One of the most important secret weapons available to the high-performance stereo equipment designer is the Field Effect Transistor, better known as the FET.
Originally envisioned by Austrian physicist Julius Edgar Lilienfeld in 1925 and then again by Oskar Heil in 1934—yes THAT Oscar Heil, the inventor of what is still to this day one of the best tweeters ever made, the Heil Air Motion Transformer—it was little more than a pipe dream because they couldn’t get it to work. It wouldn’t be until another decade later when, in the course of trying to understand their failure to build a working FET, Bell Lab’s scientists John Bardeen, Walter Brattain, and William Shockley would instead build a point-contact transistor in 1947, followed by the bipolar junction transistor (BJT) in 1948. It would take another decade of work to produce the first practical FETs, and another decade after that to enter the general marketplace.
The fundamental difference between a BJT and a FET is that BJTs are at their inputs excited into operation by current while FETs rely upon voltage. This fundamental difference—current vs. voltage—is what has such a profound effect on sound quality differences between the two structures. A FET is more closely related to another voltage amplifying device, the vacuum tube.
So it should be no surprise to find that FETs sound remarkably closer to vacuum tubes than do BJTs.
Great amplifiers, like great food, depend on the quality and nature of their ingredients.