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What's making my system hum?

I have a  Swagman Labs linear power supply feeding the Rega TT-PSU turntable controller. Lately I have noticed a hum audible through the speakers when turned up to about 50 percent of full volume. When I switch the Rega TT-PSU back to its wall-wart power supply, the hum disappears. When I move the power supply away from the TT-PSU, the hum also disappears.

The rest of my system consists of a Rogue Audio Ares phono stage, a VTL IT-85 integrated amp, Vandersteen Treo CT speakers, and various boxes (computer, DAC, linear power supply) to play digital music. There's  virtually no hum when the VTL is set to any source except the turntable.

The obvious solution is to keep the power supply and turntable controller farther apart, but I can't help wondering what's causing this. Anyone have any ideas?
john_g
ozzy's avatar
ozzy
7,461 posts
 
Why is there hum in my system?
Just one smart a-- answer...
Perhaps your speakers forgot the words to the song?

Sorry, couldn't resist.

ozzy
georgehifi's avatar
georgehifi
10,312 posts
 
Ozzy is sort of there with lifting the grounds.
Look at your systems earthing as a whole, there should only be one earth point to the mains, as earths are carried between all the components via the interconnects.

Either the preamp or the source or the poweramp should have that one earth to the mains.
  
You run the risk of an "earth loop" via your households mains cabling if you have more than one earth connected to the mains, this "earth loop" can cause mains hum.

Cheers George

ampmadscientist
6 posts
 
"When I move the power supply away from the TT-PSU, the hum also disappears."

That is the answer.

"The problem is the magnetic field coming from the power transformer in the power supply. Moving it away from sensitive phono circuitry is in fact the correct solution!"

He's right.
john_g OP
80 posts
 
Thanks again to all who responded.


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cleeds
5,947 posts
 
georgehifi3,521 posts03-02-2018 1:04am
Ozzy is sort of there with lifting the grounds.
Look at your systems earthing as a whole, there should only be one earth point to the mains, as earths are carried between all the components via the interconnects.
Ground loops aren’t caused by multiple paths to ground, they’re caused by different potential between those grounds. The proper solution is to get all grounds at the same potential - eliminating safety grounds isn’t a wise shortcut. An interconnect isn’t intended to serve as safety ground, and that’s why components typically have their own safety ground.
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