Audio Research Corporation Reference 160M Monoblock Amplifier

Higher Definition

Equipment report
Tubed power amplifiers
ARC Reference 160M
Audio Research Corporation Reference 160M Monoblock Amplifier

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.)