Audio Research Corporation Reference 160S Stereo Power Amplifier

The Audio Research Corporation needs no introduction. Its foundational contribution to the audio world is well established. I have lusted after various ARC products over the last 35 years. Pretty much all ARC’s tube gear—from the 1987 SP9 preamp a neighbor owned when I was starting out to the more recent REF250 power amps, and many products in between—has fostered a kind of “inner life” within recorded music. The even more recent Reference 160M monoblocks vaulted my interest yet higher. When I heard them at industry shows and in audio shops, they sang with a clarity, finesse, and dynamic command that struck me as a new frontier for ARC. Now, we have the stereo version of the 160M—the $22k Reference 160S.

I didn’t have a pair of Ref160M ($34k) monos on hand for direct comparison, but with the stereo Ref160S in my system I did hear qualities very similar to those of the monos in other systems. This is no surprise, since the Ref160S has the same circuitry, tube complement (four KT150, two 6H30 per channel), and power rating (140Wpc) as the monos. The feature set is also the same—output-tube auto-bias, front-panel output-tube monitoring, ultralinear/triode-mode buttons, and “floating” power meters on a see-through faceplate. On the rear panel we have 4-, 8-, and 16-ohm taps, an output-tube hour-counter, a cooling fan control, an auto shut-off, and RCA/XLR input switches. The Ref160S is a bit larger in all dimensions (mostly depth) and weighs a lot more than a single Ref160M (100 pounds vs. 56 pounds), no doubt to accommodate two channels’ worth of stuff in a single chassis. (The only circuitry difference—as far as I can tell—is that the Ref160S shares one power transformer for both channels, whereas the 160M has, of course, one transformer per amplifier.) The stereo amp actually has a slight edge over the mono in aesthetics in my opinion: The 160S’s transformers are covered in their own nice-looking vented cage with the Audio Research logo on top, whereas the 160M has exposed transformers—if one removes its larger, “whole amp” cage cover to expose the tubes. The Ref160S also has two rear handles, which the Ref160M lacks, that make moving its 100-pound chassis easier. (For a more detailed explanation of the Ref160M/160S circuit and tube complement in the context of ARC’s development as a company, please see Executive Editor Jonathan Valin’s excellent Ref160M review in Issue 294. For more information about Audio Research Corporation as a company and its contribution to the audio arts, please refer to the ARC section in The Absolute Sound’s Illustrated History of High-End Audio, Volume Two: Electronics.)

Listening

Right from the start, the Ref160S had a wonderful, fluid, agile quality. Music skipped along with engaging litheness that did not immediately scream “classic tube amp,” in the sense of imparting a slight sluggishness on transients and some looseness in the bass. Actually, the Ref160S is the most powerful, nimble, and neutral-sounding tube amp I have had in my system. (For twenty years, until 2009, I used to run mostly new [not vintage] tube preamps and power amps exclusively.) The Ref160S combines just a touch of warm-side-of-neutral tonal balance with remarkably low—for a powerful tube amp—underlying noise, so it joins a group of tube gear from brands such as VTL, VAC, Lamm, Ypsilon, and Atma-Sphere that bucks classic tube amp sound in this regard.

In keeping with tubes’ typical strengths, the Ref160S had both midrange resolution and 3-D depth—both of the larger soundscape and of individual images—in spades. Though not quite as extended at the extremes as some good solid-state amps, it also expanded midrange resolution to the immediately adjacent parts of the frequency spectrum—to a degree that helped everything sound more realistic and less obviously “tube-processed.” Mind you, the Ref160S’s top end was a little softer than I am used to from the solid-state amps (Gamut, Constellation, Hegel) I have been recently using, but I did not get the sense that I was missing much sonic information when I considered the whole picture. In fact, the Ref160S reproduced the gestalt (as TAS founder Harry Pearson liked to say) of a full orchestra in a way that made me think, “Wow, that gets a lot of it right!”

It may seem like a conundrum, but the Ref160S had such a low noise floor and its image boundaries were so free of “electronic etch” or “fizz” that its upper frequencies might strike some listeners as missing the last bit of extension and information, compared to certain other amplifiers. But the Ref160S actually made music sound more lifelike, to my ear, than most other amplifiers in terms of its refined image outlines and lack of electronic grain. Maybe it was the sense of continuousness that tubes bring to bear, or the midrange lucidity, or the sense of physical presence, or the wonderful musicians-in-a-hall effect with their trailing tails of notes lingering in space a bit longer (all of which the Ref160S does so well) that contributed to an overall “reminiscent-of-live” impression. Because of this truly fine realistic quality, I was motivated to revisit some of my classical LP collection: the Poulenc Concerto for Strings, Tympani, and Organ [Erato], Canteloube’s Songs of the Auvergne [EMI], and Mozart’s Concerto No. 21 in C Major [Phillips] were reproduced with remarkably natural-sounding details and immediacy. I found new aspects of the performances’ phrasing and developmental arc—new “musical meaning,” if you will—with the Ref160 in play. (Choreographers Glen Tetley [Voluntaries], Leslie Jane Pessimier, [Les Chansons] and Jiří Kylián [Petite Mort] used the music listed above, respectively, to create wonderful neo-classical dance works, by the way.)

Pop and rock had forward momentum in a parallel to the lucid gestalt in classical music. There was plenty of transient snap and power to give well-recorded drum kit, for example, the sense of acceleration that well-recorded drums contribute to the mix. I didn’t hear the Ref160S’s musical appeal across different genres as overtly euphonic as such; rather, the Ref160S simply brought out elements in recordings that illuminated the artistic expression inherent in music more readily—provided the recordings had decent performances and were well recorded in the first place, of course. It was as if the musicians had a particularly good night at the concert hall, club, or recording studio. We have probably all attended a live performance on one evening and then heard the same group or orchestral program again on another night and regarded one evening’s performance as better than the other. The players were clicking more with each other or the singer was in particularly good voice or the sound engineer got the levels and microphones’ phase-matching right. The Ref160S seemed to have the effect of making home listening sessions come closer to a superior evening’s performance. When one of my long-time audiophile friends said upon hearing a few cuts through the Ref160S, “Wow, the music sounds really alive—I could easily live with that amp,” I got it.

The Ref160S had a very deep soundstage, the deepest I have heard in my system. Front-to-back layering was continuous and closer to real life than many amps can muster, especially amps of the solid-state variety. Images within the soundscape were fleshed out as more completely formed sound sources created by real people and instruments in space, rather than as flat cutouts or bas-relief tableaux. The front of the soundscape was moved more forward than I am used to, so this—combined with slightly narrower soundstage width—created an overall stage that was sometimes closer to a cube in shape than to a rectangle whose width is greater than its depth. I suspect some of the amp’s slightly narrower soundstaging could be the result of the Ref160S being a stereo amp rather than a monoblock. (All things being equal, a pair of monoblocks tend to cast a wider soundstage than the equivalent stereo version.) Also, I believe the Ref160S is meant to be paired with an ARC preamp, like a Ref10 or Ref6SE, which themselves recreate very wide, expansive soundscapes. (Unfortunately, an ARC preamp was not available during the review period to test this hypothesis.)

Bass was deep reaching and powerful. The Ref160S’ plumbed the depths with ease, not exactly a typical tube amp’s forte, especially when one considers the speaker I used was the YG Sonja 2.2, which generally fares better with a high-current solid-state amp. While not quite matching the speed and definition of some solid-state amps, the Ref160S had the best bass pitch definition and stability of any tube amp in my system. Dynamics were also very good, both macro and micro. The big, meaty sound the Ref160S produced stemmed, in large part, from its ability to track bass-laden dynamic peaks with sustained control. The Ref160S never clipped or showed signs of strain while in ultralinear mode. It did lose control and clip, however, on the big orchestral stuff while in triode mode (70Wpc).  I think most folks who listen in triode mode would presume it is better suited to smaller, less demanding music (or to an easy-load speaker). Speaking of triode and ultralinear modes, I did nearly all of my listening in ultralinear. While the triode mode did offer some additional warmth and intimacy on smaller-scale music, I didn’t find the difference compelling enough to be worth switching back and forth between the two modes on appropriate music selections. On the whole, I found ultralinear to sound tonally closer to neutral and more dynamically responsive.

The Ref160 gives off a lot of heat, but that comes with powerful tube-amp territory. ARC uses cooling fans to keep operating temperatures within optimal range and extend tube life. Since I placed the Ref160S in front of my equipment rack to make connecting it to and from my system easier, I did hear the fan during very quiet music passages, even with the fan speed set to low. I believe most users would place the amp in a more room-friendly position, and that would, no doubt, be farther away from the listening position. Let me add, the Ref160M/S aesthetics are a welcome change for ARC whose typical look has tended to be more industrial and functional. I liked the see-through faceplate, but I turned off the lighted VU meters, as I found them to be a little distracting. A friend thought they looked really cool and wanted to see them with their light level all the way up. (There are three levels plus off.)

Conclusion

The winning combination of a low noise floor, which allows details to emerge in an unforced way, and very high levels of image solidity, which produces a closer-to-live listening experience, is central to the Ref160S’s appeal. Add in uncommonly good bass presence and dynamic control, and you have a tube amp that goes a long way to furthering the strengths of valves while mitigating their typical weaknesses.

To my mind, the Ref160S doesn’t try to sound like a solid-state amp as such; it is, rather, a high-quality amp in its own right, and can outperform most solid-state designs in depth layering and musical fluidity. If you feel like venturing into the glories of tubes or continuing your tube amp adventures on a different plane, consider the Ref160S. It is highly recommended.

Specs & Pricing

Tube complement: Two matched pairs KT150; two 6H30 per channel
Power output: 140Wpc (20Hz–20kHz)
THD: Typically 1% at 140 watts, below 0.04% at 1 watt, 1kHz
Power bandwidth: 5Hz to 70kHz (–3dB points)
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 21.5″ (with handles and connectors: 24″)
Weight: 100 lbs. (net)
Price: $22,000

AUDIO RESEARCH CORPORATION
6655 Wedgwood Road North, Suite 115
Maple Grove, MN 55311
(763) 577-9700
audioresearch.com

Associated Equipment
Analog source: Basis Debut V turntable & Vector 4 tonearm, Benz-Micro LP-S MR cartridge
Phonostage: Simaudio Moon 610LP
Digital sources: Hegel Mohican CDP, HP Envy 15t running JRiver MC-20, Hegel HD30 DAC
Linestages: Ayre K-1xe, Hegel P30, Constellation Audio Virgo III
Integrated amplifier: Hegel H390
Power amplifiers: Gamut M250i, Hegel H30
Speakers: YG Acoustics Sonja 2.2, Raidho TD1.2, Dynaudio Confidence C1 Signature
Cables: Shunyata Sigma signal cables, Nordost Heimdall 2 USB, Shunyata Alpha S/PDIF and AES/EBU, Shunyata Sigma NR and Omega XC power cords
A/C power: Two 20-amp dedicated lines, Shunyata SR-Z1 receptacles, Shunyata Everest 8000 and Typhon power conditioners
Accessories: PrimeAcoustic Z-foam panels and DIY panels, Stillpoints Ultra SS