The First Watt SIT-5 is the latest addition to the prestigious line of amplifiers produced by First Watt, marking its place as the fifth amplifier to utilize a Static Induction Transistor (SIT) as the primary power amplifying device. This innovation builds upon a legacy that began in 2011 with the introduction of the first SIT amplifier, which featured a custom Silicon Carbide (SiC) transistor manufactured by SemiSouth.
The Evolution of SIT Amplifiers
The journey of First Watt’s SIT amplifiers began with the SIT-1, which utilized a single power device operating in a single-ended Class A Common-Source mode. This design delivered 10 watts of power while emulating the warm, rich characteristics of a triode vacuum tube, all without the need for an output transformer. The success of the SIT-1 paved the way for subsequent models, including the SIT-2, which provided similar performance with improved efficiency and dual-channel capabilities within a single chassis.
In 2018, the company introduced the SIT-3, which employed the SIT transistor in a Common-Drain (follower) mode, again without feedback, further refining the audio experience for enthusiasts.
Overcoming Challenges: The Search for SIT Components
The path to the SIT-5 was not without its challenges. Following the bankruptcy of SemiSouth, First Watt faced difficulties in sourcing the unique SIT components that had become integral to their amplifiers. However, fortune smiled upon them when they discovered Tokin, a Japanese company known for producing industrial Silicon SIT parts suitable for audio applications. Despite the devastation of Tokin’s production facility during the Fukushima earthquake and tsunami, First Watt managed to procure these components from existing inventories, allowing them to continue their innovative work.
The newer Tokin SITs not only maintain the triode-like character that audiophiles cherish but also offer significantly higher voltage, current, and power ratings compared to the original SITs.
The Unique Characteristics of SIT Devices
SITs are a special variety of JFET invented in Japan during the 1950s. They gained popularity in the 1970s through high-end audio amplifiers produced by Sony and Yamaha, which are still revered today. However, the complex and costly manufacturing processes associated with SITs made them less competitive compared to later bipolar transistors, leading to a decline in their use until recently, when the audio community began to recognize their superior qualities.
One of the standout characteristics of SITs is their ability to closely simulate the anode-current to anode-voltage behavior of triode vacuum tubes. As noted in inventor Nishizawa’s patent abstract, the drain-current to drain-voltage characteristic of SITs mirrors that of triodes, allowing for operation on Class A load lines. This results in a harmonic structure that is rich in second-order harmonics while minimizing higher-order distortion, a quality that many audiophiles find desirable.
The Resurgence of SIT Technology
Historically, SITs have found applications in fields such as microwave and radar technology, but their foray into the audio realm in the 1970s and 80s was short-lived. After their decline, they remained primarily as industrial components until a recent resurgence led by companies like Digital Do Main in Japan, which developed audio amplifiers based on newer Tokin versions of original Yamaha parts. First Watt also continued its commitment to this technology, utilizing the custom SemiSouth Silicon Carbide SIT in its earlier models and transitioning to the Tokin THF51s for the SIT-4 and SIT-5 amplifiers, which are rated at an impressive 600 volts, 30 amps, and 400 watts in a 10 watt per channel configuration.
