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.


Sometimes transformers can hum. I'm not an expert but you can tighten the mounting screws and/or the plate screws if it has plate screws. 

This could be a number of things.


Swap the L/R inputs on the amp to see if the hum follows the cables or not.


Then have it seen professionally.  This could be bad diodes, caps or tubes.

Could be an electric phenomenon called "DC Offset" and certain MOSFET amp transformers are sensitive to it.


google it, thee are products that address it. I live in an old house and had that issue even tho I installed dedicated AC leans for my audio gear.

emotiva CMX-6 (or the 2) solved the problem for me.

n80 your amp is pretty old it wouldn't be a bad idea to have a tech give it a once over whether it's the source of your hum or not.

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Thanks guys. Will look into getting it checked out but on the other hand probably not willing to shell out big money to have it done. The place that it came from is still in business so I can check with them.

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.  

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.


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

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.