A Starting Guide to Naim Hum/Buzz

This subject seems to come up very often here, so having the issue myself, and after a lot of reading, I thought it might be useful to have a simplified starting place to visit for these issues, bringing as many of the different causes mentioned in this Forum together. There are many more detailed items on this forum that you can then lookup specific areas.

Here we are referring to Hum/Buzz from the Naim PSU/Amp units themselves, and NOT Hum through the speaker (which could be more related to a grounding or cable issue).

Will resolving the transformer Hum/Buzz in the unit help SQ? Well possibly, or possibly not, or it can also drop. More likely the SQ will be improved by removing what external influences were causing the Hum/Buzz.

Important: This post is written from a UK prospective, but the basic ideas will be global.

DISCLAIMER: Where appropriate ensure you use a qualified person to carry out any checks that require their expertise, and you abide by any local Codes and Regulations.

1) Naim PSU/Amps will Hum/Buzz

It is very common that Naim PSU/Amps will Hum/Buzz to a certain degree, and this is quite normal, so one option is to ignore it. It becomes a problem if it is so loud that it becomes annoying, in which case investigate the areas below.

2) DC Offset
This is where a DC current is over-layed on the AC current. Likely candidates for causing these are other electrical heating appliances such as electric fires, cookers, swimming pools, fridges, hairdryers, curling tongs, electric blankets, etc

The problem can be worse at certain times of the day, and possibly quietest late at night.


Unfortunately I haven’t seen any good methods to measure this value, other than getting in an electronics expert with an oscilloscope. So it’s a matter of testing by elimination.

Solar Panels: If you have these, temporarily turn them off, to help (or not) eliminate the Solar Inverter.

Is the issue on any particular circuit: First shutdown any Computer Desktops, and power off other devices in the house.

Assuming you still have the issue, power off all circuits (including lighting circuits, immersion, etc) except the one you have your HiFi plugged into. If it resolves, then turn those circuits on one at a time to find the offending circuit.

To eliminate your HiFi circuit, use an extension lead from a different Main circuit (e.g. upstairs) and plug in your HiFi. Then power off all circuits except the extension lead one.

If you locate an offending circuit, then physically unplug the other appliances on that circuit to see if any appliance is causing the issue. If that doesn’t identify any offending electrical appliances, consider calling an electrician to test the circuit.

There is also a possibility of the issue being from another building, such as a local factory. Recheck at night when factories may be closed

How To Fix:

If the above testing doesn’t find any specific appliance causing the issue, then there are some other options.

The best option which is recommended by Naim, is to have a Dedicate Circuit for your HiFi - See details later

Other options that have been known to resolve Hum issues are Mains Blocks/Main Conditioner/Balanced Power Supply that are designed to filter out DC Offset. Also see:

3) Over Voltage

For the UK, the supply to your house should be 230V +10% -6%. That means a maximum high of 253V.


If you are suitably qualified/competent, use a multimeter to check your house Voltage at several times throughout the day, or when the hum/buzz is at its worse. Typically the Voltage will be higher when other houses are least using power, and lower when the load is higher.

If you do have Solar Panels, then check your Solar App as it is likely to already measure the AC Voltage.

If you have Solar power, then disconnect it temporarily to help eliminate the Solar panel Inverter as being the cause.

How To Fix:

Your Electricity Supplier must supply electricity within the tolerance, as outside these value may cause damage to the appliances. So if you are in the UK getting Voltages >=253V, then log a call with them. In my case, they came out within 3 hours, and adjusted the tapping on the local substation, and brought the average from 255V to 245V, and resulted in a quieter HiCap. Full details at:

If you are getting high values but within tolerance, then again first try your electricity supplier. Be aware that they may not adjust it any further, as they have to ensure that all houses on that circuit are within tolerance, so if you are at the substation end, then you will have a higher voltage than the furthest property, so it’s a balancing act. What they may do is put an extra meter next to your meter that records your mains supply details over a week, and will then make a decision at the end of that. In fact that’s what they did on my case as I want to get a lower average than 255V to reduce Hum/Buzz further.

If all else fails, then you can consider:
. Active regenerating power conditioner (creates a perfect AC Sine wave)
. Advanced Balanced Power Supply solution (some of these have different input to output settings, e.g. 250->230 or 240->230)

4) Problem actually with the Naim unit

If having eliminated most of the above items, you could also investigate whether there is an actual issue with your PSU/Amp.

The following is best check by someone qualified in electronics, but there are a couple of areas they might check:

Possible transformer seating issue. E.g. if device has been in transit. Consider just loosening the screws, and re-tighten them

Possible transformer foam pad seating issue. Has the foam pad disintegrated over time. See discussion

5) Physically move the PSU/Amp

Most people wont be able to do this, but it has been mentioned as a possible workaround if the physics of your room layout allows it. You will then run the cables through the wall. You could also enclose the whole HiFi Rack inside a purposed built cupboard, ensuring isolation between the two, and air can flow freely.

Other alternative might be to move the PSU/Amp to a different place in your rack, furthest away from your ears.


Dedicated Circuit
“Transformer hum is not transmitted through the speakers and has no effect on the performance of the system; however, a separate dedicated mains radial circuit may reduce it. Such a circuit (in UK, ideally with a 30 or 45 Amp rating) will also generally improve system performance.” This was mentioned at the thread below and says it comes from Naim:

This has been mentioned many times on this forum for Hum/Buzz resolution and particularly SQ improvement, although it wont fix DC Offset or Over Voltage issues coming from the Mains Supply.

The solution here is to add a dedicated HiFi Consumer Unit and creating a separate radial circuit. In the UK you would ideally be using 10mm2 core cable (and possibly shielded), specifically with a good earth of 10mm2 also, but does assume the end socket is designed to take such a thick cable. Remember good earthing is needed for dissipation of static charges, EMI and RFI signals and interference. This solution can give a remarkable SQ boost per cost.

The following thread includes a great circuit diagram:

Also see

Also search the forum for “radial circuit”, plus check with your local Naim dealer for advice more fitting for your country.

New sockets/refit sockets:

In fact, there is no mention of this resolving any Hum/Buzz issues, but I think the following discussion which is around replacing old sockets and/or refitting all sockets on the ring, may help here, and if it doesn’t, it is a cheap thing to try, and may improve SQ.

Also try reinserting all plugs in the house a couple of times to ensure good connections (as you would do for Naim interconnects).

Mains Regenerators

Probably the “Bees knees”, as these take any old quality mains, and spit out a nice clean Sine Wave AC current. Should stop Mains Hum, and improve SQ. Problem is they are expensive at ~£10k.

Mains Blocks/Balanced Power Supplies (BPS)

A bit of a catch all section. These are known to resolve/improve dirty mains Issues, such as DC Offset and Over Voltage. They have also be known to improve SQ BUT have also been known to drop SQ, so Naim do not recommend these and therefore don’t jump in feet first without consideration.

You ideally don’t want too much mains filtering, as this can negatively effect SQ. Best to look at a solution that solves your particular problem.

TRY BEFORE YOU BUY if possible. Your local dealer may be able to help you.

BPS: Although these have great success in resolving/improving Hum/Buzz issues, it was noted in a couple of case that the BPS devices itself hummed, and therefore the hum was just moved to a different device, albeit quieter.

If you have a dedicated HiFi radial circuit, then you might consider placing a BPS next to the dedicated Consumer Unit, rather than next to your HiFi.

It’s not my place to recommend any particular solution here, but the Forum regularly mentions devices from Airlink Transformers, Isotek, MusicWorks and ISOL-8 PowerLine Axis. Just search on these names in the Forum and you ensure you read all the threads to make your own mind up.

Also have a look at:

Please “Like” this article if any of the above has helped you, or please add other fixes below?


Outstanding post. Very thorough and informative. Should be a ‘sticky’. :grin: BRAVO!


This post and the topics that it refers to may also be helpful:
Stopping transformer hum with a BPS

There is a long thread on the old forum all about it but I can’t find the old forum anymore.

Best regards, BF

1 Like

Really very useful

An OLED LG TV caused my Supercap to hum. The brighter the picture, the louder the noise. Really annoying. After months of trying literally everything, 3 changes solved the issue: (i) ASF5120MP balanced power supply for the lounge ring mains from Airlink Transformers (great customer service by the way) (ii) Change the Supercap to a Supercap 2 (iii) Plug the TV into a socket from outside the lounge ring mains. No hum at all now. :grinning:


Well following a purchase of a HiCap DR, to replace my Humming HiCap Olive I can confirm that the HiCap DR does not hum at all. So in my case for the HiCap, the underlying issue was probably the unit itself.

However I must add that some people have reported that their DR items do indeed Hum, so this is not a fix for all, and their solution is likely to be one of the other items described in this Topic

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If transformer hum is louder in a HiCap vs. NAP 140 of the same era, with both connected to the same mains, would that be a good indicator that the HiCap needs some type of service and the issue is not specific to the actual mains line condition, or is it too much to assume?

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Quite possibly a reason, although I didn’t think a service touches the transformer. However in my case both were serviced in July. I suspect a possible transportation issue, but will never know now

Thanks for this post super informative and helpful for these hum sufferers like me…

I have 250dr which was humming constantly very loud was sent back to naim for a service last year and all has been working perfectly up until just before Christmas. I’ve started to hear an intermittent hum despite having a DC blocker in place.

I’m now getting a substantial amount of DC offset as it hums like crazy when no DC blocker is in place but can reduce the hum significantly with an ISOL-8 axis in place.

Ive tried turning off all circuits in the house to try and isolate the offending device, but to no avail.

There have been a few changes both internally where we had a new consumer unit fitted with an SPD device included and externally where the council have fitted new LED street lamps.

Our voltage is fluctuating but the hum does not seem to coincide with the high voltage spikes and have had the electric board out to check out voltage who said all was within tolerance at 244v.

I’m starting to question if it’s the new LED street lamps as could not get the hum to go away when all circuits are off besides the one where the amp is on and all devices except the amp disconnected.

It does seem to be worse in the evenings but it’s an intermittent hum that happens every so often rather than the consistent one I had before Naim replaced the faulty transformer.

Any ideas of what to look at next would be appreciated?


A couple of thoughts - can you temporarily try a mains extension lead from your upstairs circuit down to your hifi, then power off your downstairs circuit - just in case you missed any local appliance. Are there particular times that you could perhaps monitor over a couple of days, and see if they are random, or precise. Are there any industries near by, e.g. garages, small factories, etc. Anybody taken up a welding hobby (OK clutching at straws perhaps). Might also be worth considering a dedicated HiFi circuit, as that seems to have had lots of success.

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Thanks for your response, so after a day of tearing down the system and cutting the circuits one by one in the house, the noise is still present and comes in waves. I tested with a different circuit as suggested and appliances disconnected and still the same intermittent hum.

I have 2 dc blockers and so have split the Hicap and 250dr onto each of them and it does seem to have reduced the frequency of it, but it is still present at certain points. As stated it comes in waves and clearly audible 3m away and then will disappear to almost silence from the listening position. I’m noticing the noise throughout the day and also in the evening /night.

We live close to a town centre and so there are shops and a garage within a ¼ mile of our house, but the issue is something that has appeared around Christmas time so wondered initially if it’s all the light displays on the road, the new led street lamps or something to do with the change to the consumer unit which all happened just before Christmas.

The electric board just called back yesterday after my initially inquiry about the over voltage and have placed a meter for the next week to measure the incoming voltage. So will see how that goes.

Additionally not sure if it’s related we have an upstairs light that is on a dimmer switch and it seems a bit dicky. The light will flicker and sometimes the bulb won’t turn on but using the dimmer/light does not correspond with the hum.

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Not strictly correct, there is no DC as such. It’s when one side of the AC power sinusoidal wave does match the other side. It causes items like transformers to react to this imbalance much as it would if that imbalanced section was DC. It causes a momentary inrush current spike & partial coil/core saturation.
Halfwave rectification on the devises you list are the most frequent causes


If you have the issue during the day, then with outside LED lights will be off, so may not be implicated.
You can of course turn off your lighting circuits in the house for an hours say to eliminate them.
Glad to hear you are having a meter fitted. They can be very helpful with this. Now they won’t understand what DC offset means, so expect blank faces if you ask, but they will measure voltage and load. Remember voltage will be at its higher when there is least load.

Dont know how a new Consumer Unit should effect things, especially after all your circuit elimination. Also if they did a good job, they would have tested all the circuits - worth checking, particularly around earth testing.

What remains after all this, is that “Naim PS’s do hum” to varying levels, or “external influences” that you cannot influence. You could try and demo a HiCap DR in case that gives an advantage that is worth paying for.

I’ve just added an XPSDR to my 272 and when doing such the 300PS started humming bit more and the XPSDR also hum more than expected even though using a DC Blocker. It’s not a level which I hear at my listening position but I found this a bit strange.

Why do some boxes hum more than others. Is it a matter of out of spec or in need to tighten the transformer to the chassi or need of re-cap service something else?

Excellent Post.

Could be the basis of a FAQ perhaps - @RichardD - ??

Thanks again, I should state that the hicap is a hicap dr as well and that has a slight continual hum to it but not audible from listening position. It doesn’t suffer from the intermittent hum that seems to come in waves from the 250dr.

When you mention checking the earth testing what should I be asking specifically about that? I’m tempted to get the electrician back in at some point due to the dicky light on the dimmer switch. I want to make sure I know what I’m asking for when asking about earth testing as I’m not getting noise through the speakers so it isn’t a ground loop.

Earth continuity and resistance would be the main thing they would check

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Wanted to update on this thread based on my recent experiences.

I had the power company out and they put a meter on the incoming supply, but they have said there isn’t an issue as it is coming in under 253v so the incoming supply is fine.

I returned the isol-8 substation axis as this didn’t improve the issue.

I tried an APC line-r as had seen that mentioned elsewhere. It didn’t do anything for the hum and did squash the dynamics. So that went back.

I have since acquired a Power Inspired AG1500 and this has so far done the trick. The hicap-dr is now quieter, and the nap 250dr is for the most part much quieter, the slight hum I hear now is tolerable and only really there if I’m listening for it. Unlike previously where it would be obvious and present from anywhere in the room.

I still need to get the electrician out to test the earth continuity and resistance but haven’t been willing to do that in the current situation. Once things start to open up again I will follow up with this.

When a toroid hums due to DC offset, the core saturates and they suddenly emit more EMI than an EI transformer ever would. So it’s not just an annoying mechanical hum, it’s having a wider negative impact on anything in the same proximity.

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Thanks for the update @Andrewjs sounds like quite a journey, but glad you found something that works. When the electrician comes, may be worth getting a quote for a dedicated HiFi circuit, ideally using 10mm cable and a separate dedicated Consumer Unit. Cant guarantee this will work, but it has solved issues by many others on this forum, and has often resulted in improved SQ.