TBT: First Watt Model SIT-1 Solid-State Monoblock Power Amplifier Review

Imagine a single-ended Class A power amplifier comprising a single transistor, that is devoid of any feedback, and which behaves similarly to a power triode? Does this scenario sound too good to be true? Well, that’s exactly what the First Watt SIT-1 is all about. It deploys a unique type of device, a variant of the JFET, referred to as a static induction transistor (SIT). It was invented in the early 1970s by Jun-ichi Nishizawa, a true genius who is considered the “father of Japanese microelectronics.” The SIT enjoyed a brief audio career in power amplifiers by Yamaha and Sony, but has continued to evolve since then mainly for UHF and S-band applications in radar and communication satellite systems. It is a voltage controlled device whereby the signal modulates the electrostatic potential barrier produced by the gate – the grid like element of the SIT. Unlike an ordinary FET whose current-voltage characteristics are pentode like, those of the SIT are triode like. One important consequence of this is the low output impedance even in single-ended operation. And because of its inherent low-voltage and high-current characteristics, no output transformer is required for matching the output stage to a loudspeaker.