Audio Research Reference 160 M MkII monoblock power amplifiers 

Audio Research Corporation, as some of you will know, is a historic company in the high-end audio field. In the late ’60s, and particularly in the 1970s, they were instrumental in bringing the tube amplification circuit, in both power amps and preamps, into the nascent field of high-end audio. It really hadn’t taken very long, but transistor amplifiers were increasingly viewed as the state-of-the-art, and with technological determinism being what it is, many audiophiles simply assumed tubes, which were the device of 1950s hi-fi, were finished. William Z. Johnson, who was the founder and chief engineer of Audio Research, did a lot of substantial work on the refinement of tube circuits. He quite clearly demonstrated to people, in particular the reviewers at The Absolute Sound, that tube circuits were indeed not dead and were maybe the next big thing.  

Here we are 50 years later, and we’re looking at a new Audio Research product. It’s a tube amplifier, and we’re considering whether (or not) this approach is still a big thing.  

The Amplifier 

The Audio Research Reference 160 M MkII, which is a mouthful, is a mono power amp. So, you need two of these amplifiers for a stereo system. They are each priced at $19,000, making it $38,000 for a pair of these. Part of the context of this discussion is that these are not inexpensive amplifiers, although, in today’s world, they are also far from the most expensive amplifiers.  

The 160 M’s are rated at 140 Watts per channel power into four, eight, or 16 ohms. As with many tube amplifiers, there are output taps on the back to match the impedance of the speaker you are using with the output impedance of the amplifier. If you have 4-ohm speakers, you hook up to the 4-ohm taps, if you have 8-ohm speakers, you hook up to the 8-ohm taps. Each 160M weighs 62 pounds. They use KT150 output tubes and have a beautiful metering system on the front that allows you to keep track of how much power you’re using. Or you can turn them off to avoid distractions. They can be operated in ultra-linear mode, which gives you the full 140 Watts of output power, or they can be run in triode mode, which gives you about half the power, approximately 75 watts per channel. Some people love the sound of triodes, and if you have very efficient speakers, that might be an interesting way to go. I’ll comment at the end about how I thought the triode mode sounded, but I am currently using moderate-efficiency speakers, (87 dB at 1 meter) and I primarily used ultra-linear mode to maximize dynamic range. 

Speaking of dynamic range, the output meters register about 50% (or 12 o’clock) on their scale when delivering an average of 1.5 Watts. When the sound in my listening room was pretty loud with these speakers (78-80 db average), 1.5 watts was a typical power indication that I saw with the Magico A5s and slightly higher with the YG Acoustics Talus in a larger room. We’ve made this point before: your general average power level is actually quite low, but you want to be able to have big voltage and current swings when the dynamics of the music ramp up. That’s because power requirements grow exponentially with sound level. Theoretically, I should have had dynamic capability up to about 100 db or perhaps a bit more with this amp.  

The other things I’ll say about the amplifiers are there are quite a few settings on the back that allow you to control the power-on operation and other parameters of the amplifier. There is an auto shut-off feature, a fan speed setting and your choice of single-ended or balanced input.  You can also have remote turn-on if you have an RS-232 remote control system. The amplifier also takes into real consideration the fact that when you’re turning an amplifier on during the warm-up process it may make some noises, so there’s a two-minute muting period.  

Sound Quality 

Some days you just wake up, and you feel right with the world, and you know it’s going to be a good day. Well, that’s feeling I had once I got these amps fired up. I was a little bit hesitant about a tube amplifier with modern lower-efficiency speakers. Knowing the range of music – from Metric to Mahler – that I like to use for my testing, I went in with a little bit of trepidation about Reference 160 M Mk II. I shouldn’t have been so hesitant. Audio Research has a history, as I pointed out at the beginning, and that history is very much on display with these amplifiers. Now, tube circuits have been around for a long time, so ARC is probably not going to do anything like gigantically new. My suspicion is that this amp is the product of decades of circuit refinement, parts selection, and careful listening to what matters and what doesn’t matter. That isn’t as intellectually dramatic as a “reverse-alphatronic non-stochastic pure-AI linearizer”. But if you are interested in music, not winning bench-racing contests at your pub, then you should care about what works. And I will say there is something happening with this amp that just makes it kind of magical. Let me try to describe that magic for you, though, in some clear terms. 

The first thing I noticed was this amplifier has a combination of qualities that usually don’t go together. There are lots of power amps that are great at “X”, but there’s always the sense that we gave up a little something in the “Y” department. And maybe they’re also great at “Q”, but we gave up some “R” and sometimes the “give” is greater than the “get”. Of course, there are trade-offs in life, an aphorism that describes general engineering reality. What I liked about the Reference 160M is that it has far fewer of these tradeoffs than I normally detect in a piece of gear.  

Here is my list of qualities that the 160 M Mark II puts together that I have essentially never heard come together like this: 

1. The first thing they do well is combining mid-range and treble clarity with an absolutely gorgeous tone color. I bring that out because that tone color was what most hit me right off the bat. Now when I say gorgeous tone color, you tend to think of coloration, but not with the 160M.  I’m talking about clarity and accuracy and detail in midrange and high-frequency sounds that has the instruments sounding beautiful and not adulterated with those little unnatural, almost inaudible artifacts and distortions. You just don’t hear those kinds of errors that make you aware that you’re listening to Hi-Fi equipment, not to real music. In the case of the 160 M Mark II, we’re talking about the ability to do the naturalness and the feel and the tonality of each instrument, together with just a laser-focused ability to bring out the overtones in the music and all the details. But without them attacking you or seeming strident or muffled or massaged. This is a combination you rarely hear. There are some great power amps and preamps that I’ve heard from Japan that do this naturalness, unlike anything else. But they often sound just a little bit reserved in their presentation. And that just wasn’t the case with 160 M Mark II. They really put this combination of midrange and treble clarity and dynamics together with beautiful tonal values and naturalness in a way that I can’t say I’ve heard from any other amplifier. 
2. I want to bring out another element of the combination of beautiful tonality with another factor that I think often doesn’t go along for the ride. And that is that the treble doesn’t feel rolled off. It feels super extended. Almost the opposite of rolled off. I don’t mean it’s bright, but it just feels like it goes out and out and out to the upper treble range. That combination of qualities is of course great on classical music, of course. But you also notice it on acoustic recordings, jazz, or rock or pop or chamber music for that matter, where you can sense the hall sound but also the uncompromised dynamics in the high frequencies. This upper range has been an issue during much of the digital era and as we move beyond it with both vinyl and high-res, getting this region right really adds to the sense of realism in the whole presentation of the 160 M Mark two.
3. The 160M is superb at the delivery of realistic tonal density. I’m not talking about tone color here; I’m talking about the sense that music, whether it is a solo instrument or 100 people playing a symphony, is made of rich fundamentals and harmonics. Listen to a Martin guitar and then a Taylor and the body tone and overtones are quite different. When you get tonal density right, you hear this and you can sense that each design has its merits and musical value. On ensembles, whether rock or jazz or classical, you want each instrument to have that richness and depth. You want to bring all that richness to the fore, but not turn it into a blob of mush. You want to keep each instrument, or each voice, separated out and yet have the tone feel rich and multivariate. The 160 M MkII delivers the tonal density without being heavy or sludgy. I often feel some equipment gets this sense of tonal density by shifting the balance a little bit to the low end, but the 160 M doesn’t do it that way. It just reveals what’s happening in tonality. This ability to do natural tonal density with delicacy, not heaviness, is, I think, a major achievement of this amplifier.
4. Bass definition is excellent. Sure, we all have our views on what technology leads to what kind of sound quality. And I try as a reviewer to erase all those thoughts from my head, but inevitably I have them. I have a sense that tube power amplifiers often sound rich, but the bass isn’t as detailed as it could be. In this case, though, I want to say that the fourth thing that the reference 160 M MkIIs exhibited is the unusual combination is bass weight combined with excellent bass definition. Now I’m saying this in the context of the 160M being a tube amplifier. Yes, there are a few solid-state amplifiers that specialize in this weighty and defined bass. To put this in perspective, I need to come back to this idea of unencumbered tone color and tonal beauty that is kind of the theme throughout this whole review. Bass instruments on the 160 M MkII just sound right and musical and beautiful in a way that combines this sense of weight with detail in a way that is unusual and fit very well with the other characteristics of the amp.
5. There is a dynamic capability here that doesn’t reach out and grab you by the neck, yet it’s a wonderful thing once you realize it’s what’s going on. The wonderful thing is that dynamics of the 160M sound natural. They don’t sound overly jumpy or hard and they don’t sound passive or wimpy. No, the dynamics with this amp sound right, meaning they sound natural. the standout thing is that the dynamic excellence is partially based on not having the instrumental separation change as the dynamics go up and down. If you listen to vinyl, you may realize that when there’s some timing variation the presentation contains a distracting element. With the 160 M MkII the instrumental separation, the imaging are stable during dynamic swings. There’s not collapsing and crushing together of things or a sudden opening of the soundstage. Things are just presented the same way they would be on stage.  Which is to say when Stevie Ray cranks up Stratocaster No. 1, it sounds like his Strat, on the same stage at all times, through his amplifier. This ability to not have things shift around and change character unnaturally is a subtle, subconscious thing that again triggers you to think you’re listening to stereo, not to the real thing. Avoiding these errors is a big achievement of these amplifiers. 

Now I just have to note that this is a 140 Watt power amplifier. As a result, you can’t drive every possible speaker with this in every possible room. I will note my general sense is that this is a very appropriate amplifier to use up to maybe 3000 cubic feet of listening room space with medium-efficiency speakers. I would say the Magicos or the YGs that I used, and other speakers that are 87-89 dB efficient, will work for people in a lot of medium-sized rooms where the listening triangle is relatively compact. Or you might be using some of the efficient Wilsons, as an example, which are in the 92, 93 dB efficiency realm. And I think then these amplifiers would then work in a larger room. I had the chance to hear the predecessor of this amplifier driving Wilson Alexx Vs in a huge room and they sounded amply powered. But this is not the amplifier for 82 dB efficient speakers in a large room where you tend to listen at high levels or to super dynamic music. Almost every amplifier has some kind of limitation like that.  

Summary 

I found these to be outstanding amplifiers. Yes, they’re expensive. With most audio equipment, progress consists of refinements that for some people are determinatively excellent and important, and for other people are super subtle and irrelevant. The Audio Research Reference 160M MkII is a very refined amplifier. 

In the context of the basic value test “show me better for less”, I think the 160Ms pass. This criterion is useful, but sometimes misunderstood. We try to apply it with the perspective “show me a product that does what this one does well for less”. Of course, there will be, for example, more powerful amps for less money and if you need that, the 160Ms are not better in that sense. And, like any reviewer, I’m far from having heard all amplifiers, so, I stand to be corrected, but I think this is an amplifier that is well worth its price tag if you need what it does well.

For people who really appreciate musical refinement, let’s summarize what the 160M does: beautiful tonality, tonal density, natural bass weight with high definition, and excellent dynamics, particularly in terms of how dynamic swings affect sound staging and how dynamic swings affect instrumental separation.  

But when you break it down analytically like that, the problem is something gets lost a little bit in the mix. So, I must also say this is just an amplifier that sucks you into the music and gets you to enjoy it, and to explore track after track after track. And in some ways, that’s really the ultimate test that some kind of “anti-realism veil” has been lifted. We’re getting closer to the music, and we’re more able to enjoy the music, which is what we’re here for. 

Coda: Triode vs. Ultralinear 

Just a brief coda, as I promised, on the differences I hear between triode and ultralinear mode with Audio Research Reference 160 M Mark II. This is not going to be a blinding insight for those of you who are accustomed to this kind of switching capability. 

Triode mode has, with the medium-efficiency speakers I used, a couple of characteristic elements. Triode mode sounded a little more focused and it sounded a little bit smaller. It sounded more rounded, and by rounded, I mean maybe slightly rolled off in the treble and in the bass. I felt like the dynamics of Triode mode were just slightly more reserved, and there were times, particularly on female vocals when I thought the tonal qualities that I talked about before with ultralinear mode were in some ways, maybe even more beautiful, but maybe not as accurate. 

I would say overall that I preferred ultralinear mode with the speakers I tried. I really enjoyed the big ultralinear sound, the instrumental separation, and as I said before, I still thought the total quality in ultralinear mode was outstanding. I could imagine situations involving smaller rooms or room-speaker combinations, where triode mode might be advantageous. 

While I couldn’t hear it per se, it looked like we might be getting closer to the limits of the amplifier’s output capability. Now with significantly more efficient speakers, say 93 or 98  db efficiency, the triode mode would be more powerful than what I heard with ultralinear mode, not in raw wattage but in effective output capability. So, you have to think of the application of the amp in terms of the whole system. 

With certain speaker systems, the rounded characteristic of triodes and the focused sound might be something that you would find really desirable. I don’t see any drawback to having this built into the amp. Switching from ultralinear to triode mode and back is so easy (you push a button) that you can even adjust according to the music you’re listening to. That said, I want to be clear if I were using typical speakers that had the balanced sonic signature that I’m accustomed to, it would be ultralinear all the time for me. But I love choices, and I think you would enjoy triode mode, too.