The SIT-5 is the most recent amplifier produced by First Watt, and is the fifth to use a Static Induction Transistor (SIT) as the power amplifying device. In 2011 we introduced our first SIT amplifier using a custom Silicon Carbide (SiC) transistor part made by SemiSouth. The amplifier also used a single power device, operating without feedback in single-ended Class A Common-Source mode to deliver 10 watts of power emulating the characteristic of a Triode, but operating at voltage and currents directly needed by loudspeakers, eliminating the output transformer.
The success of the monoblock SIT-1 led to the SIT-2, which offered similar performance at higher efficiency, and two channels in the same chassis. 2018 saw production of the SIT-3 which operated the SIT transistor in Common-Drain (follower) mode, again without feedback which was available until 2023.
Some years prior, SemiSouth suffered bankruptcy and we found ourselves unable to acquire more of this special part. However there was a company in Japan – Tokin, known for making industrial Silicon SIT parts suitable for audio use. Their production facility was destroyed in the Fukushima earthquake and tsunami, but we were able to acquire these parts from existing inventories of these devices over a period of several years. These large Tokin SITs enjoy that same Triode character, but at much higher voltage, current and power ratings than our original SITs.
A special variety of Jfet invented in Japan in the 1950’s, in the 1970’s SITs enjoyed popularity in the “Vfet” power amplifiers from Sony and Yamaha that are still highly regarded in high end audio. Ultimately the difficulty and expense of SIT manufacture made them less competitive compared to later bipolar transistors, and it is only more recently that their superior qualities have been recognized for high end audio.