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Ground Hum

I need some suggestions eliminating ground hum from my VPI Scoutmaster.

Cart is a Shure V15Vmxr (or whatever it's called)
Tone arm is JMW9 with stock wiring
Preamp is Dynavector P75.

I have tried a few different cables ranging from monster cable to cheap stock audio cables you find with most electronics. Makes no difference. If I touch the tone arm wtih my finger, the hum gets louder. If I touch the gold connectors on the back of the turntable the hum goes away. Touching any other parts of the tonearm output block or the preamp causes hum to get louder. Any suggestions?

A_L
arnold_layne
cableplex
40 posts
 
Run a ground wire from the dynavector to the tonearm headshell. Does it go away?

Run a ground wire from the headshell to your main preamp. Does it go away?

If it does go away that will tell you at what point the problem is.

Make sure your rca plugs are clean and make good contacts... Most likely you have a break in your ground wire.

Other possible cause could be the pivot point needle bearing is dirty and breaking the ground, or the contacts to your cart are damaged or dirty.
buffyjames
38 posts
 
Try turning the power plug 180 degrees...use a cheater if you need to. Sometimes the hum comes from the 3rd pin - eliminate that for further experimentation.
dopogue
1,773 posts
 
Try this. There should be a grounding point on the arm itself. See if there's a screw hole on the support for the arm post. Feel with your finger along the right edge. If there is, install a small screw and attach a ground wire which you will then connect to the arm's main grounding point. It's there on my JMW 10.5, but unmentioned in the owner's manual. If it's not there on your JM-9, forget I said anything :-)

Good luck, Dave
arnold_layne OP
141 posts
 
There's already a ground wire running from under the bottom of the tone arm assembly under the turntable to the grounding lug. I have another wire running from that grounding lug to the ground on the P75 preamp.

A_L
dopogue
1,773 posts
 
Okay, you might try removing the ground wires one by one and see if the hum inceases, decreases, or goes away. And reroute the under-turntable ground to the JMW9's main grounding point (between the output jacks). And did you check to see if the screw hole I mentioned is there or not? Dave
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