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Audio Research Corporation Reference 160M Monoblock Amplifier

Audio Research Reference 160M

Since I first heard William Zane Johnson’s D76 stereo amplifier and SP3 full-function preamp back in the early 1970s, I’ve been a fan of Audio Research electronics. Indeed, I’ve owned and reviewed more gear from ARC than from any other marque. So, you may well ask, why haven’t I written about anything new from my all-time-favorite firm in the past several years? Well…I have my reasons. (And the folks at ARC doubtlessly have theirs.)

Speaking for myself, my first consideration was the reference speakers I’ve been using, which for the last decade or so have been various Magicos. Now, it is not as if Magicos fare more poorly with tube electronics than other dynamic loudspeakers; they don’t. But they are low enough in sensitivity, difficult enough in load, and demanding enough in power delivery to make big solid-state amplifiers somewhat better matches—particularly big solid-state amplifiers from innovative companies such as Soulution and Constellation, both of whose products have the sort of untrammeled current, iron grip, and very low distortion that make Alon Wolf’s speakers sound their best.

Second, the latest Swiss and American solid-state gear, particularly the gear from Soulution, is now capable of reproducing a quality that I value highly and that used to be the sole provenance of tubes (and of ARC tubes par excellence). To wit, while an amp like the Soulution 711 may not have the bloom or midband transparency of classic ARC, it does image in three dimensions, which is not something you could say of most transistor amps in the past. HP’s bon mot (taken from Coleridge) about the flatness of instruments on digital recordings—“painted ships upon a painted ocean”—could just as easily (and accurately) have been applied to instruments played back on most solid-state amps. Today, that isn’t as true as it once was.

Finally, there is the bottom end. Tubes typically don’t have the grip, speed, and extension of solid-state in the bass octaves, and with tricky-to-drive, sealed-cabinet speakers like Magicos, that grip, speed, and extension are indispensable if you want to hear the actual notes a Fender bass is playing, rather than mere blots of color that rise and fall with pitch like mercury in a thermometer.

Audio Research Corporation Reference 160M Monoblock Amplifier

None of this is to say that today’s solid-state gear casts shade on the glories of Audio Research. Indeed, part of the reason I’m reviewing the company’s newest amplifier, the 140W Reference 160M monoblock, is because I was reminded of those glories at RMAF last fall, where I heard the Reference 160M driving Sonus faber’s Aida II four-way floorstander. As I said in my show report, “Although I’m a lifelong fan of Audio Research, it’s been a while since I’ve heard the company’s latest offerings. Given the magic the 160Ms and the Ref 6 [preamp] performed with the Aidas (speakers I haven’t always loved in the past), I’m clearly missing out on something exceptional. On every LP I played, from Chet Baker to Enescu, this was the best demo of the show—and not by a little bit. The Sonus/ARC/Clearaudio combo simply had more of the breath and bloom of life than any other exhibit.”

Breath and bloom. These have always been ARC’s signal virtues. No other gear, tube or solid-state, reproduces voices, trumpets, saxes, clarinets, violins, guitars, anything that plays primarily in the midrange with the same remarkably realistic sense of air being moved past lips, through the mouthpieces, tubes, and bells of brasses, through the reeds and pipes of winds, and from the strings and bodies of violins and guitars. Combined with a sui generis bloom that makes sounded notes seem to swell three-dimensionally, as if they are riding on the surface of an expanding sphere rather than flattening out in a single plane, ARC’s airiness has given it an edge in sonic realism from go.

Of course, that isn’t to say that classic ARC excelled everywhere it played. Audio Research gear, preamplification and amplification, has never had the grip or the discernment of solid-state in the bass; it has almost always added a little energy in the upper mids, a bit of roll-off on the very top, and a touch of suckout or leanness in the power range; and in spite of its nonpareil midband transparency, it has also added a soft graininess to the entire soundfield. Over the years, ARC has improved voicing in all of the areas I’ve just mentioned, but never really eliminated these characteristics, only ameliorated them. Until now.

Which brings me to ARC’s latest (and in some regards, greatest) amplifier, the Reference 160M monoblock. 

I should start by saying that if you’re expecting, as I rather was after hearing the Reference 160M and the Reference 6 preamp driving those surprisingly excellent Sonus faber speakers at RMAF, that familiar, bright, lively, intensely bloomy, midrange-centric ARC sound, you are going to be a little surprised and, initially perhaps, put off—at least if you’re using the amp in its standard Ultralinear mode. In fundamental ways the 160M doesn’t sound like any other ARC amp I’ve heard or reviewed. Oh, there are definite family resemblances, but in overall tonal balance, in bass response, in imaging, and even to some extent in bloom and resolution, this is a different creature than William Zane Johnson’s designs.

Of course, the REF160M should sound different since so much about it is a departure from classic ARC. To begin with, its output tubes are no longer GE 6550 pentodes. In the REF160M ARC is using Russian KT150 power beam tetrodes, with 6H30 drivers and solid-state regulation of the (much stiffer) power supply. (ARC started using KT150s to power its amps in the mid-2010s, not only for sonic reasons but because of their availability and, according to ARC, durability.) 

 

The change in output tubes would, of course, account for many of the differences in presentation that I hinted at a paragraph or so back. But it’s not just output tubes that have changed. On its website, ARC notes that the Reference 160M also “features a refined audio topology with fewer and better components in a much shorter signal path than in previous designs, switchable Ultralinear/triode operation, proprietary auto-bias, output tube monitoring and protection, and an advanced power meter—an array of features that has never been offered before in an Audio Research amplifier.” Many of the parts used in the REF160M’s circuitry are custom made, and all of them are mounted on a special four-layer circuit board—a design, previously reserved for use in ARC preamplifiers, that is claimed to “lower the noise floor to unprecedented levels.”

I’ll speculate about the sonic effect of these new (to ARC) technologies in a few paragraphs. But to start I want to talk about the REF160M’s cosmetic and functional innovations. 

Of course, that big, sexy, see-through meter is the thing that will initially catch your eye. It’s certainly not the first meter on an ARC amp (think back to the D150), but it’s undoubtedly the coolest. With markings etched into a dual-layer transparent plastic faceplate, through which you can see the glowing KT150 vacuum tubes, the power meter reads output level in watts, with separate scales for Ultralinear and triode mode. The meter’s illumination is adjustable, about which I’ll have more to say in a moment. 

Below the meter are four buttons, which (from left to right) control power (on/off), meter illumination level, tube monitoring (when you press the button repeatedly a separate LED on the meter panel lights up to indicate that the chosen tube is operating properly), and output mode (Ultralinear or triode). It’s all pretty straightforward, as are the controls on the rear panel—switches to activate auto shut-off (which turns the amp off in two hours if it’s not being fed a signal), to select high or low speeds for the fan built into the tube cage, and to choose balanced or single-ended operation depending on which inputs you’re using; gold-plated I/Os (one balanced XLR and one single-ended RCA); and gold-plated speaker terminals (ground, 4, 8, and 16 ohms). Like all ARC gear of recent memory, the REF160M uses a 20-amp power cord (supplied).

Along with that gorgeous meter, the other thing about the REF160M that will immediately grab your attention (at least if you’re an old ARC hand) is the output-tube biasing procedure. There is none! 

After all those years of unfastening dozens of tiny, easy-to-lose screws to remove the tube cages and gain access to the tube sockets and bias pots, you will find the REF160M a positive dream-come-true. First of all, there are far fewer screws to loosen to remove the cage—which you’ll still have to do to install the tubes (marked in pen, as has always been the case with ARC amps, with the letters and numbers of the sockets they are intended to fit into) and to plug in the built-in cooling fan. But the truly labor-saving benefit of the REF160M isn’t the number of screws; it’s the amp’s auto-biasing circuit—a first for ARC. 

Though other manufacturers of tube amplifiers (e.g., VTL and VAC) have long embraced auto-biasing of output tubes, ARC has up til now stuck with the DIY method of turning a pot (with that ridiculous plastic tool) and reading off the voltage via a built-in meter or an outboard one. I should note, however, that sheer cussedness wasn’t the only reason that ARC stuck to the cumbrous tried-and-true. It was ARC’s belief—expressed repeatedly to me by Warren Gehl, the guy who has done all the voicing of ARC electronics for the last couple of decades—that auto-bias circuits were never a free ride, that there was always a sonic cost to be paid for the convenience. Apparently, someone changed Gehl & Co.’s minds. Maybe the market changed their minds. But…whoever or whatever it was that led to the adoption of this undoubtedly far more expedient technology, I’d have to say—from my experience with the REF160M (and before that the auto-biasing VAC Statement 450 IQ) compared with my experience with manually biased tube amps like the Air Tight ATM-3011R or vintage ARC amps or fixed-bias tube amps like the Zanden Model 9600mk2—that there may, indeed, be a small sonic cost (as well as a big sonic benefit) with auto-biasing. (I’ll discuss this further in a moment.)

While I’m on the subject of double-edged swords, I gotta tell you that for all its sex appeal that fabulous-looking power meter is also a bit of a conundrum. First, there is the question of its accuracy. One measurements-first reviewer, who edits another magazine, found the thing to be incorrectly calibrated—and not by a little bit, at least in triode mode. The second problem is the current draw of the lights used to illuminate the meter. It has been my experience with ARC gear (and virtually every other amp or preamp, tube or solid-state) that turning displays off improves the sound, while turning them on does just the opposite. With a big, bright item like the REF160M’s power meter, the sound is unquestionably affected (darkened, I would say) by lighting up the scales. Now some of you may prefer the somewhat more bottom-up sound of the amp with the meter fully illuminated, and some may simply want to get their money’s worth and see that needle bouncing around. This, of course, is a matter of taste. But whether to light or not to light (which amounts to whether to use the meter or not) is a legitimate sonic consideration.

You may think from what I’ve written thus far that I don’t particularly like the Reference 160M. Well, niggling over meter lights and auto-biasing aside, you couldn’t be more wrong. Fact is I do particularly like it. In fact, I’m considering (ARC willing) using it as one of my tube references. No, it doesn’t sound as much like classic ARC as I expected, which, as I noted, came as a surprise. Of course, though I’m currently using just about everything else I heard at RMAF in my own system (the Reference 6 preamp, the Clearaudio Goldfinger Statement cartridge, and the Clearaudio Absolute transimpedance phonostage), I’m not using Sonus faber loudspeakers. I’m using the Magico M3s, which to my ear are the best (i.e., most realistic-sounding) moderately sized dynamic floorstanders on the market—and it is a fact that the M3s aren’t interfacing with the REF160M in quite the same way as the Aidas did. 

Even though the M3 is higher in sensitivity than many Magicos (91dB—or so Magico claims), it is still a different load than the Sonuses, and the result is a different tonal balance than I heard in Denver—and than I’ve heard from ARC amps in the past (even when I used them with earlier Magicos). Because of their characteristic suckout in the power range and touch of scintillant brightness in the upper mids, ARC amplifiers have generally tended toward a brighter “top-down” balance that emphasizes the midrange and the upper midrange (where many tones and transients live), rather than the bass and power range. Not the REF160M. 

 

Whether it’s the new tubes, the new parts, the new power supply, or the new circuit layout, this amp is considerably fuller (and more natural) in color in the upper bass and in the mids than vintage ARC—to the point that the REF160M (once again, driving the Magicos) no longer sounds a bit bright and top-down in tonal balance, but neutral to somewhat “bottom-up.” Its imaging is also different than vintage ARC—a bit more tightly focused and less midrange-forward. Its soundstaging is different too—wide, deep, and tall, but somehow less freewheeling and more tightly controlled than olden-days ARC.

Indeed, this sense of things being under tighter control applies to just about every aspect of the REF160M’s sound. It even affects the way the amp is reproducing air and bloom. Oh, those essentials are still there (how could they not be—this is ARC), but the REF160M’s reproduction of bloom is less expansive and sonically dominant and its air less bright, grainy, and pervasive than I remember from days gone by. 

BTW, I heard this same sense of tighter control of bloom and more focused imaging with another auto-biased tube amplifier, the VAC Statement 450 IQ, which makes me wonder whether tighter focus and greater control are, at least to some extent, both the benefits one derives from and the price one pays for auto-biasing—and whether the looser, brighter, noisier, less tightly focused, more freewheeling sound of older ARC is, in some part, the result of less rigorous control over bias current. (This is an observational guess, folks, not a scientific fact. It is equally probable that the effects I’ve observed have something to do with solid-state regulation of the power supply, the shorter signal paths on the new circuit boards, and the different complement of output tubes, or all three in combination with auto-biasing.)

Wherever it is coming from, there is no question that the upside of the REF160M’s newfound control is far more sonically significant than its downside. For one thing, as noted, it makes the REF’s bass and power range sound considerably better defined and fuller in color than that of its leaner-in-tone, bigger-sounding, and somewhat bloomier predecessors. Where a vintage 6550-based ARC amp would have made the cello on something like Acoustic Sounds’ new 45rpm reissue of János Starker’s justly famous traversal of the Bach Suites for Cello (a celebrated Mercury box set that has been freshly remastered from the original three-track tapes with the assistance of Robert and Wilma Cozart Fine’s son, Tom) sound bigger and less focused in imaging, leaner in timbre, brighter and more biting on attacks, and somewhat less detailed overall, the REF160M’s makes it sound better defined, more detailed, more neutral and natural in tone, smoother and more even in pace, and more solidly “there.” 

The REF160M’s improved control and definition over what it’s reproducing is clearly allied to and benefiting from several other changes in the amp’s sound and technology. That pervasive grain structure that I mentioned earlier, which added “airiness” to a vintage ARC by giving the air itself more texture and thus making it more audible as a separable element, has finally been almost completely dismantled. I attribute this dramatic improvement to another obvious difference between the REF160M and every other ARC amp that has come before it: markedly lower noise. The reviewer/editor that I mentioned earlier also measured the 160M’s noise floor and found it to be commendably (indeed, sensationally) low for a tube amplifier. But one does not need measurements to hear this drop in noise. The aforementioned absence of ambient texture and the subsequently quieter spaces between and among instruments makes for higher resolution of actual textural details, such as the supremely artful way that Sinatra (on the, alas, no longer available MoFi reissue of Sinatra at the Sands) uses different parts of his baritone instrument to add humor, irony, and heart to certain phrases from Cole Porter’s “I’ve Got You Under My Skin”—sometimes playfully letting the words rattle like dice on his palate, sometimes adding a touch of sexy, sibilant sizzle with his tongue and lips, sometimes adding power and fervency with chest tone. Through the REF160M it is a helluva performance—a bit of songsmanship that would be hard to improve on. 

Sinatra at the Sands also illustrates another aspect of the REF160M’s lower-noise/higher-control presentation—this one nonpareil. Every amplifier that I know of has its own way of reproducing the development of a note—from initial attack through steady-state tone through lingering decay. Every one of them applies its own emphasis to each phase, sometimes stressing attack at the expense of timbre (particularly with solid-state amplifiers), sometimes timbre at the expense of attack (particularly with tube amps), sometimes decay at the expense of both. The REF160M is the first tube amp (indeed, the first amp of any kind) I’ve heard that seems to be allotting precisely the same time and energy to each phase of the dynamic/harmonic envelope. You can hear this quite clearly on the brasses and winds of Count Basie’s fabulous band from the aforementioned Sinatra recording. I’ve listened to these thrillingly powerful big-band breaks (there is a good reason that Sinatra tells the Sands audience to “Run for cover” when Basie takes his turn on the Porter tune) through just about every speaker and amplifier and preamplifier I’ve had in my home, and not a one of them has reproduced them with the almost serene aplomb of the REF160M.

At first you may think you’re missing something—the band isn’t slamming you back quite the way it does with solid-state, detail isn’t getting etched by razor-edged attacks, decay isn’t quite as long and room-filling/defining. But after hearing how evenly the REF160M develops the entire utterance of those fiery brasses and winds, you realize that what you’re really missing isn’t more violent attacks or higher resolution or more languorous decay but the emphasis on attacks, timbral details, and decays that other amps are adding—and that what you’re getting instead is the smooth, uniform development of the entire dynamic/harmonic envelope, without any added accent on one part or another. This, folks, is quite remarkable—something I’m not sure I’ve heard before (to this extent) from any other amplifier. 

This uniquely even pace of presentation—for lack of better words—isn’t a particularly showy virtue. Indeed, without an emphasis on transient, tone, or decay, the REF160M doesn’t at first sound as energetic, detailed, or expansive as some of its competitors. It’s not until you listen closely, which the REF160M almost invites you to do because of the subtlety of its virtues, that you realize that—while not the body-slammers or X-ray machines or room-fillers that some amplifiers are—the REF160M aren’t really skimping on energy and detail; they’re just better incorporating these things into a more natural (less hi-fi) presentation.

This said, there are amps with genuinely higher resolution, greater impact, and, most certainly, superior bass. Indeed, the one area where the REF160M hasn’t completely overturned ARC norms is in the bottom octaves, where it is better than respectably good—far more controlled in imaging and deeper reaching and better defined in pitch than vintage ARC—but still not the equal of the best solid-state in grip or slam. Then again, I’ve never heard a tube amp that can equal a solid-state one in these regards.

Before I conclude, I guess I should note that you can easily change the REF160M’s sound, either a bit or a lot. For a bit of a difference, select a different output tap from among the 4-, 8-, and 16-ohm options. (Even though the Magico is a nominal 4-ohm speaker, I slightly preferred the 8-ohm tap over the 4-ohm one. The sound was a little tauter and slightly more neutral top to bottom, though not by much.)

 

For a bigger difference, you can choose, with the touch of a button, triode mode rather than Ultralinear. In triode mode, the REF160M is very reminiscent of the sound of the ARC Classic 60 and Classic 150 (which came wired in triode). The presentation is markedly leaner, a bit more midrange-centric (and more detailed in the mids), a bit drier, less extended, and less full and powerful in the bass and the treble—a presentation that in some (not all) ways is closer to classic ARC (or classic ARC triode). Of course, you lose half of the amp’s power in triode, but 70W is still enough to drive most speakers with a relatively high sensitivity (such as the M3s) to thunderous levels. All things considered, I preferred Ultralinear with the Magicos, though triode had (and has) its appeal, as did that 4-ohm tap.

So there you have it. The ARC Reference 160M is a definitive product from a company that has produced a long series of definitive products. Two years in development, it represents Audio Research’s latest and most advanced thinking—and its sexiest packaging. Whether you will like it as much as I do will depend on your listening priorities and, to some extent, your speakers. But at its best the 160M offers things I’ve never heard before from an ARC amp: a newfound control that makes for “higher definition” from top to bottom; a standard-settingly low noise floor; a naturally richer and more neutral tonal palette; a naturally fuller power range; somewhat better focused and less midrange-forward imaging; and an even-handed presentation of the dynamic/harmonic envelope that no other amplifier I’m familiar with can better. Oh, the sentimental part of me still rather misses some of the wild-and-woolly qualities of ARC’s vintage 6550-based WZJ amps (higher noise and all), but that doesn’t change the fact that the REF160M is a more realistic-sounding, more transparent-to-sources, and more convenient-to-use offering. Obviously, the REF160M receives my highest recommendation. It is a reference-quality amplifier (and in its reproduction of the dynamic/harmonic envelope, a standard-setting one) that every music lover should hear.

Specs & Pricing

Tube complement: Two matched pairs KT150; two 6H30 
Power output: 140 watts continuous from 20Hz to 20kHz
THD: Typically 1% at 140 watts, below 0.04% at 1 watt, 1kHz
Power bandwidth: (–3dB points) 5Hz to 70kHz 
Frequency response: (–3dB points at 1 watt) 0.5Hz to 110kHz
Input sensitivity: 2.4V RMS balanced for rated output
Gain: 25.5dB into 8 ohms
Input impedance: 300k ohms, balanced; 100k ohms, single-ended
Output taps: 16 ohms, 8 ohms, 4 ohms
Damping factor: Approximately 14 
Overall negative feedback: 14dB 
Slew rate: 13 volts/microsecond 
Rise time: 2.0 microseconds 
Dimensions: 19.0″ x 10.25″ x 18.5″
Weight: 56 lbs. (net) per amp
Price: $30,000/pr.

AUDIO RESEARCH CORPORATION
655 Wedgwood Road North, Suite 115
Maple Grove, MN 55311
(763) 577-9700
audioresearch.com

JV’s Reference System
Loudspeakers: Magico M Project, Magico M3, Voxativ 9.87, Avantgarde Zero 1, MartinLogan CLX, MBL 101 E MK. II, Magnepan 1.7 and 30.7
Subwoofers: JL Audio Gotham (pair), Magico QSub 15 (pair)
Linestage preamps: Soulution 725, Constellation Audio Altair II, Siltech SAGA System C1, Air Tight ATE-2001 Reference
Phonostage preamps: Walker Proscenium V, Soulution 755, Constellation Audio Perseus
Power amplifiers: Soulution 711, Constellation Audio Hercules II Stereo, Air Tight 3211, Air Tight ATM-2001, Zanden Audio Systems Model 9600, Siltech SAGA System V1/P1, Odyssey Audio Stratos, Voxativ Integrated 805 
Analog sources: Acoustic Signature Invictus Jr./T-9000, Walker Audio Proscenium Black Diamond Mk V, TW Acustic Black Knight/TW Raven 10.5, AMG Viella 12
Tape deck: United Home Audio Ultimate 1 OPS 
Phono cartridges: Clearaudio Goldfinger Statement, Air Tight Opus 1, Ortofon MC Anna, Ortofon MC A90
Digital sources: MSB Reference DAC, Berkeley Alpha DAC 2 
Cables and interconnects: Crystal Cable Absolute Dream, Synergistic Research Galileo UEF, Ansuz Acoustics Diamond
Power cords: Crystal Cable Absolute Dream, Synergistic Research Galileo UEF, Ansuz Acoustics Diamond
Power conditioners: AudioQuest Niagara 5000 (two), Synergistic Research Galileo UEF, Technical Brain
Support systems: Critical Mass Systems MAXXUM and QXK equipment racks and amp stands
Room treatments: Stein Music H2 Harmonizer system, Synergistic Research UEF Acoustic Panels/Atmosphere XL4/UEF Acoustic Dot system, Synergistic Research ART system, Shakti Hallographs (6), Zanden Acoustic panels, A/V Room Services Metu acoustic panels and traps, ASC Tube Traps
Accessories: Symposium Isis and Ultra equipment platforms, Walker Prologue Reference equipment and amp stands, Walker Valid Points and Resonance Control discs, Clearaudio Double Matrix Professional Sonic record cleaner, Synergistic Research RED Quantum fuses, HiFi-Tuning silver/gold fuses

Tags: AUDIO RESEARCH

By Jonathan Valin

I’ve been a creative writer for most of life. Throughout the 80s and 90s, I wrote eleven novels and many stories—some of which were nominated for (and won) prizes, one of which was made into a not-very-good movie by Paramount, and all of which are still available hardbound and via download on Amazon. At the same time I taught creative writing at a couple of universities and worked brief stints in Hollywood. It looked as if teaching and writing more novels, stories, reviews, and scripts was going to be my life. Then HP called me up out of the blue, and everything changed. I’ve told this story several times, but it’s worth repeating because the second half of my life hinged on it. I’d been an audiophile since I was in my mid-teens, and did all the things a young audiophile did back then, buying what I could afford (mainly on the used market), hanging with audiophile friends almost exclusively, and poring over J. Gordon Holt’s Stereophile and Harry Pearson’s Absolute Sound. Come the early 90s, I took a year and a half off from writing my next novel and, music lover that I was, researched and wrote a book (now out of print) about my favorite classical records on the RCA label. Somehow Harry found out about that book (The RCA Bible), got my phone number (which was unlisted, so to this day I don’t know how he unearthed it), and called. Since I’d been reading him since I was a kid, I was shocked. “I feel like I’m talking to God,” I told him. “No,” said he, in that deep rumbling voice of his, “God is talking to you.” I laughed, of course. But in a way it worked out to be true, since from almost that moment forward I’ve devoted my life to writing about audio and music—first for Harry at TAS, then for Fi (the magazine I founded alongside Wayne Garcia), and in the new millennium at TAS again, when HP hired me back after Fi folded. It’s been an odd and, for the most part, serendipitous career, in which things have simply come my way, like Harry’s phone call, without me planning for them. For better and worse I’ve just gone with them on instinct and my talent to spin words, which is as close to being musical as I come.

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