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Help me solve another speaker hum thread :)

My dealer recently installed a set of Sonus Faber Aida’s with 2x McIntosh MC901 monoblocks. I also have 4x dedicated lines.

The problem is I have have hum in both speakers (hum in the midrange only. The tweeter makes a different noise but I read that’s more normal?) One speaker is louder than the other. Neither changes with volume. The louder one can be heard at about 6 inches away, the quieter one needs my ear as close as possible to faintly hear anything. Sound from both is 50hz maybe 60hz hum. Both monoblocks also make a slight mechanical buzz that can be heard about 6 inches away.

If I have only one speaker, speaker cables, and monoblock powered (nothing else connected, powered, or even plugged in), it still makes the hum.

I have tried using a cheater plug for possible ground loop, also a DC blocker. Neither made any difference. What do you guys think the issue could be? Bad tubes?

Do I need to send the amps back? Or just live with it? I don’t hear from listening position or anything. Thanks in advance.

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james633
888 posts
 

Ok interesting, sounds like an amp issue. One thing is the electrical buzz you hear when you put your ear to the amp is normal for McIntosh. They all have a bit of buzz in the box (no idea what it is).

 

Hopefully you get it sorted. Those are complicate amps and it only take one little thing to go wrong. 

noromance's avatar
noromance
9,404 posts
 

Are you sure the small tubes are in the correct positions in both amps? What about swapping them to see if the noise follows them? You could try one at a time. Do you have any WiFi routers or APs nearby?

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battbot OP
20 posts
 

Ya I’m sure the tubes are correct. I tried swapping all the tubes out with the other amp but that did not effect anything. No wifi or AP’s. I do live about 0.2 miles from 3 AM radio towers and 1 FM radio tower... could that be causing issues? I wouldn’t think so?

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battbot OP
20 posts
 

I spoke to my dealer today, they are gonna come take a look. I'll update the thread when they do. In the meantime if anyone has any great ideas, feel free to share :)

glennewdick's avatar
glennewdick
1,500 posts
 

if its not DC or other power issues coming from your line, dimmers are bad for adding noise on the line, than its probably a tube. Try tapping the tubes when on see if your getting any microphonics out of any of them. Try taping them quite hard to see if there may be some particles trapped in a tubes grid etc.. if you have a second set of tubes try them. 

You seem to have done all the normal things we do to find hum, other than internal issues ie bad component, its most likely tubes or power delivery from your wall. maybe try an different outlet other than your dedicated lines, extension cord may be useful. 

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