Eleven XI Audio Formula S Formula S Headphone Amplifier

Product Overview

When any amplifier is not good enough... Powerful sound always on tap by Eleven Audio.

This sentence was written by the owner of Abyss. My English is not good, so I'm not good at translating it.

Design Philosophy

Let's start with Joe, the owner of the two brands Abyss and JPS Labs. The first time I met Joe and his Abyss AB-1266 headphones was at CES in January 2014. The experience in Las Vegas that year is still vivid in my memory. The petite Jojo from Final, Wilson, the silver-haired, eagle-eyed language genius and owner of Jaben Singapore, myself, and Joe shared a booth at The Venetian hotel. Joe was about 1.85 meters tall, confident and optimistic, with a thick New York accent and an animated expression. But his Abyss headphones clearly stole the show from their owner, and could only be described as insane. Guests would put on the headphones, always close their eyes in astonishment, and then sway with the sound waves, unable to stop. In 2014, the AB-1266 finally let the headphone market know that dynamics, transparency, soundstage, an unimaginable sense of energy, invincible bass, electrostatic-like detail, could finally be combined in a single pair of headphones and presented to the public.

However, the funny thing is, besides being incomprehensibly good-sounding, these headphones were also incomprehensibly difficult to drive. For their first exhibition, they used a split Woo Audio tube amplifier weighing tens of kilograms to drive them. Several people had to lift them in and out.

Later, through various coincidences, I became the promoter and spokesperson for Abyss headphones and JPS Labs cables in China. It was then that I finally made up my mind to dedicate myself to building an amplifier that could adequately drive the 1266. I estimate there were about 50 major debuggings. Joe really liked this amplifier and personally selected a full set of internal wiring for the Formula S, totaling 11 cables. He also authorized me to put the "Wired with JPS Labs" logo on the amplifier. Now Abyss also sells the Formula S amplifier. Here, I'd like to thank Joe. His JPS Labs cables imbued the Formula S with a high-end musicality, allowing the Formula S and his Abyss headphones to blend perfectly.

Technical Design Approach

In my mind, designing power amplifiers, headphone amplifiers, and preamplifiers are completely different projects, almost like being in different industries. I would like to specifically thank Philippe Chambon, a design guru at Nagra in Switzerland, for his unreserved guidance and inspiration. In recent years, I've always seized every possible opportunity to chat with him. I have benefited greatly from everything from design principles to technical details. Without him, the Formula S would not have been able to directly enter the ranks of top-tier headphone amplifiers as a new product.

Sound Characteristics and Performance

The first challenge for Formula S was to vindicate the AB-1266 headphones. Because they are difficult to drive, users often use robust, high-powered machines to handle them. As a result, the 1266 gained a reputation in the Chinese market for having a "rough sound, hot temper, and American sound." This is simply outrageous. These are clearly all shortcomings stemming from powerful, rough-sounding large amplifiers. The 1266 itself is actually extremely clean, transparent, and delicate. The Formula S + 1266 combination has been showcased many times. Listeners are invariably amazed by the boundless soundstage, delicate and clean sound, astonishing sense of scale, energy, and bass performance. No one ever says the 1266 sounds rough anymore.

Design Choices: Single-Ended vs Balanced

The second often questioned point is why it wasn't made into a balanced version. In fact, if it were simply to go from a single-ended version to a balanced version, it would just double the cost and use two more channels of amplification modules. A balanced topology would superimpose odd harmonics in the FFT to cancel even harmonics, ultimately increasing the proportion of odd harmonics. It sounds like a balanced structure would be more hi-fi, and the sound would be more "qualitative." In reality, the sound becomes harder and its delicacy is reduced. The larger the power amplifier, the less you should do this. That's why those extremely expensive high-end large power amplifiers, even with balanced inputs, have single-ended rather than balanced output stages.

Formula S achieves powerful drive and delicate sound with a single-ended structure, and I am extremely satisfied. Perhaps in the future, I might play around with balanced designs in battery-powered headphone amplifier products. But the Formula S is a powerful, fully discrete single-ended amplifier. The circuit architecture is almost textbook-level, making the name "Formula" perfectly suitable.

Class A Operation and Thermal Management

Someone also asked me, is the Formula S really Class A? Why doesn't it get hot?

The Formula S is indeed full Class A, with an output power of approximately 2W+2W, a little over 4W in total. The design efficiency is around 20%, and the total power consumption of the unit is a little over 20W. The temperature won't be too high. It's very safe. In fact, some of my peers make headphone amplifiers that can fry pancakes, which is a bit excessive. Very low efficiency doesn't necessarily mean better performance, and when it gets that hot, the lifespan of those expensive components becomes an issue. Safety also needs to be a concern.

Component Selection: MOSFET vs BJT

MOSFET or BJT? There has always been a misconception among audiophiles that MOSFETs have a tube-like sound: mellow and smooth. This is quite wrong. While the input impedance of MOSFETs is comparable to that of tubes, their input capacitance is hundreds of times larger than that of tubes, so they cannot be compared. MOSFETs cannot sound like tubes. A truly good tube sound is, of course, beautiful; please refer to LampizatOr. The Formula S features a fully discrete amplification circuit structure with a BJT output stage. Bipolar junction transistors are much superior analog amplification devices compared to field-effect transistors.

Compatibility with Other Headphones

I also recommend that customers use Formula S with other brands of planar magnetic headphones. For example, the HEKV2, which I personally like very much. High-impedance dynamic headphones like the HD800 can also open up the soundstage, while pushing out a solid and dense midrange, and can even prove to the world that the HD800 has bass!

Product Features

• High quality design and components throughout

• All aluminum construction with brushed aluminum front panel

• Provides three most popular connections for high performance headphones - The three most commonly used headphone jacks: 1/4″ (6.3 mm), 4 pin XLR, and dual 3 pin XLR

• Adjustable ALPS volume control goes from 'zero to Eleven' - ALPS potentiometer starts from position 11

• Output protection and turn-on/turn-off delay keeps your high end headphone investment safe - Complete protection for headphones

• Single set of RCA inputs wired direct to the volume control with JPS Labs Alumiloy® wire (no switches or extra circuit paths) - One set of RCA inputs, with JPS Labs Alumiloy® proprietary wiring used internally

• Mains input: 110/220 VAC switchable, standard grounded IEC AC cord socket - Standard power interface, 115/230 universal

• Circular connector for future options (battery supply, etc) - Large circular expansion interface