Formula S (English）
Let's start with the story of Joe, the founder of two renowned brands, Abyss and JPS Labs. I first met Joe and his Abyss AB-1266 headphones at the CES exhibition in January 2014. The experience in Las Vegas that year remains vivid in my memory. Joe, standing tall at approximately 1.85 meters, exuded confidence and optimism with his thick New York accent, and he was always animated. However, it was his Abyss headphones that stole the show, leaving him dancing in excitement. When people put on the headphones, they would close their eyes in amazement and sway with the music, unable to stop. In 2014, the AB-1266 finally made the headphone market aware that dynamics, transparency, soundstage, unparalleled low-frequency response, electrostatic-like detail retrieval, and more could all come together in one pair of headphones.
Ironically, these headphones, apart from sounding incredibly good, were notoriously challenging to drive. During their debut, they required massive, heavy tube amplifiers, which took several people to transport.
Later, through a series of fortunate events, I became the ambassador for promoting Abyss headphones and JPS Labs cables in China. That's when I decided to devote myself to creating an amplifier capable of efficiently driving the AB-1266. I estimate that I went through the tuning and adjustment process approximately 50 times. Joe was very pleased with this amplifier and even provided a complete set of internal wiring for the Formula S, totaling 11 cables. He also authorized me to include the "Wired with JPS Labs" logo on the amplifier. Today, Abyss also sells the Formula S amplifier. I would like to express my gratitude to Joe, as his JPS Labs cables infused the Formula S with a sense of high-end musicality, making it a perfect match for his Abyss headphones.
In my view, designing power amplifiers, headphone amplifiers, and preamplifiers are entirely different projects, often feeling like they belong to different worlds. I would like to extend special thanks to the design genius Philippe Chambon at Nagra in Switzerland for his invaluable guidance and inspiration. Over the past few years, I've seized every opportunity to engage in discussions with him. I've benefited greatly from his insights into design principles and technical details. Without him, the Formula S would not have emerged as a new addition to the world of top-tier headphone amplifiers.
The first challenge for the Formula S was to establish the reputation of the AB-1266 headphones. Due to their challenging nature, users often employed powerful amplifiers, resulting in a reputation in the Chinese market for "coarse sound, high aggressiveness, and American sound." This was simply absurd, as these characteristics were actually attributed to the shortcomings of powerful and coarse-sounding amplifiers, not the AB-1266 headphones themselves. In reality, the AB-1266 was exceptionally clean, transparent, and detailed. The combination of the Formula S and AB-1266 has consistently impressed listeners with its expansive soundstage, clean and detailed sound, remarkable scale, energy, and low-frequency performance. No one ever mentioned that the AB-1266 sounded coarse again.
The second aspect frequently questioned was why we didn't create a balanced version. In truth, transitioning from single-ended to balanced would have simply doubled the cost and added two more amplifier channels. Balanced topology tends to cancel odd harmonics against even harmonics in FFT analysis, which might make the sound appear more "hi-fi" and "refined." However, it also tends to make the sound harder and less delicate. This approach doesn't work well with high-power amplifiers. Therefore, even though some expensive hi-end amplifiers have balanced inputs, their output stages are often single-ended.
The Formula S achieved remarkable power and delicate sound with its single-ended design, which I am extremely satisfied with. Perhaps in the future, I will explore balanced designs in battery-powered headphone amplifiers. But for now, the Formula S stands as a robust, fully discrete single-ended amplifier. Its circuit architecture is nearly textbook-level, and the name "Formula S" suits it perfectly.
Some have asked whether the Formula S is truly Class A and why it doesn't get too hot. Rest assured, the Formula S is indeed Class A, with an output power of approximately 2W+2W, totaling just over 4W. Its design efficiency is around 20%, and the overall power consumption is slightly over 20W. It doesn't generate excessive heat, making it safe to use. Some of my peers have taken the idea of headphone amplifiers running hot to the extreme. Extremely low efficiency doesn't necessarily guarantee better performance, and at such high temperatures, the lifespan of expensive components becomes a concern. Safety should also be a consideration.
MOSFET or BJT? There has long been a misconception among audiophiles that MOSFETs offer a tube-like sound – round and smooth. However, this is far from the truth. While MOSFETs may have input impedance similar to tubes, their input capacitance is hundreds of times larger, making them incomparable to tubes. MOSFETs cannot
truly replicate the tube sound. True high-quality tube sound can be experienced with products like the LampizatOr. The Formula S utilizes a fully discrete amplifier circuit with a BJT output stage. Bipolar junction transistors (BJTs) are far superior to field-effect transistors (FETs) as analog amplifier devices.
I also recommend using the Formula S with other brands of planar magnetic headphones. For example, I am a big fan of the HEKV2. High-impedance dynamic headphones like the HD800 can also benefit from the Formula S, as it opens up the soundstage, adds density to the midrange, and proves that the HD800 has plenty of bass!
by Michael Xiao
