Re: P90 magnet questions
You, my good sir, are a very convincing man.
Magnets totally changed the way I look at PU's. I used to buy one after another, trying to get one that fit the wood I had, for the tone I wanted. But that gets expensive. Now, I just get a PU that has a resisitence in the range I want (like 7,000 to 8,000 ohms for a neck HB), and if the stock magnet isn't quite what I want in EQ or output, I can swap it in 10 minutes. The magnet the manufacturer puts in is just a suggestion; an HB or P-90 has many other personalities. Never give up on a PU until you've swapped a magnet or two. I'm able to make my existing PU's work with mag swaps. Putting in a replacement magnet creates a new PU.
Quick recap:
A2 - lots of mids, little treble, low output, can have a loose low end. Very popular because it adds lots of character to the tone.
A3 - also low output, but brighter than an A2. Like a weaker A5, without the strong low end.
A4 - balanced EQ, doesn't shift the EQ like other alnicos; to some guys this is bland, but it can be ideal for warming an A5 bridge PU, or brightening an A2 neck PU.
A5 - fairly high output, lots of treble & bass, scooped mids, tigh low end. Great in the bridge or neck slot, which is why it's the most popular alnico. If it's too bright in the bridge, try it with one or two 250K pots.
A6 - lots of mids, not much treble, high output, firm low end. Good for taming an overly bright bridge. Too dark for neck HB's. Hard to find.
A8 - like an A6 but with more treble. Used to add mids & boost output. Players now use this magnet in PAF, medium, and high output bridge PU's. Too dark & powerful for neck HB's.
Listen to your current PU's, and if there's something you don't like, look at the other alnicos and see if there's one that does what you want. Have a A5 or ceramic bridge PU that's too bright? Try an A2, A4, or A8. Neck A2 PU that's too dark & muddy? Try an A3, A4, or A5. Have an A2 bridge PU but need more output and a tighter bottom? Try an A8.
With P-90's, and HB-sized P-90's, you have twin magnets, so you can blend EQ's and output to really dial in what you want. Lots of territory to explore here.