NAP250DR slight hum


My NAP250DR has a slight hum. Is this normal? I mean the unit itself, no hum from the speakers.

Yes - quite normal.


Yes, it’s the transformer and is normal. Depends on mains quality and may change during the day.

Amplifier reference manual:

If you search for “transformer hum” on the forum, you will find a hundred threads, the best summary is here:

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Thx :+1:

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Have a power with Filter. I can try without it changing

HMS Energia MKII DSC Filternetzleiste


HMS Energia MK II

You can try, but depending on the cause of the hum in your particular mains power (see the linked thread above) it may or may not remove the hum. In addition, Naim is not fond of filter strips and they may (or may not) degrade SQ - depends, you have to try. The hum “has no effect on the performance of the system” (see manual screenshot above), so if it is not excessive you may prefer the hum over any degraded SQ (in case this happens).

Other people tried the HMS Energia, so if you search the forum for it you will find their experiences (but yours may not be the same, depending on various factors)


I don’t agree with Naim on this. When a toroid transformer hums for any reason other than a defective winding, it tends to imply that the core is saturated and when that happens, toroids (generally benign in terms of EMI flux radiation) generate a lot of EMI. Far more than a EI transformer. It basically negates the main reason for using toroids in the first place.

It’s important to isolate the cause and treat it. Over voltage or DC offset being the two likely culprits.

I know you don’t :slight_smile: but I suppose there are differences between degrees and that Naim engineers aren’t complete idiots either. In any case, that’s why I said that the OP has to try, and that different causes need different treatments

True. All linear transformers hum a bit. The degree to which is acceptable and problematic isn’t really defined. One person’s opinion of “buzzing like crazy” might be another’s idea of totally fine.

To what degree the transformer is really misbehaving is best determed with an EMI meter on gauss mode, though you need a good control reading of a non problematic power supply of similar type.

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Agree. If in doubt, measuring is surely best, but a bit of common sense is also helpful (for some reason often going out of the window if people come near Naim equipment. Not saying in this case, it was a sensible question, but it happens quite regularly).

I am sure that if it hums very loudly you are absolutely correct about the saturation and impact. But on the other extreme, if it is only audible if listening for it and the ear close the unit, it is surely fine - I’ve never seen a Naim amp (or any other amp with a toroidal) not do that, in any mains, so if that was a real problem the whole design would not be fit for purpose.

The OP said “slight” hum, so I figured it’s more of the latter. Though as you say, opinions and expressions differ, but if anything people tend to err on the side of exaggeration, so “slight” is most likely just that.

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