Re: Pickup to replace JB in Alder?
Note that Seymour Duncan does have a 21 day guarantee in the US, so don't be too afraid to try something you are intrigued by, as long as you can decide fast enough.
If you want all out mayhem, the PATB-2 Parallel Axis Distortion is amazing. Leads like a thicker JB, but way more massive for riffs and much tighter for thrash rhythms.
If you need jazz from the bridge pickup, it may be a bit too much, though. It's very responsive for it's high output, but...
The TB-6 would be a bit thicker and tighter than the JB, but also harsher and more biting. It might still be too thin. I don't think it's any better for jazz than the PATB-2, though. The TB-6 has a slight edge for biting thrash rhythms over the PATB-2, but you can close most of the difference by cranking the presence up half a notch on the amp. Making the TB-6 smooth out enough to solo as sweetly as the PATB-2 is a lot more work in most setups. If it was a short scale mahogany set-neck, I'd be a lot more comfortable with the TB-6's brightness... Though even there, for my personal tastes I'd still go for the PATB-2.
I went from a JB to a PATB-1b in my Ibanez RG570, but that's basswood (w/maple neck & rosewood fretboard). JB did not sit well in the guitar, flubby bass and very nasal, though it still managed to be cool for solos. PATB-1b is awesome all around in my guitar. Most flexible high output humbucker I've used. Unusually comfortable for low-gain work for a hot pickup. Can do anything from edge of distortion blues/classic rock tones to metal comfortably. Solid for thrash rhythms, though not quite as strong as a PATB-2 or TB-6.
[This is all assuming you are using jazz as in the genre, and not meaning heavier branches of fusion. If you are using it as slang for "stuff", that's a bit confusing on a music forum.

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