Magnets in Pickups

[x-pro]

If possible, please clean the posts

[Chuck H]

Cleaned

[Chuck H]

Regarding alternative guitar pickups I have to admit that if someone had told me in the past "In less than fifteen years digital simulations of amplifiers will be used by half the guitar players." I'd have told them they were out of their minds. Just like I'd have told someone they were crazy if they'd warned I would have to buy safe drinking water from the store. Things change and old guys like me never see it coming.

[Mike Sulzer]

Some Comments on Magnets in Pickups

The wildest of rumors on that subject rattle around, sent on their way by the manufacturer’s clever sales-managers, and naively and reverently believed by most guitarists. The least of what is propagated holds any truth, though.

The individual variants are said to have different sound characters, e. g.: “Alnico 2 sounds this way but Alnico 5 conversely sounds that way“, etc. It is noteworthy that many strong contradictions between such verdicts can be found. In short: these dictums are complete nonsense for the most part. Rather, the following holds: a pickup fitted with a stronger magnet will – with everything else in the pickup’s build being equal – deliver a higher output voltage compared to a pickup with a weaker magnet. For example, the output signal of the “quieter” pickup may on the oscilloscope screen look like this:


More detailed info: https://www.inside-electric-guitars.com

It is the permanent field component along the string that produces most of the string magnetization, and the direction of the magnetization changes, passing through zero (or nearly so) right over the poles piece. The field from the string passing through the coil is a result of this change in the magnetization. With alnico magnets, the string saturates for a short distance near the pole piece (on both sides of it). It seems to me that his reduces the amount signal amplitude change with different alnico types, but maybe all the necessary measurements have not been done yet. So maybe this is not so simple as implied.

[Chuck H]

It is the permanent field component along the string that produces most of the string magnetization, and the direction of the magnetization changes, passing through zero (or nearly so) right over the poles piece. The field from the string passing through the coil is a result of this change in the magnetization. With alnico magnets, the string saturates for a short distance near the pole piece (on both sides of it). It seems to me that his reduces the amount signal amplitude change with different alnico types, but maybe all the necessary measurements have not been done yet. So maybe this is not so simple as implied.

If this is so then alnico and perhaps any specific materials do indeed sound different. I interpret by your post that alnico could have a sort of compression effect. Possibly dependent on adjustments or other physical particulars. Additional research not withstanding. But this is contrary to my own beliefs regarding magnet material so I like it. I don't mind finding out I'm wrong if I can learn something. Especially if it's arcane as something mojo worthy about the use of alnico. I always thought alnico's popularity was purely vintage juju.

[Helmholtz]

With alnico magnets, the string saturates for a short distance near the pole piece (on both sides of it). It seems to me that his reduces the amount signal amplitude change with different alnico types, ...

Zollner showed that the string typically saturates right above the pole piece.
There's no indication that this only happens with alnico.
Rather it is a consequence of field distribution, orientation and strength (and the magnetic properties of the string).

[bbsailor]

Hello members,

What is your opinion about the effect of using two magnets per string like what is used on bass guitar pickups?

My observation is this. With the string resting between the two pickup magnets there is some effect on the pickup harmonics as the string moves between or near two magnets in one string vibration cycle.

Bass notes work very close or in synchronization with drum beats and need some way to stand out.

I would like to see other opinions about two magnets per string bass pickups. Has any guitar pickup maker ever tried this?

Thanks

Joseph J. Rogowski

[Mike Sulzer]

Zollner showed that the string typically saturates right above the pole piece.
There's no indication that this only happens with alnico.
Rather it is a consequence of field distribution, orientation and strength (and the magnetic properties of the string).

Right, any material that produces a strong enough field produces string saturation. Alnico was the first material to make this relatively easy to do.

The string magnetization changes direction over the pole piece. Thus it is zero, centered over the pole piece.

Zollner's Figure 5.4.10 is the relevant figure, available from this file (English translation):.
https://www.gitec-forum-eng.de/wp-co...ith-string.pdf

Also, my measurements are shown here:
https://guitarnuts2.proboards.com/th...ic-flux-string

[Mike Sulzer]

Hello members,

What is your opinion about the effect of using two magnets per string like what is used on bass guitar pickups?

My observation is this. With the string resting between the two pickup magnets there is some effect on the pickup harmonics as the string moves between or near two magnets in one string vibration cycle.

Bass notes work very close or in synchronization with drum beats and need some way to stand out.

I would like to see other opinions about two magnets per string bass pickups. Has any guitar pickup maker ever tried this?

Thanks

Joseph J. Rogowski

The component of the magnetic field from the permanent magnet(s) pointing along the string is what counts mostly. With two magnets I would expect this to have less spatial variation in the space near the string than with one. So I would not expect the effect yo describe to be signifiant.

[Helmholtz]

Also, my measurements are shown here:
https://guitarnuts2.proboards.com/th...ic-flux-string

Thanks for sharing your interesting results.
Still I don't see a relevance regarding specific sound differences between alnico grades or other magnet types - except for field strength.
Also e.g. A5 doesn't have to be fully magnetized and PU to string distance can be varied for more or less string saturation.

Correction to my earlier post:
Exactly above a polepiece the axial string B has a zero crossing, so there can't be saturation.
Saturation regions will be left and right off center, where there are positive and negative B maxima.

[Antigua]

What surprises me (and I think surprises everybody to some extent) is how little of an amplitude difference there is when the magnetic strength is halved. For example, If you replace AlNiCo 2 in a PAF style humbucker with a ceramic, the measurable strength at the top of the pickup roughly doubles, but the output doesn't seem to double. I think magnetic saturation of the guitar string is a very plausible reason for why that is.

What is certain is that the stronger magnetism pulls the guitar strings harder, and induces higher harmonics, similar to pinch harmonics in concept. If you put a neodymium magnet over the guitar strings (while making sure not to risk degaussing the pickups), you can hear these ear piercing harmonics really clearly, with the exaggerated circumstances. I think this is the reason ceramic magnets are not beloved in PAF style pickups, the sound becomes abrassive to the ears.

Single coil Strat pickups, on the other hand, with ceramic magnets, and single coil sized humbuckers, also commonly feature ceramic magnets, but because of their higher reluctance, don't pull on the strings are much and therefore don't induce that same harsh sound, despite making use of a strong ceramic magnet. But Strat pickups with AlNiCo 5 pole pieces, very strong magnetic concentration, is a sound that is also described has "harsh", and has players lowering their Strat pickup to just the right spot where they get a decent output level, without a harsh tone. AlNiCo 5 pole pieces are so strong that no other pickup type can brag that it causes something like "Stratitus", where it pulls against the strings so hard that it causes them to change ibn pitch as they vibrate. That would be a selling point if only it didn't sound awful.

[Helmholtz]

So with a given PU design it boils down to the field strength at the string.

[Chuck H]

So with a given PU design it boils down to the field strength at the string.

Which is how this thread opened and has long been my own belief.

But there may yet be be reasons to choose one magnet material over another. If magnets are used as the pole pieces then the materials permiability would affect inductance, right? Maybe not enough difference to matter? I don't know but it occurred to me.

[Antigua]

Which is how this thread opened and has long been my own belief.

But there may yet be be reasons to choose one magnet material over another. If magnets are used as the pole pieces then the materials permiability would affect inductance, right? Maybe not enough difference to matter? I don't know but it occurred to me.

The most important properties of the pole piece are the conductivity and permeability, for a few different reasons.

The conductivity and permeability together determine the degree of eddy current formation in the pole pieces, which causes a roll off of high end response, and a lower Q factor at the resonant peak of the pickup. If you take a Strat pickup and replace the AlNiCo pole pieces with steel poles, both are conductive and show eddy currents for that reason, but because the permeability in the steel is so much greater, the eddy currents are stronger, so the Q factor at resonance is lower, and the high end is attenuated. This is a plausible reason why 250k pots are common in Strat and Teles with AlNiCo pickups, where as guitars with steel poled pickup usually have 500k pots, the 250k pot in the Strat and Tele lower the Q factor more than the 500k pots will, in order to offset the brightness they cause otherwise.

The permeability of the pole pieces also has two other consequence. First, it determines how well the magnetic strength of the magnet underneath makes it's way up towards the guitar strings. The second consequence is that increases the inductance value of the coil, and together with the capacitance, the inductance it determines the resonant peak of the pickup. If you take a Strat pickup that is about 2 henries with AlNiCo 5 pole pieces, and you replace them with steel pole pieces, the inductance increases to about 3.5 henries, due to the increased permeability of steel over AlNiCo 5. Even though the permeability of steel is about hundred times greater than AlNiCo, the inductance only barely doubles, because the pole piece only accounts for a fraction of the overall magnetic circuit, or reluctance path.

From what I've read, the steel grades used for guitar pickups, possibly 1018 or 1215, which are apparently a good mix of being electrically interactive and also machinable, in order to made made into screws.

When you replace AlNiCo 2 with AlNiCo 5 or vice versa in a Strat style single coil, the same changes happen, but with respect to the metallurgic differences between AlNiCo 2 and 5, which are much smaller than the differences between steal and AlNiCo. AlNiCo 2 and 3 have slightly higher permeability and conductivity, so the inductance goes up slightly due to the permeability, and the Q factor drops slightly because of the conductivity, but the difference is small. I see the difference in bode plots, but I can't be sure I really hear the difference. But when people talk about the sound difference between Strat pickups with AlNiCo 2 or 3, or AlNiCo 5, it's possible that the pickups with AlNiCo 2 or 3 have a higher inductance, which causes a lower resonant peak, and that they reduced high end is perceptible.

The Gauss measured at the top of the D ang G pole pieces on a vintage stagger Strat pickup with AlNiCo 5 is about 1050 Gauss, for AlNiCo 2 its about 700 Gauss, for AlNiCo 3, about 600 Gauss, and for steel pole pieces with a ceramic magnet underneath, about 400 Gauss. So AlNiCo 5 is a powerful magnet in this context, because even though the ceramic is stronger, the steel pole pieces don't carry that full strength up from the bottom of the pickup. But the surprising thing is that the steel poles Strat pickup with the weaker magnetic field at the pole tops is actually louder than Strat pickup with AlNiCo, even AlNiCo 5, because the much higher permeability of the steel pole pieces greatly reduces the reluctance between the guitar strings and the pickup's coil. In other words, the steel pole pieces act a good antenna to receive to the signal from the moving guitar string, where as AlNiCo makes a poor antenna. Also worth noting at the same time, because the steel pole pieces have a weaker magnetic strength at the pole tops, the amount of string pull is very minimal, so you don't get those string pull harmonics / harshness as much. AlNiCo 5 is the only one of the bunch that is so strong to where you get ugly wolf tone sounds when the pickup is too close to the strings.

So the end result is a combination of things, where a lot of factors have more than one tonal consequence, in particular the metal's permeability. The effect of brass versus nickel silver pickup covers, and the pole piece geometry also have a noticeable effect on the performances of the pickup, but I'll cut short of describing that since it's not related to pole piece material specifically.

[Mike Sulzer]

Also, magnetization level and permeability are not completely independent. Wind a strat pickup with unmagnetized A5; measure the inductance. Magnetize it; measure again and you see it has gone up roughy 10%.