Low Impedance Over and Under Pickup Design

[David Schwab]

how the law of magnetic induction works.

Right, but magnetic pickups are also variable reluctance transducers, but you don't accept that model.

Of course any magnetically soft metal becomes magnetized in the presence of a magnetic field. But remove the magnet out of a pickup and listen to the sound. The strings are still magnetized, and you will get very little output and it will sound very thin. The reason is you are missing that magnetic field around the coil.

[Mike Sulzer]

Right, but magnetic pickups are also variable reluctance transducers, but you don't accept that model.

Sure I do. What I have said is that the variable reluctance model is not a good one for understanding how a pickup works. The evidence for this is that people who try to understand pickups in this way often make incorrect deductions about how pickups work. "Variable reluctance" is a model derived from the law of induction that provides a very easy way to make computations about some magnetic circuits, but not pickups.

Of course any magnetically soft metal becomes magnetized in the presence of a magnetic field. But remove the magnet out of a pickup and listen to the sound. The strings are still magnetized, and you will get very little output and it will sound very thin. The reason is you are missing that magnetic field around the coil.

If you remove the magnet, the strings are not much magnetized any more because the material they are made from does not retain very much magnetism when an external field is removed. That is why the pickup sounds weak: the strings (and the cores) have some residual magnetism, but it is much less than when they are in the full permanent field of the pickup. The reason pickups have magnets is because the string does not retain much magnetism unless it is in a magnetic field.

The magnetic field around the coil has nothing to do with it. Look at the law of magnetic induction. There is nothing about the field surrounding a circuit. It is the field passing through the circuit (such as a loop of wire) that counts.

[Dave Kerr]

So, is it more a subtle distinction - it's not that there's a magnetically permeable material "disrupting" the field running through the coil, it's that there's a temporary magnet vibrating above the established field inside the coil? And squat, wide coils like a P90 sound different because you have some cancellation of the signal due to opposing magnetic fields inducing out of phase signals within the outermost layers of the coil?

[Mike Sulzer]

So, is it more a subtle distinction - it's not that there's a magnetically permeable material "disrupting" the field running through the coil, it's that there's a temporary magnet vibrating above the established field inside the coil?

"Temporary vibrating magnet" says it well. But the established field inside the coil has no other function than to make that temporary magnet. You could, for example, leave the magnet out of the pickup and hold a small neo above the string.

Also that temporary magnet changes in strength a bit as it goes up and down. That is the effect that Joseph was describing.

A permeable material in the core increases the flux through the coil from the vibrating string.

And squat, wide coils like a P90 sound different because you have some cancellation of the signal due to opposing magnetic fields inducing out of phase signals within the outermost layers of the coil?

I think it is from differences in inductance. Tall thin coils have less flux linkage than flatter coils with he same number of turns.

[David Schwab]

I think it is from differences in inductance. Tall thin coils have less flux linkage than flatter coils with he same number of turns.

So while the tall coil has the bottom end of the coil farther away from the strings, the entire coil is also closer to the core/poles. So why would they have less flux linkage? Tall coils sound brighter and clearer, maybe with a higher Q. Wide coils sound mellower.

Also, if the string is magnetized, and is weaker than the permanent magnet, why wouldn't the static field from the PM over shadow the moving magnet? It's stated that the magnitude of the emf generated is proportional to the rate of change of magnetic flux, so how would the moving string change the magnetic flux if its much weaker than the permanent magnet? Wouldn't it make sense that besides the moving string as magnet model, we also have the string disturbing the PMs flux field, which gets us back to variable reluctance. Looking at it that way, the shape and strength of the field matters, as does effect the entire width of the coil.

As an example, take a look at the Zoller patent 3588311. If the string is only being sensed over the poles, why does the shape of the magnetic field in this pickup matter? While I have not heard one in person, they are very popular Jazz pickups because they do sound different. So the design is a valid one.



So if the wider magnetic pattern effects the tone, then what has been previously stated by a few people, that the width of the coil or the shape of the magnetic field effect the aperture of the pickup is valid. This can be shown in particle working examples.

I think we can find that many things are going on in pickups, which was alluded to by Helmuth's statement that we really don't fully understand how pickups work. But we can look at smaller parts without the interactions of the rest.

What do you think?

[bbsailor]

"Temporary vibrating magnet" says it well. But the established field inside the coil has no other function than to make that temporary magnet. You could, for example, leave the magnet out of the pickup and hold a small neo above the string.

Also that temporary magnet changes in strength a bit as it goes up and down. That is the effect that Joseph was describing.

A permeable material in the core increases the flux through the coil from the vibrating string.

I think it is from differences in inductance. Tall thin coils have less flux linkage than flatter coils with he same number of turns.

Mike,

I was not talking about the temporary magnet that the string forms while over the permanent magnet. I was refereing to the string peak movement of its initial vibration soon after the initial pluck. To easily see the distance of the peak string movment try this simple experiment.

1. Use a 6" metal ruler next to the string being examined.

2. Pluck the string and observe the string movement from directly overhead.

3. Move the ruler vertically near the peak movement (near the neck pickup) and listen for the string just buzzing against the ruler.

4. Measure the distance from the string at rest to the hand held vertical ruler.

On my Strat using .010" to.046", the strings move about a plus and minus .05".

I'm sure this will vary depending on how hard the string is struck and on the thickness of the string gauge used with thinner strings having a wider peak string movement.

This would indicate that when the string rotates in the downward position it is closer to the magnet by about .05" and when in the upward position be .05" higher than the at rest position. To see the real effect of this simply listen or measure how the output of a pickup changes when the pickup height is changed .05" lower and when it is raised .05" higher than the starting pickup height position. Of course, this experiment all depends on striking the string at a conststant level.

Even when quickly attaching a guitar pickup to an oscilloscope, it is easy to see that one half of the peak output for the first few to first 10 or so cycles will be different from the other half by about 20% to 30%.

This is simply due to the strength of the magnetic field at the location where the string is cutting the magnetic flux being stronger near the magnet and weaker farther away.

While the string may retain some magnetization, the effect of what I speaking about above, has minimal consequences for this temporary string magnetization.

Run your FEMM model again using plus and minus .05" and let's see the result.

Thanks

Joseph Rogowski

[Mike Sulzer]

So while the tall coil has the bottom end of the coil farther away from the strings, the entire coil is also closer to the core/poles. So why would they have less flux linkage? Tall coils sound brighter and clearer, maybe with a higher Q. Wide coils sound mellower.

I was talking about inductance. The flux linkage concerns that between the different turns in the coil. It should be pretty clear why there is more flux linkage when the turns are all bunched together rather than spread out: turns that occupy the same space have perfect linkage; others do not.

Also, if the string is magnetized, and is weaker than the permanent magnet, why wouldn't the static field from the PM over shadow the moving magnet? It's stated that the magnitude of the emf generated is proportional to the rate of change of magnetic flux, so how would the moving string change the magnetic flux if its much weaker than the permanent magnet?

The change simply adds to/subtracts from the field that is present. This is called linearity. Free space is perfectly linear. A magnetic core as used in a pickup is almost perfectly linear. (not so for strong fields in motors, etc. with ferromagnetic cores)

Wouldn't it make sense that besides the moving string as magnet model, we also have the string disturbing the PMs flux field, which gets us back to variable reluctance. Looking at it that way, the shape and strength of the field matters, as does effect the entire width of the coil.

We never left variable reluctance. It is entirely compatible with the law of induction. If you think you have a new effect based on VR, you are not thinking about it correctly.

As an example, take a look at the Zoller patent 3588311. If the string is only being sensed over the poles, why does the shape of the magnetic field in this pickup matter? While I have not heard one in person, they are very popular Jazz pickups because they do sound different. So the design is a valid one.

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So if the wider magnetic pattern effects the tone, then what has been previously stated by a few people, that the width of the coil or the shape of the magnetic field effect the aperture of the pickup is valid. This can be shown in particle working examples.

You are claiming that a 2nd or 3rd hand account of how a pickup sounds that is based on a patent that is probably nonsense (They mostly are.) is somehow more significant than an understanding of the physics!

I think we can find that many things are going on in pickups, which was alluded to by Helmuth's statement that we really don't fully understand how pickups work. But we can look at smaller parts without the interactions of the rest.

I see no reason why pickups cannot be fully understood.

What do you think?

Time spent understanding the law of induction is well spent.

[Rick Turner]

Mike, I have said that the harmonics MAY not be vibrating in exactly the same plane as the fundamental.

If you want to hear a pickup getting horizontal string motion information, just use an E-Bow to excite the string along the horizontal plane.

Mike, I think you need to work on a less simplistic level with regard to how pickups work. You're missing a lot of the subtleties that experienced winders and players hear. I do think there is a lot of smoke and mirrors in our field, but there are also issues of complex interactions with strings and coils and magnetic fields existing in a dynamic three dimensional space. You should really try winding some low Z pickups on classic cores at some point so you can hear what the "magnetic signature tone" is of standard pickups. It's amazing what happens when you're no longer listening to LCR filters in the audio band. These effects ARE NOT simply inductance and coil resonance and all that. Open your ears and learn something that isn't in the textbooks. Trained ears are amazing scientific instruments...

[David Schwab]

You are claiming that a 2nd or 3rd hand account of how a pickup sounds that is based on a patent that is probably nonsense (They mostly are.) is somehow more significant than an understanding of the physics!

No, I made no such claim. What I said was he designed a pickup, which he got patented, which gets the tone claimed in the patent, according to those who use the pickup. The pickup is popular because it gets the tone claimed. He was a player who was not happy with current pickups, so he invented a new variation. There are also recordings and even YouTube videos of the pickup. I said I have never heard the pickup in person.

What you didn't discuss is why the pickup sounds different if it's only sensing the strings at the poles.

Just keep in mind that many inventions and discoveries happen by accident, or at the hands of someone who is not trained in that field. This clearly shows we don't understand everything. To say otherwise is scientism.

[Mike Sulzer]

You should really try winding some low Z pickups on classic cores at some point so you can hear what the "magnetic signature tone" is of standard pickups. It's amazing what happens when you're no longer listening to LCR filters in the audio band. These effects ARE NOT simply inductance and coil resonance and all that. Open your ears and learn something that isn't in the textbooks. Trained ears are amazing scientific instruments...

If these LCR filters are not just related to coil inductance resistance and capacitance, pot values, and cable capacitance, then what are they related to? What is it that is not in "the textbooks"?

Are you claiming that there is something more to magnetic induction than the law of magnetic induction? You have no idea of the consequences.

[Mike Sulzer]

No, I made no such claim. What I said was he designed a pickup, which he got patented, which gets the tone claimed in the patent, according to those who use the pickup. The pickup is popular because it gets the tone claimed. He was a player who was not happy with current pickups, so he invented a new variation. There are also recordings and even YouTube videos of the pickup. I said I have never heard the pickup in person.

What you didn't discuss is why the pickup sounds different if it's only sensing the strings at the poles.

Just keep in mind that many inventions and discoveries happen by accident, or at the hands of someone who is not trained in that field. This clearly shows we don't understand everything. To say otherwise is scientism.

scientism |ˈsīənˌtizəm|
noun rare
thought or expression regarded as characteristic of scientists.
• excessive belief in the power of scientific knowledge and techniques.

The problem on this forum is to find even a minimal belief in such!


Does the pickup have a strong magnetic field along part of the string that is not over the poles? If so, then maybe that affects the sound. How would I know whether it does or not?

[David Schwab]

scientism |ˈsīənˌtizəm|
noun rare
thought or expression regarded as characteristic of scientists.
• excessive belief in the power of scientific knowledge and techniques.

The problem on this forum is to find even a minimal belief in such!

Try:

Scientism - Wikipedia, the free encyclopedia


Reviewing the references to scientism in the works of contemporary scholars, Gregory R. Peterson detects two main broad themes:

It is used to criticize a totalizing view of science as if it were capable of describing all reality and knowledge, or as if it were the only true way to acquire knowledge about reality and the nature of things;

It is used to denote a border-crossing violation in which the theories and methods of one (scientific) discipline are inappropriately applied to another (scientific or non-scientific) discipline and its domain. An example of this second usage is to label as scientism any attempt to claim science as the only or primary source of human values (a traditional domain of ethics) or as the source of meaning and purpose (a traditional domain of religion and related worldviews).

According to Mikael Stenmark in the Encyclopedia of science and religion, while the doctrines that are described as scientism have many possible forms and varying degrees of ambition, they share the idea that the boundaries of science (that is, typically the natural sciences) could and should be expanded so that something that has not been previously considered as a subject pertinent to science can now be understood as part of science (usually with science becoming the sole or the main arbiter regarding this area or dimension). In its strongest form, scientism states that science has no boundaries and that all human problems and all aspects of human endeavor, with due time, will be dealt with and solved by science. This idea has also been called the Myth of Progress. Stenmark proposes the expression scientific expansionism as a synonym of scientism. E. F. Schumacher criticized scientism as an impoverished world view confined "solely to what can be counted, measured and weighed".

Does the pickup have a strong magnetic field along part of the string that is not over the poles? If so, then maybe that affects the sound. How would I know whether it does or not?

I showed you the patent with the accompanying diagram. I see part of the field extending over the coil and past the pickup. What do you see?