Magnetic pickup cavity plate

Jon Light (deceased) · Post by **Jon Light (deceased)** » 14 Jan 2006 8:14 am

What are the effects, positive or negative, of mounting hardware that magnetically interacts with the pickup magnets? A plate that I was going to use in the cavity as part of a mounting/adjustment system) is in very close proximity to the bottom of the single coil pole pieces and you can really feel the pull when the pickup is in its approximate final position. I'm not even close to wiring this up yet to judge for myself but if this seems like a bad idea then I want to head back to the drawing board before spending too much time concocting this mounting system.

Rick Aiello · Post by **Rick Aiello** » 14 Jan 2006 4:58 pm

When any permanent magnet ... is "backed" by a ferromagnetic plate (i.e. steel) ... it "bumps" up the flux density above that magnet significantly.

That why "pseudo" horseshoe magnets like Rick Turner's or Excels ... actually do out perform the same "alnico" based pickup ... mounted on an aluminum or brass plate.

If you want to "up the juice" ... and get greater output, better bass response and brighter highs ...

Then by mounting a conventional alnico pole piece pup on a steel plate ... will do it.

You can run your own "simulations" here ... to see the results of my above description.

Magnet Tools

Compare the "plain magnet flux density" to the "magnet that is steel-backed" ... using the same set of distances, sizes, etc.

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[This message was edited by Rick Aiello on 14 January 2006 at 05:01 PM.]

Jon Light (deceased) · Post by **Jon Light (deceased)** » 14 Jan 2006 9:03 pm

Very interesting. I will use the excuse that I lack the knowledge base to convert the data to sound expectations to cover why I didn't dwell at that site.
My scenario is: A Fender 10 string pickup from a PSG in a 10 string strap-on non-pedal contraption, with the hopes of a Stringmaster-ish or at least a Fenderish sound. But a rather poor piece of wood. The potential is for an anemic result. The plate, which I was assuming was simply going to be a mistake, just might help matters, based on your response. I am working on a way to make it a removable fixture so that I can A/B the pickup, with and without the plate. Thanks, Rick.

Bob Tuttle · Post by **Bob Tuttle** » 18 Jan 2006 4:30 pm

Rick, What do you think the effect would be if you mounted a twin-blade Lawrence type humbucking pickup on a steel or iron mounting plate?

Papa Joe Pollick · Post by **Papa Joe Pollick** » 18 Jan 2006 5:26 pm

Yeah Rick, I'd like to hear your answer to Bob's question..Been thinkin long those lines myself,but I know diddly..Thanks..PJ

Rick Aiello · Post by **Rick Aiello** » 19 Jan 2006 6:45 am

Any permanent magnet (neodymium-iron-boron, alnico, ferrite, cunife) that is backed by a ferromagnetic plate ... ... will increase in flux density ... at the opposite pole to the backing ... by 20 to 30% or more.

That said ... how it will affect a pickup ... is a function of that pickup's magnets' orientations ...

In a simple single coil with alnico pole pieces ....

<pre>

N N N N N N
S S S S S S
----------------- = steel

</pre>

Well, thats a non-issue ... the flux density above the (N) poles will be greater.

But with other magnet orientations ...

<pre>

Bar magnet ... oriented thru the length

N---------------------S
----------------------- = steel

or

Horseshoe ... opposing

--------N N----------
| |
| |
--------S S---------
------------------------ = steel

</pre>

A steel backing plate could or would screw up the direction that the magnetic lines of force travel ... so badly ...

That the pickup could be rendered non-functional ... or it could even degauss the magnet (like in a Ricky hardened steel horseshoe).

Magnetic lines of force "hate" to travel through air, aluminum, brass ... materials with low magnetic permeabilities.

But "love" traveling through steel and other ferromagnetic materials ... materials with high magnetic permeabilities.

So to get them to "move" in the directions you want them to ... is sometimes quite a challenge ...

Lots of trail and error .... lots of error ...

I hope that helps ...

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Erv Niehaus · Post by **Erv Niehaus** » 19 Jan 2006 7:28 am

I have several Fender Stringmasters and they all have a steel plate underneath the pickup. The height adjusting screws go through it and it also is grounded.
Erv

Papa Joe Pollick · Post by **Papa Joe Pollick** » 19 Jan 2006 10:11 am

Thanks Rick..The mud is a little thinner now..LOL PJ

Bob Tuttle · Post by **Bob Tuttle** » 19 Jan 2006 2:49 pm

Thanks Rick, I guess that means I shouldn't put a steel plate under the 705. Sure wouldn't want to screw up a good pickup.

Rick Aiello · Post by **Rick Aiello** » 19 Jan 2006 3:44 pm

Gentlemen ... I was merely discussing the pros and cons of backing magnets with steel.

When I made neodymium-iron-boron horseshoe magnets for myself ... I preferred to use a steel mounting plate ... even though they are the most powerful magnets on the planet to begin with.

I had customers who preferred less of a "kick" ... so I made their mounting plates out of aluminum.

A couple guys asked if they could replace their aluminum Rickenbacher mounting plate with steel ones to "bump up" the power ...

And I told them "NO WAY" ... unless you wanna kill your magnets.

Some pickup guys offer steel backing on single coils as "an extra" ...

Some humbuckers are made with steel baseplates ...

I would suggest asking the maker of the unit ...

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Jeff Peterson · Post by **Jeff Peterson** » 19 Jan 2006 5:03 pm

www.billlawrence.com