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FDP Forum / Guitar Mods, Repairs, and Projects / Magnet science???

wrnchbndr

New Jersey

I'm back with the otters again
Jul 22nd, 2019 09:55 AM   Edit   Profile  

Does a non-magnetic metal such as brass have an effect on the magnetic field of a magnet? For the sake of discussion, assume that the alloy in use is completely nonmagnetic.

The intent is to understand the implications of using brass for a pickup bobbin. I made a few of these some years ago but never actually tested them. The idea here is that the bobbin itself if grounded would provide some shielding and brass polishes up to a mirror finish -- years later it will still always polish up to a mirror finish. The downside is that the coil can short to the bobbin but it wouldn't be difficult to insulate the interior of the bobbing with paper and polyurethane.

I need to build some pickups for a cigar box guitar. A P-Bass pickup is the easiest. I'm also thinking maybe plastic sewing machine bobbins -- too easy, but something unique would be cool too.

Peegoo
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Jul 22nd, 2019 11:05 AM   Edit   Profile  

Even though non-ferrous metals like brass, copper, and aluminum are non-magnetic, they are paramagnetic.

This means they react to magnetism only when the magnetic field is in motion in relation to the metal.

You may think that the metal and magnetic field are in constant stasis because the metal and magnets are locked in place and don't move. However, the ferrous strings, vibrating in the field, do generate movement in the magnetic field. Therefore a non-ferrous metal like brass does become magnetic and can influence the field.

This is all measurable on mooy expensive lab equipment, but whether it matters to a person's ears involves a whole bunch of psychoacoustics.

Achase4u
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U.S. - Virginia

Jul 22nd, 2019 01:36 PM   Edit   Profile  

Yes indeed it makes a difference. Bill Lawrence did studies on these effects. He claims it effects Eddy currents in the coil.

Peegoo
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Jul 22nd, 2019 01:54 PM   Edit   Profile  

It has to...because per Lenz's Law, the magnetic field induces eddy currents in the metal.

Here's a cool vid.

Pay no attention to his pronunciation of neodymium. He says "nee-o-DIN-ee-um." He's a neo-dummyum :o)

Hi...Eddy Current, Pledge President.

Te 52

Laws of Physics

strictly enforced
Jul 22nd, 2019 02:17 PM   Edit   Profile  

If you have a permanent magnet sitting on your bench and you place a piece of conductive but non-magnetic material (e.g., brass) near it and let it sit, the magnetic field will be the same as it was before the presence of the conductive piece. So no effect in a static situation.

BUT, if you put a piece of that same material in a *changing* magnetic field, the change in the field will cause current loops to form in the material, and those current loops will generate their own magnetic field in opposition to the field caused by the permanent magnet.

The changing magnetic field can come from relative motion between the permanent magnet and the conductive material (as in a motor), or, in the case of an electric guitar pickup, by the motion of a string which causes the magnetic field of the permanent magnet to periodically intensify and weaken as the string moves closer to, and then farther away from, the permanent magnet.

Sorry to be so wordy, but that's the best I can do at the moment.


Achase4u
Contributing Member
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U.S. - Virginia

Jul 22nd, 2019 02:24 PM   Edit   Profile  

Nice discussion!!!

Here is my contribution.

Bill Lawrence stuffs

Achase4u
Contributing Member
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U.S. - Virginia

Jul 22nd, 2019 02:24 PM   Edit   Profile  

"Pay no attention to his pronunciation of neodymium. He says "nee-o-DIN-ee-um." He's a neo-dummyum :o)"

lol

Achase4u
Contributing Member
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U.S. - Virginia

Jul 22nd, 2019 05:41 PM   Edit   Profile  

In case you are wondering what an eddy current looks like, here is one under a scanning electron magnetron microscope.

Eddy Current.

Leftee
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VA

The Escalator
Jul 22nd, 2019 06:56 PM   Edit   Profile  

That’s Eddy past.

Peegoo
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Jul 22nd, 2019 08:00 PM   Edit   Profile  

Shocking!

And here's a guy who took Nikola Tesla's prior work to new heights; made Tesla look like a rank armature, because he knew watt he was doing:

click

wrnchbndr

New Jersey

I'm back with the otters again
Jul 23rd, 2019 05:22 AM   Edit   Profile  

I did not expect such overwhelmingly educated info. Even better, I did not expect to understand but I do.
You folks are the best :)

SonicBlue

Sunbury-on-Thames

Jul 23rd, 2019 05:57 AM   Edit   Profile  

Wouldn't a brass bobbin be a shorted turn?

Peegoo
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Jul 23rd, 2019 04:47 PM   Edit   Profile  

Mark, get yourself some magnet viewing film. It's extremely inexpensive.

You can use it to view magnetic fields and do a rudimentary comparison of two identical magnets to see if they're equal in Gauss (flux density).

It also allows you to see the orientation of the field as you move the magnet around beneath it: a light green color means the flux lines are running parallel to the film. A dark green color means the flux lines are perpendicular to the film.

"Burn it! It's a WITCH!"

wrnchbndr

New Jersey

I'm back with the otters again
Jul 26th, 2019 02:45 PM   Edit   Profile  

Thanks for the reminder. I need to get some of this. I've been working on something evil that I know you're gonna appreciate.

Peegoo
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Jul 26th, 2019 03:18 PM   Edit   Profile  

Yeah, when you disappear into your lab-BOR-a-tory for three days, we all start to winder what creature is taking form.

rfrakes331K
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IL USA

RonHalen Jokingly He Says
Jul 30th, 2019 07:39 PM   Edit   Profile  

So this is why you can get brass plates for Telecaster bridge pups?

Peegoo
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If irritation occurs

discontinue use.
Jul 30th, 2019 08:18 PM   Edit   Profile  

Yeah, the type of metal does matter. It's subtle, but it does affect the tone of the pickup.

The big hunk of steel or brass that surrounds the pickup (the bridge plate) also affects the tone. It's the reason why mounting a Tele bridge pickup into a Strat's plastic pickguard gets close to a Tele tone...but not all the way there.

(This message was last edited by Peegoo at 10:19 PM, Jul 30th, 2019)

Achase4u
Contributing Member
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U.S. - Virginia

Jul 31st, 2019 10:16 AM   Edit   Profile  

Indeed. That cold rolled steel bridge that surrounds the T bridge is one of the reasons it sounds like it does.

FDP Forum / Guitar Mods, Repairs, and Projects / Magnet science???




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