Specification :

Active humbuckers have a distinctive sound: powerful, clean, open-sounding, with excellent harmonic overtones and very tight lows. This also fits the description of a great 7-string pickup, if the problems associated with active pickups – sterile sound and limited headroom – could be eliminated. The D Activator 7™ does just that. The neck model has both power and clarity – the low B string stays solid and doesn’t sound like mud with extreme overdrive, and the high strings sing all the way up the neck. And it doesn’t need batteries.
Recommended For: Neck. Can also be used in bridge position
Tech Talk: It’s tough to get a clear tone from the low B string in the neck position without making the unwound strings sound brittle, and even harder with a high-output pickup. The two D Activator 7™ coils are tuned to different frequencies that complement each other and allow the pickup to “speak� clearly, with the power concentrated in the most effective frequency range. Like all passive pickups, D Activators™ require controls with a minimum value of 250Kohms. 500K is the standard all around value, and our 1Megohm tone control is best for long cable runs.

review : http://reviews.harmony-central.com/reviews/Electric+Guitar+Pickup/product/Di Marzio/D+Activator/10/1