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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 tsouthworth

tsouthworth
59 posts
 
Melodious,

To rid my tube system of hum (just so I could crank it to full gain to hear tube hiss with no stylus in the groove), I had to resort to grounding my tonearm separately to the preamp and then run a second wire from the 'table to the same spot. It worked the best for me to ground it right at the bearing in my old system. I was getting somewhere - the final step was to ground the preamp to my all metal stand! At high gain, there was a hum that would disappear when I touched the preamp and rack at the same time, thankfully no jolt or electrical buzz in the fingers. My system worked best grounded only at the preamp.

Todd
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