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Why is a 1.5-2 volt AC signal on my Neutral line?

I have several music sources e.g. DVD, Phono, DAC, Tuner etc...

I just purchased a NAIM integrated amp and I am experiencing a hum but only from the DVD player.

I have circuit tested the entire house wiring and all is well.

After a lot of investigation I found that some units have a 1.5-2.0 volt AC signal (sounds like a 60Hz signal i.e. hum) between the neutral side of the interconnect and the earth at the power bar.

Panasonic, Pioneer and Sony units I have measured all have this signal present and it varies between 1.5 - 2.0 volts

Luxman and Cambridge Audio gear does NOT have the signal present

All units have a polarized plug with no ground pin

How can the hum be eliminated using the Pioneer DVD with the NAIM Amp?

Thanks
williewonka
shadorne's avatar
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shadorne
7,477 posts
 
I am glad that we were able to pinpoint the problem as being due to a Ground Loop and help you solve it!
jea48
4,515 posts
 
UPDATE: turns out NAIM only ties the neutral side to the ground in their source components - not at the amp.
07-07-10: Williewonka

Williewonka,

?? Your use of the word neutral is confusing....
From reading your posts I believe you use the word neutral in reference to the outer shell of the RCA jack, the signal ground.

Are you saying on your NAIM amp the signal ground is not connected to the chassis? The chassis is only connected to the safety equipment ground?

On the rear panel of the amp is there a signal ground lift switch by chance?


Lifting the ground makes the amp hum more
06-25-10: Williewonka
That would make sense if the signal ground of the amp is not connected to the chassis.
williewonka OP
3,082 posts
 
My use of the word Neutral does refer to the outer shell of the interconnect/phono socket

Using a multi-meter continuity tester and resistance settings I placed one probe on the outer shell of the amp and the other probe to the earth pin on the amp and there was no beeping from the continuity tester and the resistance setting showed a completely open circuit.

I asked NAIM about this and they confirmed this was how they designed the amp.

The ground on the amp is connected to the amp case/chassis for safety

They ground the neutral side of the signal in their systems at their source components

I did try "lifting the ground" on the amp and the hum got louder, but NAIM did not condone this practice and warned against it sighting safety.
hifitime
715 posts
 
One thing I've done in the past is bond all the metal cases together with a 14 or 16 gauge wire.That helped get rid of hum a lot of the time.
williewonka OP
3,082 posts
 
Hifitime -
One thing I've done in the past is bond all...

Be careful about doing this - components are designed very differently e.g. NAIM and Luxman - this could cause other problems that may be damaging - although I've read this solution many times on several forums- NAIM warns against this approach.

Cheers
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