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Old 13th December 2004, 07:14 AM   #11
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I doubt the magnetism changed significantly between the two in the space of a few weeks. They were probably like that to begin with. As others have mentioned, getting both of them remagnetized is highly recommended. Depending on the design, the magnets can sometimes be remagnetized without any disassembly. Sometimes they have to be partially or entirely disassembled.
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Old 13th December 2004, 09:49 PM   #12
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Hi, bad luck with your magnet. The same thing happened to me once and I made some research regarding Alnico magnets. If you break the magnet circuit it will always lose about 50%. You will need to assemble it and have it remagnetized. Alnico magnets are always assembled and then magnetized.

Check with local magnet suppliers, they usually have a magnetization rigg and may be able to help you. I have some Altec driver that I have remagnetized and it worked OK.

Best regads: Ulf
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Old 11th February 2014, 08:56 AM   #13
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Quote:
Originally Posted by ulf_audio View Post
Hi, bad luck with your magnet. The same thing happened to me once and I made some research regarding Alnico magnets. If you break the magnet circuit it will always lose about 50%. You will need to assemble it and have it remagnetized. Alnico magnets are always assembled and then magnetized.

Check with local magnet suppliers, they usually have a magnetization rigg and may be able to help you. I have some Altec driver that I have remagnetized and it worked OK.

Best regads: Ulf

Damn. This happened to me too yesterday. I took apart a rusty JBL 2470 for cleaning. Looks good but plays 6 dB lower than it should.

Where should I send it for magnetization?
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Old 11th February 2014, 11:51 AM   #14
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Read about magnet load lines, e.g. here: DYNE Analytics • View topic - Magnetic Load Lines

Alnicos have a very "curvy" so-called intrinsic curve. As soon as the magnet is put under load (that means the magnetic flux "sees" some resistance, for example an air gap) the magnet gets partly demagnetized (depending on the load). It won't demagnetize any further as long as the load isn't increased, but you'll have to magnetize it again to bring it back (and it will demagnetize itself at once if the load is still there). Therefore magnetized Alnicos should not be disassembled.

Neodyms or Ceramics have a nearly rectangular curve. They won't get partly demagnetized under load, but if you push them too far they're nearly completely demagnetized.
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Old 11th February 2014, 12:21 PM   #15
Rewind is offline Rewind  Sweden
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Originally Posted by Baseballbat View Post
Read about magnet load lines, e.g. here: DYNE Analytics • View topic - Magnetic Load Lines

Alnicos have a very "curvy" so-called intrinsic curve. As soon as the magnet is put under load (that means the magnetic flux "sees" some resistance, for example an air gap) the magnet gets partly demagnetized (depending on the load). It won't demagnetize any further as long as the load isn't increased, but you'll have to magnetize it again to bring it back (and it will demagnetize itself at once if the load is still there). Therefore magnetized Alnicos should not be disassembled.

Neodyms or Ceramics have a nearly rectangular curve. They won't get partly demagnetized under load, but if you push them too far they're nearly completely demagnetized.
Yes, I have learnt this through stupidity. Now the question is where to magnetize my JBL 2470 in Northern or Central Europe.
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