Magnet strength

[Brian W.]

Somebody told me that "less pull does not necessarily mean weaker magnet". I have many different alnico [2,3,4,5] and ceramic mags laying around and some have much more "pull" than others. I always equated stronger magnets with more pull and able to push a pickup into higher volume. All I know is that some of these magnets can hold a screwdriver in the air and some will not.

[mozz]

Where or who told you that? Less pull could be a stronger magnet that is not fully charged. I just put a A5 on a old cassette demagnetizer and basically wiped it out down to 150 gauss.

[Brian W.]

Maybe that's how he meant it [ in regards to the magnet not being fully charged].

[Helmholtz]

Somebody told me that "less pull does not necessarily mean weaker magnet". .

Sorry, that statement doesn't make sense to me. A weaker magnet generates less field and has less pull, no matter what the composition/grade of the magnet is.
There is no chance to identify the magnet type/grade by strength without being/making sure that the magnets are fully charged. And even then it works only in some cases.

[Brian W.]

So a fully-charged A 2 can have more pull then a de-gaussed A5 ?

[Helmholtz]

So a fully-charged A 2 can have more pull then a de-gaussed A5 ?

Sure, in principle any alnico can be (deliberately or accidentally) de-gaussed to zero. But that would require a strong (neo) magnet or electrical demagnetizer.
Some PU manufacturers charge their A5 magnets only to 50% or so in an attempt to reproduce the sound of vintage PUs.

[Antigua]

Somebody told me that "less pull does not necessarily mean weaker magnet". I have many different alnico [2,3,4,5] and ceramic mags laying around and some have much more "pull" than others. I always equated stronger magnets with more pull and able to push a pickup into higher volume. All I know is that some of these magnets can hold a screwdriver in the air and some will not.

I think the language might be getting confused. Since the context is guitar pickups, maybe weakness is meant to mean lower voltage output. A weaker magnet can produce a similar output if what is lost in magnetism is made up for in permeability. AlNiCo 2 is weaker than AlNiCo 5, but it's also more permeable, so if it's serving as a pole piece, the output might end up being about equal.

[Brian W.]

Moving the A2 mag closer to the strings increases the output but the overall tone would have less treble then the A5 mag [?]

[Brian W.]

Sure, in principle any alnico can be (deliberately or accidentally) de-gaussed to zero. But that would require a strong (neo) magnet or electrical demagnetizer.
Some PU manufacturers charge their A5 magnets only to 50% or so in an attempt to reproduce the sound of vintage PUs.

Is that what a A5 unoriented rough-cast would be?

[Helmholtz]

A weaker magnet can produce a similar output if what is lost in magnetism is made up for in permeability. AlNiCo 2 is weaker than AlNiCo 5, but it's also more permeable, so if it's serving as a pole piece, the output might end up being about equal.

I am not sure about that. Faraday's law of induction states that induced voltage (EMF) only depends on the number of turns and the rate of change of flux - not on inductivity or permeability.
So as long as signal flux through the coil stays the same, inductivity should not matter.

[Helmholtz]

Moving the A2 mag closer to the strings increases the output but the overall tone would have less treble then the A5 mag [?]

The results of Prof. Zollner indicate that both stronger magnets and closer PU to string distance shorten the sensing window and thus increase treble.

[Antigua]

I am not sure about that. Faraday's law of induction states that induced voltage (EMF) only depends on the number of turns and the rate of change of flux - not on inductivity or permeability.
So as long as signal flux through the coil stays the same, inductivity should not matter.

It's just like the core of as transfomer, the permeability of the steel reduces the reluctance between the two coils, as it does between the pickup coil and the strings.

[Antigua]

Moving the A2 mag closer to the strings increases the output but the overall tone would have less treble then the A5 mag [?]

Stronger magnetic pull increases the treble by shifting the kinetic energy from the fundamental to the higher harmonics. It does that because it's causes the string to have asymmetrical damping along it's length, promoting the higher narrower harmonics and demoting the lower wider harmonics. The effect is more dramatic if the stronger magnetic pull is closer to the end of the strings because the smaller harmonic divisions are concentrated at the end points. You can even hear it with your own ears if you hold a neodymium magnet over the ends of the strings as they ring out, it will start to sound like a sitar. It's also similar to how pinch harmonics work, the magnet is like a very soft finger.

Since AlNiCo 2 is about half as strong as AlNiCo 5, it would show less of that effect.

Something that Ive never seen talked about, but relating to this issue of permeability, and what probably explains what sets a lot of pickups apart, is that it's a two way interaction between pickup and string, and that the two parts could be expressed as a ratio: the pickup gives the string magnetism, and then the pickup's own permeable core receives that magnetism back again. And I have to thank Mike Sulzer for helping me understand how that worked, he might get upset to see me repeat him almost verbatim without giving credit. So there is a ratio at play percentage of induced voltage that owes to the static magnetism, over the percentage that owes to a higher or lower reluctance path. AlNiCo 5 pickups are one one extreme end of the spectrum, having a strong magnetic field, but a low permeability, while P-90's are on the other end of the spectrum, having a weak magnetic field, but highly permeable screws for cores. AlNiCo 2/3/4 are somewhere in between. If we're talking about bar magnets, that's a different story, in that case the permeability is the same, because the screws define the reluctance path, and only the overall magnetic strength is changing.

[Helmholtz]

Is that what a A5 unoriented rough-cast would be?

No, I was speaking of regular (anisotropic) A5. Unoriented A5 is just incompletely processed A5. It only charges up to around 70% of regular A5 and I wonder if it was ever used commercially in the old days.

[mozz]

If it was cheaper, and i think it was, i'm sure it was used. I've read A2, A3, A4 are all unoriented.