Star Grounding

Posted by: Arthur Bye on 07 August 2000

I have a Linn Kremlin tuner plugged into my 52 and it works fine. The same tuner (using the second set of RCA outputs on the tuner)when plugged into my Sony A/V system produces a noticeable hum. The Linn has a grounded main, the Sony does not. The Linn is plugged into a wiremold power bar with all of my Naim stuff.

If I unplug the tuner from the 52 the hum in the Sony A/V goes away.

How do I get rid of the hum? or can't I be connected to two pre's at once?

Arthur Bye

Posted on: 07 August 2000 by Martin Payne
Yes, you have an earth (ground) loop. Presumably your tuner is grounding it's 0V signal line.

Your Naim pre-amp MUST have one-and-only-one earthed (grounded) source connected.

This would normally be either your P9 or your CDS. It's up to you to make sure that all other sources to your 52 are not grounded.

Just for effect, unplug everything from your 52 except your CDS & listen, then plug everything back in and listen again. The mush that's now descended on your system is an earthing fault.


Posted on: 07 August 2000 by Arthur Bye
Martin: I don't get it, but I'll give it a try. Why does Naim sell all of their sources with grounded plugs then?

Does this include my power supplies?(Nat-01, P9, and CDS)

So I should go out and buy 3 into 2 adapters to functionally remove the ground plug? (or else cut off the ground from the mains?)

Arthur Bye

Posted on: 08 August 2000 by Steven Phee
Naim equipment all come with grounded plugs as the ground wire only grounds the electrostatic shield within the transformer and the casing. This goes for their power supplies too. Only their cd players have the signal negative connected to the case, which is earthed.

And yes, ideally there should only be one grounded equipment connected to a Naim pre-amp. But if one connects 2 grounded equipment connected to the same powerblock, there would be hardly noticeable hum.

As to Arthur's problem regarding the audible hum... it's a common problem with tuners. Although your tuner does not have a ground at the mains plug, the unit's signal negative is connected to the signal negative of the antenna input. Most tuners I know are like that. My marantz is. You could use a simple multimeter to check. The signal negative of the antenna or cable input is grounded, but that ground is not a clean one and is not connected to the ground of your mains anywhere nearby, hence a difference in potential between the 2 grounds and when connected together, introduces a hum. Just unplug the antenna input and you would hear the hum would go away.

The solution would be to go to an electronics diy store and ask for a "75-ohm ground-breaker feed-through surge protector", which goes between the 75-ohm cable and the antenna socket. It's basically a small 1:1 transformer in there that allows the radio signals to pass through the transformer, but electrically separating your tuner from the antenna. And another benefit of this device would be should lightning strike your antenna, it wouldn't enter your tuner. I have a similar device, because without it I would have exactly the same problem as you have. With this you wouldn't need to unplug your tuner everytime you want to hear something else.


Posted on: 08 August 2000 by Dev B
Martin wrote: >>>Your Naim pre-amp MUST have one-and-only-one earthed (grounded) source connected.

Martin, In my system with Turntable, CDS2, NAT01, CDR, and VCR how do I tell which one is the grounded component, and how do I remove the offending 'grounds' to ensure that the preamp is only grounded from one source.


Not technical Dev.

Posted on: 08 August 2000 by Arthur Bye

Thanks for the explanation. In my situation though the tuner, a Linn Kremlin, does have a grounded mains. The tuner also has two pairs of audio outs. One pair goes to my 52(grounded mains) and the other to my ungrounded A/V Sony system(ungrounded mains. When using Naim, no hum. When using Sony, audible hum.

I also have a Nat-01 hooked up as well. I've tried the prior suggestion of plugging and unplugging different sources. Only the P9 has hum with the Naim set up. All of the other sources (CDS1, Nat-01, Kremlin) have grounded mains and I am unable to discern a hum or an audible difference in sound isolation of sources to just one ground.

It did get rid of the hum on the P9 though when I removed the ground(Grado Reference "Reference" MC).

I am reluctant to add a transformer to the antenna input(Ron Smith Galaxie 17) as prior experience has shown a significant degradation in sound quality.

For now I'll just disconnect the Linn from the Sony A/V stuff.


Arthur By

Posted on: 08 August 2000 by Steven Phee

yup, I also did notice a drop in sound quality with that transformer, but since my tuner is a cheap horrible unit and all stations here in germany send out heavily compressed program material, I'd rather have no hum from my system.