Help Trouble Shooting a Hum

I’ve finally got my kit setup in my dedicated listening space over the past couple weeks & last night noticed a hum in the one speaker, was going to reach out to the factory but thought I’d ask here first.

All the pieces are fairly recent, with the SCDR being the oldest, 2018 I believe. I noticed the hum after I was done listening & muted the 252. It was just coming from one speaker, its a hum or maybe a ground loop noise (not the normal “static” noise), audible from the tweeter & mid, not so much the woofers. With the unit un muted its harder to notice but when muted the one speaker is basically silent while the other has a hum (volume has no impact on the hum level).

Did some trouble shooting, first swapped speakers & cables to rule those out, unplugged both source cables, moved the 300DR XLR input cables around (as I don’t believe their shielded) but that didn’t seem to make a difference. Turn just the SCDR off & the noise stops, as does just turning off the 300DR by itself as well. Currently have the XLR’s connected to outputs 5 & 4 on the SCDR. Swapped those around & the noise switched speakers. So what I found was whatever one was plugged into output 5 was silent & the one plugged into output 4 had the hum. I tried moving from output 4 to output 3 & it too would hum. I then plugged them into output 3 & 4 & both speakers would hum.

So no hum from output 5 but hum from both output 4 & 3 on the SCDR. Wondering what would be the cause of this? Now both my sources aren’t Naim, so is it a possible ground issue?

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If you disconnect the sources from the preamp, does the humming remain?

Hi Robert, yes, did mention it above, that I tried disconnecting both sources, with no change to the hum.

If 5 is silent and 3 and 4 both hum, with multiple sources and with all boxes and wires and other connections unchanged, then that suggests (to my very amateur grip) that it is a fault in the box or that wires interact when reaching most sockets but not when reaching socket 5.


A bit of a strange one. A couple of questions -

How do you have the kit arranged on your racks ?

You say you’ve swapped all the cables. Are they the standard Naim cables between 252, Supercap and 300 ?

Wouldn’t think stacking would be an issue, as the issues appears to be specific to output 3&4 but not 5 & when I was swapping back & forth it would eliminate each xlr as the cause. Not sure if the Burndy from the 252 could be a source of the issue (no way to swap that out) & believe what I have done would also rule out the supply cables between the 300DR PS & head unit. But yes, all the leads are the factory supplied ones, stacking order is as below, brain & brawn


Turn table
300 PS

The simple view would be to say its a SuperCap fault - probably with poor earthing for some reason. But… it could still be the XLR leads.

Do not believe is an induced problem - its not something jumping between the leads. Its conducted - its thru the leads.

Could it still be the xlr leads when I tried (only swapping at the SC end) :

4&5, hum on 4
Swap leads 4&5, hum still on 4
3&5, hum on 3
Swap leads 3&5, hum still on 3
3&4 both channels now hum

Are the 300 XLR leads handed - is there a Left & Right…? I only have a 250… which is a Stereo lead.

As far as I know they are, that’s why I was only swapping them at the SC end.

I figured someone having the same issue might be a bit of a long shot but know a couple of the Naim tech guys are on here, wondering if @Richard.Dane could maybe point them in this direction?

You probably mean @NeilS or @110dB:thinking:

The DIN-XLR leads are indeed handed - Green banded cable for CH1 LEFT, and the Red banded cable for CH2 RIGHT.

However, the fact that the hum seems to not be on socket 5 of the Supercap until you’ve done a load of cable swapping and now on all output sockets leaves me rather stumped. Have you opened up the DIN plugs to check the wiring/soldering is OK? I wonder whether @NeilS has any ideas here.

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Thanks Richard, the plug in combo’s that I’ve tried below (as posted above), still stand in that if either of the channels is plugged into 5, its still quiet, the hum is only on output 3 & 4.

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Sockets 3,4 & 5 on the Supercap are electrically identical, so I’m puzzled as to how you are getting the results described - and these results are repeatable?
Have you tried gently flexing the cables while listening for the hum?


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Thanks Neil, the results seem to be repeatable, as I tried the 5 different combo’s above plus a few extra times, but I can try again & I can try flexing the XLR’s as well. Is it possible that any of the other cables could be the source of the hum, like the Burndy from the 252, etc? Would it be possible that output 3&4 have a bad solder joint in the SC?

The hum, when the 252 is muted is rather noticeable in my treated dedicated listening space on output 3 or 4, when plugged into 5 the same hum is audible only if you basically stick your ear right beside/against the tweeter/midrange.

Edit: when swapping the XLR’s around (SC end only), do both the SC & 300DR need to be powered down? This is what I was doing, but would be easier if I didn’t have too.

It’s difficult to rule anything out at present!
Do the DIN sockets on the Supercap appear normal? Any contamination (normally white in colour) on the black centre insert?
Does the 252 mute button work as expected while listening to music?
You can just power down the 300 while swapping the signal cables, but do leave it a minute or so to discharge beforehand to avoid speaker damage.


I don’t recall seeing any contamination on any of the sockets but will double check. Yes, the 252’s mute button functions normal, when music is playing it mutes as expected, when I’m done playing music I always mute it to reduce the static noise, which it does (operates same as my previous 202 & 282). So the static noise (or I believe its high gain noise) gets muted, but the hum level isn’t reduced.

Are the 5, 4 & 3 outputs daisy changed together with any of their wiring, that first goes to 5, then followed by 4 & then 3? This might makes sense if there’s a bad connection between 5 & 4, which would also impact 3 down the line? With the amount of times I swapped the cables, & it always being 3&4 having an issue & never 5, just doesn’t seem to point towards the XLR leads.

Yes - they are daisy chained from the Burndy socket, so 5 → 4 → 3 when using a 252.
While checking the DIN sockets, you may be able to see if any of the “jaws” of each pin seem splayed wider than others.


Thanks Neil, had another look. Swapped the leads (SC end only) back & forth between 5 & 4 a few more times & wiggled them around. Every time the hum was always on 4 & never on five & giving them a wiggle didn’t make a difference. So I’m pretty confident its not the XLR’s. I couldn’t get a perfect view as the SC is down on the bottom of my fraim stack but as best as I could see, every connection appears as new/no contamination. I’m in Canada, so not abnormally high humidity & not located near an ocean. I was going to pull the SC to take a better look at it, check the DIN’s for splayed wider connection & verify wiring/continuity. Is there anything else I should be checking?