Magnets & Copper Wire: A Pickup Building Thread

[Verner]

Hello tidbits;

Yes, you are generally right, with one clarification. There really isn't a primary and secondary magnetic field. It's one magnetic field, which surrounds the group of magnets and pole pieces. The size and shape and power of the field is a summation of the size, shape, power, and pole orientation of the magnets.

The whole idea of a magnetic pickup is that the strings pass through one end of the magnetic field, and the coil of teeny wire is positioned nearby, within the field. When the string wiggles, it makes the field wiggle, which creates a tiny wiggling electrical current in each turn of the wire in the coil. Multiply that times several thousand turns, and a wiggling audio signal comes out of the coil. Which is a pretty close match to the wiggling of the string.

If the output signal is weak, it means that something isn't getting enough wiggling. The string may not be immersed enough in the field, and not making it wiggle. Or, the coils may not be immersed in the field enough to detect the wiggling.

So the root of the failure is the proximity of the coil to the disturbance in the magnetic field? I want to reverse the orientation, magnets at the coils and a rail or pole pieces at the center, which should make a standard sidewinder. If that works then it seems to imply that magnetic transference is directional, although I may be reading that wrong.

My other wonder is whether there is some sort of disruptive effect caused by the close proximity of the magnet sides/bottom pole to the coils. Is it possible this is causing a cancellation of the signal from the long rod magnets?

I guess the primary question is, if you had two single spools of a multi-coil pickup, one with the magnet protruding 1/8” and one protruding 1/2”, both placed 1/8” under a vibrating string, would the output be different, all else being equal?

 

[Bruce Johnson]

So the root of the failure is the proximity of the coil to the disturbance in the magnetic field? I want to reverse the orientation, magnets at the coils and a rail or pole pieces at the center, which should make a standard sidewinder. If that works then it seems to imply that magnetic transference is directional, although I may be reading that wrong.

My other wonder is whether there is some sort of disruptive effect caused by the close proximity of the magnet sides/bottom pole to the coils. Is it possible this is causing a cancellation of the signal from the long rod magnets?

I guess the primary question is, if you had two single spools of a multi-coil pickup, one with the magnet protruding 1/8” and one protruding 1/2”, both placed 1/8” under a vibrating string, would the output be different, all else being equal?

Hey Verner;

On that pickup arrangement, the weak signal problem could be from either or both ends of the magnetic field. When you put those magnets and iron slugs together, they form up a single field around the whole group. Looking from the side, it's probably roughly triangular shaped, or a rounded inverted T shape. A vertical lobe, rounded on the top, surrounding the vertical rods. Two horizontal lobes, rounded on the ends, out through the coils.

You need to make sure the string will be within the rounded end of the vertical lobe, ideally within 1/8" of the end of the vertical rods.

And, the horizontal magnets need to extend all the way through the coils. All the turns need to be within the wide bottom section of the field.

If you had those two single spool coils, with different extension lengths of the magnets, the output signals should be the same as long as: The magnets were the same length and the magnets went all the way through both coils. Moving the position of the coil within the field doesn't make too much difference, as long as the coil is all within the field.

 

[Verner]

Hey Verner;

On that pickup arrangement, the weak signal problem could be from either or both ends of the magnetic field. When you put those magnets and iron slugs together, they form up a single field around the whole group. Looking from the side, it's probably roughly triangular shaped, or a rounded inverted T shape. A vertical lobe, rounded on the top, surrounding the vertical rods. Two horizontal lobes, rounded on the ends, out through the coils.

You need to make sure the string will be within the rounded end of the vertical lobe, ideally within 1/8" of the end of the vertical rods.

And, the horizontal magnets need to extend all the way through the coils. All the turns need to be within the wide bottom section of the field.

If you had those two single spool coils, with different extension lengths of the magnets, the output signals should be the same as long as: The magnets were the same length and the magnets went all the way through both coils. Moving the position of the coil within the field doesn't make too much difference, as long as the coil is all within the field.

Ok, I think I understand a bit more now, i'm going to have to go research a bit more on magnetic field shapes.

 

[T_Bone_TL]

Ok, I think I understand a bit more now, i'm going to have to go research a bit more on magnetic field shapes.

Sweep up some of your iron filings and drop them between two sheets of clear plastic, which you tape at the edges. Instant magnetic-field-visualizer.

A clear "flat" bottle or container/dish with water (for temporary, then dump it, use) or clear oil (if you trust the seal really well and don't want the filings to rust over time for permanent use) can give more of a 3-D view than the trapped sheet deal. You can also buy (the horror!) fancier trapped sheets with oil or drop by your friendly neighborhood physics/science teacher's classroom (you work in a school, make use of that) to borrow the use of the ones they may well already have in the "magnetic stuff" drawer/cabinet.

As you may have already observed, based on your pictures, loose iron filings have a nasty tendency to show up stuck to things you'd rather not have them on, ultimately, so trapping them is helpful.

 

[Honkey tonk]

Is this close to how you visualize the effect of the base (on right)?

I think that design might be more interesting if you could some-how mechanically move the coil up and down whilst playing

Back the bottom piece with some pyocarbon , so as it moves it lowers the volume while producing a brighter tone

Hooked to a moving thumb rest and your all set

 

[Verner]

Sweep up some of your iron filings and drop them between two sheets of clear plastic, which you tape at the edges. Instant magnetic-field-visualizer.

A clear "flat" bottle or container/dish with water (for temporary, then dump it, use) or clear oil (if you trust the seal really well and don't want the filings to rust over time for permanent use) can give more of a 3-D view than the trapped sheet deal. You can also buy (the horror!) fancier trapped sheets with oil or drop by your friendly neighborhood physics/science teacher's classroom (you work in a school, make use of that) to borrow the use of the ones they may well already have in the "magnetic stuff" drawer/cabinet.

As you may have already observed, based on your pictures, loose iron filings have a nasty tendency to show up stuck to things you'd rather not have them on, ultimately, so trapping them is helpful.

Great ideas! I did contact a physics colleague, we will be getting together soon for some insight.

And yes, I have never worked with these strong magnets, and it found all sorts of filings hiding everywhere, what a pain!

 

[Verner]

So I am working through this thread, but it is pretty dense so it is going to take a bit. It is really fascinating though, I am loving everything.

I am interested in learning more about winding multi-coil pickups. I saw this Gibson EB-4 pickup and saved a pic a few years back, I was unaware multi-coil pickups were a thing back then.

Can someone explain the coil wiring to me? It seems the white wires are connected and coming out in reverse directions from the neighboring coil. I also see the black wires from the middle coils going to the red hot wire. The coil furthest to the right has a black wire going to ground, while the coil furthest to the left is going to the black wire (another ground?) going out of the pickup.

So what I think I am seeing: each set of coils next to each other is reverse wound, and cancelling the hum, and each set is wired in series. I am also thinking the two separate sets are wired parallel, but I am just learning these concepts, so I am not 100% sure. I can't find a pic of the magnets underneath, so I don't know, but I am assuming it is configured in a way that polarizes the pole pieces reverse in relation to the other set.

Does any of that sound accurate?

 

[Bruce Johnson]

So I am working through this thread, but it is pretty dense so it is going to take a bit. It is really fascinating though, I am loving everything.

I am interested in learning more about winding multi-coil pickups. I saw this Gibson EB-4 pickup and saved a pick a few years back, I was unaware this was a thing back then. View attachment 5456838

Can someone explain the coil wiring to me? It seems the white wires are connected and coming out in reverse directions from the neighboring coil. I also see the black wires from the middle coils going to the red hot wire. The coil furthest to the right has a black wire going to ground, while the coil furthest to the left is going to the black wire (another ground?) going out of the pickup.

So what I think I am seeing: each set of coils next to each other is reverse wound, and cancelling the hum. I am also thinking the two separate sets are wired parallel, but I am just learning these concepts, so I am not 100% sure. I can't find a pic of the magnets underneath, so I don't know, but I am assuming it is configured in a way that polarizes the pole pieces reverse in relation to the other set.

Does any of that sound accurate?

Yes, I think you are reading that correctly. That's the usual way to make up multi-coil pickups. The coils are made so two are North Up magnets and two are South Up. Then they are all wired in series, with the coil directions hooked up opposite for the Norths and Souths. The group of four becomes one big humbucker. Actually two humbuckers side-by-side. But the coils all work together to buck that hum.

That's how I made and wired mine. Most one-coil-per-string designs are done that way. In the 8-coil versions (2 coils per string), each pair on a string are opposites. So each string has its own little humbucker.

 

[Verner]

Yes, I think you are reading that correctly. That's the usual way to make up multi-coil pickups. The coils are made so two are North Up magnets and two are South Up. Then they are all wired in series, with the coil directions hooked up opposite for the Norths and Souths. The group of four becomes one big humbucker. Actually two humbuckers side-by-side. But the coils all work together to buck that hum.

That's how I made and wired mine. Most one-coil-per-string designs are done that way. In the 8-coil versions (2 coils per string), each pair on a string are opposites. So each string has its own little humbucker.

Great, thank you! I love learning about all of this! While I was looking up info on interesting designs, I ran across an interview snippet between Seymour Duncan (I think) and Seth Lover regarding the first single coil EB1 pickup. He asked Seth how he came up with the 250k wind count and he answered something like “I just wound it until it couldn’t hold any more”.

Loving the interesting designs and clever solutions I am running into, so cool!

 

[ricardol]

Is this close to how you visualize the effect of the base (on right)?
View attachment 5457047

That could not work...The pickup principle is to have magnetic field lines along the axis of the coil:

If the direction of the field lines is not going inside the coil axis hole, no voltage signal will be induced by the movement of the string...

 

[Verner]

That could not work...The pickup principle is to have magnetic field lines along the axis of the coil:
View attachment 5457089
If the direction of the field lines is not going inside the coil axis hole, no voltage signal will be induced by the movement of the string...

So in my failed design, the magnetized plate induced the field around the coils, which would have been in relation to the top and bottom of the plate going through the coils. So the rod magnets providing the magnetism would perhaps have a more isolated field directly around themselves?

Here is a kindergarten style rendition of my thought:

 

[ricardol]

So in my failed design, the magnetized plate induced the field around the coils, which would have been in relation to the top and bottom of the plate going through the coils. So the rod magnets providing the magnetism would perhaps have a more isolated field directly around themselves?

Here is a kindergarten style rendition of my thought:View attachment 5457257

I didn't intend to judge, prescribe, or criticise Verner. Again, Bruce's comment got me wondering how inert iron (in this case, the base) might shape the magnetic field. That something I haven't seen discussed very much, and it can be hard to describe verbally, thus the drawings.
View attachment 5457451

Since steel is more permeable (?) than air, plastic, or copper, I would expect the field to follow the steel more, making it wider at the bottom. But which of these field shapes is most true? I don't know of an easy way to measure the field shape of a pickup, but you can probably infer some things about it from measuring coil output at different positions.

You can simulate the magnetic field using FEMM...
The horizontal steel plate must be inserted in the coils:

 

[1n3]

FEMM... new to me. Cool. One of the inaccuracies of my illustration is, it doesn't show the field as a gradient. Your image also shows discrete lines, but conveys the gradient better than mine.

From this, it seems like Verner's coils should be well-placed. Can you show what happens without the base plate?

 

[T_Bone_TL]

I didn't intend to judge, prescribe, or criticise Verner. Again, Bruce's comment got me wondering how inert iron (in this case, the base) might shape the magnetic field. That something I haven't seen discussed very much, and it can be hard to describe verbally, thus the drawings.
View attachment 5457451

Since steel is more permeable (?) than air, plastic, or copper, I would expect the field to follow the steel more, making it wider at the bottom. But which of these field shapes is most true? I don't know of an easy way to measure the field shape of a pickup, but you can probably infer some things about it from measuring coil output at different positions.

Thing being, Verner's design (which didn't work as well as hoped in the intended direction) is NOT like those pictures - the coils are around the baseplate, not above it as you have drawn them.

 

[ricardol]

FEMM... new to me. Cool. One of the inaccuracies of my illustration is, it doesn't show the field as a gradient. Your image also shows discrete lines, but conveys the gradient better than mine.

From this, it seems like Verner's coils should be well-placed. Can you show what happens without the base plate?

 

[1n3]

Thing being, Verner's design (which didn't work as well as hoped in the intended direction) is NOT like those pictures - the coils are around the baseplate, not above it as you have drawn them.

You're right. My apologies to Verner and all. Corrected image here; deleted earlier posts.

 

[Verner]

I didn't intend to judge, prescribe, or criticise Verner.

No, please, judge, prescribe, and criticize away! I am profoundly ignorant on this subject and I want to learn from those who know more than me! I jumped in blind to a concept without the fundamental knowledge in place, and thought I was a pretty clever lad for coming up with it, until I was properly humbled by physics.

Years ago I built an electric cello to gig with, it looked like a baseball bat with strings on it. I ran a wire to both ends of the cello strings through the neck, and buried some magnets in the neck below the strings. I figured the strings themselves could be the coil after reading some basics on single coil pickups. I used a small mixer and maxed out the gain to get the signal strong enough to go into a stage board, and gigged with it mounted to a drum stand for many years.

If I had done the proper research, I would have known that I made a very low impedance pickup, and I maybe could have used a transformer to boost the signal onboard, or explored other options that many have tried before me. In that case, just jumping in paid off, in this case it didn't. I really want to understand why now, so I can keep exploring.

 

[Verner]

You're right. My apologies to Verner and all. Corrected image here; will probably delete earlier posts.
View attachment 5458201

How do you make these lovely pictures so quickly?

 

[1n3]

How do you make these lovely pictures so quickly?

Adobe Illustrator. The flux lines are imaginary/schematic. I'm sure Ricardol's FEMM images are more correct in that regard.

 

[Beej]

How do you make these lovely pictures so quickly?

Seconded, they are great!