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?
4197d8ef 0ecf 47d9 9002 6a5320603594john_g
Possibly your cables are not shielded.
So you know that the linear power supply is the culprit. Probably from the transformer.
Grounding can be a problem with low level turntable cartridges . Your LPS probably has a 3 prong plug whereas the standard ( wal-wart) has only 2. Try reversing and/or lifting the plug of the linear power supply at the wall with one of those 2 prong adapters.

ozzy
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!
Thanks for the suggestions, folks. 

lowrider57, the cables are all pretty good quality, including the one between the power supply and TT-PSU. 

ozzy, the cart is a Rega Apheta 2 moving coil. I tried running a ground wire from the tonearm to the grounding terminal on the phone stage and only got more hum. I'm a little leery of flipping hot and neutral on the power supply but may give it a try if I can find a cheater.
john_g.

Don't mess with the cartridge connections, only bad things can happen. 
Changing the orientation of the AC plug at the wall won't hurt anything to try. Also just lifting the ground may help.
Atmasphere has a valid point about moving the transformer.

ozzy
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
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

"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.
Thanks again to all who responded.


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.
My point was to try to find out if the ground is causing the hum. If so then work on corrections.

ozzy
ozzy
My point was to try to find out if the ground is causing the hum. If so then work on corrections.
Yup, that's a very good way to diagnose ground loops.

For what it's worth, all the devices except the integrated amp are plugged into the same power distributor, and it's plugged into the same wall outlet as the amp. That wall outlet is the only thing on the circuit, and that circuit's breaker is the top one in the breaker box.
I suspect to that the cable is not good shielded