I am about to upgrade the pickups in my Ibanez 1527 7string guitar, so I was looking into this model for the bridge: Seymour Duncan JB Modell 7 Bridge black 4-phase, 7-string. Could someone explain what "4-phase" means? I would like to avoid buying the wrong pickup.
I think this means 4 conductor which gives you the option of wiring the pickup to a switch so that you can use it as full humbucker (with both coils) or as a single (just using one coil). You can just hardwire it without a switch in full humbucking mode if that is all you need.
Some pickup manufacturers produce their pickups with both 2 & 4 conductor wiring. 2 conductor will only allow you to have the humbucker option, but simplifies the wiring a little.
Looking at the specs for the Ibanez 1527 it has a 5-way switch which allows you to get both single coil and humbucking tones, so yes, you will need four-conductor wiring on any replacement pickups if you want to keep the range of sounds you have currently. Looking on the Seymour Duncan website a wiring diagram you could use is:
It might be worth looking on the Ibanez website as they may publish the exact wiring diagram for your guitar (I had a quick look but could not see it), or you could try e-mailing them.
If in doubt, get a competent guitar tech to install the pickups for you. Hope this helps.
I'm looking around at different sites and I'm not seeing four-phase as a description anywhere.
What I do see is that they have signal and ground from both coils. From there, you can do signal from one coil or the other, or both coils in serial or parallel.
I don't know how you play, so I don't know what the right pickup for you would be, but Seymour Duncan is one of the bigger and more trusted names in pickups, and the JB pickup is one of their flagship models, so I would suspect that this pickup would be decent for you.