Audio Research Corporation Reference 160M Monoblock Amplifier

Higher Definition

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

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.