How to debug quiet (loudspeaker) hum on left channel?

Hi, I have an all Naim set up. NDX2 XPS NAC252 SC DR NAP300 DR Kanta.

This is all fairly new kit.

Recently I’ve noticed a slight hum out of the left loudspeaker. Sounds mains related. Right channel is quiet.

The symptoms are:
it’s only on one channel (left)
It’s source independent (changing source has no effect)
Equal when source playing or when source switched off
It’s volume independent, the music gets louder and softer but the hum remains constant (suggest not in the source at all)
It disappears completely when I engage the mute button on the NAC252.

That suggests it’s somewhere in the NAC252? Or a poor (high resistance) connection downstream between pre/supercap and power amp?

Normally I’d expect a ground loop or poor ground connection to be the source of the problem. But everything is DIN connected with SNAIC, so there’s only one ground path, and the problem is only one channel.

Normally I’d swap channels etc. to see if the fault moves or stays, but that’s not easy with DIN interconnects. e.g. the NAP300 interconnect cables are channel specific L R.

Any suggestions for further debug?

Measure cables with a multimeter?


Can you try other inputs or borrow other cables from your dealer?



I’m a step further.

Waggling the Green DIN to XLR interconnect cable for the left channel Supercap → NAP300 removed the hum.

Looks like it really is a high resistance contact that was the problem. Now to check if it’s the cable itself, whether it was poorly seated, or the socket on either the Supercap output or the NAP300 input is the problem.

You could swap the speaker cables over from CH1 to CH2 and vice versa. However it seems like you’ve identified the possible culprit. One other thing to check is whether it’s the dressing of the cable that is making it pick up hum (perhaps crossing or running near mains power)?


I checked the dressing before. The signal interconnects, Burndy’s and power cables are all well spaced.

I’m pretty sure it was a physical problem with a single cable. And after visual inspection it looks like there was a potential intermittent short to the casing (which would explain a ground loop where none could exist). No comment on the build quality :neutral_face:

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That looks just like UK Mains Cable… :open_mouth:

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Well documented. The cable used here (DIN-XLR) is one that was specified as mains flex - not just any old mains flex of course, but this one just worked really well and sounded better than other alternatives that were evaluated at the time.

You might conclude that I own such a Cable (DIN-4 to XLR), which came with my 1985 NAP250.
Still works… well.

I think you have found the cause of your issue.
Do you know the history of this cable? I’d be astonished if it came out of the factory like that! :flushed:



Do you know the history of this cable?

I’m the 1st private owner. 252 manufactured late 2018, Supercap DR manufactured early 2019 according to the serial numbers. Bought from main Naim dealer early 2020 as “ex-demo”. So it could theoretically have happened in the shop. The rest is absolutely spotless (as new) so they certainly didn’t abuse the kit. Although it looks to me like the insulation was incorrectly stripped before solder terminating. It’s typical of what I’d expect to see when you use a wire cutter or knife to strip the insulation rather than a dedicated wire stripper. I’ll re-terminate this myself (I’m no stranger to a soldering iron).

That’s good to hear.
Whoever has been in there beforehand certainly needs some improvement! It looks like the blue wire has been seriously overheated.


Not pointing fingers at the dealer or the factory because I simply don’t know. I won’t mention the dealer’s name either because that’d also be very unfair, and they’ve been good to me. I do know this is how I received the cable, and it hasn’t been moved around since the initial installation.

Actually the insulation on the blue/neutral has been clearly cut, rather than burned. But it’s an easy fix for me so “no harm, no foul”.

Just glad it is a plug, and not a socket.

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I think we might conclude that the cable was damaged at some point - and what you have is a bad repair, perhaps…?

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