To connect old turntable to mains earth or not?

[lecky_bob]

Hi Guys,
I am renovating an old vinyl turntable (Thorens TD-150 mkII is anyone cares)

It is fitted with a 2-core mains cable, but there are lots of metal parts including sub-chassis and a 240v motor! Normally this is all earthed via the amplifier (phono leads), but I have swapped the 2-core for a 3-core and earthed the sub-chassis to the mains earth. The arm itself is still earthed via the amplifier but is not connected to the sub-chassis or motor.

Question for the experts: which is safer? Have I done something dangerous by earthing to mains this way?

Thanks

 

[Spoon]

Hi Guys,
I am renovating an old vinyl turntable (Thorens TD-150 mkII is anyone cares)

It is fitted with a 2-core mains cable, but there are lots of metal parts including sub-chassis and a 240v motor! Normally this is all earthed via the amplifier (phono leads), but I have swapped the 2-core for a 3-core and earthed the sub-chassis to the mains earth. The arm itself is still earthed via the amplifier but is not connected to the sub-chassis or motor.

Question for the experts: which is safer? Have I done something dangerous by earthing to mains this way?

Thanks

What was the reason for changing the cable?
According to the manual, it looks like it doesn't need an earth.
You may have introduced some interference in sound quality by adding it though. I do remember a bloke at work talking about 'earth loops' in amps, but I would wait for more knowledgeable people in this to confirm my thoughts.

 

[lecky_bob]

@Spoon Thanks for the reply. You are right about the sound quality, but that is another whole topic!! I went for the earth to mains because of an earth-loop hum, and for safety.
Sound is perfect, but is it safe?

 

[LeeH]

Is any of the outer case metal?

 

[lecky_bob]

Is any of the outer case metal?

No. Plinth (outer case) is all wood.

 

[Shoei]

@Spoon Thanks for the reply. You are right about the sound quality, but that is another whole topic!! I went for the earth to mains because of an earth-loop hum, and for safety.
Sound is perfect, but is it safe?

It can't be made less safe by earthing the metalwork and it may be the insulation wouldn't meet current standards for double-insulated products. I'd leave the earth on if it isn't affecting performance.

The point about earth loops is correct but it looks like the arm is isolated anyway, so adding an earth to the chassis shouldn't create a loop with the ground between cartridge and amplifier.

 

[DPG]

Have had a few Thorens turntables over the years, including a TD150 MkII and a couple of TD160s. I would personally leave it as it was with the 2 core and the flying earth lead. It will be safe and may well work OK how you have it, but there is a risk of low level hum.

Great turntables the Thorens, although the price of them has now become a bit extortionate lately! Still cheaper than a Sondek though eh.

 

[Lucien Nunes]

Adding an earth will not cure an earth-loop hum because this type of hum is caused by too many connections to earth in different places. It might cure other types of hum, such as those caused by unscreened cables near large pieces of floating metalwork.

If the arm ground is not connected to the chassis, e.g. because the arm is on an insulating armboard and its cables make no connections within the TT other than to the arm, then adding your 3-core flex will not create an earth-loop either, and you won't have made the TT any less safe. So, as per Shoei, there's no harm in it.

If you still have a hum problem, tell us about the rest of the configuration. Although this is an electrical forum, I (and maybe others) have a background in professional audio electronic engineering.

FWIW I use both a TD125 and an LP12

 

[telectrix]

never heard of a thorens turntable.is it something like this?

lots of metal there for earthing.

 

[Lucien Nunes]

I'd like to see that going round at 45 rpm

 

[DPG]

Lucien, interested to know what speakers and amplification you use. I don't think you'd use Naim amps - I'm thinking probably valve amp as your main one.

 

[LeeH]

Is any of the outer case metal?

No earth required.

 

[DPG]

No earth required.

Incorrect - it needs the flying earth lead connecting to the earth terminal provided on the amplifier. You will get hum if not.

 

[telectrix]

 

[LeeH]

Incorrect - it needs the flying earth lead connecting to the earth terminal provided on the amplifier. You will get hum if not.

Manufacturers instructions state no earth does it not?