Audio Research • Reference 160S Stereo Amplifier

by Dennis Davis | September 29, 2021

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A year after releasing the Reference 160 monoblocks, Audio Research Corporation (ARC) began shipping the stereo version of the same amp, the Reference 160S. The stereo amp satisfies the demands of a small but significant number of audiophiles: those who need more than 100 watts of high-quality power but do not have the real estate or inclination to commit to two large mono amplifiers. As such, the 160S is the fourth in a series of Reference stereo amplifiers (after the Reference 110, Reference 150, and Reference 150 SE) catering to audiophiles who eschew integrated units, do not need the power to run a small town, but want something sufficiently large to power speakers with enough bandwidth to be genuinely musically convincing.

I first encountered the Reference 160S when ARC displayed a prototype at the 2019 High End show in Munich. The new amplifier bore the same general architecture as its predecessor, the Reference 150 SE, but turned heads because of the gorgeous new see-through display of the "Ghostmeters," one per channel, all the more noteworthy given that more than one commentator bemoaned the absence of the monoblocks’ meters on the previous stereo amp. Peer inside, past the Ghostmeters, and you will notice that the new amplifier has the same tube complement (four matched pairs of KT150 output tubes and four 6H30 tubes, two for input and two drivers) as the Reference 150 SE. According to Dave Gordon at ARC, "The 160S actually puts out more power on the bench than the 150SE, but our engineers are rating it more conservatively, especially given the wide variance in power lines." The rated power of the 160S is 140Wpc, down 10 watts from the 150 SE's rating, a situation that demonstrates just how variable audio specifications can be. Rest assured, however, that the Reference 160S, like the 150 SE, is essentially a 150Wpc amplifier.

As for the new meter, ARC had included a meter on a stereo amplifier, with its GS 150, but it looked nothing like this one. It’s a feature that proved popular on the recent mono amps, especially since ARC brought in the new see-through design for the Reference 160 monoblocks. In the words of ARC, the Ghostmeters “incorporate an innovative dual-layer construction with distinctively etched markings that create an integrated power meter. The power meter’s output-level markings illuminate via hidden LEDs, and the illumination brightness is adjustable.” As well as indicating output level, the Ghostmeters offer a second advantage: their transparency allows owners to see inside the amp. The Ghostmeters are certainly visually attractive, but as they were not visible from my seated position, I usually left them dimmed -- except when showing off the amplifier to audio tourists passing through my home.

The Ghostmeters are the most visible but far from the only change in the new amplifier’s design. The big news is inside the unit’s chassis. Those changes can be pieced together from the details of the monoblock version that preceded it by a year and the changes in the ARC Reference line-stage that swiftly followed. When the mono version of the Reference 160 was released, ARC stated that it used “fewer and better” components in the signal path than with previous models. And when it released the Reference 6 SE preamplifier, ARC advised that the "better” components of the Reference 160 had trickled down to the new preamplifier. The main component changes consisted of new proprietary capacitors and better wiring runs. As to the ability to use fewer components, in part that may have been made possible by switching over to four-layer circuit boards, as in the Reference 160.

The Reference 160S looks significantly different from a Reference 150 SE, Ghostmeters aside. The first, and most obvious change in appearance involves the tube cage and overall anatomy of the chassis. On all the Reference amplifiers leading up to this new design, the tubes were protected by a large flexible piece of sheet metal with ventilation holes, bent into a “C” form, and fixed to the chassis by 18 machine screws. Tap that cage and you were rewarded with a resonant ting, so it was no surprise to find that it benefitted from the application of additional damping (I used an HRS damping plate on top of the cage, and blue tape between the cage and the chassis at each screw tap, to favorable effect).

For the Reference 160S, the cage is shallower (it extends only 5 1/2" down the sides rather than 8 1/4") and it slides into retaining slots and over the rear handles, requiring only three screws to hold it in place. There is no sign/sound of tinging when you tap it. The chassis sits above is a full metal box that encloses and hides from sight all the components other than the vacuum tubes and a second, interior cage covering the transformers. When you removed the tube cage of earlier ARC designs, you’d look down on a horizontal expanse of circuit boards and associated components. The circuit boards eventually accumulated a buildup of dust that could only be partly removed by the occasional blast of compressed air. I cannot be certain that dirty resistors and capacitors sound worse than clean ones, but I am sure that I sleep more soundly knowing that an amplifier’s circuit boards are better shielded from environmental detritus (not to mention increasingly pervasive RF) in this new design.

The combination of a stiffer chassis and a less resonant tube cage results in an amplifier that is less susceptible to vibration. Using thicker, four-layer circuit boards also brings advantages: The added ground plane allows for improved layout of the parts and a reduced noise floor, along with the deletion of all jumpers in assembly. With older Reference amplifiers, the tube sockets were soldered directly onto the circuit boards, and when you inserted or removed tubes, you could feel the boards flex. With the Reference 160S, the sockets connect to the thicker boards and are supported by a metal frame. Inserting or removing tubes doesn’t just feel more secure. This is a connection that will better resist both damage through ham-fisted handling and mechanical vibration while running.

As well as providing greater stability and resistance to microphonics, the new chassis makes it much easier to access the amp's innards, eliminating those 18 tiny screws that had to be removed and then reinserted every time you wanted to swap a tube, change the fan speed or adjust the bias. The switch for the cooling fan has even been moved to the rear panel, allowing much easier access. Yet another sign of global warming?

About the biasing: as tubes age, the amount of current they draw can drift, and part of owning any tube amp has been the requirement for you (or the amp) to monitor and adjust the bias voltage for each tube or pair of tubes, to ensure that the tubes operate within their and the amplifier’s design specifications. With the older Reference units, adjusting bias was a royal pain. For me, it meant lifting a 75-pound lump out of the rack, fetching the Fluke multimeter out of the shed, removing those 18 screws to remove the tube cage, waiting for the amplifier to warm up, and then testing and adjusting at four different contact points. Thankfully, the auto-bias system that ARC finally introduced on the 160 monos has been carried over to the 160S, so the manual labor involved in biasing the amp is a thing of the past. In addition, pressing the front panel Tube Monitor switch activates the eight small LEDs spread left and right of the main buttons, one for each output tube (look closely and you see that each LED is labeled for a specific tube). If any of the LEDs fails to light, there is a dead output tube, requiring replacement of that tube.

In addition to these major changes, several other changes improve convenience and aesthetics. The old-style rocker on/off switch has been replaced with a soft-touch button. Along with the switch for the cooling fans, the tube-hour counter, which used to be inside the unit, visible only through ventilation holes using a flashlight, is now also on the outside, on the back panel. Instead of pulling the amplifier forward and out of my rack to look down to read the meter, I simply hold my iPhone camera at the back of the amplifier and take a snapshot. Flip-phone owners will have to resort to holding a mirror up to the meter.

Given the requirement to access the rear panel and also slide the amp's cover rearward to remove it, inserting or removing the amp from your rack is a serious consideration. Weighing in at 100 pounds, the Reference 160S is about 25 pounds heavier than the 150 SE. Thankfully, to help deal with the extra weight, ARC attached an extra set of handles at the back of the unit, to allow for easier lifting. Those used to the uniform weight distribution of the Reference 150 will notice that the center of gravity has shifted toward the back of the 160S, making those rear handles especially useful. As there was never a second man around when the amplifier needed moving, I used the time-honored method of sledding the amplifier on a large piece of cardboard. The extra weight is spread over a slightly longer chassis, 21 1/2" deep compared to the old 19 1/2", but the ubiquitous ARC rubbery feet still fit within the confines of my HRS rack.

Another feature carried over from the Reference 160 monoblocks is the choice between ultralinear and triode modes. Of course, choosing triode mode means you are giving up half the power output (as well as potentially compromising the match between the output tubes and transformers). Given the relative inefficiency and wide bandwidth of my speakers, that’s not a compromise I felt inclined to make, so I stuck firmly with ultralinear output. The Reference 160S has a fully balanced circuit topology, and previous generations of Reference amplifiers offered only XLR inputs. As a result of customer requests, single-ended inputs are now included alongside the standard balanced XLRs. Speaker outputs remain the same five-way binding posts for 4-. 8- and 16-ohm loads. One will sound best, and it may not be the one that coincides with the stated nominal impedance of your speakers (with Wilson speakers, it's almost always the 8-ohm taps).

When Audio Research announced its latest round of product upgrades and launches, it was the new preamplifiers and phono stages that really caught my attention. That in part explains the year and a half delay in getting around to working the Reference 160S into my system. Truth be told, I almost expected to be disappointed. The Reference 150 SE was exceptionally good -- and why give up 10 watts of output power in return for some fancy meters? At least that’s what I thought, before I knew better. Within moments of powering up the new amplifier and slipping a CD into the Neodio Origine player to warm up the system, my doubts were banished. Something was happening in the upper bass/lower midrange -- something I was not expecting. Intrigued and a little perplexed, I allowed the system to warm up some more, and I returned a couple of hours later armed with a few discs that I knew could in some ways sound better with a solid-state amplifier of sufficient output -- music with dynamic bass guitar and plenty of work on the drum kit. The tradeoff for ARC’s strong suits -- the ability to re-create subtle differences in timbre, the retrieval of the space between notes and, consequently, the gorgeous soundstage -- is the added kick afforded by the best (and inevitably the most expensive) solid-state amp. What became abundantly clear was that, while the Reference 160S offers improvements across the board compared to the 150 SE, it utterly transformed the performance in the lower registers.

One LP that has been giving this tube-amplifier-owning audiophile bass envy since 1992 is Janis Ian’s Breaking Silence [Analogue Productions APP 027]. I am guessing that the first ARC amplifier I heard it through was the Classic 60, followed by all the subsequent Reference stereo models. The band consists of five musicians, with a mix of electric and acoustic instruments. The album is well recorded, and you might think that it should not be that hard to reproduce. But the drums and the bass guitar line play right into the weakest point of ARC’s earlier stereo amplifiers; just when the music’s lower frequencies call for speed and definition, the pace seemed to slow down and instruments in the same frequency range seemed to homogenize. I would play the music on comparatively small solid-state amplifiers, and I was left wondering whether I could give up everything the ARC stereo amplifiers did to gain that kind of speed and punch. Of course, the answer was no, but that didn’t alter the awareness or eliminate the desire. The Reference 160S changes all that, with improved attack, decay and grip in the bass, and improved layering among the instruments. Is it the last word in tighter bass definition and speed, when compared to a top-notch solid-state amplifier of comparable output? With the CH Precision A1.5 in-house, the answer is not quite, but the ARC amp is close enough to at least assuage that nagging bass envy.

That is not to suggest that the Reference 160S is a substitute for a larger speaker or a set of subwoofers. It does not transform my Wilson Yvette speakers into Alexia 2s, but at times the Reference 160S promotes that impression. It seems to require a slightly higher volume setting than its predecessor but also delivers greater headroom without the risk of distortion. Indeed, it sounds like a more powerful amplifier than the Reference 150 SE. What it does is set up a much more coherent organization of the music through the lower midrange and bass. It is not so much that the bass is deeper or more dynamic with the new amplifier, even though it is both of those things. It is simply more effective. Where it shines is in bringing greater lucidity to the music’s engine room. It organizes the timing of events in that range better than any other stereo amplifier ARC has made.

This became clear listening to Joe Jackson’s Summer in the City: Live in New York [Sony Music/Intervention Records IR-018]. Jackson is accompanied by Graham Maby, his regular electric bassist, and drummer Gary Burke. I have heard this LP sound spectacular on bigger and far more expensive systems than mine, but at home I found the record slightly disappointing because the integration of the musicians did not match up to what I had heard elsewhere. It was one of the first LPs that I pulled out with the Reference 160S. Bass guitar covers the range of about 40 to 260Hz, while the drum kit runs from around 90 to 210Hz. This was a musical rediscovery, and what stood out was how the music seemed completely sorted, with the parts fitting seamlessly together, sounding more coherent and better integrated than they had with the Reference 150 SE. Cleaning up the timing in that region made this record’s reproduction with the 150 SE seem a bit ponderous by comparison. More than hearing new things in the music, I was hearing new music in the things I was hearing, as if the musicians had finally gotten into step with each other.

I next pulled out one of my current favorite bass tests, Kraftwerk's Autobahn [Klingklang 50999 3 08300 2 8], a guilty but (at least I can claim) necessary pleasure. The Reference 160S retained and improved upon the already great clarity and intelligibility of the Moog lines that I noted in my review of the Reference 6 SE preamplifier, but it also stiffened up the bass. When that car door slams shut and the engine fires up in the opening bars, what previously sounded like an Audi A4 was now transformed into a Mercedes S-Class sedan.

But the improvements found in the Reference 160S are not limited to the lower regions. Two further aspects stood out. First, the reorganization of the lower bits carried along the rest of the frequency ranges, no doubt because the improvements in the foundation work like a pyramid. If the bottom layer is not level and steady, what rests above it wastes precious energy trying to find its footing. Second, the Reference 160S, mated in my system with ARC’s Reference 6 SE preamplifier and Reference Phono 3 SE, really showed the advantages that come with genuine synergy of components. Each of these products has the same new capacitors and wiring changes; these are significant in isolation, but when added together they result in improvement that exceeds the sum of the parts. The preamplifier and phono stage each opened up the soundstage and better defined the space between notes. Adding the Reference 160S to the mix added pitch stability and speed, inching the sound of the combination bit by bit closer to the best that solid state has to offer, while at the same time maintaining and improving upon the bloom and grace that define ARC’s tube sound. Symphonic recordings kept getting better with the addition of each piece of ARC’s latest-generation equipment, the addition of the Reference 160S adding the powerful tone of the amp’s bottom end to the nuanced sound of the front-end components. Hearing Kleiber’s famous (and familiar) rendition of Beethoven’s Fifth [Deutsche Grammophon Gesellschaft 2530 516] through this amplifier convinced me that this recording, even after countless plays, still has layers of detail previously submerged and dynamics tamped down awaiting excavation.

Nothing better illustrated the sonic strengths of ARC electronics than Ben Webster’s tenor saxophone, and I always, seemingly, find my music choices leading that way with each new generation of ARC equipment. If the lower midrange/upper bass invites constant comparison to great solid-state equipment, the frequency range where Webster’s horn lives falls right in the sweet spot of that range that ARC has always seemed to own. That singing tone, rich in harmonic complexity and color, can sound like heaven on the right amplifier, but on any but absolutely the best solid-state equipment, it quickly writes that amp’s epitaph. Webster’s Soulville [Verve/Analogue Productions AP-8274] is a fitting example. One of the most beautiful jazz recordings ever made, Soulville is a selling tool for high-end audio. You almost have to go out of your way to make it sound bad (I have heard some systems that succeeded). The better the system, however, the more ecstatic the experience. Webster’s trademark breathy, fluttering sound seems made for tubes, and the Reference 160S reproduced his closely miked acrobatics with a perfect mixture of tube warmth and solid-state clarity.

The Reference 160S is, I dare say, the sexiest-looking amplifier Audio Research has ever built. The rolled edges of the chassis and tube cage soften the classic boxy ARC look. Although ARC does not recommend running the amplifier with the cage removed, I have no cats or small children to injure and find the “naked” look especially attractive. The faceplate, with the addition of the stunning Ghostmeters, has just enough added curves to remind us that, for a while, ARC was owned by Italians. Add to that the shallower tube cage and the enclosed bottom chassis and the overall effect is quite fetching, looking rather more Milan than Minnesota.

I have never had Audio Research's giant mono amplifiers in my system, but I have lived with many of the company's recent stereo amps. So after much experience, I can say without reservation that this is the best-sounding stereo amplifier ARC has ever built, and by a significant margin. It is a Reference 150 SE on steroids -- greater refinement coupled with even  better dynamics and control. Tubes are starting to sound more like solid state and solid state more like tubes, and ARC has successfully incorporated the important aspects of the competing technology without losing its grasp on reality or its own identity. Perhaps that’s the real key to the significantly improved performance of the latest line of Reference products -- growing your expertise while staying true to who you are.

Associated Equipment

Accessories: VPI MW-1 Cyclone record-cleaning machine, Record Doctor cleaning fluid and brush, VPI "magic bricks," Audio Physic cartridge demagnetizer, Shunyata Research Dark Field Elevators, Acoustical Systems SMARTractor, RPM app for fine-tuning turntable speed, Starrett No.98-6 machinist's level.

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