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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
lowrider57's avatar
lowrider57
5,417 posts
 
Possibly your cables are not shielded.
ozzy's avatar
ozzy
7,497 posts
 
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
atmasphere's avatar
atmasphere
11,856 posts
 
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!
john_g OP
81 posts
 
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.
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