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Ground loop hum

I recently purchased a VTL 2.5 pre-amp (with integral VTL phono stage) and a VTL-ST85 power amp. They sound gorgeous, except for the grounding hum which appears only when phono is selected on the pre-amp.

This hum is volume-dependent and not insignificant, and is present even with nothing connected to the phono input on the back of the pre-amp. It is not present when any other source is selected. I have tried lifting the phono ground wire, cheating the ground on all power cables (turntable, pre & power), powering each of the individual components from different circuits, and most recently, running a dedicated audio circuit using #8 stranded copper. None of these has helped.

Interestingly, the hum does not exist when my entire system (including interconnects and the AudioPrism power conditioner I use) is hooked up at the local audio shop. So the problem is definitely in my house. My panel is grounded via a water pipe. Any ideas or suggestions?
melodious_vibrationz

Showing 1 response by jameswei

jameswei
883 posts
 
I had a hum that came from a light dimmer switch installed in the wall. When I flipped the switch, the hum would go away for a while.

I also had a hum when using the VPI PLC to power my turntable. It broadcasts a lot of hum. You don't describe your phono setup, but if you have a PLC, it needs to be really far away from the cartridge and phono interconnects (and the preamps for that matter, as well).

There are probably others who may address possible ground loop issues in the electronics. Good luck.
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