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First Watt F7 Power Amplifier
The F7 is a very unique power amplifier.
Aa two-stage push-pull JFET/MOSFET topology with fewer parts than any First Watt amplifier to date and incorporating a very interesting balance of very low negative voltage feedback and a little bit of positive current feedback to give an astonishing measure of control over reactive loudspeaker loads.
First Watt SIT-4 Power Amplifier
The SIT-4 is the First Watt power amplifier using the industrial grade Static Induction Transistors. It is preceded by the ground breaking SIT-1, 2, and 3 and follows their technical philosophy and construction. An important difference in the SIT-4 is the SIT device itself.
The previous three designs used Silicon Carbide to make a custom vertical power Jfet with a low impedance Drain whose character nicely emulated a power Triode tube, but directly operating at the current and voltage that would drive loudspeakers without the requirement for an output transformer.
SITs lend themselves to high quality audio performance with very simple Class A circuits with little or no dependence on other active circuit elements or negative feedback.
First Watt Sit-5 Power Amplifier
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.
