Mains hum from amplifier

I have an annoying mains hum coming from the body of the amplifiers. It is present regardless of volume and regardless of input sources, connected or off. Not sure it it is the amp or pre-amp body but is is very annoying at low volumes. I have a NAC112 and NAP150 with original Naim cables. There is no unwanted humming coming through the speakers. Any ideas to solve this?

It’s mechanical hum from the mains transformer in the 150. Here’s a good thread to get you started…

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Is the hum continuous or only at certain times of the day? I had a SuperCap at one time that the transformer would hum very loudly when the input voltage from the mains supply would drop below 110V when the service was supposed to be 120V. This could be a similar issue for you. If possible check the voltage on your line when the equipment is humming to see if the voltage is below what it should be in your area. Do any other electrical appliances hum or say, in the case of an electric kettle, take longer to boil water, when the cases are humming?

Steps to eliminate the hum are well outlined in the previous posting by james_n.

Not just overvoltage can cause the hum (thou the most likely issue) but also too low a voltage (as I have experienced).

There are many DC offset removers out there. One popular one right now is the Audiolab DC Block. If you can stretch the funds a bit more, Puritan makes great conditioners with DC offset built in. I know ppl on this forum do not like using them, but you have an issue that needs to be corrected and I can tell you that the Puritan units do not affect dynamics in any way. I run the PSM 136 as I too have transformer hum due to DC on the AC line.

Recently Added a Audiolab DC blocker to my humming Rega Aethos amp and it’s completely silent now.

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Many thanks for the good suggestions for dc blockers. Considering that I am not getting any hum through the speaker and the noise is from the inside of the amplifier, do you believe the dc blocker will do the trick for my symptoms?


As mentioned by @james_n I think you need to first address the points he raised In his attached link. All we can say is a DC blocker may, or may not be the answer.

Yes I have read James’ article, I do not have any Devices like solar panels causing unusual interference, I cannot install a separate ring main, nor can I adjust my mains voltage, and I do not have another room to place the amp separately. So although all scientific solutions none are really practical.
Maybe my amp is broken but will take a punt on the Audiolab ds blocker in the interim.
Otherwise I’m going to ditch Naim equipment.


If you can obtain one on “sale or return” basis, then you have nothing to loose. Good luck

I’d not spend a penny on a DC blocker without first ruling out over voltage. Can you measure your mains output and see how close it is to what you expect?

The three causes of transformer hum are:

  • DC offset. Requires a DC blocker or isolating transformer to correct.
  • Over voltage. Requires a variac tranaformer to correct.
  • Defective loose winding on the core. Requires a replacement power supply.

Over voltage is actually the most common. Always get a diagnosis before taking medicine as they say.

Yes, mine did. Order thru amazon, send it back with no hassle if not satisfied.

I have a similar problem. Hum through the speakers at 100 mhz or below. Usually at 50-55 dB. Not obviously dependent on the preamp (changing the power level does not alter the noise), but if I turn off the preamp, all goes quiet (I suppose because there is nothing to amp). The mute button for the record line on the 552 needs to be on or else the hum increases.

All this is on a dedicated power circuit, so there should not be interference from house appliances etc. In the past this was seasonal and time responsive (mid-day and late night were best). A couple of years ago unmuting the record outputs actually improved the sound. I thought this was DC related, but an Isotek Mosaic Genesis power conditioner has had no effect – I guess if the problem is with the amp, the power conditioner doesn’t rebuild the voltage for a high input device.

Where to next? My thought is to try another amp to see if the hum persists. If so, try another preamp. It’s driving me crazy.

It sounds as though the 552 is picking up a hum from something close by. Is it possible to temporarily move it to test? (I know its a pain)

Thanks, bruss.

I’ve disconnected all electrics in the room apart from the Naim system. No change.

I’m now starting to think there is something wrong with the electronics in the 552 that was intermittent but now constant. That might be hard to locate.

A description of your system and what is connected to the 552 would be useful. How old is the 552 and has it and its PSU been serviced ?

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Yes, as James asks above, what do you have connected up in the system system? It sounds like it could be either something picking up hum from something else nearby or maybe an earth loop somewhere. Perhaps strip back to a single Naim source and then see how that is and then start adding anything else.

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Still got the hum if I disconnect all sources. The 552 is old but was upgraded to DR perhaps 6 years ago. I would imagine that it was recapped at the same time. I turned off all devices in the room for the day — no effect on the hum. Certainly sounds like an earth loop, but the preamp and amp (along with everything else) are on the same dedicated spur.

OK, what about the proximity of cables to one another (especially mains power cables and signal cables where running parallel should be avoided) or proximity of power supplies to sensitive head unit?

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Brain and brawn stacks, so burndies are more or less horizontal, power lines vertical. It’s all tight, but wiggling lines doesn’t seem to do anything.

Puzzling. I think this may need to looked at by a professional.

Yes, it sounds like it needs to be looked over with some fresh and experienced eyes.