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Faint hum....

I've been struggling to understand this issue for a while...my integrated amp has 2 RCA inputs, 1 XLR input, and a few digital inputs (Toslink, Coax, etc). When I turn the system on, i'm usually on either RCA1 (CD player) or RCA2 (phono stage connected), there is a low hum in the speakers. If I increase the volume, it gets louder. If I mute the amp, the hum goes away. It's noticeable, but it doesn't bother me when the music plays. What I find it somewhat strange is that it has the same volume if i switch between RCA1 RCA2, and XLR (I have nothing connected to this input!!!). But when I switch from one digital input to another (Coax, Toslink1, Toslink 2), there is no hum. Everything is dead quiet.
So what's going on? Is there anything I can do to eliminate this hum? I tried all sorts of interconnects, speaker cables, the hum remains when I switch from one analog input to another. It might have different intensities, but no cable got rid of it.
iasi
erik_squires
16,009 posts
 
Hi iasi!! 

This probably has to do with how the switching is being done internally. Sounds like you may have an analog ground loop, something which digital inputs are very good at ignoring.


Did you try removing all analog inputs, then adding them one at a time?



Best,
E
andrewkelley
272 posts
 
Is the hum coming from the speakers or the amp? I chased a loop for almost a year. I tried everything from power conditioners to low noise Power supplies (I have electrostatic) to noise harvesters.
I finally found the hum.
It was coming from an old bug zapper hooked up in the garage. It was on a different circuit, I can’t explain it. When I unplugged it to do some maintenance I noticed all my ps audio noise harvesters stopped blinking and my hum was gone. It must have been putting dc on my line. My amps are Mcintosh too. 
schmitty1
46 posts
 
Bad filter cap in the power supply could be at fault. IMO
Post removed 
iasi OP
115 posts
 
i unplugged everything from the int amp...turned it on and the faint hum is present whenever one of the three analog inputs is selected...the hum disappears when one of the 4 digital inputs is selected...i changed the power cable for the int amp to the one with 2 prongs...no difference...anyway, it is not that obtrusive when the music is playing. i was just trying to understand why is the hum present only on the analog inputs and not on the digital ones.
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