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Steel Beneth The Pickup


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Steel screws under single coil pickups? I may have missed something but I have never seen it! A singe coil is made out of vulcanised fibre sheets (non magnetic), copper windings (non magnetic) and magnetic rods (magnetic). The screws are placed on the side of the magnetic field, not under, directly into the fibre. No metal at all UNDER the pup. And yeas, the humbucker use a metal plate under the coils, but it is made out of non magnetic material. The Tele bridge pup has a steel (magnetic) plate under the magnet rods, and everybody knows that removing this have a HUGE effect on the sound. I have tried this.

Then you haven't been looking too hard. Most guitars equipped with trems have a lot of steel under the pickups--trem springs, screws, claws, etc. Some even have neck joints where the pocket and screws wind up under the neck pickup.

My point is that you're probably worrying about nothing. Build the guitar and if it sounds like crap, it's probably NOT because you used steel inserts directly under the neck pickup.

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VOICE OF REASON

Okay, it's probably NOT going to affect the sound of the guitar at all, at least in any noticeable fashion. Manufacturers have been using steel screws under pickups for years and nobody seems to complain that the guitars suddenly sound bad. Any distortion in the field is going to be towards the bottom and will probably not affect string sensing at all.

I second this. Did anyone else even read that article on magnetic shielding?

Yes, the magnetic field BELOW the pickup will be altered and will tend to go through the steel. But think about how pickups are designed and where your strings are vibrating. As a not so scientific test you could always just pluck a string and wave a chunk of steel around under the pickup and see what happens...I'll take a wild guess and say "nothing."

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Then you haven't been looking too hard. Most guitars equipped with trems have a lot of steel under the pickups--trem springs, screws, claws, etc.

OK that’s true. There are steel beneath the pickups, but not directly beneath. If you compare the distance to those steel parts you are referring to and the way I might have to build this guitar (look at the picture) there is a significant difference. If you are familiar with the laws of physics the magnetic field decrease a lot with distance. If I remember my university physics correct they decrease with the square of the distance. So the impact of a chunk of metal right beneath the pup will affect the sound much more, but I do not know in what way, and that’s why I started the thread. Hey, it might actually contribute to the sound!

Some even have neck joints where the pocket and screws wind up under the neck pickup.

Now we’re getting somewhere!! What guitars? Do they have traditional wood screws/neck plate, or do they have the type of steel inserts that I use? What are the distance between the pups and the steel parts?

Yes, the magnetic field BELOW the pickup will be altered and will tend to go through the steel. But think about how pickups are designed and where your strings are vibrating. As a not so scientific test you could always just pluck a string and wave a chunk of steel around under the pickup and see what happens...I'll take a wild guess and say "nothing."

Did you have a look at the Steven Kersting link? It shows how the magnetic field BELOW the pup is changed with the Tele steel base plate. And everyone knows that a Tele-pup sounds different if the steel plate is removed/added. BTW how would you wave a something under a pickup in an ordinary guitar?

Have anyone made/heard of comparisons between guitars with similar pups, but with/without metal beneath the pups in the way I describes? I haven’t but I was hoping that someone already had made the tests that I’m preparing. I have designed the test rig “in my head”, and will start the building today. It will have a SC pup mounted in a wooden frame, suspended above a strat. The rig will have a sliding piece of wood above the pup (opposite side from the strings). The slider will have steel inserts in one. By sliding the piece of wood I will hear EXACTLY what impact the steel will have on. Nevertheless it will take a few days to do the test, but I will publish the result here.

And for the record: I'm not sure the sound will change, but I prefer to know what will happen before I go on with the customers design

Edited by SwedishLuthier
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Reverend guitars have --or used to have-- a 'steel sustain bar' added into their center block. I believe it runs from the neck pocket to the bridge. One source says it runs through the center block, another says it's placed on the bass side.

I can't find any photos of that on their web site--and they don't mention it anymore--but judging from the width of the guitars, that would have placed that comparatively massive bar of steel very close to the pickups --and probably within a similar distance to what you're dealing with.

But then, they also add magnets to their pickups...probably something your client, with his ultra-fancy high-end pickups might not want to do...(why not contact the pickup maker, maybe they'll have a better idea whether this is an issue or not?)

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Why not contact the pickup maker, maybe they'll have a better idea whether this is an issue or not?

As always good advices from you idch. I'll try that.

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Also: Change from a steel base Tele bridge to a brass, and you WILL notice a difference in sound. I have tried that too

And remember that the bushings are no small piece of metal, like a pickup screw. They are about ½” wide and about the same length. Quite a lot of magnetic material, and much bigger then the magnetic rods themselves. What I think is that this steel would probably direct the magnetic field down and away from the stings quite a lot if placed directly against the magnetic rods. Anyway it will affect the magnetic field in one way or another. I don’t think we need to debate this. The question is how much that would affect the sound. For those of you that doubt the effect of steel under magnetic rods, pls have a look at the link to Steven Kersting’s FEMM simulations of magnetic fields in pups.

Now I will of cause have some distance between the rods and the inserts. The magnetic field decrease quite a lot with distance so a larger distance between the rods and the inserts will consequently lessen the impact.

As I said, I will run a couple of tests and get back with the results.

Looks like we are on the same page. We just seem to have differing opinions on how this will effect what we hear. Do you have any sample sound clips of the tele with and without the steel plate?

Are these inserts going to be touching the bottom of the pickup? I was under the impression they were not....

Some even ordered harmonics will be altered when the magnetic field strength changes...just interesting enough that it has me curious :D

To me, it seems fairly silly to be so worried about changing the sound of a pickup when we slap on tone controls to every guitar.

BTW - Unless your steel inserts are really high strength steel, you can easily find a brass out there that has the close to the same ultimate & yield strength of steel...in which case all of this would be a moot point...plus it would be easier to machine. Just a thought.

Edited by Sparky
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PRS CE guitars extend the bolt-on neck joint under the neck pickup with no ill-effect, although they are using humbuckers with bar magnets.

HB pups have a quite different magnetic field, more or less with two different sides, one upwards embracing the strings, and one downwards that would be affected by the steel inserts.

A question: Does PRS use threaded steel inserts in the neck for those guitars? Do you know how they sound (compared with set neck versions of the same model, if there are any)?

Looks like we are on the same page. We just seem to have differing opinions on how this will effect what we hear.

I have no clear opinion of how it will sound. I have only a few ideas and no hard facts. That why I asked from the beginning.

Do you have any sample sound clips of the tele with and without the steel plate?

No sound clips, sorry. But a Tele without steel plate will loose some of its famous high end twang. Removing the plate makes a more unidirectional magnetic field and less high end bite. A piece of steel under the magnets of a strat pup might focus some of the magnetic field downwards (creating longer magnetic poles when the inserts become part of the magnetic structure), away from the strings. This MIGHT attenuate the high end response in the same manner as a steel plate beneath enhancing it. But I don’t know for sure. Pure speculations…

Are these inserts going to be touching the bottom of the pickup? I was under the impression they were not....

Not touching, but in CLOSE proximity. The picture I drew was just a “quickie”

BTW - Unless your steel inserts are really high strength steel, you can easily find a brass out there that has the close to the same ultimate & yield strength of steel

Yeah, I know, but I’m sooo happy with the way my current design works (ten years without any complaints), so I’m not to keen on changing it. Brass is my second option, if

1 the sound is altered in the test

2 I cannot find stainless steel inserts

The test is on its way. The rig is built, the flatwork for the pup is finished (yeah, I do my own flatwork for pups) and I will wind the pickup tonight. Tests result within a day or two

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OK I’ve done the test.

I wound a strat pup and made up a jig that allowed me to suspend the pup over the strings on a strat between the original pups to decrease the influence of their magnetic fields). Over the pup (or under if the pup were to be mounted in a guitar) there were a piece of wood with steel inserts in one end. This piece can be mover, thus moving the inserts closer to/further away from the magnetic poles of the pup. The distance between the magnets and the steel were about 2mm, about the distance that I will use in the guitar to be. For amplification I had to settle with my guitar port, as my mesa rig isn’t available at the moment.

So what’s the verdict? Moving the steel had a clearly noticeable effect on the sound. A quite drastic dip in treble, almost the same feeling you get when somebody is moving in front of a speaker! But that was when the steel was in motion (sliding the piece of wood). When the steel was in place the effect was very subtle. A slight decrease in treble was audible, but not much. The biggest difference I noticed was when the steel inserts were at a 45 degree angle from the magnets, or beneath/beside the magnets so to speak. But even in this position the change was not big. Now remember that this was done with very crude amplification, so I might have to repeat the test in my real rig sometimes soon.

So for now I can say that my worries that the sound were going to be altered was right, but the effect was so small that I will probably just build the guitar with the steel inserts that I ordinary use. If a test with “the real thing” show any different results, I will post them here.

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