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How to ground old turntable with no grounding wire

I have an old Marantz turntable that I want to start using again. I have a terrible hum through my speakers when it is turned on--worse when the tone arm is on its rest, better when it's over or on a record. I'm guessing it needs to be grounded (although it was never grounded when I used it years ago). But, it has no grounding screw or wire that I can locate. Suggestions? Any ideas for other causes of this new hum? The other thing I'm wondering about is electrical polarity, because it has an old (non-polarized) plug, plugged into a polarized extension cord. Any and all suggestions welcome!
flowergarden129
herman
2,253 posts
 
So probably the cartridge is picking up hum from some other equipment in the vicinity. Try moving the table, rotate it 90 degrees or move it further from the other stuff.
shackman55
2 posts
 
If this is any chance a Grado cartridge, they are notorious for hum. If you post your Table and cart models, it would make it easier to give a good answer. I have several Marantz (6100 6200 etc) all have ground wires. I suspect it would be easy to locate the ground point inside the table and run a wire. When I am messing with them I use a long piece of 20awg with alligator clips on each end. Clip one to the ground on my amp or pre then poke around on various grounding possibilities in the table till I get the best results. Be careful not to short out anything hot though.
andy76
1 posts
 
I have a similar issue only i made it worse. My wife gifted me a  turntable with shelf(non powered) speakers combo from amazon. The TT has 3.5mm L + R connections in the back. The speakers that came with the TT sound awful. So i decided to plug a pair of yamaha hs50m (powered monitors) to it. As soon as I connect the TT powersupply i get the hum even if the TT is off. However if the plate starts spinning the hum goes away.

So i started googling and visiting boards in which the consensus seemed to be that TT needed ground conection. Sooooo I soldered a wire to the ground labeled spot on the pcb. Grounded the TT to the powerline ground and the hum went away. I felt triumphant until the plate started spinning.... now i get a clicking sound (about 1.5 clicks per second). As part of the trobleshooting i connected the non-powered speakers back to TT, no hum,no clicks.

If i connect 1 powered and one non-powered speaker to TT without turning the yamaha speaker on I get the click through the non-powered speaker until i disconnect the power cable from yamaha.

Anyone has any insights or ideas as to what the issue may be?



atmasphere's avatar
atmasphere
11,800 posts
 
Anyone has any insights or ideas as to what the issue may be?
Yes. Your turntable has a preamp built in. When powered off, any preamp can exhibit a buzz. Get rid of the wire, which is causing noise to be picked up, and turn the speakers off when not in use.
So probably the cartridge is picking up hum from some other equipment in the vicinity. Try moving the table, rotate it 90 degrees or move it further from the other stuff.
If this is any chance a Grado cartridge, they are notorious for hum.
The reason there is a buzz is that the tonearm is not grounded because the ground wire got torn off or removed. So a spot connected to the arm itself should be found for the wire and the wire in turn grounded to the preamp. This will maintain the grounding/shielding system of which the tonearm tube is a part.

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