Earthing a Garrard 401

andreweast

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I've just set up a 401 with an AO modded RB250 and a Grado Platinum Ref cart. Unfortunately I have a big ground loop hum.

The arm cable is earthed via the phono stage, the sub-chassis is earthed via the standard tag, as on this picture:



However it is not earthed through the mains plug. I'm presuming this is what I need to do now. Pardon my ignorance with all matters electrical, but can anyone advise me where to connect the earth in the deck? Where the earth and neutral are connected to the motor there is a screw in between, which holds the plastic cover in place. I could connect it here, as in this cack-handed attempt (for purposes of demonstration...)



Any suggestions would be most appreciated.

 

graham67

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Sometimes it can help to loosely weave the cables from the phono stage to the amp. Or the SUT to the phono stage if applicable.

As an alternative, it might be worth earthing the arm direct to the pre-amp, instead of the phono stage. It may make no difference, but it is always worth trying different configurations.

Also, have you tried changing the cables? Some I/Cs are not shielded as well as others and can induce hum.

 

andreweast

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It's ok; I've sorted it out now, but thanks for the advice folks.

Essentially I followed some advice given by someone on pfm who had their deck set up by Loricraft. His had the mains earth connected to the sub chassis tag, so I have done the same, and the hum is now gone. A lot of faffing and time wasted, but a good result.

 

Cable Monkey

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I can't see any Garrard/Grado issues reported on that spreadsheet. I've been told now to earth from the mains to the same tag as the sub-chassis earthing. I'll try this and if that doesn't work I'll take the Grado off and try another cartridge.
That is why I said 'may not'. However there do seem to be some Platinum Ref issues with other tables. With regards to the safety earth, I would sort that by speaking direct to one of the 401 gurus who post here via PM. From experience the AO arm should have an earth wire with a shorter tag to go to the place where that green wire terminates on the chassis, and a longer one to go to the phono amp. That assumes it has Johnnies earth pin mod. That is all it should need, but that safety earth should be advised by an expert.

Edit: Loricraft is as good as any for the right advice!

 

graham67

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Sometimes it can help to loosely weave the cables from the phono stage to the amp. Or the SUT to the phono stage if applicable. As an alternative, it might be worth earthing the arm direct to the pre-amp, instead of the phono stage. It may make no difference, but it is always worth trying different configurations.

Also, have you tried changing the cables? Some I/Cs are not shielded as well as others and can induce hum.
Sorry Andre, I am not sure I read the original question correctly :( My comments are more about earthing the tonearm not the mains.....

Glad you got it sorted though and yes I can also highly recommend Loricraft, Terry is a fountain of knowledge on these.

 

SergeAuckland

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My method is to earth the turntable's metal work to mains earth for safety reasons. The arm metalwork, which should be insulated from the turntable's metalwork by the armboard/plinth, is earthed to the amplifier's earth tag. That way, safety and no hum loops. If the turntable's construction is such that the arm's metalwork is connected to the turntable metalwork, such as, for example, a Gyrodec, then the turntable is earthed through the arm assuming, as in the Gyrodec, there's no mains earth.

Electrical safety must come first.

S

 
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stewartwen

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"Electrical safety must come first" To right Serge! And this is covered in the original user guide, this is avaliable online!

S

 

andreweast

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I read the user manual before set-up. I don't believe it shows the mains earth connected to the sub-chassis, but do let me know if I missed it.

 

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