Massive sudden hum - frightening!

At about midnight last night, there was a sudden and loud hum coming through my system. It woke the wife and I up and thought there was someone smashing down the front door, quite frightening actually.

I left the 5si on (as usual) and the volume was pretty low - set for casual TV viewing with the TV & DAC as the source. From now on I will turn the volume all the way down but does anyone know why this happened?

I’m sure some real experts will be along in a moment, but I would check all your connections at the rear -it sounds like something has created a circuit perhaps to ground which shouldn’t be there and hence you get the humming…

Agreed it sounds like an earthing hum most likely coming from your turntable source so check your leads and connections. If the hum disappears when you change inputs then that is your answer. If you disconnect all sources is the hum still present? If so it could be something more serious.

I really have no idea, but I had a similar event with my Lindemann 830S/858 pre-power amplifier a few years ago.

I had left my amplifier switched on (at a moderate volume setting) while I went out to cut the grass in my lawn. When I returned, there was a horrendously loud low pitched hum from my hi-fi system, and I could see that the volume had been turned up to maximum level. There was no one else in the house at the time, so I have no idea how this happened.

I hope your speakers are OK. Initially I thought that the drive units on my Magnepan 3.6R speakers had been blown, but luckily it turned out that the speaker fuses had done their job, and my speakers were back to normal with a fuse replacement.

I sent the amplifiers back to Lindemann, but they couldn’t find anything untoward with them. However, they did replace the main control board on the pre-amp (free of charge) as a precaution, but I never got an explanation as to why this might have occurred.

Hope you get an explanation.

Sorry - I should have been more clear. It was a very sudden and incredibly loud blast of noise, rather than a typical hum.

I will check all the connections regardless.

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If I connect my AV receiver through the hifi, when the reciver goes off there is a hum - and loud because of settings on the hifi. I think that in effect when it turns off the receiver becomes a large unshielded object connected to the signal wire. Normally I disconnect the receiver, and back to music source, and turn the hifi amps off if not tgen playing music. The receiver has an auto power off some time after the active signal stops - on a couple of occasions when I have left it connected and amps on the subsequent switching off of the receiver has the effect you describe!

Could there have been an electrical spike? Did any house alarms go off at the same time? What’s the current status of the issue!

Quite possibly…no alarms went off apart from mental ones! It’s all OK now.

Compact fluorescent lamps can sometime interfere with the remote, especially when recently turned on. I’ve had the volume knob turn all the way round to maximum on a couple of occasions but I’d guess this wasn’t the cause during the middle of the night.

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?