The First Watt SIT-4 Power Amplifier stands as a pinnacle of audio engineering, offering a rare and exquisite blend of vintage technology and modern precision. Designed by the legendary Nelson Pass, this amplifier embodies the essence of purity and musicality, setting itself apart from conventional amplifiers in the audiophile market. At its core lies the revolutionary Static Induction Transistor (SIT) technology, a hallmark of the SIT series amplifiers from First Watt. This unique transistor design brings forth a sonic signature that is often described as a harmonious marriage between the warmth of tube amplifiers and the speed and accuracy of solid-state circuits. What truly sets the SIT-4 apart is its unwavering commitment to sound quality and musical fidelity. Operating in single-ended Class A mode, it offers a pure and direct signal path that preserves the delicate nuances and dynamics of your favorite music. With a modest power output of 12 watts per channel into 8 ohms, the SIT-4 is not about sheer wattage; it's about precision, detail, and a deeply engaging listening experience. This low-power design makes it an ideal match for high-efficiency speakers, ensuring that every note is delivered with clarity and finesse.

Moreover, the user-adjustable bias allows enthusiasts to fine-tune the amplifier's performance to suit their preferences and the characteristics of their speakers. For audiophiles who demand nothing but the best in sound and performance, the First Watt SIT-4 Power Amplifier is an unparalleled choice. It represents the pinnacle of craftsmanship, with a meticulous design that prioritizes musicality, clarity, and precision. Whether you're rediscovering your favorite vinyl records or immersing yourself in high-resolution digital audio, the SIT-4 promises an audio journey like no other, where every note is rendered with the utmost purity and emotion.

In terms of features, the SIT-4 leaves no audiophile desire unmet. It boasts custom-designed output transformers, finely tuned to extract the utmost performance from the SIT transistors. The inclusion of both balanced XLR and unbalanced RCA inputs offers flexibility for connecting various audio sources, while the soft-start power supply protects the amplifier and connected speakers from power surges. The aluminum chassis not only adds a touch of elegance to its appearance but also aids in effective heat dissipation, ensuring optimal performance over long listening sessions. Moreover, the user-adjustable bias allows enthusiasts to fine-tune the amplifier's performance to suit their preferences and the characteristics of their speakers. For audiophiles who demand nothing but the best in sound and performance, the First Watt SIT-4 Power Amplifier is an unparalleled choice. It represents the pinnacle of craftsmanship, with a meticulous design that prioritizes musicality, clarity, and precision. Whether you're rediscovering your favorite vinyl records or immersing yourself in high-resolution digital audio, the SIT-4 promises an audio journey like no other, where every note is rendered with the utmost purity and emotion.

Dragon Cable Recommendation: we recommend pairing the SIT-4 power amplifier with our award-winning Silver Dragon Interconnects. The Silver Dragon Interconnect is one of our best-selling cables at Moon Audio. Sold in Pairs, it is our top-of-the-line silver conductor-based interconnect. With a braided geometry and amazing shielding, this interconnect is a remarkable solution where noise isolation is key. The Black Dragon Power Cable is also recommended to provide the cleanest and unbridled power to your high-end amplifier.

The First Watt SIT-4 Power Amplifier is designed with a range of features that contribute to its exceptional performance:

Static Induction Transistor (SIT) Technology: The SIT-4 utilizes Static Induction Transistors, a rare and vintage technology that delivers a unique sonic character, combining the warmth of tubes with the speed and precision of solid-state.
Single-Ended Class A Operation: The amplifier operates in single-ended Class A mode, providing a pure and direct signal path for superior sound quality and musicality.
Low Power Output: With a power output of 12 watts per channel into 8 ohms, the SIT-4 is designed for efficiency and ideal for use with high-efficiency speakers, ensuring optimal performance without excessive heat generation.
Pure, Uncluttered Design: The minimalist design of the SIT-4 focuses on the essentials, with a clean layout and straightforward controls for ease of use.
Custom Output Transformers: First Watt has designed custom output transformers specifically for the SIT-4, ensuring efficient power transfer and impedance matching for optimal performance.
Soft-Start Power Supply: The SIT-4 features a soft-start power supply to protect the amplifier and connected speakers from sudden power surges, extending the lifespan of the components.
Aluminum Chassis: The amplifier is housed in a rugged and stylish aluminum chassis, providing durability and effective heat dissipation.
User-Adjustable Bias: Users can adjust the bias of the SIT-4 to fine-tune its performance to match their preferences and speaker characteristics, allowing for customization of the sound signature.

The SIT-4 is the First Watt power amplifier using the industrial grade Static Induction Transistors. It is preceded by the groundbreaking 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 operated 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. The Common Source mode SIT-1 could do the job surrounded by only passive elements, and the SIT-2 required only bias from a current source. The SIT-3 upped the game with Common Drain design biased by a novel Pass circuit, MUFF (Mu Follower/Follower). The SIT-4 follows in the Common Source footsteps but ups the game with an industrial SIT. The SIT-1/2/3 gain transistors were rated at a few amps and about 50 watts of dissipation. This amplifier uses a Tokin THF51s rated at 600 volts, 30 amps, and 400 watts. As a practical matter, the limitations of the SIT-4 circuit are the size of the heat sinks. And this big Jfet manages a bandwidth of 50 megahertz… The circuit of the SIT-4 is simple. Q1 is a new-old-stock Toshiba 2SK170 which drives the Gate of the Q2 SIT, whose output is biased by a mu-follower current source Q3.

The SIT (Static Induction Transistor) series of power amplifiers from First Watt stands out as a unique and innovative offering in the audiophile market. These amplifiers are characterized by their utilization of Static Induction Transistors, a technology that brings a rare and vintage flavor to modern audio systems. Designed by the legendary Nelson Pass, the SIT series harks back to the early days of transistor amplification, providing a sound signature that is often described as remarkably smooth, warm, and dynamic. What sets the SIT series apart is the meticulous attention to detail in its design, focusing on delivering a pure, uncolored sound with a touch of vintage charm. These amplifiers are not about raw power; instead, they excel in presenting music with nuance, texture, and a sense of musicality that captivates audiophiles seeking a more intimate and engaging listening experience.

One of the key features of the SIT series is the use of a single-ended Class A topology, known for its simplicity and purity of sound. These amplifiers are not concerned with pushing high wattage; rather, they focus on the quality of amplification. With relatively low power outputs compared to mainstream amplifiers, the SIT series emphasizes the importance of efficient and accurate power delivery, resulting in a musical presentation that is detailed, transparent, and emotionally engaging. This emphasis on quality over quantity makes the SIT series an intriguing option for those who prioritize musicality and a more organic sound reproduction. In a market saturated with high-power, complex amplifiers, the First Watt SIT series stands as a refreshing alternative for audiophiles who appreciate the artistry and craftsmanship behind true high-fidelity sound.

Pass Labs and First Watt

Pass Labs and First Watt were founded by hi-fi legend Nelson Pass. After co-founding and later selling Threshold Audio, Pass began working out of his Auburn, California, home in the early 1990s to develop prototypes of single-ended Class A amplifier designs under the name Pass Labs. Pass Labs quickly became known for its commercially produced Aleph, X, and XA Series amps, and preamps. Pass later started First Watt as a passion project focusing on low-power amps for a niche audiophile audience. Today, Pass splits his time between the two companies, with production happening in Pass Labs' facility in Foresthill, California.

First Watt amplifiers represent a unique and specialized approach to audio amplification, crafted by the renowned designer Nelson Pass. These amplifiers are distinct from Pass Labs, another brand under Nelson Pass's purview, in that they are designed with a specific focus on low-power, single-ended amplification. First Watt amplifiers prioritize purity and simplicity in their design, aiming to deliver exceptional sonic performance with a minimalist approach. While Pass Labs focuses on higher-powered amplifiers for more demanding applications, First Watt amplifiers cater to audiophiles seeking a refined, nuanced, and often more intimate listening experience. With a dedication to quality components and meticulous engineering, First Watt amplifiers stand as a testament to Nelson Pass's pursuit of audio excellence in its purest form.

F.A.Q.

What is Static Induction Transistor (SIT) technology, and how does it impact the sound of the SIT-4?

Static Induction Transistor (SIT) technology is a unique transistor design utilized in the SIT-4, known for its vintage sound characteristics reminiscent of tube amplifiers. SITs provide a warm, dynamic, and detailed sound signature, blending the best aspects of tube and solid-state amplification.

How does the SIT-4 compare to previous models like the SIT-1, SIT-2, and SIT-3 in terms of performance and design?

The SIT-4 follows the technical philosophy and construction of its predecessors but utilizes an industrial-grade SIT for improved power handling and efficiency. It continues the tradition of simple Class A circuits with minimal reliance on additional active elements or negative feedback, focusing on purity of sound and musicality.

What kind of speakers are best suited for the SIT-4's 12 watts per channel output?

The SIT-4's 12 watts per channel output is designed for high-efficiency speakers. These speakers typically have a higher sensitivity rating, making them ideal for pairing with low-powered amplifiers like the SIT-4. They can deliver excellent sound quality and dynamics without requiring a lot of power.

Is the SIT-4 user-adjustable for bias and customization?

Yes, the SIT-4 offers user-adjustable bias settings, allowing enthusiasts to fine-tune the amplifier's performance to match their preferences and the characteristics of their speakers. This feature provides flexibility and customization for achieving the desired sound signature.

Who is Nelson Pass?

Nelson Pass, the man behind Pass Labs and First Watt, has been designing and building amplifiers for decades. His early passion, however, was speakers; at age 14, he started assembling loudspeakers. As a college student studying physics at the University of California-Davis, he co-founded a speaker company called PMA. He also worked for ESS, where he designed crossovers and enclosures. After college, with his interest having shifted toward amplifiers, Pass co-founded Threshold Electronics (now Threshold Audio). His achievements during the Threshold years include developing the first dynamically biased Class A amplifier circuit; developing a fully cascade audio power amplifier; and developing the STASIS stereo preamplifier and power amplifier. During the 1980s, Pass designed the Adcom GFA-555 amplifier. Later, after selling Threshold, he started Pass Labs in 1991 and First Watt in 1997. Pass holds several patents related to audio circuits.

How did Pass Labs make its name?

Pass Labs helped popularize solid-state, Class A power amplifiers. Pass Labs' first product, the Aleph 0 amplifier, operated as single-ended Class A up to its 70-watt rating and in push-pull Class A at higher wattage. The Aleph series of amplifiers, some of the first solid-state amps that were said to be "tube-like" in sound, operated pure class A and contained internal circuitry using MOSFETs. The Aleph amplifiers had a unique appearance, a cube with heat sinks on all four sides, a solution to the heat generated by the class-A design. This can be attributed primarily to the specific MOSFETs used and the minimum number of gain stages that were implemented in the design. Pass Labs also developed the Super-Symmetry™ ("Su-Sy") circuit, which achieves exceptionally low distortion and noise levels. In 1998, Pass Labs released the X1000, the first amplifier using the patented SuperSymmetric™ topology. The X1000 achieved 1000 watts with high performance, local feedback, and only two gain stages: a cascaded differential pair of transistors and a large bank of complementary output followers. This groundbreaking design informed all subsequent Pass Labs amplifiers.

What else does Pass Labs make?

In 2002, Pass Labs unveiled the first XA amplifiers, combining the X and Aleph topologies into balanced single-ended Class A amplifiers with many of the characteristics of both the X and Aleph series. The current Pass Labs lineup includes Class A amps (XA and Xs Series), Class AB amps (.8 Series), line preamps (Xs and XP Series), phono preamps (Xs and XP Series), integrated amps (INT Series), and one headphone amp.

What is the relationship between Pass Labs and First Watt?

When he started Pass Labs, Pass did everything out of his home. In 1997, having outgrown the space, Pass Labs moved into commercial space in Foresthill, California. When Pass started First Watt, it was a "kitchen table" venture, with work once again happening in his home. In 2016, with production demands not leaving him enough time to pursue the vast array of yet-to-be-designed amps, Nelson handed the business end of First Watt over to Pass Labs. Pass Labs took over the building of First Watt amplifiers as well as marketing and distribution. There's a synergy between the two operations, in that Pass Labs gets to gather up some of the more interesting First Watt finds and repurpose them as more commercially viable designs. Today, Pass splits his time between First Watt and Pass Laboratories.

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