How does the material a pickup is made from affect tone?

[Antigua]

Not having a chart nearby makes it impossible to site any percentages of aluminum, cobalt, etc. etc. that make up the different rod magnets for Fender pickups but how do the differences in A5 , A4, A3, A2 manifest in the sound of the particular pickup?
Would a higher percentage of cobalt impart more treble ??

It's long been known that a less electrically conductive pole magnet will give a higher Q factor, meaning more treble at peak resonance, and more permeability will give you more inductance, meaning a lower peak frequency, meaning less treble, and more recently established that the stronger magnetic field does in fact result in more treble.

The question then is, what effect will more cobalt have on those different parameters? It's complicated by the fact that the final properties of the AlNiCo have partly to do with the composition, but also how it's annealed or otherwise made. Cobalt is more conductive than iron, that should mean a lower Q factor, less treble at resonance. But this is a small difference you'd probably never hear, because this change in Q factor can be seen in bode plot tests, and while it's there, it's a very small difference.

Cobalt is less permeable than iron, so the inductance will drop by some amount, that will increase the treble. In the case of a Fender style single coil, the permeability of the pole piece can swing the over inductance of the pickup enough to move the resonant peak quite a bit. The degree of change will depend on how much cobalt is added. For reference, a few years ago I measured the inductance of a Strat pickup with different grades of AlNiCo:

Steel - 3.975H
AlNiCo 2 - 2.203H (13 parts cobalt, says wikipedia)
AlNiCo 3 - 2.244H (no cobalt)
AlNiCo 4 - 2.184H
AlNiCo 5 - 1.882H (24 parts cobalt, says wikipedia)
Air - 1.493H

And I didn't test AlNiCo 8, but wikipedia says it's 35 parts cobalt, it's especially strong (and brittle) . From these data points, you can get an idea for how permeability / inductance drops, and strength rises in proportion to cobalt.

Cobalt apparently makes the magnetic field stronger, or the "residual magnetic flux", and that increases the treble in how it both causes higher harmonics to be created due to string pull, and received by the pickup when the guitar string is magnetically saturated.

Subjectively when guitarists will say that pickups with AlNiCo 5 sound brighter than AlNiCo 2, even across a variety of pickups with difference inductances. Raising the pickup closer to the strings also creates a stronger magnetic coupling between the pickup and the strings, and is also said to bring out more treble, so I think the evidence is there to say that the increased treble from stronger magnetism is audible by itself.

In summary, cobalt increases the treble for three different reasons, with how it effects the magnetic strength and the inductance being the most prominent.

[Brian W.]

It's long been known that a less electrically conductive pole magnet will give a higher Q factor, meaning more treble at peak resonance, and more permeability will give you more inductance, meaning a lower peak frequency, meaning less treble, and more recently established that the stronger magnetic field does in fact result in more treble.

The question then is, what effect will more cobalt have on those different parameters? It's complicated by the fact that the final properties of the AlNiCo have partly to do with the composition, but also how it's annealed or otherwise made. Cobalt is more conductive than iron, that should mean a lower Q factor, less treble at resonance. But this is a small difference you'd probably never hear, because this change in Q factor can be seen in bode plot tests, and while it's there, it's a very small difference.

Cobalt is less permeable than iron, so the inductance will drop by some amount, that will increase the treble. In the case of a Fender style single coil, the permeability of the pole piece can swing the over inductance of the pickup enough to move the resonant peak quite a bit. The degree of change will depend on how much cobalt is added. For reference, a few years ago I measured the inductance of a Strat pickup with different grades of AlNiCo:

Steel - 3.975H
AlNiCo 2 - 2.203H (13 parts cobalt, says wikipedia)
AlNiCo 3 - 2.244H (no cobalt)
AlNiCo 4 - 2.184H
AlNiCo 5 - 1.882H (24 parts cobalt, says wikipedia)
Air - 1.493H

And I didn't test AlNiCo 8, but wikipedia says it's 35 parts cobalt, it's especially strong (and brittle) . From these data points, you can get an idea for how permeability / inductance and strength rise in proportion to cobalt.

Cobalt apparently makes the magnetic field stronger, or the "residual magnetic flux", and that increases the treble in how it both causes higher harmonics to be created due to string pull, and received by the pickup when the guitar string is magnetically saturated.

Subjectively when guitarists will say that pickups with AlNiCo 5 sound brighter than AlNiCo 2, even across a variety of pickups with difference inductances. Raising the pickup closer to the strings also creates a stronger magnetic coupling between the pickup and the strings, and is also said to bring out more treble, so I think the evidence is there to say that the increased treble from stronger magnetism is audible by itself.

In summary, cobalt increases the treble for three different reasons, with how it effects the magnetic strength and the inductance being the most prominent.

Thanx!
...and then there is ceramic...

[soundmasterg]

Another thing to consider when comparing tones of modern pickups to vintage pickups is how the metals are made and how that has changed over the years. No foundry these days uses the Bessemer process as there are more efficient ways to make better quality (more pure) metals these days, but back when PAFs were made, companies who did supply metals used in pickups for parts like base plates, covers, and even the wire, they were all using the Bessemer process for making those. So the short answer is wire today is more pure copper, but is different than what the vintage pickups used. The metals used for base plates, covers, and steel parts in pickups are not exactly the same as they were back in the day. Generally speaking the older metals had more impurities in the parts. Even if you say 'I want to use 1018 steel for x part' 1018 steel today is not quite the same formulation as what it was in 1959. Or if you say 'I will use 42 gauge PE to wind this PAF copy to 5000 turns per coil, and then it will be the same as a vintage pickup' but that is not the case as the wire is different today.

All of these considerations change the sound to varying degrees.

Magnets have generally got better today also as far as strength of magnets. So a full charged modern alnico 5 rod can hold more charge than one from 1959 could when fully charged. The metallurgy is 'better' today in that a more pure part can be made, but the impurities and the less perfect parts from the past actually contributed something to the sound that people find beneficial. Add to that the fact that everyone hears differently, and not everything with sound can be defined with test equipment and equations as it is not fully understood, and you have a lot of different effects to account for.

Greg

[Helmholtz]

The poles in my original 1959 Strat-PUs measure between 900 G and 1200 G.
These are typical values with modern A5 PUs.
The original magnets have never been recharged.

From this I conclude:
1) Magnet material is A5.
2) A5 does not age within 65 years.
3) The old A5 wasn't any weaker than today's.

[Antigua]

All of these considerations change the sound to varying degrees.

I realize that seems like a safe assumption, but when you get into the specifics, how does a given impurity result in some change in the operation of the guitar pickup, you will find that a) the change it would make is too small to hear, or b) the change it does make, is not unique, but can be (and is) achieved in many other ways.

For the most part, all of the considerations either change the Q factor of the pickup, more modify the inductance to some degree. As mentioned above regarding cobalt, any other kind of variance in the metals will alter the conductivity or the permeability of the metal, It's more of less a two dimensional plane of possibility. And theorizing that these changes have a more unique effect on tone, ones that go beyond change of Q factor or inductance, is mostly a product of imagination.

If the wire used in old pickups had less copper, there would just be a little more series resistance, that would just lower the Q by a small amount. Or, if the 1018 steel was imperfect, it will probably have a lower permeability, and so the pickup would have a slightly lower inductance and slightly less magnetic strength at the tops of the screws and slugs. These are not interesting differences that would ever justify seeking out a vintage pickup in and of themselves. And if you wanted to make a modern pickup that performed worse in those respects, you would probably save money on production costs by using a budget foundry that has poorer quality controls. This should make a pickup cost less, certainly not hundreds of dollars.

Magnets have generally got better today also as far as strength of magnets. So a full charged modern alnico 5 rod can hold more charge than one from 1959 could when fully charged. The metallurgy is 'better' today in that a more pure part can be made, but the impurities and the less perfect parts from the past actually contributed something to the sound that people find beneficial. Add to that the fact that everyone hears differently, and not everything with sound can be defined with test equipment and equations as it is not fully understood, and you have a lot of different effects to account for.

Unoriented AlNiCo 2 or 3 are more susceptible to demagnetization in general, but it still would take some sort of external field to have moved the magnetic domains out of their resting alignment. AlNiCo 5 is oriented though. Aside from Hermolts, I have seen other sources and testimony that old AlNiCo 5 having pickups are still fully charged. The only time I ever had them lose charge is when I stuck three Strat pickups in a little box, side by side, because I didn't realize that the RW/RP middle pickup would demagnetize with the neck and bridge pickups, when all stacked together. I think a lot of demagnetization experience might be due to improper storage or handling, but it might also just be a myth that goes around, because our bias is to believe that any given thing loses strength over time.

[freefrog]

The idea that magnets were not weaker in the past has been abundantly illustrated by James Finnerty (Rewind pickups) on the MLP forum, with pics of his measurements.

That said and to share some of the data that I have in my own archives: the 18 rod poles of a 1962 Strat that I've periodically in maintenance are in average 1,25 times less "gaussed" than those of a set of Duncan SSL1's, 1.49 less than a set of hand wound Onamac 69 and 2,22 less than the magnets of a Fender American Standard set from 2000 (to evoke some examples among others)... At least that's what our lab teslameter told.

The rod magnets of this old Strat have never been recharged but they haven't been exposed either to any condition explaining their consistently weak "gaussing". So, they don't seem to be of the same kind than the A5 rods in the other sets aforementioned. Given the inductance measured on these vintage Fender single coils, they don't even appear to be loaded with A5.

I think that's what pickups makers try to mimic when they use degaussed magnets: this degaussing doesn't emulate the effect of time but seems to reproduce the lower "performances" noticed with at least some vintage mags, for whatever reason - non typical alloy, imperfect magnetization from the start (?) ...

Another thing to consider when comparing tones of modern pickups to vintage pickups is how the metals are made and how that has changed over the years. No foundry these days uses the Bessemer process as there are more efficient ways to make better quality (more pure) metals these days, but back when PAFs were made, companies who did supply metals used in pickups for parts like base plates, covers, and even the wire, they were all using the Bessemer process for making those. So the short answer is wire today is more pure copper, but is different than what the vintage pickups used. The metals used for base plates, covers, and steel parts in pickups are not exactly the same as they were back in the day. Generally speaking the older metals had more impurities in the parts. Even if you say 'I want to use 1018 steel for x part' 1018 steel today is not quite the same formulation as what it was in 1959. Or if you say 'I will use 42 gauge PE to wind this PAF copy to 5000 turns per coil, and then it will be the same as a vintage pickup' but that is not the case as the wire is different today.

All of these considerations change the sound to varying degrees.

An instructive experiment is to swap vintage and modern humbucker parts (magnets but also keeper bars / pole shoes + screws and slugs) while keeping the same coils and baseplates then to compare what it gives magnetically, inductively, and when it comes to induced resonant peaks... The simple fact to change a modern stamped keeper bar for a vintage milled one of the same size and mass (+supposedly same alloy) can alter simultaneously several factors. Such changes aren't huge. They can even be inexistent when a single element is swapped, even for a super precise lab meter. But when all the parts are swapped, it can end on noticeably different measured specs with the same coils, and therefore different tones, yes, I agree. :-)

It's also interesting to compare an early Duncan SH1 to a modern one, or a Gibson T-Top to a recent "T-Type": granted, their measured DCR and inductance are very close. But deeper tests reveal dissimilar parasitic capacitances / resonant frequencies / Q factors / magnetic properties / transients, etc. So these pickups logically sound different under a same or similar name, supposed to perpetuate an unchanged recipe...

EDIT - "Vintage" and "modern" don't mean "better" or "worse" in this answer. It's a testimonial and not an advertising nor an argument. ;-)