Turntable Hum - Can't find solution.

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MJC87

5 posts

Wannabe Geek

#107079 6-Aug-2012 19:18

Hi,

I am relatively new to the hobby of listening to Vinyl. I have got a record player and amp setup.

I am experiencing a lot of hum when I turn the amplifier on. I have done some research and the most common solution seems to be to add a grounding wire. I have tried this and no luck.

The turntable is an old one but still in good condition but it doesn't have a grounding point at the back??? so how do I ground it to the amp? I tried putting the wire on the screws at the back and nothing.

I am not running through a preamp, I have just got a Sony STR Amp that has phono inputs. I tried a mates turntable through it and it was fine, so its definately something to do with my turntable.

Any help would be appreciated! I am new to all this so not really sure what I am doing, would love to be able to listen to the old mans record collection.

Thanks

Pock

156 posts

Master Geek

#668543 6-Aug-2012 19:52

There will be a grounding point, you just may have to take the turntable apart to find it. The other (but more expensive) thing you can do is add an inline ground loop isolator.

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Pock

156 posts

Master Geek

#668544 6-Aug-2012 19:53

Hmm, maybe not so bad. There is one on trademe for $15.

MJC87

5 posts

Wannabe Geek

#668583 6-Aug-2012 21:13

Hey thanks for the quick reply.

Ground loop isolator looks like it could be a potential fix. Does this connect between the turntable and the amp???

Pock

156 posts

Master Geek

#668607 6-Aug-2012 21:46

Yup.

techricky

25 posts

Geek

Subscriber

#668617 6-Aug-2012 22:03

I spent a lot of time lookig after turntables in the past and even a bit now! These are a few things to check..

Turntable signal earth leads are connected to the metal parts of the tonearm, there will usually be an earth tag of some sort underneath where the signal leads are connected.
To test you can try touching a wire from the amp earth to a metal part of the arm. Or just try touching the arm and see if the level of hum changes.
The earth is needed as the signals are extremely low level and the circuit of moderately high impedance, so very good at picking up mains hum fields.
Fine unsheilded wires are used from the carrtridge/connector through the arm to the base to allow free rotation, so the whole system relies on the earthed metal tube to keep hum out.. very occasionally one of the wires may break, but this usually will affect only one channel.
There is also usually a connection from one of the Cartridge signal earth pins to any metal parts of the pickup cartridge itself. If the signal leads get reversed on the cartridge for some reason then there can be hum from that part too.
Sometimes the signal leads or connectors will get broken from being moved a lot, but usualy that's on DJ decks.

Line level isolating transformers will do horrible things to the phono level signals, being lower impedance devices. Besides that they are made for breaking an earth loop which you are highly unlikely to have there, especially since it doesn't look like a mains cable with an earth on the turntable.
There are a lot of small things that can break on older gear like that, but the good thing is they are usually pretty easy to fix..

stevenz

2802 posts

Uber Geek

#670187 9-Aug-2012 17:41

Clamping a ferrite bead onto the wire(s) may help, not much if it is definitely an earthing issue, but can clean up other RF.

@KnightNZ

Pock

156 posts

Master Geek

#671047 11-Aug-2012 15:02

techricky:...
Line level isolating transformers will do horrible things to the phono level signals, being lower impedance devices. Besides that they are made for breaking an earth loop which you are highly unlikely to have there, especially since it doesn't look like a mains cable with an earth on the turntable.
There are a lot of small things that can break on older gear like that, but the good thing is they are usually pretty easy to fix..

Noted.