Reviewers' ChoiceBeauty and brains

I have a head for business and a bod for sin!

Those words from Tess McGill (Melanie Griffith) caught Jack Trainer (Harrison Ford) hook, line, and sinker, and propelled the remainder of Working Girl, Mike Nichols’s romantic comedy-drama of 1988 -- the intoxicating sentiment stated, appropriately, in a bar. The allure of intellectual prowess coupled with emotional hedonism is great, not only because it is elusive but because it promises to satisfy so completely. It’s hard enough to find one of those qualities; to find both together is exponentially more difficult. Nonetheless, the combination has been heroically sought across many disciplines, including audio reproduction.

One product that came close to embodying both was Ayre Acoustics’ original MX-R monoblock power amplifier, released in July 2006 at $16,500 USD per pair (later increased to $18,500/pair). I bought a pair of MX-Rs for my big rig in January 2007 -- and a second pair later, for a smaller reference system. Ever since, the four MX-Rs have served as my reference amps. I thus have an unusually deep understanding of how close Ayre’s founder and designer, Charles Hansen, got to realizing the goal of perfection -- and which I tried to convey when, a few years ago, I reviewed the original MX-R and the companion KX-R preamplifier. Yet Hansen will be the first to acknowledge that, as good as his company’s products may be, there’s always room for improvement. The “perfect” audio component will probably never exist, but that doesn’t seem to discourage the pursuit. Ayre Acoustics celebrated its 20th anniversary in 2013. To commemorate that milestone, Hansen designed an updated version of the MX-R, the MX-R Twenty. It was released in 2014, along with Twenty editions of the KX-R preamplifier, the VX-R stereo amplifier, and some 5-series components.

Ayre Acoustics MX-R Twenty

I’d already had my KX-R preamp upgraded to Twenty status, and have found it the single most pronounced advancement of an already superlative product in my experience. The effect is that of an emotion supercharger. I was eager to find out how much additional magic might be wrought by the MX-R Twenty ($29,500/pair).

Outwardly identical . . .

Other than the addition of a small “Twenty” badge on the right side of its faceplate, the MX-R Twenty is outwardly identical to the MX-R. The same goes for Ayre’s standard R-class packaging: each monoblock is double boxed and, inside the inner box, double bagged in a padded velvet sleeve encased in a thick poly sheath, this in turn cocooned in form-fitting, closed-cell polystyrene. Also in each package is a bag containing the user’s manual, a registration card, and a pair of white gloves. It’s hard to imagine what sort of cataclysmic transportation mishap might breach these protective measures to damage, scratch, or otherwise blemish the MX-R Twenty’s jewel-like finish.

Each monoblock weighs about 51 pounds. Think dense rather than big, as the MX-R Twenty’s dimensions are compact: 11”W x 3.75”H x 18.5”D. While the practice is now more common, Ayre’s R-class components were among the first to be hewn from solid billets of metal -- in the MX-R Twenty’s case, 75 pounds of aircraft-grade aluminum. This machining takes place in three stages.

Ayre Acoustics MX-R Twenty

The first stage establishes the amp’s outer dimensions and contours, including the integral heatsinks that dominate the rear two-thirds of the case, running across the top and halfway down the sides; as well as the beveled edges that have kept the MX-R looking contemporary and fresh for the better part of a decade.

In the second stage, the chassis is flipped upside down for the hogging-out of several individually shielded chambers and chaseways, including cavities for the amplification circuitry and output devices (opposite the external heatsinks), the two EI-core transformers, the logic controls, the combination of input IEC and Ayre Conditioner (see below), and the leads for the Cardas Audio binding posts. Wiring channels are routed into the interior walls to provide further shielding of critical circuits and signals.

In the final step, Ayre applies a “lenticular” finish -- a variant of circular graining. Its microridges resist fingerprints, and catch and reflect light to give the case a sheen and a luxurious solidity. The MX-R Twenty is available in a natural, silvery aluminum finish, or an anodized black (add $500/pair) of which I am particularly fond.

. . . but under the skin . . .

. . . almost everything is different. While the MX-R Twenty’s chassis and transformers remain unchanged, the entire audio board is new. Accordingly, when an MX-R is upgraded to Twenty status, the old audio board is removed and the new one installed. In line with Ayre’s long practice, the price of the upgrade is the difference between the final retail price of the original MX-R ($9250) and the retail price of MX-R Twenty ($14,750): $5500. Voilà! A brand-new monoblock. Of course, this begs the question: What about the new audio board is new?

Not the specifications, or certain key design approaches and components, or anything else cited in this paragraph. Like the MX-R, the MX-R Twenty is an entirely analog power amplifier producing continuous power outputs of 300W into 8 ohms, 600W into 4 ohms, or a massive 1200W into 2 ohms. It has an input impedance of 2 megohms (2 million ohms), which approaches the theoretical ideal of an infinite input impedance. On the parts side, the MX-R Twenty has circuit boards made of Ayre’s favorite ultra-low-loss material, proprietary polystyrene capacitors, and, as always, an Ayre Conditioner to filter radio-frequency interference (RFI) out of the juice from the wall socket. In typical Ayre fashion, the audio circuits are complementary (dual differential) and fully balanced, with no negative feedback. Befitting so purist an approach, each amp sports a single, balanced (XLR) input at the center of its rear panel. (If a single-ended output is the only choice offered by the partnering preamp, adapters are available from Ayre or Cardas.) Rounding out the rear panel: On the left is a Cardas binding post that can handle single or, for biwiring, double-stacked spades; on the right, a standard 15A IEC power input; and between them, a pair of AyreLink communication ports (RJ-11 phone jacks).

The differences between the MX-R Twenty and the MX-R include a Double Diamond output stage and AyreLock power-supply circuitry. These claimed enhancements follow on the Diamond output stage that debuted in the Ayre line in 2013, in the AX-5 integrated amplifier, KX-5 preamplifier, and VX-5 power amplifier. My first extended exposure to the sound of the AX-5 told me that something interesting was in the air. (The AX-5 similarly impressed Uday Reddy; see his January 2014 review in SoundStage! Hi-Fi.) While unable to attain most of the hi-fi-oriented characteristics easily attained by pairing the original MX-R and KX-R (total cost $37,000), the little AX-5 ($10,000) nevertheless made possible for me an emotional engagement with the music that seldom happened with its costlier brethren. Knowing how Ayre constantly refines its designs, then attempts, whenever possible, to apply what it discovers up and down its product hierarchy, I suspected that revisions of the R-series models were forthcoming, and as time went on, assumed that that meant continuing innovation. A long, recent exchange with Charles Hansen told me that I hadn’t suspected the half of it.

An Ayre-ducation by Prof. Hansen

I asked Hansen about his version of the Diamond output stage for Ayre products, and what had driven him to further develop it into the Double Diamond circuit for the MX-R Twenty. He obliged, but not without first checking my grasp of a few basics.

In the output stages of Ayre amps and preamps, an emitter-follower circuit is used for current gain (as opposed to voltage gain), to keep the output impedance relatively low. (To drive loudspeakers, power amps need a lower output impedance than preamplifiers.) Also, because coupling capacitors always color the sound, Ayre prefers to eliminate them altogether by using complementary circuit design. While partial adoption of this approach has become widespread in audio in the past several decades, Hansen doesn’t like to do things halfway, as he told me:

All Ayre products ever have always been “full complementary,” meaning that the entire circuit -- all the way from the very input transistors to the final output transistors -- is complementary, with twice as many parts required. . . . These mirror-imaged parts must be carefully matched. [In addition,] all Ayre products ever made have been fully balanced from input-to-output. Balanced is better (period!), not because a balanced input will reject hum and noise picked up on long cables (required for recording studios), but because true balanced circuitry rejects any imperfections from the power supplies. . . . All circuits in the world, whether digital or analog, audio or computers, are nothing more than modulated power supplies. That is why the power supplies are critical to the performance of any circuit. Since there is no such thing as a perfect power supply, a balanced circuit will always sound better (assuming all else is equal) as it will reject the imperfections. . . . You can see that all Ayre products ever made actually have four times as many parts as “normal” equipment. The parts are doubled once to make them fully complementary, then doubled again to make them fully balanced. [A]ll these parts must be carefully matched.

The fundamentals behind us, Hansen talked about the Diamond circuit:

Richard Baker of MIT conceptualized what he called a “Diamond” circuit that is now commonly called a “diamond buffer.” A diamond buffer is most often used inside of ICs [integrated circuits] because of the matching requirements between the devices. I’ve only ever seen one or two other audio products that have used discrete diamond buffers in the history of solid-state. A diamond buffer comprises two emitter-followers in series (current gain = 10,000x), but wired up in such a way that the inputs are also tied together (like the outputs of all complementary emitter-followers). The first pair provides the bias voltage for the second pair without the need for a bias network. We have found that this sounds better than a single emitter-follower with a bias network. We have also found some modifications that make the Ayre diamond buffers sound better than the standard diamond buffers that other IC and audio manufacturers use.

A diamond buffer has more than enough current gain for a preamp, but still not enough for a power amp. I invented a new kind of single-stage emitter-follower that solves the bias problem of a normal emitter-follower and sounds as good as a diamond buffer. The disadvantage is that it has just as many parts as a diamond buffer (4x that of a normal emitter-follower). The resulting combination is what we called the “Diamond output stage” as it is not just a “diamond buffer” but instead a complete system of three emitter-followers (giving a current gain of 1,000,000x) that makes the entire output stage. It sounded better than our triple emitter-follower (as used in the original MX-R) but created more heat, as the diamond circuit requires the use of equal sized transistors.

That heat proved to be a problem in the context of the dissipation capability of the R-series amplifier chassis, so Hansen rearranged the building blocks to achieve cooler operation (assembling three stages of emitter-followers for a current gain of 1,000,000x), yet with a single-point drive at both input and output. The result is the Double Diamond output stage. “It sounds even better than the original Diamond output stage,” Hansen boasted, “yet runs slightly cooler than the original triple emitter-follower of the MX-R.”

Having developed a better-sounding output stage for the MX-R Twenty, Hansen couldn’t resist revisiting the VX-5 power amp and AX-5 integrated with a Twenty upgrade, despite those models’ recent vintage, replacing their Diamond output stage with the Double Diamond and thereby lowering their operating temperatures by 40 degrees F.

Beyond the circuit design itself, and consistent with Ayre’s preference for custom-developed audio-grade resistors, in the MX-R Twenty metal-foil resistors replace the metal-film types used in the MX-R. According to Hansen, the higher parts cost is more than justified by the increase in sound quality. Ayre continues to use the EquiLock gain circuit, which debuted with the MX-R, but in a somewhat evolved form. EquiLock applies a cascode topology to an audio circuit, wherein the EquiLock transistor stabilizes the operating parameters of the gain transistors, for greater linearity. Hansen told me about his refinement of AyreLock, which appears for the first time in the Twenty models:

Ayre has always used discrete, zero-feedback regulators for all analog circuitry and critical digital circuitry [and for two decades] has been continuously improving and refining our zero-feedback discrete regulators. The culmination of this technology is called the “AyreLock” because the regulator “locks” the output voltage in a radical new way. Conventional regulators add an adjustable resistance in series with the audio circuit (load for the power supply). If the audio circuit draws more current, the regulator’s resistance is lowered to keep a constant voltage at the output of the regulator. [Unlike these and other approaches (e.g., chokes, switch-mode supplies), which are one-way systems that either pull an output “up” (not down) or push it “down” (not up), the] AyreLock regulator has a push-pull output stage that can both pull the output “up” (higher) when the audio circuit draws more current, and also “down” (lower) when the audio circuit draws less current. This dual-action regulator is a radical breakthrough in power supplies and moves the performance mark forward greatly.

Conclusion: There’s a lot of new thinking under the hood of the MX-R Twenty. But what about the sound?

Sound: more evolutionary than revolutionary

My quartet of MX-R monoblocks long ago proved to be sonic jewels. Having paired one set of MX-Rs with a series of preamps from Audio Research -- a review sample of the Reference 5, a purchased Reference 5SE, and, most recently, a Reference 10 -- I know firsthand how much of music’s emotional content can be passed from source to speakers through the MX-Rs. While I was confident the MX-R Twentys would produce nothing less than that, I was unsure how much more they could offer. But having upgraded to Twenty status only two of my four MX-Rs, I could now easily compare the originals to their successors in real time, without having to rely on fickle aural memory or old listening notes.

I heard evolutionary changes in multiple parameters. Overall, these could be described as a greater robustness in the MX-R Twenty’s sound over the MX-R: more meat on the bone. The MX-R Twenty did away with the faintest sheen of electronic haze that I heard in the MX-R only in direct comparison with a pair of Aesthetix’s Atlas Signature tubed/solid-state monoblocks. What I’d incorrectly attributed to the faintest remnant of LP surface noise or master-tape hiss in the otherwise effervescent sound of Louis Armstrong and Ella Fitzgerald’s Porgy and Bess (180gm LP, Verve/Speakers Corner MGVS-6040-2) was revealed as an artifact introduced by the solid-state MX-R. There was no hiss with the MX-R Twenty. The increase in contrast made possible by eliminating the perception of a noise floor (rather than artificially boosting the top) opened the door to greater enjoyment regardless of volume level, and never at the expense of long-term listening pleasure. There was nothing etched about the MX-R Twenty’s sound.

Where even the MX-R clearly bested the Atlas in the sense of an immediacy or “direct connection” of source to speakers, the gap between the MX-R Twenty and the Atlas was even wider. An interesting example of such a feeling of direct connection was when I compared the sounds of the Atlas and MX-R Twenty with Daft Punk’s surprisingly fulfilling Alive 2007 (180gm LP, Atlantic RP1-791369). Having come to the electronic duo’s work through their breakout album, 2013’s genre-bending Random Access Memories, I wondered how such electronically manufactured music would work in a live concert. Would creativity and spontaneity even be possible? While I’m still unsure of what, precisely, is created “live” at a Daft Punk concert, the melding and overlaying of multiple songs in each track is inventive and impressively executed. In “Around the World/Harder Better Faster Stronger,” the explosiveness of the electronica and the cheering response of the obviously pulsating audience were more completely captured in all their live immediacy by the MX-R Twenty than they were by the Aesthetix Atlas Signature. Harder better faster stronger indeed!

Ayre Acoustics MX-R Twenty

Like the ARC Reference 250, the Atlas has a beguiling midrange and expansiveness that the MX-R could never quite match -- but that the MX-R Twenty did, leaving none of that behind. Especially in the lower registers, there was greater, more palpable presence. A perfect example of the difference between the MX-Rs old and new was the double bass of the great, late Charlie Haden on his and pianist Keith Jarrett’s presciently titled Last Dance (16-bit/44.1kHz AIFF, ECM). Thelonious Monk’s “’Round Midnight” not only showcases Haden’s gift of selecting just the right note to complete each phrase, but the MX-R Twenty revealed more heft in Haden’s bass while unveiling a remarkable warmth of tone that previously had been cloaked.

Speaking of lower registers, one complaint sometimes levied at Charles Hansen’s zero-feedback approach to amplifier design is a lack of bass control. Using my MX-Rs to drive my Vandersteen Sevens (with built-in powered subwoofer sections), I’ve never heard or felt any such lack of low-end control, and have favored the Ayres’ textural and timing coherence. Nor have I heard any gross deficiency in the pair of MX-Rs that have long driven my entirely passive Vivid Audio Giya G3s. In fact, Laurence Dickie’s design for the Giya G3s, which emphasizes bass quality and timing accuracy over quantity, is consistent with the approach Hansen has taken with his amps. Nevertheless, in back-to-back comparisons using bass-quality tracks such as Haden and Jarrett’s “’Round Midnight” and the bass-quantity tracks on Daft Punk’s Alive 2007, it was clear the MX-R Twenty exerted more control over the lowest frequencies, and revealed in the sound a more full-bodied character, than did the MX-R. I will grant that other, invariably feedback-dependent amplifier designs may have more intense bass-oriented personalities. Yet, while that vise-like character may be a particularly “hi-fi” quality that appeals to certain listeners with certain types of music reproduced over certain types of transducers -- it has never, to my ears, equated to musical truthfulness.

The improvements wrought by the MX-R Twenty may necessitate a rebalancing of system priorities and/or preferences, and open the door to a wider range of satisfying partnering choices. With the MX-R, and despite the revolutionary (for solid-state) advancements of the KX-R Twenty preamp, the almost-larger-than-life expansiveness of the ARC Reference 10 preamp more often than not edged out the KX-R Twenty in that system. But when I replaced the MX-Rs with the MX-R Twentys, a flip-flop occurred. The synergistic coupling of the expanded competencies of the MX-R Twenty and the KX-R Twenty produced a more neutrally balanced sound and gave me greater satisfaction in listening. It makes some sense that, with a commonality of circuit design, parts quality, and overall approach, the audible result of a Twenty-Twenty system is more than the sum of its parts. In the case of the KX-R Twenty and MX-R Twenty, it was perhaps on the order of 4 + 2 = 7. This Twenty duo was unequaled in my experience in its ability to simultaneously present macrodynamic and microdynamic information, while conveying, as fully as I’ve experienced, the emotional impact of the musical performances that now live again and again through my stereo system. If you already have the original KX-R and MX-Rs and can’t afford to upgrade all three at once, go for the KX-R Twenty -- but know that, sooner or later, you’ll want to upgrade to the MX-R Twentys to capture all the sound quality now possible.

Pushing boundaries and elevating solid-state

Charles Hansen loves tubes and hates tubes. He’s always loved what they can achieve sonically, but hates that they wear out, need to be replaced, and are generally less than plug-and-play. It has been his quest to advance solid-state electronics past the level of musical engagement possible with the best tubed audio circuits. The original MX-R monoblocks may have signaled the dawn of an era in which Hansen’s goal had come into view; with the Twenty-series models, and particularly the MX-R Twenty monoblocks, I’m convinced that Ayre Acoustics has closed the gap between tube sound and solid-state sound.

Perfection may always elude us, and sonic signatures may remain that force us to choose one component over another -- but no longer must those choices be dominated by having to choose between tubes and transistors. Time will tell how close Ayre Acoustics can get to perfection, and I intend to pay vigilant attention to their endeavors. Meanwhile, I can enjoy the best of both worlds, mind and body satisfied at the highest levels I’ve ever experienced in my decades of immersion in this hobby. What more could any music lover and audiophile want?

. . . Peter Roth

Associated Equipment

  • Speakers -- Vandersteen Model Seven, Vivid Audio Giya G3
  • Sources -- Brinkmann Balance turntable with Tri-Planar U2-SE 10” tonearm (with Lyra Kleos Stereo Cartridge) and Brinkmann 12.1 tonearm (with Lyra Kleos Mono Cartridge); Ayre Acoustics DX-5DSD A/V Engine, Ayre Acoustics QB-9 DSD USB DAC, Wavelength Audio Balanced Crimson USB DAC
  • Preamplifiers -- Audio Research Reference 10, Ayre Acoustics KX-R Twenty
  • Power amplifiers -- Ayre Acoustics MX-R monosblocks, Aesthetix Atlas Signature monoblocks
  • Phono preamplifier -- Audio Research Reference 10 Phono
  • Interconnects -- AudioQuest Wild Blue Yonder, Cardas Clear
  • Speaker cables -- AudioQuest WEL Signature
  • Power conditioners -- Ayre Acoustics L-5xe, Shunyata Research Hydra Triton
  • Amp stands and rack -- Harmonic Resolution Systems M3 amp stands, MXR and SXR rack systems, both with M3X shelves

Ayre Acoustics MX-R Twenty Mono Amplifiers
Price: $29,500 USD per pair; black anodized finish, add $500/pair.
Warranty: Five years parts and labor to original purchaser with registration of product.

Ayre Acoustics, Inc.
2300-B Central Ave.
Boulder, CO 80301
Phone: (303) 442-7300
Fax: (303) 442-7301