Magnetic substructures for JM pickups?

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loveinathens
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Magnetic substructures for JM pickups?

Post by loveinathens » Thu Feb 06, 2020 8:13 pm

Hey everyone! Was throwing some ideas around and noticed that EGC made hybrid EGC500/Jazzmaster pickups, and they appear to be built similar to JMs, but with this strange substructure underneath:

Image

I'm thinking this would affect the sound like the backplate on a Telecaster bridge pickup would. Would you know of anywhere I could order a small aluminum plate like these that I could stick behind my Jazzmaster pickups?
Last edited by loveinathens on Thu Feb 06, 2020 9:05 pm, edited 1 time in total.

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Re: Aluminum substructures for JM pickups?

Post by mbene085 » Thu Feb 06, 2020 9:01 pm

From my understanding of pickup construction, aluminum underneath a pickup shouldn't produce anywhere near the effect of a Telecaster baseplate, as aluminum is not ferromagnetic. It is paramagnetic. Telecaster baseplates are copper-plated steel, with the ferromagnetic steel having a huge impact on the shape of the magnetic field. Aluminum wouldn't have the same effect at all.

Aluminum does produce some eddy currents to my knowledge, but being below the pickup, I believe they would be far less significant (possibly insignificant) in reducing highs compared to when it is used as a pickup cover.

If you want to test the principle, you could stack a few layers of cut up coke cans under the pickup and see what happens. I'm guessing...not much.

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Re: Aluminum substructures for JM pickups?

Post by loveinathens » Thu Feb 06, 2020 9:05 pm

mbene085 wrote:
Thu Feb 06, 2020 9:01 pm
From my understanding of pickup construction, aluminum underneath a pickup shouldn't produce anywhere near the effect of a Telecaster baseplate, as aluminum is not ferromagnetic. It is paramagnetic. Telecaster baseplates are copper-plated steel, with the ferromagnetic steel having a huge impact on the shape of the magnetic field. Aluminum wouldn't have the same effect at all.

Aluminum does produce some eddy currents to my knowledge, but being below the pickup, I believe they would be far less significant (possibly insignificant) in reducing highs compared to when it is used as a pickup cover.

If you want to test the principle, you could stack a few layers of cut up coke cans under the pickup and see what happens. I'm guessing...not much.
Hmm, you have a point. I might've mistakenly assumed it was aluminum because of the EGC association, but what do you think is going on here?
https://reverb.com/item/17242030-electr ... hite-cover

The listing says it's a magnetic substructure, apparently. What material could this thing be made out of?

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Re: Magnetic substructures for JM pickups?

Post by timtam » Thu Feb 06, 2020 9:49 pm

It would be easy for the manufacturer to demonstrate the claimed effect on frequency response, eg ...
http://guitarnuts2.proboards.com/thread ... ting-brass
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Re: Aluminum substructures for JM pickups?

Post by sgarnett » Fri Feb 07, 2020 5:05 am

loveinathens wrote:
Thu Feb 06, 2020 9:05 pm
The listing says it's a magnetic substructure, apparently. What material could this thing be made out of?
Yes, an aluminum plate underneath might affect the tone slightly due to eddy currents, but I doubt if anyone could tell without lab equipment. I suppose it could also reduce buzzing slightly, depending on how you stand relative to the noise source. The plate is most likely to be made of mild steel.

If you want to try it and have a Dremel (or hacksaw, file, and patience), you could get a piece of steel at Lowe’s/HD and make one.

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Re: Magnetic substructures for JM pickups?

Post by mbene085 » Fri Feb 07, 2020 5:42 am

If it's steel and not aluminum, it would impact the magnetic field. That's been established for years...telecaster pickups do it, and from what I recall I think the original WRHBs did as well? Fender's 1961 Bass VI pickups did too (the ones with the big chrome mounts) Fralin sells steel baseplates you can add to strat pickups (they have wax on one side so you just warm it and press it to the bottom of the pickup, then ground the plate).

I actually added one of those base plates to a bridge pickup on a CV 50's strat. Unfortunately, I did it at the same time that I rewired it to the middle tone control. It became a little thicker and more usable, but that could easily have been just from the pot loading the pickup and lowering the resonant frequency, so I'll never know if/what the base plate did...

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Re: Magnetic substructures for JM pickups?

Post by jvin248 » Fri Feb 07, 2020 6:18 am

.

The design in the picture looks more like a shielding plate, especially with the pickup magnet holes cut out so no contact there.

You want a carbon steel plate to go under the pickup and connect physically to the magnets so you can reflect the magnetic field back at the strings. That's how the Telecaster gets it power.

Best I've found is get a house electrical octagon box cover, as they are around 1/8th inch thick, and cut that down to fit your pickup.

If you run a ground wire to the plate you can also cut noise to the pickup (shielding the guitar cavity can also do that though).

I have rummaged in the junk drawer before and found random metal plates that fit and have enough thickness to make a difference on Strat and Tele coils before. Experiment :)

Magnet pole piece magnetic field
Image

Magnetic pole piece with a steel baseplate magnetic field
Image

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Re: Magnetic substructures for JM pickups?

Post by ChrisDesign » Sat Feb 08, 2020 9:54 pm

Why don’t more pickups have basplates? If they work well for the telecaster neck... I know the jaguar pickup’s claw dis toss. Why don’t Humbuckers have them fit even more power?
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Re: Magnetic substructures for JM pickups?

Post by mbene085 » Sun Feb 09, 2020 11:35 pm

ChrisDesign wrote:
Sat Feb 08, 2020 9:54 pm
Why don’t Humbuckers have them fit even more power?
Firebird pickups do. I believe the effect of a ferromagnetic baseplate is different with magnetic-poled pickups (fender single coils, firebirds, WRHBs) than steel-poled pickups with bar magnets at the bottom of the pickup (PAFs, P90s), so 99.9% of the humbuckers out there wouldn't behave this way...

Vintage Firebird pickups have magnetic pole pieces (an alnico bar), and do take advantage of this effect, though. I don't know offhand whether the CuNiFe WRHBs did.

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Re: Magnetic substructures for JM pickups?

Post by timtam » Mon Feb 10, 2020 12:18 am

mbene085 wrote:
Sun Feb 09, 2020 11:35 pm
I don't know offhand whether the CuNiFe WRHBs did.
Yes the original WRHB has the ferrous (steel) 'reflector plate' ...
Image
https://www.tdpri.com/threads/fender-wi ... 490/page-3

There is little discussion of its effect AFAIK. Most of the boutique non-CuNiFe magnetic pole piece WRHB 'clones' have it; Fender's bar magnet version doesn't. Creamery does (magnetic pole piece) WRHB versions both with and without the plate, with this explanation for the 'Modern 71 ' without it ...
https://www.creamery-pickups.co.uk/cust ... ments.html
"I make these without the internal reflector plate to help keep more brightness with coils handwound around full-size Wide Range Humbucker bobbins"
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Re: Magnetic substructures for JM pickups?

Post by mbene085 » Mon Feb 10, 2020 3:31 am

Ah, there you go. So both of the magnet-polepiece humbucker designs of yesteryear used ferrous steel plates.

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Re: Magnetic substructures for JM pickups?

Post by epizootics » Sat Feb 15, 2020 11:50 pm

ChrisDesign wrote:
Sat Feb 08, 2020 9:54 pm
Why don’t more pickups have basplates? If they work well for the telecaster neck... I know the jaguar pickup’s claw dis toss. Why don’t Humbuckers have them fit even more power?

The Gibson-style humbucker design doesn't allow the use of a ferromagnetic base plate. Since the bar magnet is positioned at the bottom of the pickup, any ferromagnetic elements placed below the magnet would actually weaken the field that permeates the string by providing a much easier return path from one pole to the other. Magnetic fields are just as lazy as an electric current - they will try to find the easiest path :)

This is actually why some people cut out whatever length of screws sticks out underneath the pickup. It's a way to reduce the efficiency loss in the magnetic system, which also has the effect of reducing eddy currents by reducing the amount of conductive material in the vicinity of the coil. We're only talking about a small amount of steel here so the effect is far from dramatic, but people do report a slight increase in treble response by doing that to their pickups.

I use steel base plates in many of my single coil designs. They are a cool way to beef up pickups with a low turn count. Since they can be used to force the magnetic field to flow through a certain path, I've also been using them to emphasize the harmonic content of certain portions of the vibrating strings. I make a Rod 90 with 'half a claw' that can be oriented either towards the neck of the bridge, resulting in a change in the general color of the tone. It's a simple design, I'm surprised not to see it used more often.

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Re: Magnetic substructures for JM pickups?

Post by loveinathens » Sun Feb 16, 2020 11:19 pm

epizootics wrote:
Sat Feb 15, 2020 11:50 pm
ChrisDesign wrote:
Sat Feb 08, 2020 9:54 pm
Why don’t more pickups have basplates? If they work well for the telecaster neck... I know the jaguar pickup’s claw dis toss. Why don’t Humbuckers have them fit even more power?

The Gibson-style humbucker design doesn't allow the use of a ferromagnetic base plate. Since the bar magnet is positioned at the bottom of the pickup, any ferromagnetic elements placed below the magnet would actually weaken the field that permeates the string by providing a much easier return path from one pole to the other. Magnetic fields are just as lazy as an electric current - they will try to find the easiest path :)

This is actually why some people cut out whatever length of screws sticks out underneath the pickup. It's a way to reduce the efficiency loss in the magnetic system, which also has the effect of reducing eddy currents by reducing the amount of conductive material in the vicinity of the coil. We're only talking about a small amount of steel here so the effect is far from dramatic, but people do report a slight increase in treble response by doing that to their pickups.

I use steel base plates in many of my single coil designs. They are a cool way to beef up pickups with a low turn count. Since they can be used to force the magnetic field to flow through a certain path, I've also been using them to emphasize the harmonic content of certain portions of the vibrating strings. I make a Rod 90 with 'half a claw' that can be oriented either towards the neck of the bridge, resulting in a change in the general color of the tone. It's a simple design, I'm surprised not to see it used more often.
Got any links to yr stuff?

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Re: Magnetic substructures for JM pickups?

Post by elektrovac » Sun Feb 16, 2020 11:27 pm

loveinathens wrote:
Thu Feb 06, 2020 8:13 pm
Hey everyone! Was throwing some ideas around and noticed that EGC made hybrid EGC500/Jazzmaster pickups, and they appear to be built similar to JMs, but with this strange substructure underneath:

Image

I'm thinking this would affect the sound like the backplate on a Telecaster bridge pickup would. Would you know of anywhere I could order a small aluminum plate like these that I could stick behind my Jazzmaster pickups?
I had Lindy Fralin make me a base-plate for a Jazzmaster bridge pickup some years ago. He made a set of two plates connected with a wire, one plate going at each side of the magnets. As far as I remember, they did have the desired effect of enhancing the lows (I don't own this guitar anymore).

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Re: Magnetic substructures for JM pickups?

Post by epizootics » Mon Feb 17, 2020 10:13 pm

loveinathens wrote:
Sun Feb 16, 2020 11:19 pm
epizootics wrote:
Sat Feb 15, 2020 11:50 pm
ChrisDesign wrote:
Sat Feb 08, 2020 9:54 pm
Why don’t more pickups have basplates? If they work well for the telecaster neck... I know the jaguar pickup’s claw dis toss. Why don’t Humbuckers have them fit even more power?

The Gibson-style humbucker design doesn't allow the use of a ferromagnetic base plate. Since the bar magnet is positioned at the bottom of the pickup, any ferromagnetic elements placed below the magnet would actually weaken the field that permeates the string by providing a much easier return path from one pole to the other. Magnetic fields are just as lazy as an electric current - they will try to find the easiest path :)

This is actually why some people cut out whatever length of screws sticks out underneath the pickup. It's a way to reduce the efficiency loss in the magnetic system, which also has the effect of reducing eddy currents by reducing the amount of conductive material in the vicinity of the coil. We're only talking about a small amount of steel here so the effect is far from dramatic, but people do report a slight increase in treble response by doing that to their pickups.

I use steel base plates in many of my single coil designs. They are a cool way to beef up pickups with a low turn count. Since they can be used to force the magnetic field to flow through a certain path, I've also been using them to emphasize the harmonic content of certain portions of the vibrating strings. I make a Rod 90 with 'half a claw' that can be oriented either towards the neck of the bridge, resulting in a change in the general color of the tone. It's a simple design, I'm surprised not to see it used more often.
Got any links to yr stuff?
I'm still in the process of putting a website together...I've been operating on a small scale so far, mostly with local luthiers and a few fellow OSGers! :)

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