Earth hum, again. Nac 62

I have two cb 62’s and an Olive 62. The cb’s each feed a 140cb, no hicap just the link pin. There is no earth hum from either.

The Olive has a hicap and feeds a 140. There is no earth hum.

When I take any of the cb 62’s and replace the Olive 62 with a cb (no link plug obsv) I get a very loud earth hum.

Why! Are the cb and Olive 62’s wired differently internally?

What are your connected inputs in the ‘humming’ scenario?

Are these exactly the same as what was connected to the Olive NAC62-HiCap-NAP140.

Are you connecting each (in turn) of the CB NAC62s to the HiCap with the same SNAIC-5 that you used successfully with the Olive NAC62?

There being no hum with the Olive NAC62 configuration should eliminate a fault in the SNAIC-5. Providing (see above) you are using the same SNAIC-5.

That you have hum with two CB NAC 62s seems to eliminate a defective, previously link-plugged, DIN power socket as an,unlikely, possibility.

“To lose one parent, Mr. Worthing, may be regarded as a misfortune; to lose both looks like carelessness.”

“it is quite a three pipe problem and I beg that you won’t speak to me for fifty minutes.”

This should be considered a bump as I’m at a loss.

Yes just a straight replacement of the box only. Same connections and leads. At first I suspected it was an unserviced nac, but the recently serviced one was just the same. Swap back to the Olive nac and all quiet on the western front.

I have a spare hicap dr so I will try a test connection with that and the cb kit when I get a chance.

Edit. They hum without any connected input and as I move away from them the hum decreases. Also I can eliminate the hum by touching both outer shields of the din plugs on the hicap and the nac thereby providing an earth path.
I just don ‘t have to do this with the Olive nac.

Connected the Hicap DR to the unserviced nac62/140. NO hum.
Connected the Hicap olive and hum returns.

Therefore suspect the Olive Hicap needs servicing

BUT connecting the Olive Hicap back with the Olive 62/140 and NO hum.

All very strange.
Conclusion- leave it as it is.

Sidenote. The cb62/140 with the Hicap DR sounds amazing! :grinning:

Update 2.

Partially solved. If I remove all inputs from the Olive Nac 62 i get the hum even with all Olive hc/62/140. I can only lose the hum when I connect an input to the Tuner input from the Streamer, which of course has its own earth from the mains. This points to an earth loop failure somewhere in the system. Next thing is to find out where.

So the question to all is

What causes an earth hum in Nait components when connected to each other, bearing in mind that both the hc and the 140 are earthed to the mains, the 62 gets power from the hc.

Just to check - you do have the 62 connected to the HiCap then the HiCap to the 140?

There should be no direct connection of the 62 to the 140 when a power supply is being used.

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I think I shall be taking the cover of the hicap and having a look at any obvious earth connections and why the tuner input provides an earth.

Correct connections and I have now swapped all leads including power leads.
Still a three pipe problem. :slightly_smiling_face:

Oscar Wilde and Arthur Conan Doyle, I think?

“it is quite a three pipe problem and I beg that you won’t speak to me for fifty minutes.”

Conan Doyle.

Three box problem rather than three pipe.

As far as I understand it a ground loop occurs when there is an ‘odd’ resistance in one commonly earthed circuit but not the shared circuit. A potential difference between the two common ground circuits occurs and that difference generates the hum.
In the Naim arrangement of hicap/nac/140 what is the normal earth path for the audio circuits. Nac generates the audio for the 140, the hicap has no audio circuit merely providing power. So does the nac earth via the hc then on to the 140? I am guessing at this as the Naim design requires the hc to power the nac and then audio returns to the hc before being passed on to the nap.
I can bypass the problem by applying an additional earth connection but I’d like to understand what is happening.

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