I’m new to Naim so apologies if this is a stupid question. Wondered if anyone could answer this for me?
I have an NAP 250.2.
When I switch it on I get the pop sound through my speakers, which I know is normal. Then there is then a fairly quiet hum which sounds through the speakers. It builds a bit, then immediately disappears after almost exactly 30 seconds. If the unit is turned off and I wait a few minutes, the duration of the hum is a lot shorter. The noise never returns once switched on.
Is that normal, sounds amazing otherwise? I’m guessing it is the sound of something charging up perhaps?
Interestingly, I get a constant ground hum when the pre amp is not connected to the 250. This sounds remarkably similar to the hum that appears on switch on with the pre amp connected, which then disappears.
It’s almost like something kicks in after 30 seconds of it being switched on whereby it grounds itself to the pre amp to stop that hum.
Yes, so the pre-amp should always be switched on first before the power amp (unless the power amp is one that powers the pre-amp).
When did the issue start occurring? Has anything changed recently? Is the DIN-XLR lead OK?
FWIW, I have never had any hum through the speakers at switch on with either my NAP250.2 or my NAP250DR. Perhaps @NeilS has an idea what’s a play here?
Just to be clear - are you switching the 272 on followed immediately by the 250? Or is the 272 switched on all the time?
There is a switch on delay in the 272 before the output is enabled - you can probably hear the relay click in a few seconds after it has booted up.
Hi Neil, yeh so I’m giving the 272 time to pass any delay before turning on the 250. Same thing happens even if the 272 has been on for ages.
In case it’s also useful, music will play through the 250 as soon as I hit the power on button if a suitable source is selected on the 272, but the hum like noise will still be there as before, then vanish.
I think it needs looking at - the usual fix is to replace the input matched transistor pair.
As you say, from cold the duration of oscillation is longer, then as they warm up it goes away.
I don’t think it will cause any damage to anything, just undesirable.