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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 26th Aug 2015, 8:52 am   #1
'LIVEWIRE?'
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Exclamation Reducing Hum Pickup by B&O Turntable

A Vibntage B&O Turntable (I didn't make a note of the model no.) was being used with a different make of Amplifier, nessesitating the use of a DIN to phono adaptor lead to connect the TT to the Amp. Some hum was being picked up, which was due to tere being no earth lead on the turntable. To rectify this, I soldered a short length of standard connecting wire to the metal clamp of the DIN Line Socket, then connected this to the earth terminal of the amplifier. Bingo!! Job done without having to open up the turntable and look for a suitable earthing point.
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Old 26th Aug 2015, 8:58 am   #2
Nickthedentist
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Default Re: Reducing Hum Pickup by B&O Turntable

This is a common problem with DIN-Phono conversions.

As you've discovered, pin 2 of the connector is generally used as the common ground for the L&R cartridge connections but is NOT connected to the turntable's chassis.

Nick.
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Old 26th Aug 2015, 10:54 am   #3
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Default Re: Reducing Hum Pickup by B&O Turntable

I realised that was the case, Nick, but I wondered why B&O didn't fit, as most other tutntable manufacturers do/did, an earth lead. I guess it could be due to the way their TTs connect to other B&O Equipment.
Another thing crossed my mind, which was, and I should know the answer to this, but don't, why is only a thin wire, sometimes up to a couple of metres long, used for TT earthing, when I recall being taught that 'interference currents travel along the surface of a wire, thus, for many applications, a braid about 0.5" wide is used to ground items in order to provide a low impedance path to earth for interference.
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Old 26th Aug 2015, 9:26 pm   #4
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Default Re: Reducing Hum Pickup by B&O Turntable

At mains frequency, the skin effect is all but non-existant, so thin wire is fine. Any RF entering the amp should usually be filtered out by design.
The earth connecton from a turntable sometimes causes more problems than it solves; depending on the power and signal arrangements, earth-loop hum can be induced.
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Old 31st Aug 2015, 10:43 pm   #5
Michael Maurice
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Default Re: Reducing Hum Pickup by B&O Turntable

B&O did fit an earth but not to pin 2, instead it goes to the body of the DIN plug.

There are two ways of dealing with it.

Make your own DIN socket to phono but with an extra wire for the earth.

or

Connect pin 2 to the body of the din plug.
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Old 1st Sep 2015, 9:19 am   #6
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Default Re: Reducing Hum Pickup by B&O Turntable

I had exactly this problem - till I got the matching Tuner amp to mate to the record player.

I used an extra earth wire I made up between amp and player.

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Old 1st Sep 2015, 10:18 am   #7
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Default Re: Reducing Hum Pickup by B&O Turntable

I basically did as Michael Maurice says, i.e., connected an earth wire to the body of the DIN Socket of the DIN-Phono Adapter, though I left the screens of the audio leads connected to pin 2 of the socket. The lead & plug fitted to the deck I left as B&O had wired it. No problems arose from doing it this way
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Old 1st Sep 2015, 10:27 am   #8
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Default Re: Reducing Hum Pickup by B&O Turntable

Quote:
Originally Posted by Michael Maurice View Post
B&O did fit an earth but not to pin 2, instead it goes to the body of the DIN plug.
B & O sold their products as a 'system' and they were all compatible with each other and would not cause earth loops etc. Plug & play is the current term. Using one of their products with other connectors/adaptors often resulted in a problem. They expected you to only buy their products.
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