Okay gang, consider this a 1-part review of alnico magnets as used in guitar pickups. After finishing my epic six part deep dive on AlNiCo magnets, I happened to stumble across a pickup builder who claimed THIS on their website:
"Alnico 4 magnets generate a flatter “EQ” overall which can sometimes sound bland to some players, yet have been the hidden little secret for others. This magnet tends to sit between the Alnico 2 and Alnico 5 in magnetic strength and tone – rounder lows than a 5, tighter lows than a 2 with crisper highs than a 2. With the ALnico 4’s flatter “EQ”, the guitar’s true colour and character really shine through – this is where Alnico 4’s can sometimes sound bland. Some guitars just simply don’t work with Alnico 4 magnets, but when a guitar works with Alnico 4 it’s pure PAF magic. In my personal opinion, these magnets work best in a naturally big-sounding SG, Les Paul or PRS type guitar. Since Fender style guitars typically sound tighter and thinner, I’d personally go with one of the other magnets in the Alnico range to better compliment them. This is one of my favorite magnets for both bridge and neck positions when in the right guitar."
Wow! seriously. This pickup builder also lists "scooped mids" as a quality of Alnico 5, And he lumps SG's, Les Paul's and PRS guitars into the same camp, I won't go on, it's embarrassing. soooo ... yeah .... um .... WTF??
Anyway, that got me to thinking about some of the other insanely WRONG things people have broadly presented as FACT on various forums, like:
"Alnico 2 is pretty weak, it's never used by rock players. Alnico 3 is very similar to A2, but weaker. Typically gives a little more clarity than A2 ime. Alnico 4 is stronger, has a more balanced EQ. Not as much mid range as A2 or A3, not as scooped as A5. Alnico 5 is the most common. Stronger, and typically more mid scooped than the A2, A3, and A4. Unoriented Alnico 5 (referred to as UOA5) is a good middle ground between A2 and A5. Has the strength of an A5, with tonal characteristics more like an A2. Good magnet if you have an A2 pickup you like the tone of but want a little more output. Alnico 8 is a strong magnet. The strength is similar to a hot ceramic magnet, but with the warmth and sweeter top end of alnico magnets."
So much of this is wrong!
So folks, I'm going to make this a super-short overview of alnico magnets in guitar pickups for those who want a FAST but accurate comparison. If you want to dive deep, click on each magnet's link for the deep dive. Please note, I'll be speaking in generalities and using the most basic of terminology here, if you don't know much about the specifics of alnico in general, PLEASE begin with this OVERVIEW!!
Alnico III - The weakest of all currently available alnico grades, Alnico 3 was produced AFTER alnico 2 for one reason, to be less expensive than alnico 2 to fit the needs of manufacturers of the day. Alnico 3 magnets were the first magnets Leo Fender used in the late 1940's and early 1950's in the first Broadcaster, Nocasters, Telecaster, an Strat pickups. The lower magnetic pull on the strings means this magnet leaves the strings to vibrate quite freely and the resultant tone has more harmonic content than the stronger magnets, giving it an airy and natural quality, at least when not wound with a ton of coil wire. This is a good fit in Leo's original designs which were not wound terribly hot and the alnico magnet rod IS the pole-piece, so the full charge is brought to the strings. When heavily wound, the magnetic force (Gauss) is overwhelmed by the coil and the pickup will begin to get muddy, flubby, and indistinct sounding. Takeaway: A3 is the tone of the earliest Fender Tele's and Strats, they were never really used in P-90 or humbucker designs by Gibson because they just got too muddy in that design. (although SOME found their way into early pickups when Seth (Lover) was simply messing around or the supplier shipped it instead of A2.) Measured at the pole-pieces, a Fender style A3 will measure about 650 Gauss.
Alnico II - This is the magnet first used by Seth Lover in the original design of the P-90 and original Gibson hum-bucking design (later dubbed PAF). In all of it's specs, A2 produces more energy than A3. A2 is still a rather weak magnet by comparison to later magnet mixtures. This weakness once again makes it have very low string pull, especially with Seth's designs, which used magnetic bars BELOW the pickup and steel screws and slugs brought the magnetic field through the coil and under the strings. Seth's original humbucker designs only had about 4000-5000 turns of 42-gauge coil wire on each bobbin, so this was a good combination. , a "PAF" style humbucker will measure about 325 Gauss at the pole slugs and screws, THIS is the main reason why Humbuckers sound so very much darker than Leo's single-coil designs. An Alnico II P-90 or humbucker is a very warm tone, that is ALSO rich in upper harmonic content due to the VERY low magnetic pull on the strings, even more so when wound to original PAF specs. By comparison, a Fender style single coil with A2 rods will When measure about 750 Gauss at the pole-pieces. Seth chose NOT to use the less expensive alnico 3 magnets in his designs for Gibson because of their lower electromagnetic properties, they would sound too dark.
Alnico V - This was, and pretty much still is, the most powerful grade of alnico, there is Alnico 8 which has a little more coercive force, but less energy and induction, and those last two are what contribute to the output of a pickup. Alnico 5 was produced for one reason, to be strong, it was more expensive than A2 because of it's higher amount of cobalt. This slight boost in inductance and energy was just what the humbucker and PAF designs needed, and they were immediately made the specified magnet in Gibson's PAF and P-90 pickups making those designs a little brighter and stronger. Leo also immediately began using them in his designs, and the result is that BOTH designs provided a slightly higher output voltage and could now be wound with more turns before sounding too dark. It's very difficult for the coil of a guitar pickup to be wound so high as to overwhelm an A5 magnet, especially in the Fender magnetic pole-piece designs where the magnetic energy measures about 1000 Gauss. In a humbucker there is about 365 Gauss at the pole screws and slugs.
Alnico 5 (unoriented) - Again, basically a scam in my book, it's still anisotropic, which can only be magnetized on one axis, it just does a worse job of holding a magnetic charge because the particles are NOT fully lined-up in the proper north/south axis. In case you are curious, when used in a humbucker design, the magnetic force will read about 325 Gauss at the pole screws and slugs. Yep, VERY A2 like indeed.
And last, I'll mention "ceramic" magnet design. This is a much less costly magnet to produce (no cobalt, easier heating process), and can in some cases be blended to produce somewhat higher inductance and Gauss than even A5. They crumble easily and can NOT be used as direct Fender-style pole-pieces. They simply don't sound as good as alnico in most designs with one VERY important exception: VERY HIGHLY WOUND HUMBUCKERS. When you go down in size from 42gauge wire to 43 or even 44, you can pack a bunch more turns on, this overwhelms even A5, so here, the most powerful ceramic magnet you can find sounds good ... well, by late 1980's standards anyway, take the Gibson Dirty Fingers or Dimarzio Super Distortion as examples.