Massive sudden hum - frightening!

I seem to recall you having a problem a while back with a low level hum. Did you ever fix this ?

It would be useful to know what is connected to the Nait.

Interestingly, back in my days of Naim customer service, it seems that one of the most common causes of weird behaviour in pre-amps - particularly volume controls seemingly with a mind of their own - was due to remote control handsets getting stuck down the side and back of a chair or sofa.

Rico, is your TV connected directly to the NAIT? Or does it go via a DAC using an optical connection?

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@james_n well remembered, the low level hum is still present. I initially thought it was the hard drive motor in the Sky+ box but alas it isn’t that. The hum disappears however if I unplug the power cable to my Pro-ject phono stage. That isn’t really convenient if I want to listen to some records though! It is a cheap phono stage which I am also considering replacing so the noise may be the straw to break this particular camel’s back.

Currently I have the below connected to the NAIT:

  • Pro-ject Phono Box
  • Yamaha WXAD streamer
  • TV via a cheapo Fisual DAC w/optical connection

From what you say with disconnecting the TT, it sounds initially like you have a ground loop, but looking at the components listed, they all seem to have wall warts so it’s difficult to tell without getting a DVM and measuring whether this is the case.

I suspect the system signal ground is floating. It would certainly be worth trying a signal ground to mains earth connection to see if this gets rid of the low level hum as I don’t think you have one. I’m assuming that the hum is there regardless of input ?

Are you in the UK ?

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@james_n thank you for the reply once again. What is a DVM?

How can I go about trying a signal ground to mains earth connection?

There is hum regardless of input but all hum disappears when I power down the phono stage.

Yes, London.

NB: all my sources are currently connected to the NAIT with RCA, not DIN.

DVM - digital volt meter. It’s useful for continuity testing in these cases.

Give this a go. It’s just a wire between the signal ground (RCA socket outer ring) and mains earth.

Just plug this into a spare rca socket on the Nait. Does the hum go ?

I have a decent digital multimeter. What I don’t have is a spare mains plug of the type you’ve pictured, or indeed an RCA plug.

Thank you for your help so far.

Can you borrow a mains plug from something else ? I know most things come with moulded plugs these days but have you an old lamp etc with a rewireable mains plug on it ?

If you haven’t got an RCA plug then you could always bare the end of the wire and touch it to one of the RCA socket outer rings just to try this setup.

I will have a hunt. I have some cheapo RCA cables knocking around that I can butcher. Will update by reply.

Perfect :ok_hand:

That seems to have really helped, it’s lowered the noise floor substantially. It’s a flimsy mains plug - is it OK to leave it plugged in permanently?

That’s good news. It can be used permanently with no issues. I would get a decent mains plug where you can ensure the cable clamp mechanism (either a jaw type or the two screw clamp type can be used) so the wire can’t get pulled away from the earth terminal in the plug.

If you don’t want to use a mains plug then this type of earth bonding plug from an Antistatic kit (with no resistor) will do the job too. You’ll just need a 10mm female stud to connect it. It’s the safest option as the L & N pins are plastic.

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@james_n thank you for your help, it’s really appreciated.

I think I will make up a decent earth cable with a high quality mains & RCA plug.

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This type of plug is what I would recommend because there’s absolutely no chance of any accidental live connection, for example of the wire gets pulled and separates from the earth but then manages to touch the live terminal.

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Agreed. The other way is potting the internals of a standard plug to be completely sure of no accidental contact if pulled and the strain relief fails, but the bonding plug is the safest approach with no live pin.

I’m struggling to find an earth bonding plug with a binding post/banana jack without a resistor. Any guidance please?

As a temporary measure, can I just remove the L&N prongs from my plug?

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Try here Rico

csi-products

And yes you could pull the L&N pins if they will come out. Good thinking.

Thanks James, i’m trying to avoid the versions with a snap connector, purely because I don’t want to buy a minimum quantity of 100 snaps!

Pulling the live and neutral pins is maybe not a good idea - it’s then possible to put the plug in upside down, which will open the shutters and expose live and neutral in the socket.

It’s also possible to twist the plug body, which could easily crack either the plug or socket.

If the issue with a conventional plug is the cable grip, some insulation tape wrapped round the wire might make it more secure - but I guess ideally find a plug with a grip that works!

Good point Andy about an inverted plug and shutters. Certainly the Earth bonding plug is going to be the safest approach for a permanent installation.