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.
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.
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.