Re: Turning passive pickups into active pickups?
Yes, I've built my own custom "EMG/Live wire" style circuitry and tweaked them each time. It give a lot more clarity and effortless drive/harmonics than passives. It can be modded to sound more tubey or Djent clinical.
It gives same drive as a 18v mod, using just 9v....haven't changed a battery on 4 guitars in 6 months either.
There is a trade off though.
The "charm" that people talk about passives is what I call "The cheesey spongey quality" [signal having to mechanically travel through 1st coil, some damping before exits the second coil ] Humbuckers.
It's there if you listen closely compared to actives (some people call it warmth and body, but it's sponge-like) ; also clear sounding passives can't sound meaner than the actives equivalent (the differential amp chip sound)
I am also able to kick out frequencies below 70hz, and above 10250hz [ leaving the most useful range]
Dimmer switches and TV screens only robs your signal from 1 metre away.
I would say in summary : Making your favourite passive pickup into active is like putting it on steriods...sustain is natural and more too.
Good results with 8K to 15K humbuckers. I always find you lose something in the tone above 15.2K
Also be prepared to hear all your mistakes when playing with such high clarity.