AV Hum on 112

Gary,

Have you seen this recent thread? It could be an earth loop. There has also been a few other posts on this...hope that helps.

http://forums.naim-audio.com/eve/forums?a=tpc&s=67019385&f=48019385&m=9491918006

Gary,

Definitely a ground loop problem. Some forum members including myself use one of these on the antenna cable into the sky box:

Magic Box

You can find more info here:

Audio Isolators

I did see the other thread, but before I go spending any more money...
I've just tried having everything else turned off and any sort of aerial (including sky dish) unplugged, but I still have the hum.
Could something else be causing it?

Gary

Did you unplug the sky box completely from the system? If so then it does sound like its coming from somewhere else. I used to have a TV that had this effect so it could be that.

Here's what I would do:

Connect the P3, CD5 and Naim amps - this should produce no hum.

Disconnect all of you AV gear from each other, including connection to the tv and plug them into your 112 one at a time, independently of each other. The reason that you need to do this is because the ground loop problem travels 'through' components.

This way, you will find if one or more of them in isolation is causing the hum.

However, I noted that you say that you get hum when just the interconnects are in place, I'm assuming that they are just dangling from the back of the 112 not connected to anything (the NAD). If so, it is worth talking to Naim about as you may be picking up RFI or other such nasty.

If you do find that it is one of the components then we have a small problem because in my experience the ground breakers that you can get that fit into the audio signal chain degrade the sound. They usually come in the form of phono leads with capacitative links.

Harris,

After much plugging and unplugging the following seems to be true...

If unity gain is turned off, then there is no hum no matter what is plugged into what (equipment interconnects or into the mains).

Unfortunately all my equipment is on a ring rather than a spur (rented accom at the moment), so this may have so impact on the following...

Starting from everything in the room barring 112/150/flatcap/cd5 turned off at the mains with NO hum:

Turning on a Sega Dreamcast at the mains (different socket to hi-fi), but not turning it on on the box a very noticeable hum appears.

The same applies to doing the same with a sky+ box even though it is not plugged into any other equipment (same power block).

No other equipment causes this.

The obvious questions are:
Why does this only happen with AV and unity gain and no other inputs?
Why doesn't it happen if the CD5 or stageline is plugged into the AV?

Shall I just give up until I move and get a spur or two???

just yet anyway.

I can only answer some of this.

The 112, when set to unity gain, causes the system to be more susceptible to hum since you are effectively bypassing it (at unity gain) so that the power amp responds to the already attenuated signal from your AV preamp. Its not dissimilar to the extra hiss I get through my speakers at full volume on my Nait - my system is more sensitive at full volume as it amplifies any low level noise.

The Naim equipment shares a common ground and are star earthed within your system and so the hum will not occur even if you connect them to the AV input.

My AV system is very similar to yours and I cannot reproduce the effects that you are getting with my boxes as I do not have a unity gain (I only have one shared ring). The fact that the Dreamcast is doing it may mean it is dumping alot of noise onto the mains or that something strange is going on with its earthing. Sky/Cable boxes are notorious for this unfortunately.

My suggestion is that unless another forum member has a solution that you contact Naim at this point. They have things like RFI kits which may help and are also very clever. IMHO a separate spur would solve this but i'd check first.

I'm experiencing the same humming problem with av connected to my Nait 5 and it's driving me round the bend. No problem with my other amps, just the new Nait.I'd be grateful if anyone in the UK found a supplier of these antenna ground isolators and can enlighten me.

[This message was edited by bigmick on SATURDAY 14 December 2002 at 10:24.]

I have a similar problem. When AV is selected in my 112, my CD5 and Arcam AVR 200 cause an earthing problem and resulting hum. It is only audible when AV is selected. The only way to get rid of the hum is unplug the CD5 while watching a movie.

The good people at Graham's are coming to work on it next weekend. I will post the results of their visit.

Gary, Bigmick & Willito JOIN THE CLUB!!!

I have the same problem.

One additional comment. If I use the "level" adjust facility on the remote, the hum level reduces BUT when you drive the signal back up to listenable levels of course the hum returns. It seems like the hum derives from a mismatch between the pre-out output on the AV Kit (In my case it's a DENON AVR3802) and the AV input on the 112 BUT ONLY when unity gain is enabled.

You can get round it by disabling unity gain on the 112 AV input but you then have to manually balance the volume of the front channels coming out of the 112 with the other channels coming from your AV kit. I have a dB meter and a test disc which made it pretty easy to do a calibration run with various volume settings on the 112 then just use the same settings every time I use the AV kit.

I still want to fix the problem though. Based on what Harris said it sounds more and more like we should consult with Naim.

This is because you have signal earth attached to mains earth in two places in the system. The AV2 has an internal link that can be removed. See your dealer. With other equipment you may need to take it to a competent technician to have the link removed.

Hope this helps
Chris

Chris Murphy may well be right,contact your dealer who in turn can work with Richard Dane here at Naim to help solve this problem.

quote:

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Original posted by Chris Murphy:
Earth link

This is because you have signal earth attached to mains earth in two places in the system. The AV2 has an internal link that can be removed. See your dealer. With other equipment you may need to take it to a competent technician to have the link removed.

Hope this helps
Chris

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quote:

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Originally posted by Paul Stephenson:
Chris Murphy may well be right,contact your dealer who in turn can work with Richard Dane here at Naim to help solve this problem.

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Thanks for the input. A couple of things:
1) It's not an AV2 its a 112 I have
2) Surely if there is an earthloop it's still there even when unity gain is disabled.
How come with everything still connected if I just cancel ünity gain the Hum goes away.
3) I am an english ex-pat who purchased my kit in the UK but live in the Netherlands. The UK dealer did an excellent job of helping me during listening trials and purchase but he is now of course unable to physically help because of my move to the netherlands. Can I get any help by phoning NAIM and if so who do I contact? Richard Dane?

We understand how exasperating this problem can be and we are working hard to find a possible solution.

From my discussions with our guys in R&D I gather that the hum could be caused by a number of things but one of the most common problems can be from one or more items of equipment connected to the system having it's mains polarity the wrong way round. This is most common with items having a floating earth, identifiable by having only a two-core mains lead connected to the mains socket.

Figure eight input mains leads should be inserted the right way round - a tricky one as they are so easily reversed by accident. You should also ask your electrician to check that your mains sockets are wired the right way round - he may be able to lend you a simple plug-in device which will identify this for you.

Beyond that there's currently no modification that we can envisage to our amplifiers which will cure the problem and certain devices already mentioned which tackle the problem at source would be the best bet. Our R&D department will be trying to get hold of some of these devices to test their effectiveness and we'll let everybody know the results as soon as we can.

On a separate but related subject, for owners of AV2s who experience hum problems, contact your dealer who can arrange for a simple modification of the unit where the signal to mains earth link is removed. We found that hum can be caused by two pieces of equipment in a system which both have signal to mains earth connections, cured by this simple modification.

We'll keep you all posted. Likewise if anybody has any constructive advice to give on the subject, please either contact us directly or post your thoughts and findings on the forum.

I too have same problem: CDX/112/150/FC2/nac5/Credos/Yamaha dsp E800 processor. Loud hum when unity gain activated on A/V imput, stopped when CDX signal din plug disconnected from CDX. Would XPS (1 or 2) added to CDX cure problem perhaps? (isolate cdx from pre-amp?)