All About Rough Cast & "Polished" AlNiCo Magnets

What's your favorite magnet type in a humbucker?


  • Total voters
    47

cooljuk

Transducer Producer
Premium Member
Joined
Mar 11, 2009
Messages
15,659
Reaction score
21,929
This comes up fairly regularly so I thought I'd just put together a comprehensive post, outlining some of what I've learned through my experiences and experiments with different foundries and magnets.



Rough cast guitar magnets and “polished” guitar magnets are made the same way (at a given foundry). The AlNiCo alloy is mixed, heated in a crucible until molten, then poured into green sand molds. Once filled, the molds are then subject to a calculated and complex series of heating and cooling cycles at different temperatures for different times, and usually exposure to strong magnetic fields during some of these cycles. All of this depends greatly on the particular type and properties of the magnet being made and the particulars of a given foundry. Variation in any of these can result in a different sounding magnet, at the end of the day.


The difference in manufacturing process comes after this. The "polished" magnets, having been cast a bit larger, are then run through a surface grinding process which grinds off the rough surfaces, bringing them to the final size on all sides, while being cooled in a solution to prevent heat from physically changing the material. That’s why I keep putting “polished” in quotes. They aren’t really polished at all and usually show tooling marks from the surface grinding. This same process is done to rough cast magnets, but only on the North and South polar faces, leaving the other four surfaces rough. Many rough cast magnets also end up being ground flatter on the other four surfaces, as well, if they are so rough and unusual in shape that they are outside the range of tolerance to fit the order. That’s why some rough magnets may appear to be smooth on only part of a surface.



Any differences heard between rough cast and polished magnets are likely due to the magnets coming from different foundries, or being made in different batches with loose tolerances or sloppy practices, rather than the actual surface texture of the magnet. Especially regarding inexpensive modern magnets.

Three “polished” magnets from three different foundries will likely measure and sound a bit different from each other.

Similarly, three rough cast magnets from three different foundries, will also likely meter and sound a little different from each other.

From the same foundry and time, a rough and “polished” magnet of the same type are likely to sound the same. Especially if they are from a precise and automated foundry with high standards and tight tolerances (but most aren't).


There are some rare times that a rough cast magnet can change the sound of a pickup due to the rough surface. It's not common, because generally both the polar faces of the magnet, which contact magnetic surfaces in the pickup (keeper bar and slugs), are surface ground flat, even on rough cast magnets. An example is some of the A3 magnets that Gibson used in P-90s in the early 1950's. They were made with only the South face of the magnet polished, with the North face left rough like the other four surfaces. That’s because in P-90s, the North polar surface faced the outside of the pickup, not making contact with anything, and only the South sides faced inward, contacting the keeper bar. In that case, when some of these magnets made their way into PAFs in 1957 (and, although very rare, I've seen them in pickups as late as the mid 1960's) this rough surface on the North polar face of the magnet which contacts the slugs could be so rough that it creates an air gap by having very poor contact with the slugs. Small air gaps cause magnets to do strange things in physics. This can change the sound, in rare cases.


So, generally, when a difference is heard between rough or "polished" humbucker bar magnets, it's because they came from different foundries or at least different runs of AlNiCo production. Some foundries, especially the lowest-bid type, can be extremely inconsistent. Not just the alloy used, but the heating/cooling cycles temperatures and times and field exposures all change the resulting properties of the magnet. I've seen how some of these foundries are run and experienced the results. The processes are not automated and terribly inconsistent. On the other hand, some magnets are cast here in the US with military precision and produce extremely consistent results. ...and one will pay for those. They cost quite a great deal more than the offshore alternatives. Further creating differences in magnets, some manufacturers go so far as having foundries alter the alloy or process to achieve somewhat different results for a given magnet type, intentionally. Some foundries follow these instructions well, some don’t. Others likely just ignore them entirely and ship what they ship. It can be a real mess depending who one deals with in manufacturing.



There is another type of polished-looking AlNiCo magnet, which is not sand cast at all. It's called a "sintered" magnet. Instead of having a molten iron-like alloy poured into green sand molds like the two described above, sintered magnets are made by pressing a powdered AlNiCo dust into a die, then compressing it under huge amounts of pressure and heat until it solidifies into a permanent shape. These magnets are magnetically weaker but cheaper to make.


I've not seen typical guitar magnets which are made with a sintering process yet, though it's possible they are out there. If you see flaws/exposed cavities in polished magnets, you know they are cast, then surface ground. Those flaws are bubbles and the sintering process doesn't allow for those bubbles/cavities.



At the end of the day, not all magnets of a given type achieve the same result in a guitar pickup. There are a great deal of variables in materials, process and tolerance that result in different chemical, physical and ultimately sonic properties of a pickup magnet. Control and consistency is how a manufacturer can use that to their advantage, rather than experience it as a problem. Personally, as I've tried to simplify and cut down on the types of magnets I use, over the years, I've only found valid reason to increase them. For example, I now stock five different A5 types, to achieve significantly different voicings in pickups. They really do sound noticeably different and measurements do reflect that they are different, as well. Magnets are relatively cheap, even for American ones. That's one upside. Pickup magnets are a rather inexpensive thing for musicians to play around with and experience the differences for themselves, in their own gear, compared to most of the equipment in the music industry. Happy swapping!


Favorite magnet poll added just for fun.
 

jlee

Senior Member
Joined
May 4, 2010
Messages
612
Reaction score
395
I sway towards UOA5, but A4 is great too! Limited experience with A3 and not a fan. Of course, it could be more the wind I don’t care for rather than A3.

A2, not the biggest fan. I did keep the A2 in my ReWind Low Winds and swapped the bridge for an A5. One of my dessert island sets.
 

mdubya

Senior Member
Joined
Jan 24, 2010
Messages
19,759
Reaction score
32,638
Great post, James. :thumb:

I even read the whole thing, no lie! :fingersx:

My experience tells me I prefer A2 magnets. Though I have tried a little bit of everything. Not through choice so much as circumstance. And too lazy to do anything about it. :oops:

Thanks for sharing.
 

mdubya

Senior Member
Joined
Jan 24, 2010
Messages
19,759
Reaction score
32,638
Question: If I put an A4 magnet in the bridge '57 classic in my ES 335, will that give me enough "extra" to help it balance more with the neck pickup and maybe cure the desire for a '57 + in its place?

I know you are not a big fan of 57's, but I like 'em and like to leave my guitars (that sound good enough as is) stock, as much as possible.
 

NorlinBlackBeauty

Senior Member
Joined
Oct 28, 2017
Messages
21,534
Reaction score
59,344
Rough cast guitar magnets and “polished” guitar magnets are made the same way (at a given foundry). The AlNiCo alloy is mixed, heated in a crucible until molten, then poured into green sand molds. Once filled, the molds are then subject to a calculated and complex series of heating and cooling cycles at different temperatures for different times, and usually exposure to strong magnetic fields during some of these cycles. All of this depends greatly on the particular type and properties of the magnet being made and the particulars of a given foundry. Variation in any of these can result in a different sounding magnet, at the end of the day.
Magnetized during heating and cooling? Is that what that makes them a permanent magnet?

When you rewound my T-Top you wrote "charged magnet" on the sales slip. How long should the original magnetization last? Does a recharge change its effect on the outputs sound?

I'm really ignorant on the topic. Thanks for a good primer.
+1. Same.
 

ehb

Chief Discombobulator
Joined
Feb 20, 2013
Messages
32,022
Reaction score
141,233
A great read, especially the rough surfaces section. I had pondered on that before with what I know about flux/maxwells/gauss/inductance/etc. and just didn't buy off on some of what some have said about rough surfaces and flux disturbance.

The bold and underlined in quote below does make all the sense in the world....

Again, a great read...

Thanks....

Ed

this rough surface on the North polar face of the magnet which contacts the slugs could be so rough that it creates an air gap by having very poor contact with the slugs. Small air gaps cause magnets to do strange things in physics. This can change the sound, in rare cases.
 

ehb

Chief Discombobulator
Joined
Feb 20, 2013
Messages
32,022
Reaction score
141,233
In reference to the magnets vs. tone color, I've mentioned before seeing a vid where just the magnets were rolled, same pickup, same strings, same guitar, same everything...

Remarkable difference in tone colors. It also makes sense the variations within a type magnet.
So many things can affect the final characteristics of a compound, 0% variance in compound may be a pipe dream... Temp, rate of temp change, etc. can affect a final outcome. May be immeasurable and insignificant, may not be. As you stated too, bubbles... It is not unheard of even for high dollar metals to fail inspection because of an anomaly in the process like in a batch of steel... A cousin was paid a lot of bucks a good while back to inspect steel for an oil company. It happens...
 

cooljuk

Transducer Producer
Premium Member
Joined
Mar 11, 2009
Messages
15,659
Reaction score
21,929
Question: If I put an A4 magnet in the bridge '57 classic in my ES 335, will that give me enough "extra" to help it balance more with the neck pickup and maybe cure the desire for a '57 + in its place?

I know you are not a big fan of 57's, but I like 'em and like to leave my guitars (that sound good enough as is) stock, as much as possible.

On one hand I think the '57 Classics are probably my favorite humbuckers Gibson has made in decades. On the other, I do think they missed the mark in a number of places that could have easily made them much more clear and detailed without being harsh and much more full and bold without being dark and muddy. The name is also frustrating, as they aren't really anything like 1957 PAFs.

But my opinion is just that. To answer your question about the A4 - swapping out the factory A2 for an A4 (going by the average A4 I've heard, as some are much brighter than others) should give you more output, a bit more treble, and less compression. The bass may seem about the same or less because of the increase in the other frequencies and volume, but it will be a punchier bass, focused in a higher frequency range.

The extra output of the A4 in the bridge may help you with balancing the bridge/neck volume but the extra treble and tighter feel may just leave the neck sounding even darker and more mushy, comparatively. You could try an A3 or A5 in the neck, also/instead.

If the solder is original on the covers, this is when you have to make those tough decisions about the time/money you want to put into pickups that may not be right for your guitar/rig/preferences even with magnet swaps or just cut your losses and sell them with original solder joints for a bit more than unoriginal solder joints. That's all personal preference.

You can also play with pot values but the '57 Classics do have limited range so even very high value pots in the neck may not give you much more treble/clarity. Lower value pots in the bridge could warm it up and perhaps balance it better, by comparison.
 

mdubya

Senior Member
Joined
Jan 24, 2010
Messages
19,759
Reaction score
32,638
On one hand I think the '57 Classics are probably my favorite humbuckers Gibson has made in decades. On the other, I do think they missed the mark in a number of places that could have easily made them much more clear and detailed without being harsh and much more full and bold without being dark and muddy. The name is also frustrating, as they aren't really anything like 1957 PAFs.

But my opinion is just that. To answer your question about the A4 - swapping out the factory A2 for an A4 (going by the average A4 I've heard, as some are much brighter than others) should give you more output, a bit more treble, and less compression. The bass may seem about the same or less because of the increase in the other frequencies and volume, but it will be a punchier bass, focused in a higher frequency range.

The extra output of the A4 in the bridge may help you with balancing the bridge/neck volume but the extra treble and tighter feel may just leave the neck sounding even darker and more mushy, comparatively. You could try an A3 or A5 in the neck, also/instead.

If the solder is original on the covers, this is when you have to make those tough decisions about the time/money you want to put into pickups that may not be right for your guitar/rig/preferences even with magnet swaps or just cut your losses and sell them with original solder joints for a bit more than unoriginal solder joints. That's all personal preference.

You can also play with pot values but the '57 Classics do have limited range so even very high value pots in the neck may not give you much more treble/clarity. Lower value pots in the bridge could warm it up and perhaps balance it better, by comparison.

Great info.

The 2 standard 57's actually do work fine together. I have a '57/'57 + combo in a similar guitar that is close to perfect for what they are. I was looking for a short cut that might get me there. I like the spongy/compressed tone with the A2 magnets. Maybe I should leave well enough alone. I have more pickups than guitars at this point. :oops: And at least one of those sets would be close to perfect in this 335. :hmm:
 

cooljuk

Transducer Producer
Premium Member
Joined
Mar 11, 2009
Messages
15,659
Reaction score
21,929
Magnetized during heating and cooling? Is that what that makes them a permanent magnet?
Not all types of AlNiCo are magnetized during the heating/cooling cycles. The most famous for this is probably the isotropic (unoriented) A5. The alternative for creating a magnet out of AlNiCo material is to charge it after it has been cooled and processed to final shape. Both result in permanent magnets, which just means that they hold their magnetic charge on their own after the source of the charge is gone. The difference is that, when an AlNiCo alloy (and most metals) are heated to a certain point, the molecular structure becomes more fluid and easily influenced. In a way, this is how forging iron into shapes works. Much like the "grain" of the iron becomes movable when heated, so do the "magnetic moments" (the parts of the material which are magnetic, like millions of tiny magnets inside the material) also become more easily movable. If those magnetic moments are moved into position and aligned by a strong magnetic field while the alloy is heated enough, then held there in position by that field while the alloy cools, they will stay put and create a magnet which can hold a stronger overall charge. The goal for this in industry is a stronger mechanical cohesive force. The magnet can lift and hold more weight for the same size/mass of material.

You could also relate an anisotropic (oriented / aligned) magnet to a polarized lens on sunglasses, there all the material is oriented in the same direction, like a million little tubes, and the energy flows more easily in the same direction of the tubes as it does in a perpendicular direction to them.





When you rewound my T-Top you wrote "charged magnet" on the sales slip. How long should the original magnetization last? Does a recharge change its effect on the outputs sound?

+1. Same.

The charge on that magnet should essentially last forever. The only way it will be diminished is by an extremely strong electromagnetic field, a very strong permanent magnet very close to the pickup, or by serious shock, like a fall that would certainly break the guitar before it demagnetized the magnet.

Why some magnets aren't fully charged or properly aligned when they come to me probably has more to do with them having never been properly charged at the factory to begin with than having lost charge over their lifetime. However, some do loose charge from any of the above reasons.

Yours, if I remember correctly, was pretty well charged but not entirely evenly, so it shouldn't really change the sound. When a magnet is first charged to saturation, it can hold an artificially high charge that will die down to its "settled saturation" natural level shortly after. Imagine magnetizing a steel paperclip with a magnet. It will become magnetic, even after you take away the source magnet, but not for long and will soon return to non-magnetized steel. The same thing happens to non-magnet parts of magnet alloys.
 

cooljuk

Transducer Producer
Premium Member
Joined
Mar 11, 2009
Messages
15,659
Reaction score
21,929
Great info.

The 2 standard 57's actually do work fine together. I have a '57/'57 + combo in a similar guitar that is close to perfect for what they are. I was looking for a short cut that might get me there. I like the spongy/compressed tone with the A2 magnets. Maybe I should leave well enough alone. I have more pickups than guitars at this point. :oops: And at least one of those sets would be close to perfect in this 335. :hmm:
If you're real close with them, as is, and like that signature A2 sound, try to dial them in with pickup height / pole screw height adjustments and maybe pot values. You might get there with just that.
 

cooljuk

Transducer Producer
Premium Member
Joined
Mar 11, 2009
Messages
15,659
Reaction score
21,929
btw - yes, the degree of charge a magnet holds can change its sound in a pickup.

What's interesting is that it's not the same for all magnet types. As the charge decreases (degaussing magnets), some types loose treble, others loose low end or mids. Most loose dynamic range and output. It really depends on the magnet and to what extent they become degaussed. Eventually, they will all become silent with no charge. ;)
 

Thumpalumpacus

Senior Member
Joined
Nov 28, 2010
Messages
76,005
Reaction score
186,327
[...] however,I do know that I don’t care much for the ceramic.
My Ibanez has ceramics. It took a little time and work getting used to them, especially once I replaced the Epi VJ with my Tweaker 15. I actually had to spend time dialing my rig -- yikes! :p But this particular set doesn't seem to have the "brittle"/"harsh" criticism working against now that I've accomodated it with the rest of the signal chain.
 
Last edited:

NorlinBlackBeauty

Senior Member
Joined
Oct 28, 2017
Messages
21,534
Reaction score
59,344
You could also relate an anisotropic (oriented / aligned) magnet to a polarized lens on sunglasses, there all the material is oriented in the same direction, like a million little tubes, and the energy flows more easily in the same direction of the tubes as it does in a perpendicular direction to them.

The charge on that magnet should essentially last forever. The only way it will be diminished is by an extremely strong electromagnetic field, a very strong permanent magnet very close to the pickup, or by serious shock, like a fall that would certainly break the guitar before it demagnetized the magnet.

Why some magnets aren't fully charged or properly aligned when they come to me probably has more to do with them having never been properly charged at the factory to begin with than having lost charge over their lifetime. However, some do loose charge from any of the above reasons.

Yours, if I remember correctly, was pretty well charged but not entirely evenly, so it shouldn't really change the sound. When a magnet is first charged to saturation, it can hold an artificially high charge that will die down to its "settled saturation" natural level shortly after. Imagine magnetizing a steel paperclip with a magnet. It will become magnetic, even after you take away the source magnet, but not for long and will soon return to non-magnetized steel. The same thing happens to non-magnet parts of magnet alloys.
Great analogy to a polarized lens. I totally get that.

Mine was not entirely even? Are the gauss tests you do that precise on a given spot on the magnet?

Somehow I picture you in a white lab coat while doing what yo do … :p
 


My Les Paul Classifieds



Top