the mains has begun to cause it, so it’s worth trying to figure out what that might be through a process of elimination. Of course, depending on where you live, it may also be down to something from your neighbour, which is a bit trickier. If that’s the case you could try a DC blocker.

However, changing the transformer is not just extremely expensive but also no guarantee that it would be any better, maybe even a little worse because whatever is causing the buzz on your transformer would still be there.

This will almost certainly be down to DC offset on your mains. That is the upper and lower cycle of the mains is offset due to more load being applied to one part of the cycycke compared to the other.

Large toroidal transformers are very efficient and have low internal resistance and therefore good load stability, which is why Naim use them, but the flip side is they can saturate easily if there is a DC mains offset… even of a tiny amount. A saturated transformer will make its laminates buzz at the point of saturation

If this DC off set occurs before it enters your house there is not much you can do… other perhaps using a large isolation transformer.

If this occurs in your house, say from washing machine heater, laser printer, hair dryer etc… then you might find setting up a different spur minimises it.

Failing that have it checked by dealer/Naim as you might have an overly noisy transformer. You can also try a DC blocker, some are available commercially, ensure try before you buy to check no undue impact to the audio performance and make sure it is sized for the current load of your amplifier.

But there is confusion by some… buzzing is not caused by any interference on the mains… it’s caused by the condition of the symmetry of your mains caused by non symmetrical loading.

I take from that that even though it’s technically due to asymmetry on the mains, that asymmetry can be caused by the hairdryer or whatever. So in layman’s language it’s still due to interference on the mains caused by said hairdryer. Maybe I’m still confused!

Positive news: my SN1 hums less since we have a new fridge 3 weeks ago. Still hums, but at least 30% less.

In layman’s you can say it’s interference to the mains supply… not interference on the mains, which usually refers to additive unwanted signals interfering to the wanted mains voltage signal.
From a layman’s and technical perspective they are different.

I suppose the generic term encompassing both options in layman’s language is ‘there is an issue with the mains supply such that it causes your NAP250.2 transformer to loudly buzz’

Surely it should be “Mains Electric”? I don’t think the Mains Gas will affect SQ - although on here you never know…:wink:

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Using the water mains can give the music a flowing fluid quality although some people might find this shocking! :rofl:

Only when the meter has fully run in though…:joy:

Thanks Simon! ‘To’ rather than ‘on’. I’ll try to remember…

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Guinless - you are absolutely correct of course - I was assuming mains electricity - as opposed to mains gas, or even water … :grinning:

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Mention elsewhere, our daughters hair straighteners are by for the worse culprit.

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yep - some of these devices use cheap heat adjusters with diodes - so half heat is one half of the mains curve - full heat is both… so half heat can cause DC offsets

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