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Plasma tv & preamp hum-not a loop

Can tubes pick up some type of radiation from a plasma tv? I had to move my entire system to refinish the floors and when I put everything back (all exactly the same except perhaps the same plugs in the power condition were not used as before the move)I sometimes get a hum from both speakers. Mute the pre and it stops. It comes and goes and varies in loudness. Sometimes it just stops only to start again a few minutes later. I know it is not a ground loop because of its behavior and sound. It does not seem to occur as much if I warm up the pre for 20-30 minutes. Thanks for any answers.
yohjo
yohjo OP
83 posts
 
I forgot the important part. The hum only appears when the plasma is on.
macdadtexas
1,794 posts
 
To quote Crush from Finding Nemo, "Dude!!" That is strange.
blindjim
3,092 posts
 
Sounds to me like you are picking up some interference from the plasma, possibly from the cabling attached to it. Moving the rig out & in again, perhaps the video cables are in too close a proximity to the audio ones.. or same thing with the power cables attached to the components.

Try moving them farther apart from one another and rechecking their connections that they are snug.
gmood1
1,251 posts
 
Yeah..a lot of plasmas give off a low level hum or noise all by themselves. Some won't notice it. I didn't notice mine until I replaced it with an LCD..whisper quiet.

I think the power supply has something to do with it. Unshielded transformers are very susceptible to electromagnetic interference. My TVC preamp was like a antenna to this kind of hum.
saki70
907 posts
 
Try removing the TV from the equation , no connections to anything . Let any capacitors discharge .

If that does not do it , check to see if you have two outputs from a source connected to the pre .
I had a problem like yours when I had two output connections from my cable box going to my pre/pro . One analog for the CD quality music channels and one toslink for the surround sound 5.1 broadcasts . Disconnect one of the two and the hum stopped !

Good luck.
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