Hum is doing my heid in

Now that lockdown is easing, I finally got my Linn LP12 back with a rebuilt Troika installed. So far so excellent. But… I can’t get rid of the damn hum.

It seems to be the 60Hz variety, which, I know, suggests poor shielding or cable problems. The LP12 ground cable runs into a Dynavector P75 Mk. 3. Another ground cable runs from the DV to an SN2. I’ve tried removing all other components from the area, leaving only the Linn, DV and SN2. It still hums, and gets worse at higher volumes.

Could it be the DV power supply? The interconnect between the DV and the SN2? Everything was working fine with a loaner Rega/high output MC cartridge. As soon as the LP12/low output Troika was reintroduced, the hum began.

Do any of you fine folk have any clues as to what this could be – and how to fix it?

Why are you running 2 ground leads? They shouldn’t be daisychained unless intermediate units specifically have no chassis earth and have dedicated signal ground in and out posts marked with signal ground marks as opposed to chassis ground (which is always in, not out).

I’ve had hum issues with a P75/2 and my Well Tempered. I had the P75/2 working well with a P3/24-Benz Ace combo and when I upgraded to the Well Tempered with its Switch Mode PSU I had noise. Lots of it. I got two linear wall wart psu’s made and all was good. Both psu’s are opposite earthing wise. I also could get a wee bit of hum if I didnt get the seperate earthing leads just right. I think I ended up wth both the TT and P75/2 earthed straight to the SN2 . I once tried Van Den Hull The First I/C’s which created hum as well. No problems now with the Stageline and I’m thinking its quite a step up from the P75/2.

Looking at the rear panel of the Dynavector, that is indeed just a chassis ground in. Try running just a single ground lead from LP12 to the SN instead and nothing to the ground on the Dynavector.

It may be down to the closeness of any power supplies (or the Supernait) as the high gain needs with LO MCs tends to make the associated phono stage and cabling very sensitive to this. Try speaking things out as much and you can and see if the hum reduces.

Do you mean “try spacing things out”

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yes, that’s it Don. Thanks Apple auto-correct!

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Thanks all.

@feeling_zen I’ve tried grounding directly to the SN2, but it didn’t make any difference.

@Richard.Dane I’ve experimented with various forms of placement, and will take another crack at it.

@Mechanalogue Yes, I’m considering switching to a Stageline. I prefer the P75, but the hum is unbearable.

I’m not sure what this tells me, but when I disconnect the LP12 from the P75, I still get hum on the Aux 1 input.

I’m wondering if the combination of lack of signal to mains earth and the DV switching PSU is causing the issue. I’d suggest connecting a ground wire from the SN2 ground post to a mains earth connection and removing the earth wire between the phono stage and SN and see if this helps.

That creates a ground loop. The chassis ground on Naim amps is internally connected to mains earth.

Chassis ground terminals are intended to accept a signal ground in.

I think the biggest clue is that the hum persists on aux2 even without the LP12 connected. Sounds like the dynavector is creating the loop somehow. I’ll admit it seems very odd.

That makes sense otherwise it wouldn’t be a safety Earth…

Signal ground is not connected to mains earth here hence my suggestion…

The wording in the Naim manual isn’t great. A signal ground in is a chassis earth. That connector on the SN2 grounds to chassis and then to earth.

It is not a signal ground out. If you connect a lead from that to anything that is earthed, you create a loop. Hypothetically, if you did that and it resolved the issue, it would imply a problem with the SN2 earthing somewhere.

No - it connects to signal ground - it’s isolated from the case (and hence mains earth)

Have you got the ND5XS2 floating or grounded?


Good point - the Op didn’t mention another source which can provide the signal ground to mains Earth link.

I’m now beyond the limits of my technical knowledge!

@james_n I’m not sure how you’d connect a ground wire to a mains earth connection. Likewise, I’m not clear about how I’d use another source to provide the ground to a mains earth link.

@AndyR I don’t have a ground wire connected to the ND5XS2.

I had the same issue yesterday but some wise folks pointed me to a grounding issue with my other source. I flipped the switch on my ND5XS2 from “Default” to “Floating”. That fixed my humming issue as my DAC is the only thing set to “Chassis”

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I’ve tried flipping between “default” and “floating” but it doesn’t make any difference.

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Have you tried different interconnects?

@Richard.Dane I haven’t. I was hoping to borrow some from my dealer, but he’s an hour away. Any particular interconnects you’d recommend trying?