NAP 250.2 Power on Hiss

A bit odd... hissing would generlly be indicative of either a 'poluted mains' or a grounding problem in a system. A bit of  hiss is normal in highly revealing Naim systems though.

What sources are you using?

Hi Adam, I have another thread called ‘back to the source’ where I am looking at the options for upgrading and that answers that question.  I believe that what I am hearing is the internal regulation system in the 250.2 settling down.  It is a noisy 10 minute period of audible hiss, with the pre-amp on mute btw, after which the noise suddenly disappears.  It is too long to be capacitor charging time, to my mind, but perhaps some other circuitry is warming up.  The fact that it goes away means that it does not spoil my listening, but the 250.2 is under warranty still (or so I believe) and if it is the early warning of a problem then I need to get it attended to.

Well - you seem to have all the answers figured out. My advice - jus leave your amp on all the time 

With reference to your other thread:

There is a signal earth connection normally through a Naim CD player, DAC or streamer if you run a Naim system, with your Mojo you're not getting a signal earth connection. This is not the same as a safety earth. There is an earth post on the back of the preamp that can provide one if you run a wire to a to something at earth potential (eg the earth pin of a plug in the same block as the Naim amps are in).

Keep the switching mode power supplies plugged in somewhere else if you can, if you have a dedicated hifi spur put the SMPS on another spur/ring main as long as it's the same phase but definitely not sharing a multiblock with the Naim boxes.

Most of us rarely switch our amps off so won't know much about a transient hiss.

Adam Zielinski posted:

Well - you seem to have all the answers figured out. My advice - jus leave your amp on all the time 

Exactly — problem solved. And as we all know, it is Naim’s recommendation to leave our beloved boxes on. 

I would leave it on, but we do get a lot of storms and I fear for it getting damaged by spikes. There are threads saying that surge suppressors cause other unwanted effects on the quality of the mains. Therefore it only stays on when I am about to ensure it is off the mains if a storm blows through. 

To respond to previous comments, I have a few theories but just want confirmation from other users that other 250.2 are like that. 

Mine just hums, no hiss.....oh and it's on all the time too