C. Active Pickup Systems
Typical examples are EMG pickups and the Duncan/Basslines Active Pickups. These generally use low-impedance pickups with a smaller number of wire turns. This causes less loss in the high and low end, and generally allows a much broader, full-range, hi-fi sound. Unfortunately, it also means the voltage produced by the pickup is very low, not nearly enough to drive an amp through a long cable. So these pickups have miniature amplifiers, called preamps, built into the pickup housing itself. Thus the signal only has to travel a fraction of an inch before it gets amplified and buffered into a low-impedance output. These systems often, but not always, provide a higher output signal than passive systems, so you dont need to turn up the gain as much on your amp, which can add noise.
To confuse matters, active systems can use passive volume and tone controls just like passive pickups. These controls are almost always have different values for potentiometers and capacitors, and you usually must use the parts supplied by the pickup manufacturer. In addition, because the connection from the pickup coils to the preamp is made inside the pickup housing, options like series/parallel switching and coil tapping are rare and generally not available unless the manufacturer has specifically designed the pickup for it.
