2. amps-preamps
  3. 172484-115924

Amp hum.

My system used to be dead quiet with no music playing. No hum whatsoever. Lately I’m getting hum I can hear across the room in the right channel. Unplugging peripherals like Sonos Connect and Mac Mini has no effect. Touching the amp or pre amp changes the volume of the hum. The amp is a Mardigal Proceed HPA2 and the pre amp is an Audio research LS-16 (tubes). Speakers are Aerial Acoustics 7Bs. High quality cables throughout including power cords. Decent power conditioner bar and somesort of power conditioner that plugs into the main outlet used for the system.

 

Yes it is an old system but with music playing there is no detectable change or loss in sound quality. Nothing has changed in the electrical system of the home. No recent changes to the hi fi system.

 

After playing music for a few minutes and then stopping the music the hum is gone and does not return until the system is turned back on at a later time.

 

Is this anything to be concerned about? What could have caused this issue? Bad tube? What are things I should look for or look into? Or should I ignore it since it goes away after a few minutes and has no effect on SQ? Any help much appreicated.

n80
willgolf
932 posts
 

It sounds like a bad tube. Swap one tube at a time from L to R and vice versa.  If the hum changes to the other speaker you have found your problem.  I have had this happen to me a couple of times.  This is a process of elimination with the tubes until you find the bad tube.  

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oldhvymec
5,101 posts
 

What willgolf said, simple. Unplug and plug the valves back in, TOO. Same with your connections. Unplug and plug ALL the way back in.. Just 101 service.. Easy and quick. ZERO dollars, too. Move the valves left to right one at a time you’ll figure it out pretty quick.. You have a valve going under water 10 to 1. Their suppose to.

Regards

n80 OP
2,100 posts
 

Thanks guys. That's all easy enough so I'll give it a shot.

atmasphere's avatar
atmasphere
11,575 posts
 

Touching the amp or pre amp changes the volume of the hum.

That isn't a tube. That's some sort of ground problem; apparently its affected by heat.

Does it do it on all inputs to the preamp?

Since its in the right channel only, power cords and the like are off the hook. This seems like good advice:

Same with your connections. Unplug and plug ALL the way back in.

 

 

n80 OP
2,100 posts
 

Update on right channel amp hum.

Was changing the hookups on my Sonos Connect into my Oppo (which I use for DAC and CD) and I noticed a little Oppo USB device which I think is a sort of Bluetooth or digital signal receiver that I had plugged in a while back to see if the Oppo would do AirPlay (it does not; too old apparently). So I unplugged it and threw it in a drawer. No hum since then.

I also changed the Sonos Connect from coaxial to optical into the Oppo at the same time so I can't say for sure which relieved the problem. Changing from coaxial to optical did seem to solve a lot of the glitching in the old Sonos Connect though.

Anyway, both problems seem to be solved. Baffled but happy.

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