Transformer Hum (chrome bumper kit)

Hi everyone,

I know this is a fairly age old topic and I have already searched the previous threads and already know that a bit of hum is normal from most Naim Power Amplifiers (especially older kit) but how much is too much? It’s not through the speakers but from the amps themselves. Reason I ask is my CB 135’s have been doing since I got them (about 5 years ago) and I also own an older bolt down CB 250 which hums a little but not as much as the 135’s. Is this a cause for concern or not? I don’t think it is, as like I say they have done it since day dot and they sound fantastic but I was just curious as to why it is more audible from the 135’s than the 150 despite the fact they are ‘younger’.

Every transformer is unique in its way and in the way it will respond to artefacts and pollution on the mains. Similarly every mains install is also unique in the particular type and mix of mains pollution it will be carrying. Once not all units of the same type will respond in the same way. Similarly, a unit that may have a humming or buzzing transformer in one site, may be quite silent in another site, and vice versa.

On older kit it’s worthwhile just checking that the bolt securing the transformer to the chassis has not loosened. Similarly, check that any padding between transformer and chassis has not degraded.

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Key piece of insight here.
If there is padding, or anything else to mechanically decouple the Tx from the chassis, then this is a good place to start. Especially with kit that is 15y or more old.
Would be interested to hear if changing this is covered during a service.

@NeilS would know…

Thanks gents. I haven’t looked inside for a while but will do and report back.

Hi Guys,

All of the toroidal transformers will have a foam pad beneath them. Replacement would not be carried out as part of a routine service unless specifically requested.


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if push comes to shove, use this :


Or the alternative is to move the power amp to another room.

You might get an improvement if a dedicated mains spur were installed. It makes things better allround.
When I had 135s they were on the floor under a record cabinet. Not ideal in todays thinking-long before Fraim and other supports were thought of. My listening seat position was and still is with all my kit directly behind me.
They used to hum but not any great extent and not enough to be a distraction when listening. Mostly classical music with a lot of silences. However when not playing any music the hum would just appear and often reduce in volume after a few minutes.
From memory my 500 hummed a bit before being DRd. Now totally silent.
What the 135s did do in the summer due to their location was trigger the built in fans even when not playing.

I have some strange issue regarding hum on my Supernait 3. It definitly sounds like a mechanical hum from the tranformator, but it gets transported to the left speaker channel only. It does not get noticeably amplified when i turn up the volume knob, neither is it very loud.

Some further information for troubleshooting:

  • i live in Germany
  • the SN3 is only connected to the power outlet and to the speakers. I have a powerline cable and the regular EU cable. The powerline seems to generate slightly less hum.
  • the cables are not touching each other. Moving the cables around does not affect the intensity of the hum.

Now this is not a real bothersome issue but the hum beeing on a such low frequency i do hear it across the whole room when it is quiet, which i would happily live without.

Any information that could help would be appreciated.


If you hear it through the speakers then it’s something else (not transformer hum), and possibly an earth loop or earthing issue somewhere.

Does it don’t his regardless of source? What you disconnect all sources?

I had the feeling that the ground loop would be higher pitched but i may be wrong.

Connecting a source does not have any impact on the issue. I disconnected everything in the room to eliminate other devices from interfering.

But how is it possible that only one channel is affected?

It may indicate an issue within the amp. Best confer with your dealer. Maybe try their demo unit.

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