Active electronics were originally a way of matching a low impedance pickup/transducer device (built for DI recording) to an amplifier designed to accept regular medium-to-high impedance pickup signals. I suspect that the idea was borrowed from studio mixing console electronics. It would come as no surprise if the culprit turned out to be one Lester William Polfuss. He certainly championed low impedance guitar pickups in his own work. On the first low impedance LP guitars, the buffering/matching electronics came in a separate box and required special cables. On the later Personal, Recording and Triumph models, the output value is selectable via a switch on the control panel.