unity gain query

Posted by: Mario on 10 November 2003

Hello all,

After a couple of weeks with the new 282/250 things are getting pretty good, even though the initial warm-up period had me worried. Anyway I dont have any av equipment connected to the 282 but wanted to access the unity gain function to check it. After selecting AV and putting the pre into program mode, I hit the source mute buttion twice and then backed out of program mode. Things appear to be working ok as the lights on the volume and balance were no longer lit up. The problem was when I took the source mute off and heard a loud hum through the speakers. Does anyone know what is going on here? Does there have to be something connected to the AV input for the unity gain to work quietly? I don't recall having this problem with the 112 although I can't really remember if I checked it. I'm assuming that when unity gain is used, the source mute button is not lit up.

Regards Mario.

Posted on: 10 November 2003 by Martin Payne

Mario,

try electing any other unused input on your amp and turning the volume (slowly & carefully) up to full.

This is really all that the unity gain does, and presumbly you know that plugging a CD player or similar directly into a U.G. input will probably damage your speakers?

cheers, Martin

E-mail:- MartinPayne (at) Dial.Pipex.com. Put "Naim" in the title.

Posted on: 10 November 2003 by Mario

Thanks Martin, full volume on any other input is quiet except the hiss. It's just the U.G. that makes the hum. Any body else have any ideas?
Mario.

Posted on: 10 November 2003 by Geoff P

Mario

I have a 282/250 and use the ünity gain option on the A/V input. When I disconnect the signal cable from this input I also get Hum.
I believe that the A/V input is intentionally decoupled from the star earth inside the 282, the logic being that it will find earth inside the A/V amp. In fact this approach prevents an earthloop which would be setup if the A/V signal was earthed at both ends.
Removing the signal cable (and the connection to earth that this cable provides} causes the A/V input to hum.

All the other inputs on the 282 ARE earthed inside the 282, hence don't hum when there is nothing connected.

regards
GEOFFP

Posted on: 11 November 2003 by Mario

Thankyou Geoff, well explained. I connected my cd player to the av socket, selected unity gain and the hum was gone, you are a genius.

Mario.