Nelson Pass: They use a new output semiconductor called an IGBT—which stands for Insulated Gate Bipolar Transistor—which is a couple of years old as an n-channel switch device. Toshiba recently developed very linear complementary devices, specifically for audio. When we ran across those they looked extremely interesting; we acquired some and began working with them. I should point out too that I don't take the design credit on that particular product. The front end and some other pieces are mine, but the amplifiers are primarily the work of a Swedish engineer, Michael Bladelius—we brought him over a year ago.
The IGBT is a very interesting device. It's a hybrid, functionally between a MOSFET and a bipolar. It has more or less the input characteristics of a MOSFET and the output characteristics of a bipolar. Its input is characterized by transconductance—its transconductance is higher than you find normally with a MOSFET, but it's still a transconductance characteristic. It has a low output impedance, as is found in a bipolar, but wider bandwidth than you see with a bipolar. It's also quite linear, in this case sufficiently linear that the performance that we get on the Forté amplifiers is achieved without a feedback loop, much as in the Stasis amplifiers, but with a different approach.
