Hum sorted, but I don't understand what I've done

Hi-Fi Corner
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I’ve had a low level hum since adding a NAC 282 - always present, independent of source selected or volume. I finally got around to looking into it last night, and after a bit of experimenting and searching on the forum I’ve fixed it by switching the signal ground on the ND5XS2 from Default to Float :slight_smile:
I don’t understand this though, can anyone explain in very simple terms what is happening here ?

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There should be one and only one earth connection in a Naim system. The default is for the nd5xs2 to provide it. Sometimes there can also be another device that provides it. If you have two, they can have a potential differential, causing hum. The float position means that the nd5xs2 does not provide the earth connection and leaves it to the other device.

Search for ground on

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Thanks, I understand, and many other posts now make sense! I wonder (a little) where the earth is now coming from.

Out of interest, can I flip between Default and Float with the system powered up, or is that a bad idea ? I( think it sounds better now, but would like to experiment)

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Can be flipped when turned on, no problem. Yes, a proper earth is actually important, so it can sound better one or the other way even if there is no hum.
Maybe your Qutest is now the earth? But I think it can sometimes be a bit of black magic with several devices connected. Luckily there are only two options on the switch and what works better is fine

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I take it you are using the Qutest as a DAC to the ND5XS2 ?

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Yes. I was using that before I added the NAC 282 too

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Is there any other kit connected to the 282 ? The Qutest doesn’t have a mains earth connection if using its standard wallwart and as the ND5XS2 is connected to the Qutest via the digital S/PDIF output, the signal ground switch shouldn’t make a difference so I’m surprised you’ve found it does.

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Feels like black magic, so really glad I’m not having to debug this!
There’s the power supplies and also the ND5XS2 is connected directly using DIN -> DIN. Also an RCA -> DIN cable from a TV. The latter was my first thought, but disconnecting it made no difference. A SN2 as power amp has a REL subwoofer connected to the speaker outputs but unplugging the REL had no effect.

Good to hear I can easily switch between the Default and Float and satisfy my curiosity.

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Ah ok - that makes a bit more sense. Out of interest why do you have the DIN connection in place between the ND5XS2 and the 282 if you’re using the Qutest as the DAC ?

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I set it up that way when I first got the 282 so as to compare with and without the Qutest, and haven’t got round to removing it

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Try removing it. The Signal ground switch position should not make any difference once this connection is removed.

If you still have got a hum then there is some more investigation to be done.

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Yes, that does it! So the ND5XS2 has an earth connection too ?

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Yes. The ND5XS2 provides a signal ground to mains earth connection (switch set to default) as Suedkiez mentioned. If the hum has now gone (as it did when you set the switch to float when the Din connection was in place) then it sounds like you have another signal ground / mains earth path already and have now broken the ground loop.

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Got it, I think, something else in the system is providing an earth and that causes a ground loop when the DIN - DIN is in place and the ND5XS2 in on default. I can’t work out what component that is (not the TV or the SW) but I understand more now at least. And it sounds great! Thanks

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Where there are two earths the area enclosed between the wires involved determines the magnitude of the signal. If wires run parallel and close the effect is much smaller. Just physics. But the ND5XS2 earth switch should help.

Phil

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If you have the ND5XS2 connected via S/pdif to a DAC (and then on to the NAC282), as well as being connected directly via analogue, then you’ll probably have an earth loop. Best to have either one or the other. Oh, and if comparing, only ever have one or other physically connected as when both are connected then the ND5XS2, and possibly even the DAC will be somewhat hobbled.

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It shouldn’t do Richard as the S/PDIF output is via small pulse transformer so it’s galvanically isolated via this connection.

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Ah, Ok, thanks James.

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Thanks, good to learn a bit about this.
Out of interest I disconnected the Qutest, switched back to ‘Default’ - hum back. So it’s the not that that is the culprit.
Anyhow I’ve now disconnected the DIN from the ND5XS2 and am just using that from the Qutest. After an hour or so of listening I’m confident it sounds better than it did a couple of days ago when I started on this. Of course I’m expecting it to, so can’t be 100% sure, but sounds great whatever the reason!

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Interesting. I also have an AV amp preout into the AV channel (4) on the 282. Don’t use it often, but was listening to the TV through it at the weekend and noticed a very similar hum when on that channel. Here however changing between default and float on the ND5XS2 makes no difference, and disconnecting the cable from the AV amp stops it (this had no effect on the initial issue). So although it sounds the same it doesn’t act the same - could it be related at all ?