Shielding for diy arm wiring when DIY arm itselve cannot not provide it? - diyAudio
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Old 25th October 2003, 07:17 PM   #1
hybris is offline hybris  Netherlands
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Unhappy Shielding for diy arm wiring when DIY arm itselve cannot not provide it?

My WOODEN DIY arm needs a kind of shielding for its cartridge wiring. How must this wiring be executed? I want to prevent hum. How can I provide a kind of suitable shielding? I have built this arm without bore within the arm beam.
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Old 29th October 2003, 03:10 AM   #2
Nui is offline Nui  Thailand
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Default shielding may not be necessary

I just finished mine last week too (wood DIY tonearm). Fighting the hum up to yesterday and finally eliminated it

If you want to shield anyway, a ground wire (connected the chasis of the turntable and then connected to the ground terminal at the preamp) can be wraped around the four signal wires from cartridge for shielding. After all, putting the wires inside of the wood arm wouldn't give better shielding anyway. So you can do it outside of the arm. It has been suggested that the - wires (blue and green) be connected to this ground at the preamp, not at the turntable ground.

But then, I found (for my case) that my arm didn't need shieldling at all when I earthed my ground by connecting the ground terminal of the preamp to the water tap in the bathroom (through a 3 meter long wire). The noise, hum, all the annoying sounds are all gone.

Just an alternative...

Nui
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Old 29th October 2003, 10:01 PM   #3
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Hi,

Hybris,

Why don't you just twist the + and - of each channel?

If you have a MM cartridge this should kill the hum and the extra capacitance will benefit the carts' frequency response.

Cheers,
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Old 30th October 2003, 10:34 AM   #4
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Even nicer, twist them and use a balanced preamp.
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Old 30th October 2003, 07:29 PM   #5
hybris is offline hybris  Netherlands
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Default shielding

Thanks for you answers. I think this will rescue my arm.
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Old 30th October 2003, 10:30 PM   #6
Duo is offline Duo  Canada
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balanced right off the MM cart must have a good CMRR. I would like to try converting my single ended turntable into balanced.

Does anybody have any ideas or want to start a thread on it?
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Old 30th October 2003, 10:38 PM   #7
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Hi,

Quote:
balanced right off the MM cart must have a good CMRR. I would like to try converting my single ended turntable into balanced.
Keep in mind that alot of MM and MI carts have one of the negative legs connected to the body of the catridge internally making them useless for balanced inputs.

With MCs this usually not the case so the are good candidates for a balanced input.

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Old 30th October 2003, 11:00 PM   #8
Duo is offline Duo  Canada
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yeah, that's what I notice is that they ground one side of the setup.

Either way. I can try to find a cartrige and then modify it if possible too.
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Old 30th October 2003, 11:06 PM   #9
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Hi,

Quote:
I can try to find a cartrige and then modify it if possible too.
Not so easy to do on most but you may get lucky...

The easiest ones are those on which the tie to ground is run at the outside of the cartridge body.

I can't guarantee you they won't buzz like a yellowjacket in the wind once that ground is disrupted though.

You'll need a good TT with good magnetic shielding of the motor too.

Cheers,
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Old 31st October 2003, 12:14 AM   #10
BrianL is offline BrianL  United States
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If you remove the connection between the MM cartridge
body (shield) and the low side of one channel (they are
usually only connected to one channel), then you really
should have a 5th wire running to the cartridge shell.
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