Designing A Pickup

[JoeAArthur]

A string does not have to be magnetized to work with a pickup - all it has to do is change the magnetic flux in a manner so that it (the flux) cuts across the coils to induce a voltage. In other words, a string only has to conduct magnetism, not be a magnet itself.

Seriously, think about what would happen if the string really needed to be magnetized in order to be picked up by a pickup. Not provable in practice.

[Mike Sulzer]

Peter, I apologize for not yet responing to this:

"Everybody:

Try this: Lay down two magnets or one magnet and a magnetic (not magnetized) object on your desk pretty close to each other. Put a piece of paper on top. Sprinkle carbon steel (or other magnetic, not magnetized material) file dust/shavings (or what ever it might be called). The metal dust will lie down, following the magnetic field lines, pretty much like Steven Kerting’s FEMM simulations. Watch the pattern close to magnet 1. Move magnet 2. What happens with the pattern close to magnet 1? The pattern close to magnet 2? The pattern changes around both magnets/magnetic objects."

The field from each magnet fills all space, but is largest close to the magnet. Two magnets far apart appear to have their own individual fields because the field from the other one is small. As they brought together, what you see is not the pattern of individual magnets, but a new pattern. Remember, the magnetic field is a vector field. This means that the value at any point is the vector sum of the two fields. This field can have a new direction and magnitude, or even cancel out in some places, depending on the relative orientation of the two magnets.

It is also true that the magnets can affect each others internal state. Whether this is a big effect or not depends on the type of magnet and how close they are.

[Mike Sulzer]

A string does not have to be magnetized to work with a pickup - all it has to do is change the magnetic flux in a manner so that it (the flux) cuts across the coils to induce a voltage. In other words, a string only has to conduct magnetism, not be a magnet itself.

Seriously, think about what would happen if the string really needed to be magnetized in order to be picked up by a pickup. Not provable in practice.

Joe, you must be thinking that when you move a wire loop through a magnetic field in such a way as to change the flux cutting the loop, you induce a voltage around the loop. In a guitar, the string is not acting as a conductor, it is the magnet.

[black_labb]

i have made a similar pup that is to go into my current guitar. i made the top with a bit of wenge (offcuts from a piece for my neck laminate) and used some pick guard material for the base. i got some alnico magnets (like strat pups) for the poles. its basically a strat pup with a larger cover. if you want the warmer sound of p90's then you can get a shorter magnet and make the winding wider and not as deep. you could also cut the regular strat magnets shorter (it is a hard and brittle material, havent cut it myself) which will also weaken the magnets pull (good in that it wont effect sustain so much, but also effects output) or you could have the magnets exending a ways below the end of the winding window, if you want the extra output from the coil from the stronger magnetic pull.

i go on http://music-electronics-forum.com/forumdisplay.php?f=11 for my pup questions and discussion (there are plenty of people who know alot more than i, i dont know much more than the basics, and havent heard any of the pups i have wound as i have been waiting for me to finish this guitar. i do plan on making all the pups for my guitars from now though.

if you are interested i can post a pic of the pup i wound.

[Geo]

Hey black labb, thanks for the reply. I'd like to see a picture of your pickup of you don't mind posting. I'm thinking now that I will just build a pair of "normal" P-90's. It hadn't occurred to me how different the magnetic fields would be, and how much that would affect the sound.

[SwedishLuthier]

The field from each magnet fills all space, but is largest close to the magnet. Two magnets far apart appear to have their own individual fields because the field from the other one is small. As they brought together, what you see is not the pattern of individual magnets, but a new pattern. Remember, the magnetic field is a vector field. This means that the value at any point is the vector sum of the two fields. This field can have a new direction and magnitude, or even cancel out in some places, depending on the relative orientation of the two magnets.

It is also true that the magnets can affect each others internal state. Whether this is a big effect or not depends on the type of magnet and how close they are.

Exactly. I agree with you almost all the way. That has also been my point all the time. The only thing is that we draw different conclusions from this. My conclusion (or my thoughts or whatever) is that the resulting magnetic field *in the bottom of the coil* will also change when the string moves. And that will affect the sound. Thus the shape and strength of the magnetic field plays a big role in the sound of the pickup. Even at the bottom of the coil. But as I probably have said before: I do not have any “science” behind my last statement. It is a mix of gut feeling and personal experience. But then again there is of cause a possibility that I experience something completely different and account that to the shape of the magnetic field (and its changes due to the movement of the string) at the bottom of the coil.

[JoeAArthur]

A string does not have to be magnetized to work with a pickup - all it has to do is change the magnetic flux in a manner so that it (the flux) cuts across the coils to induce a voltage. In other words, a string only has to conduct magnetism, not be a magnet itself.

Seriously, think about what would happen if the string really needed to be magnetized in order to be picked up by a pickup. Not provable in practice.

Joe, you must be thinking that when you move a wire loop through a magnetic field in such a way as to change the flux cutting the loop, you induce a voltage around the loop. In a guitar, the string is not acting as a conductor, it is the magnet.

Nope. In my guitars, the magnets are in the pickups - not the strings.

A magnetically conductive (or attractive, if you prefer) material - which does not have to be a magnet itself - does attract the lines of flux from the magnet. And in doing so, since we are talking about strings, causes some of these lines of flux to cut through the coil of the pickup inducing a voltage.

But heck, if you need to believe that strings are magnets, more power to ya!! Ignore that the poles of this string magnet might have to change over pickups of different polarities. Should I use south pole magnetic strings or north pole magnetic strings. Where on the package of strings is the magnetic polarity specified?

[black_labb]

http://img.photobucket.com/albums/v643/bla...b/pupbottom.jpg

there is the one ive done, sorry for taking so long with the photos. the top needs to be finished properly, i did one coat of danish oil and then got fingerprints on it.

[billm90]

I think it looks pretty cool!

[Mike Sulzer]

But heck, if you need to believe that strings are magnets, more power to ya!! Ignore that the poles of this string magnet might have to change over pickups of different polarities. Should I use south pole magnetic strings or north pole magnetic strings. Where on the package of strings is the magnetic polarity specified?

Consider this: is an electromagnet a magnet? Of course, but only when the current in the coil is flowing. The magnetic field from the current causes the small domains of atomic current in the steel to line up, producing a much stronger field than from the current alone. So is the part of the guitar string over the pole piece a magnet? Of course, but only if the magnetic field from the pole piece causes the atomic currents in the steel string to line up. Just like the electromagnet, but the field that causes the alignment is from the aligned atomic currents in the pole piece rather than from current in the coil of wire.

But your comment quoted above indicates that you do not understand how a pickup works. If the string were magnetized permanently, the permanent magnet in the pickup would be unnecessary, and even if present, the relative polarities would be irrrelevant. When the string vibrates in this case, the field fluctuatons through the coil would be essentially unchanged if you changed the polarity of the pickup magnet. I think your sarcasm is getting in the way of clear thinking.

[psw]

For me it comes down to this. The permanent magnetic field and all that it contains that is a part of that field (metal poles,strings, steel base plates, the magnet, etc) has an influence on it...this is what I refer to as the sape of the field. Anything that disturbs that magnetic field (the vibration of the strings (hopefully), neon light's stray EMI, a TV or computer monitor (unfortunately), etc) will create an analogous signal in the coil of wire within it.

The sensitivity of the coil, the shape of the field and strength of the coil and how much of the string is open to disturbing the field, all influence what an how much and to what degree these things are transfered into electrical energy.

Are the strings "magnets"...yes, where they are over a magnetic pole of a pickup they are magnetized...but how did this come up...they may as well be magnets if they exist within the magnetic field and influence.

The sustainer, effectively a pickup in reverse, is quite instructive as to these things and the influences that are brought to bear.

It is odd that there is no "perfect" pickup...we are not looking at efficiency. People by and large do not seek a wide response pickup but one with pleasing characteristics...like the P-90. Similarly the desire for a valve tone over a sterile clean hi-fi response.

Some of this conversation has already crept into the sustainer discussion and been instructive...certainly got people considering a few things. Mike's point about the influence of the coils closer to the strings having more influence, has given me some food for thought on understanding why my driver design may be working as well as it does. In the pursuit of a theoretical "perfect driver" (ie reverse pickup)...the most efficient electromagnetic configuration...we are starting to understand that efficiency and power is only a part of the equation.

Anyway...a few random thoughts and I too have trouble understanding the point of the discussion about magnetic strings...as far as I can see, where they dissect the permanent magnetic field of a pickup, they are magnetized and form a part of this system...by vibrating within it, the magnetic field is pushed and pulled and so the rest of the field and the coil "picks up" an this and creates an electrical signal.

A string driver in a sustainer type device (ebow, etc) is similar, but instead of electrical energy being put out, it uses the coil to put out magnetic energy and the string, caught in the sway of this field, moves with it. Such devices have particular problems (the magnetic energy that is put out can disturb nearby magnetic pickup fields and cause a signal) that highlight these forces and influences in ways that pickups alone can not. The extent to which the EMI from a string driver influences other devices in the guitar, is obvious when an overt effect is generated.

Still, interesting thread, I imagine that no one would expect it would come to this... pete

[Mike Sulzer]

" Anything that disturbs that magnetic field...."

A way of analyzing the disturbance to the total field (that is, making that general statement more specific) is to represent the total field as the sum of two or several fields, and to examine the individual behavior of each.

"The sensitivity of the coil, the shape of the field and strength of the coil and how much of the string is open to disturbing the field, all influence what an how much and to what degree these things are transfered into electrical energy."

Yes, and what the analysis shows is that the shape of the fluctuating part of the field (from the vibrating string "magnet") through the coil matters, while the shape of the permanent field from the pickup's magnet only matters at the string because the purpose of this field is to magnetize the string.

[SwedishLuthier]

what the analysis shows is that the shape of the fluctuating part of the field (from the vibrating string "magnet") through the coil matters, while the shape of the permanent field from the pickup's magnet only matters at the string because the purpose of this field is to magnetize the string.

Just trying to follow you here... What analysis are you referring to?

Out of curiosity: How strong is the magnetic field in a magnetized string? How long will the string stay magnetized? I have some ideas but I have no clue about those factors.

[Mike Sulzer]

"analysis"

I am just referring to the discussion in this thread. The thing that needs to be determined is that the fluctuating field from the magnetized string is small compared to the steady field. Then you can ignore the effect of the fluctuating field on the internal state of the permanent magnet as far as significantly altering its strength. Consider:

1. The string is a small weak magnet.*

2. The string moves just a little bit so the fluctuating part is even smaller.

*How weak is a good question. I think the permeability of the steel used in strings is not as high as that of the soft steel used for the pole pieces. It is hard to find a material that does everything that you want! But the field that the string is in from the permanent magnet is quite a bit weaker than the field inside the pole piece. You can see this from the line spacing in the FEMM plots shown earlier in this thread. Then the field from the "string magnet" falls of with distance also. But the core stops it from falling off too fast. Could someone who knows FEMM do the case of a very small magnet (the string) over a steel pole piece? That would show how fast the field falls off.

[SwedishLuthier]

As I am still (with some scepticism) trying to grasp the concept of the string being magnetized by the pickup I tried measure the remaining magnetism in a string moved away from the pickup. I cut the string on a guitar and measured the remaining magnetism in the string. The result: Nill remaining magnetism on my gauss meter (0 to 50 gauss range). Are we not talking permanent magnetism in the strings? Or are we talking something that transfer/conduct (please help me with the term) magnetism? Like any piece of magnetically soft metal paced in a magnetic field?

[Mike Sulzer]

As I am still (with some scepticism) trying to grasp the concept of the string being magnetized by the pickup I tried measure the remaining magnetism in a string moved away from the pickup. I cut the string on a guitar and measured the remaining magnetism in the string. The result: Nill remaining magnetism on my gauss meter (0 to 50 gauss range). Are we not talking permanent magnetism in the strings? Or are we talking something that transfer/conduct (please help me with the term) magnetism? Like any piece of magnetically soft metal paced in a magnetic field?

We are talking about a temporary magnetization. Materials vary as to how much they retain. In fact, a permanent magnet could be just thought of as a ferromagnetic material where the retention time once the exterior magnetization is removed is essentially forever. I am not surprised you cannot measure any retained magnetism in a string, but that was a good measurement to make! I thought it would retain very little, and there is not a lot of material there to start with in a string, so it is hard to detect.

[GregP]

black labb-- how does that thing attach? I see no screw holes or other methods of fixture!

[Geo]

Hey black labb, thanks for sharing the pics! DIY pickups are so awesome.

[JoeAArthur]

We are talking about a temporary magnetization. Materials vary as to how much they retain. In fact, a permanent magnet could be just thought of as a ferromagnetic material where the retention time once the exterior magnetization is removed is essentially forever. I am not surprised you cannot measure any retained magnetism in a string, but that was a good measurement to make! I thought it would retain very little, and there is not a lot of material there to start with in a string, so it is hard to detect.

So, this "save" keeps your theory about strings having to be magnets in order to have a pickup work... intact?

Seriously, do you really expect any one to believe that strings are designed to be instant magnets the moment they are put on the guitar... and instantly not be a magnet when they are removed?

Some things are not so hard to detect as others.

[black_labb]

black labb-- how does that thing attach? I see no screw holes or other methods of fixture!

oh, should have mentioned. there will be holes in either 2 or 4 corners to attach it. (of the outside wood) i made the coil on the bottom as small as possible as it is mounted within the neck and i didnt want the neck strength to suffer too much, which means i can drill the holes without worrying too much about the coils being damaged aslong as i keep a bit of care. i might even find that i have enough room in the centre, but that might be pushing it a fair bit.

[Mike Sulzer]

So, this "save" keeps your theory about strings having to be magnets in order to have a pickup work... intact?

Seriously, do you really expect any one to believe that strings are designed to be instant magnets the moment they are put on the guitar... and instantly not be a magnet when they are removed?

Some things are not so hard to detect as others.

Joe, there is no belief involved here. I am describing how ferromagnetic materials work. If you want to understand this topic, do some reading or take a course. I repeat: when you put a ferromagnetic material such as steel in a magnetic field, the small domains of atomic currents, if they are initially disorganized or randomly oriented, tend to line up making a magnet. I think I gave you a clue as to how to learn about this above. An electromagnet is a coil of wire with a core, often soft iron or steel. When you run current through the coil, the resulting magnetic field is much stronger than if the core were not there. Look up electromagnet on Wikipedia. If you do not believe that, find some other references. I am not sure if you are purposely arguing with me or just ignorant. This is the last time I wil respond to one of your posts until you have something worthwhile to say.

[psw]

This is getting exceptionally silly and very much off topic.

If a metal string is strung up through a permanent magnetic field (as it is over a pickup) it effectively becomes a magnet, or at least considered an integral part of the magnetic circuit, field or however you may wish to describe it. The ability for a string to hold this "magnetism" if it were removed from the field (or taken from the magnetic circuit, or whatever) is obviously not an issue...it remains in the vicinity of the pickups magnetic field and therefore is effectively permanently magnetized (as long as it remains there and for that immediate part of the string) and therefore the string is effectively a "magnet".

SO...

Seriously, do you really expect any one to believe that strings are designed to be instant magnets the moment they are put on the guitar... and instantly not be a magnet when they are removed?

YES!

If they were non-magnetic a pickup wouldn't work now would it. It is only because of the ferro-magnetic qualities of the string that a pickup works...I would have thought obviously.

Of all the things discussed in this interesting conversation, this debate has got to be the silliest. Of more interest is ideas like the top part of the coil sensing more than the lower part and ways of measuring inductance and the like.

Things like this...

while the shape of the permanent field from the pickup's magnet only matters at the string because the purpose of this field is to magnetize the string.

...obviously I take issue with. The amount of the string that is magnetized, and what the string is doing within that area (or shape) is very important. The differences in location of the pickups (bridge or neck for instance) is related to the spacing of nodes within the area of the pickup which greatly influences the "harmonic content" of the pickup. A wider aperture (HB vs. SC) makes a big difference. A wide pickup will span several nodes and cause cancellations of various harmonics (they will sense both the up and down swing on either side of the node).

So, a design like the p-90 with a wide aperture or magnetic "shape" will be sensing more of the string than a traditional single coil pickup. By using traditional magnetic SC poles in such a design, you are combining a wide flat sensing coil with a magnetic field..."shape"...of a SC. This will be quite different from a P-90, but may well be quite a good design.

While the topic sparked the conversation, it is a shame that it will likely disappear where no one will find it over time (possibly a good thing)...perhaps we should consider taking it to another thread that would be more "on topic"...it may well outlast the sustainer thread and attract more participants

In the end, there is a lot more to this than we can really understand and the intrepid DIY'er must rely a little on serendipity for a happy outcome. Good luck to those actually making this type of design, let us know how it goes.

pete

[black_labb]

psw, believe what you want, but it is the ironand nickel in the guitar string that changes the magnetic field, not the nickel/steel becoming magnetic itself.

they are magnetic materials, meaning that they are effected by magnets, not because they are magnetic themselves. they can be magnetised to an extent, but they are not magnetised when on a guitar.

do you know how tele bridge pickups are quite bright (brighter than strat pups, using the same materials and construction techniques. the difference is the steel plate below the pup. this changes the magnetic field and makes the magnets more "focused" so they give a brighter output. this is because the magnetic field is aimed more at a certain spot on the string, as opposed to a wider range (think of it as light or youur vision even, the steel base plate works like a magnifying glass dirrecting the magnetic field to a much smaller place.). if the reason tele bridge pups sounded different is because the baseplate was being magnetised (it may well become magnetised, but that doesnt effect things to a noticeable extent if at all) then it would infact give a warmer sund, as the magnetised baseplate would be widening the area in which the magnet "picks up movement". it doesnt make it warmer, it brightens the sound by effecting the magnetic field. this is an example of how a iron/steel effects the magnetic field.

strings effect the magnetic field in the same way, and their vibration creates an alternating current with the same frequency as the strings vibration. you are essentially saying that magnets stick to iron/steel because they turn the material into another magnet so that they are attracted, when really they have a magnetic pull towards them. if you consider this statement you can go onto some physics websites and check your theories.

keep in mind we are not calling you an idiot, just we/thousands of scholars with more expirience and research on the subject support a different theory to you. obviously you are quite intellingent to come to your conclusions from whatever info you have found/gathered, but its not the common belief amongst the learned.

Edited September 21, 2007 by black_labb

[Mike Sulzer]

psw, believe what you want, but it is the ironand nickel in the guitar string that changes the magnetic field, not the nickel/steel becoming magnetic itself.

If you take some time to learn about the physics, you would see that the only way something put in a magnetic field can make a a big difference is by becoming magnetized. Magnetic field are produced by currents. All materials have atomic currents. In ferromagnetic materials these small current domains can line up to reinforce each other and have a big effect.

[Mike Sulzer]

The amount of the string that is magnetized, and what the string is doing within that area (or shape) is very important.

pete

But the wide sampling as related to the width of the coil does not stand up to analysis. Look at the FEMM plots on page one. For both the P-90 and the Fender type, the magnetic field has a large vertical component only very nearly over the pole piece. Away from the pole piece, the field becomes weaker and more horizontal. Remember, it is only the vertical component (that is, perpendicular to the plane of a loop of wire) that matters.