The al New SIT-1
is the first of a new generation of power amplifiers using Static Induction Transistors (SIT) in single-stage, single-ended Class A circuits delivering superlative sound without feedback or degeneration. This is made possible by the unique characteristic of First Watt's custom SIT devices, which combines a square-law input character with a low impedance output to form the only solid state gain device which behaves like a Triode tube.
This character has long been sought as a potential replacement for tubes, but the realized devices have several advantages. The Pass SIT device has higher gain and lower distortion and also conveniently operates at the voltages and currents required by loudspeakers. This means that an output transformer, with all its bandwidth and distortion limitations is eliminated.
You can read more about SITs here: SIT Introduction
The SIT-1 has only one active device in the circuit. All the other components are passive, as illustrated in the following diagram:
Dick Olsher famously remarked that “The first watt is the most important watt.” This sentiment has also been expressed by others as “Who cares what an amplifier sounds like at 500 watts if it sounds like crap at one watt?” With this in mind, I created First Watt in 1998 as a "kitchen-table" effort, exploring unusual low power amplifiers with an emphasis on sound quality.
Small amplifiers have a number of advantages over “big iron” in that very high quality can be achieved with simple Class A circuits using little or no feedback.
There is no such thing as a perfect amplifier. Every audiophile and his associated equipment has specific needs, but in each case there is such a thing as a best amplifier - the one that makes you happy.
First Watt exists because I wanted to explore a variety of amplifier designs in what I think of as neglected areas - amplifiers that might not fit into the mainstream and are probably not appropriate to my more commercial enterprise, Pass Labs.
With oddball characteristics and output power ratings of 25 watts or less, First Watt is not for most people. If you have efficient loudspeakers, listen at reasonable levels and are obsessed about subjective performance, then you probably have come to the right place.
If you want reliable audio product, then you really have come to the right place. For twelve years First Watt has an essentially zero failure rate.
There have been eight designs released in limited quantities, all simple Class A circuits, each offering a unique approach to sonic quality. The F1 and F2 are both current source (as opposed to voltage source) amplifiers with no feedback. The F3 offers single-stage single-ended operation with new Jfet power transistors. The F4 is a push-pull current buffer with no voltage gain or feedback, and the F5 is a uniquely high performance push-pull amplifier with feedback. The new J2 and M2 continue to push the envelope in different ways.
First Watt amplifiers are routinely compared with tube amplifiers, although I make a point that they are not designed to mimic tubes as such. These amplifiers share some of the characteristics of the better tube products in that they have simple circuits with minimal or no feedback and emphasize performance of individual gain devices. In some ways they are better than tubes, in other ways perhaps not.
As these pieces have been limited in production, most are now only available on the used market, and you do not see them very often, although there are numerous clones, and you can always consider building them yourself, as the schematics and such for older products are available here for the DIY enthusiasts (and not for commercial cloners). We are altering the approach with the J2 and M2, which are slated for a longer production cycle, giving our distributors something to sink their teeth into. We will continue to release new “F” series, but in very limited production, with the schematics posted for you DIYers after the first run is gone.
For the first eleven years I built these by hand all by myself. More recently my son Colin and nephew Sean have joined me in the shop in Foresthill.