Guitar Hero: Van Halen

You've most likely played through all 4 Careers and are wondering why the EVH achievement didn't pop, Playing Band career will unlock the final 3 guitars needed, at 50, 75 & 100 stars.

Edit: just got the achievement. The gist of it is:
100 stars in band career
150 stars in guitar career
80 stars in bass career
25 stars in vocals career (maybe)

Guitars
Black and White Stripe - default
Wolfgang Ivory - default
DLR Acoustic - Band career 50 stars
Star Guitar - Band career 75 stars
Destroyer - Band career 100 stars
Wolfgang Black - Guitar career 40 stars
Franken Guitar - Guitar career 80 stars
Black and Yellow Stripe - Guitar career 110 stars
Sunburst Wolf Guitar - Guitar career 150 stars

Basses
Franken Bass - default
Black and Yellow Bass - Bass career 40 stars
Wolf's Bass - Bass career 80 stars

You do not unlock any Van Halen Axes in the vocals or drums careers. If the achievement description is accurate, you don't need to play those careers at all to get it. If anything from the vocals career is required, it'd be Diamond Dave's mic and stand, unlocked at 25 stars.

You get this for unlocking all of the VAN HALEN AXES, which can be viewed and purchased in the EDIT ROCKER tab in the VIP Lounge.

You unlock guitars by getting an X amount of stars in respective careers (Normally unlocked at 50, 100, 150, 200, that stuff.)

There are 6 to unlock in the GUITAR career, 3 to unlock in the BASS career, 1 to unlock in the VOCAL career, and 3 to unlock in the BAND career. There are none in the Drum Career.

Sadly, I don't know the exact amount of stars you need, but I think the farthest you have to go is 150 Stars (in the Guitar Career is where it was for me, and every other career has less than 110 stars).

You should get this on the way to getting the Unchained achievement.