Berning/Hi-Fi One Reference SET Power Amplifier

In 2016, I reviewed the Berning/Hi-Fi One 845/211 power amplifier based on Berning’s output-transformerless ZOTL concept ($80,000, 60W push-pull) and found it to be supremely musical. Hi-Fi One is a high-end audio retailer and specialty manufacturer based in Carlsbad, California, which partnered with David Berning to bring Berning’s designs to market. Although the 845/211 exhibited some limitations—softish bass, slightly rolled-off treble, and limited dynamic impact when compared with solid-state amplifiers—it had an absolutely glorious midrange, vividly realistic timbre, and a natural ease that brought music to life.

Based on that amplifier’s musical and commercial success, Rick Brown, proprietor of Hi-Fi One, envisioned the ultimate realization of David Berning’s output-transformerless concept. This new amplifier would have a single-ended-triode output stage and be designed and realized with no compromise. The amplifier would be built without regard to time or cost, with the retail price set after the amplifier was created. Working with David Berning, audio legend Steve McCormack, and other partners around the world, Rick and his team spent six years developing what would become the Reference SET.

I can’t overstate the monumental execution of this amplifier—not in a lavish chassis or sculpted metalwork but in the attention to detail of every design element that matters sonically. I explain the design and build in the sidebar but consider just this example: Each outboard choke—key to the amplifier’s performance—contains 14 pounds of pure silver wire sourced from Switzerland that is hand-wound by a craftsman, with one week of labor required to wind a pair of chokes. This is an extremely esoteric amplifier with a very specialized application, but also one that demonstrates what the single-ended triode amplifier can achieve when realized at the highest level. There’s never been an amplifier like the Reference SET.

The Reference SET is a four-chassis affair—two mono amplifier chassis and two outboard chokes, each connected to their respective amplifiers by an umbilical cable. The function of the chokes is explained in the sidebar, but they are the keys to the Reference SET’s performance. As with other Berning designs, the power supply is the switch-mode type. The amplifier has balanced and unbalanced inputs along with two pairs of binding posts. The input stage is built around the 12AT7 tube, with a 6V6 and a 6SN7 in the second stage driving the output stage. The input tube can be swapped for a lower-gain 12AU7 when the Reference SET is driving extremely high-sensitivity speakers. The output stage is either a single 211 or 845 triode tube, selectable by the user, that emerges from the chassis top plate. This large output tube amplifies the entire musical waveform (the definition of “single-ended”). By contrast, most tube and transistor output stages are “push-pull,” in which a pair of output devices (tubes or transistors) work in tandem, with one device amplifying the positive half of the musical waveform and the other device amplifying the musical waveform’s negative half. The single-ended triode is the very first amplification topology, invented by Lee DeForest in 1907.

Although this amplifier costs nearly a quarter of a million dollars, you won’t find lavish casework and gold-plated bling. Rather, the chassis is decidedly utilitarian, exemplifying the form-follows-function ethos that is at the heart of the Reference SET. Every Reference SET is personally delivered and set up by Rick Brown—anywhere in the world. During the installation, Rick will swap tubes and tweak the amplifier to tune the performance for your system and taste.

Listening

Rick Brown was prompted to contact me with a review offer after seeing that I had the AlsyVox Caravaggio full-range ribbon loudspeaker (reviewed last issue) in my listening room for review, which he thought would be a good match for the Reference SET. The Caravaggio is ideal in the sense that it is so transparent and lifelike that it would likely fully reveal the amplifier’s characteristics. The Caravaggio has a sensitivity of 94dB with a 4-ohm impedance, which is, in my experience, about as low in sensitivity as you would want to be driven by 20Wpc. I’ve driven a speaker of 94dB sensitivity with an 18W SET in the past with good results (Magico Q7 powered by a Lamm ML2.2). Rick’s own system, however, is built around the Reference SET and a loudspeaker of 89dB sensitivity, which he says delivers satisfying listening levels. In the sidebar I describe considerations when choosing a loudspeaker for a low-powered amplifier. In addition, you can find on our YouTube channel a video of Rick and me in my listening room discussing the Reference SET.

The Reference SET sounds different depending on the input tube selected and your choice of output tube. The input tube is either a 12AU7 or 12AT7; the lower gain of the 12AU7 is a better match when the Reference SET is driving high-sensitivity speakers. The two tubes also sound different; after listening to both, Rick and I preferred the 12AU7 in my system. Similarly, the choice of output tube, 845 or 211, will change the amplifier’s sound. In my experience with both tubes, I find the 845 to be more neutral and involving, with better bass control. Of course, there are sonic variations in brands and vintages of tubes, as well. The experience I had with Rick in evaluating the system’s sound with different tubes is the same experience you would have as a customer.

When I started listening to the Reference SET, I couldn’t help but be aware of its 20W power-output specification—not because I heard the amplifier run out of power but because of my expectations of a 20W amplifier’s limitations. This bias was exacerbated by the fact that I was driving full-range ribbon speakers, which have a long history of being difficult loads for an amplifier (as explained in last issue’s cover story, the AlsyVox speakers shatter that stereotype). I experienced cognitive dissonance—a 20W SET driving a huge full-range ribbon to realistic listening levels boggles the mind. I listened at low volumes at first, afraid to turn up the level and run up against the amplifier’s maximum output power. At this low-to-moderate volume, I heard an extraordinary realism of timbre, truly startling immediacy of images, stunning resolution, and a sense of hearing any trace of artifice stripped away. As I continued listening, my concern about the limited output power gradually faded, and I turned up the volume . . . and turned up the volume . . . and turned up the volume. Soon, I forgot that only 20W was powering the speakers and simply enjoyed the music.

The Reference SET doesn’t sound like an SET. Although I love the sound of SETs with an appropriate loudspeaker (the Lamm ML2.2 first convinced me of the SET’s virtues), I say that the Reference SET doesn’t sound like an SET as a compliment. That’s because this amplifier has the glorious midrange for which SETs are justly celebrated but doesn’t suffer from the shortcomings of other SETs—lack of dynamics, soft bass with reduced visceral impact, and an absence of ultimate top-end extension. Rather the SET’s magic was no longer confined to the midrange but extended to the entire spectrum. The Reference SET was doing something no other SET I’m aware of has accomplished—overcome the performance limitations in the bass and treble.

Specifically, the Reference SET has midbass control, weight, and dynamic impact that doesn’t sound anything like a conventional SET. Rather, the bass and midbass have, for an SET, a shocking degree of weight, power, definition, control, and dynamic impact. Unlike other SETs that have a distinctive and immediately identifiable sonic signature, the Reference SET is so neutral, transparent, and uncolored that you would never know that you were listening to an SET. Based on how loudly the Reference SET played into the Caravaggio, I would have believed that the speaker was being driven by 100Wpc of push-pull power. That’s how dynamically authoritative this amplifier is. I recently discovered a fun Latin-dance instrumental track called “Cinco Cinco Seis” by a group called Four80East. It’s not my usual listening fare, but this track has a catchy energy driven by a powerful pulsating bass line. I called up this track as an “acid test” of the Reference SET’s bottom-end capabilities and was astonished that I could play this bass-heavy track as loudly as I wanted without any hint of amplifier distress. Forget your preconceptions about SETs and their limited bass definition, lack of impact, and need for a judicious hand on the volume control. The Reference SET is an entirely different animal.

It helps that the load the Caravaggio speaker presents to the amplifier is largely resistive rather than reactive. Consequently, the speaker has no large phase-angle swings that would make life difficult for an amplifier like the Reference SET with its high output impedance. (See the sidebar for an explanation.)

Not only is the Reference SET’s bass full and rich, but it is also beautifully textured in the way it reveals the timbres of instruments with energy in the lower registers. An instrument like an acoustic bass reproduced by the Reference SET has a density of tone color and “roundness” that sound like the real thing. Bass clarinet, cello, baritone sax, bassoon, and other instruments rich in low-frequency energy were reproduced with a wonderful combination of warmth and textural resolution. Many solid-state amplifiers have greater weight and muscularity but lack the nuanced subtlety of the Reference SET. They can sound a bit flat and sterile in the bottom end by comparison.

Of course, 20W has its limitations. Although I found the bass fully satisfying driving the Caravaggios on most music, it was far from the last word in the startling dynamic impact you get from a big solid-state amplifier. The only time I ran up against the Reference SET’s bass and dynamic limitations was with bass drum in orchestral music; the amplifier audibly ran out of power on bass-drum transients. Interestingly, the Reference SET seemed to be more comfortable with continuous low frequencies than with a sudden transient that contains very low frequencies. For example, the Reference SET reproduced the organ pedal tones on Rutter’s Requiem with solidity yet audibly clipped on orchestral bass drum. It could be that the Caravaggio has an impedance dip around the frequency where the bass drum has substantial energy, a condition that would overly tax the amplifier. I’m sure that the amplifier clipped at other times, but I was never aware of it. A tube amplifier driven into momentary clipping sounds much more benign than the hard crunch you hear from a solid-state amplifier when it clips. Although the Reference SET delivers unprecedented bass and dynamic performance for an SET, you wouldn’t mistake it for a big solid-state amp. But that’s not the Reference SET’s raison d’être.

You also wouldn’t know that the Reference SET is a tube amplifier from its noise floor. I put my ear up to the tweeter and didn’t hear the faintest trace of hiss or tube rush. This is by far the quietest tube amplifier I’ve experienced. That’s an important factor when pairing the Reference SET with a very high-sensitivity speaker that will reveal any amplifier noise.

Paul Seydor obliquely commented on the Reference SET in his sidebar to Jacob Heilbrunn’s review of the Avantgarde Trio G3 loudspeaker in Issue 346. Paul visited the home of a local audiophile who owned the Trio G3 to listen to the speaker and provide his comment to Jacob’s review. That audiophile happens to own the Reference SET (actually, he owns two pairs) and was driving the Avantgarde Trios with them. Paul commented, in part, that “Headroom was unlimited. How much power did this require? The main amplifiers were the Berning/Hi-Fi One 20-watt SET References with Ypsilon silver chokes. The combination made me wonder if most of the very large speaker systems in my experience, driven with enormous amounts of power, didn’t exhibit a subtle, or not so subtle, sense of strain and effort that are completely absent from the Trios. Clarity was likewise state of the art, at least in my experience, with eye-popping detail yet without sounding analytical as such.”

Now let’s explore the qualities that separate this amplifier from any other I’ve heard. First, the Reference SET has an unparalleled ability to conjure the illusion of instruments and voices existing in your listening room, so realistic is the amplifier’s rendering of both imaging and timbres. The stunning immediacy of the imaging—the feeling of the instrument or voice right in front of you—combined synergistically with the timbral realism to startling effect. In this quality that goes a very long way toward creating a convincing illusion of live music, the combination of the Reference SET and the Caravaggio was the most realistic I’ve heard from an audio system. Instrumental textures are complexly devoid of grain, grit, and metallic hardness overlaying timbres. Moreover, the Reference SET’s gorgeous liquidity of timbre and immediacy of expression doesn’t come at the expense of neutrality. This isn’t the typical SET midrange that sounds voluptuous, but you know is not quite accurate. Indeed, the Reference SET’s midrange doesn’t sound like the midrange of other amplifiers, even SETs. Rather, it sounds neutral and transparent, with the voluptuousness a result not of coloration but rather from the sound of the instrument itself. Listen, for example, to Gene Ammon’s big round tenor sax on 1960’s Boss Tenor or Dexter Gordon’s instrument on his masterpiece Go (Music Matters LP). The Reference SET beautifully renders these instruments with all the tonal richness and density of the real thing.

The Reference SET has a sense of ease and naturalness—a kind of musical “rightness”—that removes a barrier between you and the music. I think this is the result of two qualities. The first is the utterly realistic timbral rendering I’ve just described. The second is that the sound is relaxed without sacrificing resolution. The Reference SET’s resolution is manifested as the very fine inner detail that reveals the mechanism by which the instrument produces sound and, in so doing, brings the instrument to vivid life. The Reference SET is the antithesis of analytical, yet the sound is highly resolved. Very fine transient information, such as the sound of a gently struck ride cymbal, becomes musically vivid without being sonically vivid. The great drummer Roy Haynes’ brush and cymbal work on his superb album Love Letters is a good example; the treble is richly infused with detail and a full measure of energy yet never crosses the line into brightness. The Reference SET’s complete lack of treble hardness and grain is likely a contributing factor to this impression.

The Reference SET reveals subtle nuances of musical expression in a way that deepens immersion in the listening experience. This is partly due to the amplifier’s uncanny ability to present each instrument as a separate musical line rather than congealing them tonally or spatially. As a result, each instrument’s contribution to the musical whole is immediately audible. In the just-mentioned Roy Haynes album, pianist Kenny Barron’s comping during the sax and guitar solos surprised and delighted in a new way. It’s as though each instrument in a jazz ensemble complements the other rather than competing for your attention. There’s room for everyone with this amplifier, so open, free, and natural is the rendering. The Reference SET’s spatial presentation, which boasts a tangible sense of air around and between instruments, contributes to this impression. Soundstage depth was outstanding in part because of this air and three-dimensionality, but also because of the fine resolution of low-level reverberation decay which reveals the size of the acoustic space. The sense of “action” (Jonathan Valin’s term for the way the bloom around an instrument expands outward dynamically) was vividly realistic. On the album Jazz Samba, Stan Getz’s sax has a tremendous sense of air around it that expands to light up the acoustic of the Washington DC church where this album was recorded. (There’s a great interview on YouTube with engineer Ed Greene about recording this album.)

After the AlsyVox Caravaggio went back to the distributor, I returned to my long-term reference system, the Wilson Chronosonic XVX loudspeaker driven by the CH Precision M10 monoblocks. I still had the Reference SETs, but driving the big Wilsons with the Reference SET is not a combination one would choose in the real world. The XVX has a sensitivity of 92dB, a 4-ohm nominal impedance, and a minimum impedance of 1.6 ohms at 326Hz. That 1.6-ohm minimum impedance presents a challenge for many amplifiers, particularly an SET with its high output impedance and limited current delivery. The challenge of a 1.6-ohm impedance dip in the XVX is exacerbated by the speaker’s large phase-angle swings at that frequency. It’s no surprise that Wilson specifies that the XVX should be driven by a minimum of 100W.

Yet, I had to see how the Reference SET would sound with a speaker I know intimately. First, the Reference SET defied all expectations for bass performance, dynamic contrasts, and loudness. In fact, I was shocked by the SET’s full-bodied bottom end, dynamics and apparent lack of strain at even moderately high listening levels. The Reference SET’s bass was less controlled and precise than that of the CH Precision M10s, yet it was still deep, powerful, and dynamic. Not unexpectedly, however, the Reference SET couldn’t realize the full potential of the XVX’s fabulous low-end extension, articulation, and dynamics. But beyond this technical assessment, the XVX deepened my appreciation for the Reference SET’s sound quality. The XVX is very much like the Reference SET in that the speaker is highly resolving, but in a natural and musical rather than a “hi-fi” way. Like the Reference SET, the XVX sounds gentle, relaxed, subtle, and sophisticated, yet is highly resolving. The resolution is of the rich harmonic beauty of timbres, the density of tone color, and of fine inner detail rather than transient hype. It’s a very “un-hi-fi” sound, and I mean that in the best way. The pairing of an amplifier and speaker with such similar (and rare) attributes was magical through the midrange and treble. Listen to the gorgeous tone colors of Duke Ellington’s orchestra on the fabulous new 65^th anniversary 45-rpm double-LP of Ellington Indigos on Impex Records (rapturously reviewed by WG in Issue 349). The Reference SET and XVX combination was stunning in its ability to convey the harmonic richness of the blend of the brass and woodwind instruments.

Alas, it’s not a combination I would recommend—you’d miss out on the XVX’s prodigious bass performance—but nonetheless reveals both the Reference SET’s audacious dynamic performance and its utterly natural rendering of timbre. When I connected the Reference SET to the XVX, I thought it would be for a day or so to test the amplifier’s dynamic capabilities. Two weeks later, I’m still reveling in the musical pleasure this unlikely pairing delivers.

Conclusion

The Berning/Hi-Fi One Reference SET redefines what is possible from a single-ended triode amplifier. The innovative technology of David Berning’s output-transformerless topology is realized with cost-no-object implementation by people with a driving passion and uncompromising ethos, resulting in an SET that sounds like no SET before it. This amplifier’s bass power, extension, and dynamics are simply unprecedented in an SET. On either the AlsyVox Caravaggio ribbon or even the Wilson Chronosonic XVX, I would have believed those speakers were powered by 100W of push-pull power based on the amplifier’s dynamic authority.

Best of all, the way the Reference SET brings music to vivid and immediate life is rapturous. The midrange and treble are simply stunning in their timbral realism and in the feeling that there’s nothing between you and the music. This quality is not the result of some euphonic coloration that sounds pleasant but is a departure from neutrality. Rather, it is realized by removal of some artifact to reveal the natural timbres of instruments and voices. The transparency, immediacy, and palpable presence must be heard to be believed.

As great an achievement as the Reference SET is, this is still a very esoteric and expensive amplifier that will find a very exclusive audience. You must match it with speakers of appropriate characteristics for it to perform its magic. But if you have the budget and the right loudspeaker, the Berning/Hi-Fi One Reference SET has no peer.

Specs & Pricing

Type: Single-ended triode monoblock power amplifier
Tube complement: One 12AT7 or 12AU7, one 6SN7, one 6V6, one 211 or 845
Chassis: Two per channel
Output power: 22W into 6 ohms, 16W into 4 ohms at 1% THD
Typical output power at clipping (3% THD) into 8 ohms: 22W
Inputs: Balanced and unbalanced
Input impedance: 50k ohms
Output impedance: 1.4 ohms (845 tube), 1.9 ohms (211 tube)
Signal-to-noise ratio: 86dB (845 tube); 83dB 211 tube (20kHz bandwidth, unweighted)
Power consumption: 150W to 200W each mono amplifier
Dimensions: 19″ x 8″ x 19″; tubes extend 3″ above top of chassis, and the tube cage adds 4″ to height.
Weight: 50 lbs. each amplifier; 55 lbs. each choke
Warranty: Two years
Price: $230,000 per pair, including delivery and custom setup

THE DAVID BERNING COMPANY
12430 McCrossin Lane
Potomac, MD 20854
davidberning.com

HI-FI ONE (U.S. and Worldwide Distributor)
6978 Corte Langosta
Carlsbad, CA 92009
(612) 817-1599
rbhifi1@gmail.com
rbhifi1.com

Associated Equipment

Loudspeakers: AlxyVox Caravaggio XX full-range ribbon, Wilson Audio Chronosonic XVX
Analog source: Basis Audio A.J. Conti Transcendence turntable with SuperArm 12.5 tonearm; Air Tight Opus cartridge; Moon 810LP phonostage; DS Audio ST-50 stylus cleaner, DS Audio ES-001 Eccentricity Detection Stabilizer, Levin record brush, Degritter ultrasonic LP cleaner
Digital source: Wadax Reference DAC with Reference DC cables, Wadax Reference Server with Reference PSU, Wadax Akasa optical interface.
AC Power: Shunyata Everest 8000 and Shunyata Typhon 2 conditioners, Shunyata Omega and Sigma NR V2 power cords, Shunyata AC outlets, five dedicated 20A lines wired with identical length 10AWG
Support: Critical Mass Systems Olympus equipment racks and Olympus amplifier stands; CenterStage2 isolation, Ayra Audio RevOpods isolation
Cables: AudioQuest Dragon interconnects, AudioQuest Dragon Zero loudspeaker cables
Grounding: Shunyata Altaira grounding system
Accessories: The Chord Company GroundARAY noise reduction
Acoustics: Acoustic Geometry Pro Room Pack 12, ASC 16″ Round Tube Traps
Room: Purpose-built; Acoustic Sciences Corporation Iso-Wall System