In my mandolin I've got a K & K system. It works well using a Boss Bass eq then to a passive Whirlwind di ahead of everything to a given mixer. No battery required.

For my guitar I've got an older LR Baggs out of a Seagull guitar along w/a Joe Mills mic w/a separate volume control run through the Baggs volume/eq. combo. A 9v battery is required. Also, to a Whirlwind di.

Also, I've got a 12-string Takamine 'Logo Era' w/a stock pick-up. If I use the 3 together I run them all thru small Mackie mixer. It has separate 3 eq pots per channel.

It takes time to set it all up, but once it's dialed in it's a great combination.