Hum on AV

Posted by: Tom H on 02 August 2011

Not sure if this should be in HiFi Corner or Home Theatre, but here goes anyway....

 

I have an n-vi which goes into the 282's AV input, which is set to unity gain. All was well until we moved house last week, and now when switching to AV input there is a noticeable hum from the front speakers. I have checked the interconnect and all seems to be ok. I sounds to my untrained ears like some kind of earthing problem, but strange that is was fine until the house move...

 

Could this be some earthing problem in the new place? CD input from the CDX2 works fine with no hum, the problem only comes from the n-Vi.

 

Any ideas?

 

Cheers,

 

Tom

Posted on: 03 August 2011 by KRM
Sounds like an earth loop hum. Are you plugging the NVI and the 282 into different mains sockets? If so, you can get earth loop breakers which cure or partially cure he problem. I got one called an Xitel from Amazon. Maplins do cheaper ones. They are supposed to degrade the sound, but it's better than the hum. Ideally, you should address the problem at source, but that may not be possible.

It's interesting that you are getting this problem with a Naim product. I am getting it with an Onkyo receiver and I had assumed that its inferior earthing was all or part of the problem.

Keith
Posted on: 03 August 2011 by James L

What happens when you unplug the TV/monitor from the n-vi?

 

As KRM mentions, use one mains outlet for all audio and AV gear and see if this cures it and then work backwards from there.

 

You may need to look at using the optical connection for audio.

 

And is the picture via the n-vi OK? No slow moving lines/bars?

 

Posted on: 03 August 2011 by Richard Dane

Tom,

 

try to isolate the source of the problem first.  I would start off by disconnecting any connected screen, TV, tuner/sat box etc from the n-Vi.  If the problem goes away, you know that it's one of those items that is causing it.  If not, then check mains and the interconnect joining the n-Vi to the pre-amp, which may have a broken earth wire.

 

Moving this one to the Home Theatre room.

Posted on: 03 August 2011 by Tom H

Thanks for the replies folks.

 

I checked all connections and did a mains check to ensure that the earthing is ok - no problems found. Everything is plugged into the same outlet via a 5-way socket extension. I tried unplugging everything from the n-vi but the problem persists.

 

Bit of a mystery but I'll continue to invstigate....

 

Now however I have another (I think unrelated) problem! The mute button on the 282 is flashing constantly. From searching elsewhere on the forum it looks like this may be a power supply issue. I know the NAPSC is working ok, so maybe this is a problem with the power coming from the NAP 200? Does anyone know if there is some internal fuse or similar in the power out from the 200?

Posted on: 03 August 2011 by Ismaningerman

This is often caused by an earth loop through the aerial connection. Disconnect the aerial and if the hum goes away, that's your problem. You can get an isolator for a few quid that goes in-line with the aerial co-axial cable.

 

Posted on: 03 August 2011 by NickSeattle
I had this issue when I added my cd5x.  My Naim dealer suggested I disconnect TV cable at point of entry to the house:  that was it.  Alternatively, I could disconnect the Naim kit from AV: also good.  I had Comcast Cable TV improve their grounding, which helped a lot.  Ultimately I had to install ground loop blockers on both line-in and line-out between the NAC 112 and AV system to completely eliminate the hum.  If there IS any degradation in the sound, it does not overwhelm the benefits of listening to the Naim system via the AV system relayed to other zones, vs listening to somewhat lesser sources directly connected to the AV system.  Radio Shack provided the two isolators at $17 each.

Nick
Posted on: 03 August 2011 by NickSeattle
I wonder sometimes if cheap gear has ground-loop suppression built-in, at the expense of ultimate SQ, whereas e.g. Naim would rather go for the ultimate in sound while having us be responsible for fixing our poor grounding elsewhere.  I was "happy" until I added my cd5x.  Now that grounding is better sorted, everything sounds better!  Mr. Dever?
Posted on: 04 August 2011 by Richard Dane

Tom, please let us know what the full system is and details of how it's connected.  A flashing Mute button usually indicates a missing link plug or no PSU connected.  Are you using a Hicap or SUpercap, or are you powering the NAC282 from a suitable power amp? 

Posted on: 04 August 2011 by Tom H

Hello Richard,

 

The 282 is powered from the NAP200 and from the NAPSC. I was thinking perhaps there was a problem from the NAP200 power output?

 

The full system is:

 

NAP 200

NAC 282 (Powered from the 200 and NAPSC)

CDX2

N-vi

 

Also an LP12 via Stageline, but sadly unable to enjoy any of that right now!

 

The system was working ok up until a couple of days ago (even after the house move) so it's a bit of a mystery why it's having problems now. I think this is unlrelated to the earth hum issue.

 

Thanks for your help!

 

 

Tom

Posted on: 05 August 2011 by Richard Dane

Tom,

 

is the system working OK once the n-Vi is disconnected?  Check your link plugs are correctly fitted on the NAC282 - particularly the big paddle link on the top.