Audio Research Reference 160S power amplifier Page 2

In Ultralinear mode, a smaller (lower-voltage) version of the audio signal is taken from a tap on the output transformer primary winding and applied to the second grid. The keys to Ultralinear operation are choosing just the right signal level to apply and choosing precisely where on that coil—usually expressed as a percentage—you want the tap. Get those things right and distortion is minimized. Ultralinear is a form of feedback.

The other big advantage to Ultralinear operation is that you get more power. The 160 is specified to put out twice as much—140W—in Ultralinear mode than in triode mode, where it is specified at 70W.

To invoke a clichè, triode is for your right brain and Ultralinear is for your left. Triode sound is sweeter and rounder, while Ultralinear sound is punchier, and perhaps more extended. "Most will default to Ultralinear and use triode on certain recordings," Gordon told me.

That's all the adjustments it is possible to make. The Reference 160 S is not really an amp to play with. It's an amp to listen to . . . and also to look at, because the Reference 160S is lovely in an uncommon way—unique in my experience except for its untwinned twin, the 160 M. I don't know if they were thinking about it this way—I kind of doubt it—but to me, visually, the 160 S is a slightly arch, minimalist riff on what Audio Research amps are supposed to look like. With its pale faceplate and starlit power meters—all silver and white light—there's a heavenly austerity to it that complements its sound. Fairy dust.


That sound
I wonder what Bill Johnson would think of today's transistor amplifiers. You've probably heard this before, but Bill wasn't against transistors—his company built amplifiers out of them for years—he just didn't think they sounded as good as tubes do. He acknowledged during his lifetime that transistor amps had gotten better.

Johnson also made the point, from the company's earliest days, that Audio Research doesn't make euphonic tube amps. He claimed to be aiming for honest, accurate, undistorted sound. So I wonder, if he were still around, how he would judge the Reference 160 S's performance against that of any of a number of very good solid-state amplifiers that, like the Reference 160 S, defy sonic clichès. I started my listening with that question in mind.

Weeks ago, I de-crated the 160 S, added the tubes, and hooked it up to my system. I left it in as we—the amp and I—got used to each other. Finally, I got down to business. I put on the first movement of Mahler's Symphony No.2 with Benjamin Zander and the Philharmonia Orchestra (Linn Records, 24/192 ALAC download). I turned up the volume to the lowest point where I could hear the quietest passages distinctly. This recording has such a wide dynamic range that, at this volume setting, the loudest passages were over 95dB.

At this volume, with the amplifier in triode mode, with these 86dB/W/m speakers, during the loudest peaks, the needles drifted into the "caution" zone and occasionally beyond. This amp should have been at or near clipping, according to the meters, but I heard only the same relaxed clarity. The soundstage was deep, rising toward the back as if the orchestra was on, well, risers.

It's difficult to articulate the change I heard when I switched the Reference 160 S from triode to Ultralinear. I did not hear more bass extension. There was, I suppose, a touch more air. Articulation and detail may have been a touch better set to Ultralinear—I felt I was now hearing a suggestion of individual instruments within an instrumental section. ("You're the best one in your row!") Punchier? Maybe, but not obviously so.

In triode mode there was a fine velvet, burnished beauty. In Ultralinear, voices and instruments had pure, penetrating edge and the music was more explicit—but the sound was just as lovely. What was happening sonically? There was obviously a little more top-end energy in Ultralinear. I don't consider my other sonic observations trustworthy because they're tainted by my expectations. (Was there more second-harmonic distortion in triode mode? Less third harmonic? I would say yes to both.)

As I was busy writing, just now, Roon Radio took over from Zander and Mahler (who were finished playing) and delivered me to a series of familiar tracks, and then on to some unfamiliar ones.


I was having a blast listening to this music, familiar and unfamiliar. It happens sometimes, but not that often, and Roon Radio is often at fault: I forget about reviewing and start having fun. It's that clichè about the reviewer staying up late listening to records. So forgive me for setting aside the serious business of direct comparisons and familiar tunes.

Roon Radio took some odd turns, at one point playing what sounded like Korean Christmas music (Tell me, Roon, how do you get from Zander's Mahler to music on the Wellmade Yedang label?) Soon, I was on to some chamber music: The Borodin Trio playing Arensky, and then a piece I didn't know but now love: the Sonata No.1 for Piano and Cello by Brazilian composer "Mozart" Camargo Guarneri (what a name for a composer!), performed by Antonio Menenses and Celina Szrvinsk on the album Soirèes Internationales, which features music composed in Paris during the 1920s (CD-rez stream from Qobuz, originally Avie Records AV2162). Recommended.

Roon Radio soon returned to more familiar tunes: the Brahms Violin Sonata No.2 in A, performed by Augustin Dumay and Louis Lortie, on Onyx Classics (FLAC rip from CD, Onyx 4133). It sounded gorgeous, but before I could finish writing this paragraph—guess I was doing too much listening and not enough writing—we were on to the Granados Piano Trio performed by the LOM Piano Trio on Naxos (Naxos 8.572262), and one particular moment when Joan Orpella's violin, just inside the left speaker, sounded startlingly real, as if her bow had poked a hole in space. This was in Ultralinear mode.

They say that every amplifier has its own sound, and I'm sure that's true. But not every sound imposes itself on music in ways that matter. Through all of this, I noticed no particular coloration; in fact, the sound was more open than I'm used to, which I take to be the absence of coloration. The soundstage was three-dimensional, sometimes startlingly so. On some recordings, images seemed etched; on others they seemed loose, bloody, and abundant. Whether from a violin's bow or a piano's hammer, transients seemed natural. On well-recorded piano, the balance between woody impact and string tone seemed ideal—this all still in Ultralinear mode. To paraphrase JGH describing the D-150 years ago, if the Reference 160 had a sound of its own, I couldn't hear it.

Except: I was consistently aware of beautiful tone. Perhaps a bit more in triode mode than in Ultralinear, but always present, always there. This is the Itzhak Perlman of amplifiers. And like any good tonalist, the 160 S could also make scratchy, strident sounds when the music required it.

It was time for some jazz. With albums in Roon arranged by "most played," I noticed Patricia Barber's Nightclub on the first page and put it on. On "Bye Bye Blackbird," I heard big, rich, close-miked midrange piano notes, mainly from the left side of the soundstage, sounding natural if larger than life. On the next track, "Invitation," about 23 seconds in, Barber's voice hits the t in the second syllable of "after" with real force: She practically spits it, soon followed by a sustained, accentuated "sssssssss." Through the ARC, there was appropriate harshness in that spat t, and the extended "s" was hissing-intense, but without unnatural sibilance—only the natural kind, harsh but not alien. It sounded bad in a good way, or good in a bad way, or something.

On several albums, the sound closed the gap between electronic sound and physical, mechanical, real-sounding sound. Sound that's been recorded and reproduced always has a certain amount of electronic character. Often it's baked into the recording. The best purist recordings come close to getting rid of it, but the reproduction system can add it back. This system, with this amp, was adding back less of it. The electricity stayed inside, where it belongs.

Michael Fremer reviewed the Audio Research Reference 6 line preamplifier in the December 2016 issue of Stereophile. The ARC preamp, he wrote, "was an exceptionally skilled and unerringly convincing teller of sound stories that revealed, with every record I played, musically significant information not found in the usual checklist of sonic attributes." Intriguing.

I've got one here, in a box in the spare bedroom. Sometimes I love this job.

Conclusion: With the Audio Research Reference 6
After the change of preamp, I lost my sonic bearings. There was too much change. I couldn't keep track. The late hour surely had something to do with it, as, I'm sure, did the fact that the preamp itself was new and fresh from the box (although the tubes are pre-aged). At a minimum, it needed a good warmup. I let the music play overnight and tried again late the next day. By then, things had settled in a bit.

I've been thinking a lot lately about the twin, possibly conflicting, goals of audio: on the one hand, to deliver fidelity, and on the other, to provide pleasure. (Any allusion to love and marriage is unintentional—really!) Is honesty aligned with beauty or opposed to it? William Zane Johnson was committed (or so he claimed) to delivering as much accurate musical information as possible, to not pretty things up with tubey euphonic coloration, but his ultimate goal was musicality.

This Audio Research combo—the Reference 6 preamplifier and the Reference 160 S amplifier—combined gorgeous tone with physicality: horsehair on gut, hammer on strings, soft wood buzzing in brass, the harshness of spat vocals or an intentionally scratchy violin. I didn't know that so much of the music in my collection possessed so much tonal beauty.

Maybe it doesn't. Maybe the beauty is added, not revealed. I'm not sure I care.

Audio Research Corp.
6655 Wedgwood Road N., Suite 115
Maple Grove, MN 55311
(763) 577-9700

Bogolu Haranath's picture

May be JCA could review the new Rotel Michi M8 mono-block amps, 1080 WPC into 8 Ohms and 1800 WPC into 4 Ohms, $14,000/pair :-) ........

Bogolu Haranath's picture

Also, JCA could review the new McIntosh MC901, tube/transistor amplifier, $17,500 :-) .......

volvic's picture

The best sound at any show I ever heard came from an AR integrated along with an AR CD9? CD player, paired with Verity Audio speakers. CD after CD played revealed detail and lifelike presentation that no system at any show I've attended has ever matched. I can only imagine how good this combo sounds. I wish I could borrow for a month and call in sick from work for 22 straight days.

Ortofan's picture

... irresistible could well be the characteristics of the polypropylene plastic cones used in the mid-range and woofer drivers of the Verity Audio speakers combined with a dose of second harmonic "sauce" generated by the ARC electronics.

For comparison, try Spendor or Harbeth speakers driven by a tube amp.

volvic's picture

Not sure how to respond, but at the same show in another room were the more prominent Verity Audio speakers with Nagra tube amplification and DCS digital front end and it did not sound as intimate as the smaller Verity's with the ARC electronics. As for Harbeth, they are one of my faves and have heard them with the top end Rega electronics, they sound beautiful and I want them but none of them captured that sound in that room that day. I suppose this was one perfectly matched system, but I do not doubt that the ARC integrated tube amp and CD9 contributed significantly to that fantastic sound. I have not heard ARC in any other configuration, but if they all sound like that, then I am sold.

Bogolu Haranath's picture

William Z is smiling :-) ......

nirodha's picture

Not surprising... dCS is the antithesis of musicallity ;-). Nagra, on the other hand, is a synonym of this elusive term.

volvic's picture

This was back in 2008 or 2009, don't exactly remember, it was a while ago, maybe the dcs gear back then had a different sound, I am no expert in that gear. But it didn't have the "I could almost reach out and touch the musicians" feel the way the cheaper ARC/Verity combo did.

nirodha's picture

Have to admit that my experience of dCS was also some time ago but now I have been playing with a Nagra CDP, I know what I missed in the "old days". But it is all subjective, if dCS touches your heart, go for it. If it doesn't, steer away from it.

Bogolu Haranath's picture

You can get '22 Days Nutrition' organic nutrition bars and powder, for 22 straight days :-) .........

volvic's picture

So maybe they might help. First, someone has to lend me the amps.

MhtLion's picture

Jim - thanks for the great review. Do you have any comparison to other amps? Not that I don't trust what you heard, which you have very good skills at describing. But, in this subjective hobby of ours, it provides tremendous value when you compare it against other options the readers may have or other well-known amps. You have Pass Labs XA60.8, which is another amp known to produce a beautiful sound. How did ARC compare against it in its sonic bliss? You also have PS Audio BHK 300, which has a great dynamic. How did ARC compare against it on dynamic or driver grip? I would very much appreciate it if you can add some comparison. Because without a meaningful comparison, a review can be just too subjective or personal.

Ortofan's picture

... with distortion levels approaching those of the Benchmark AHB2?
If so, would it be likely to exhibit the same sort of "musicality" and/or "tonal beauty" that JA2 has observed from the Reference 160S?

Regarding the "impressive price" of $30K for a pair of ARC Reference 600 monoblocks in the mid-1990s, back then there were other manufacturers offering monoblock amps at that price point - and well above.
Among them were the Accuphase M-100 ($30K), Audire Monarch ($60K), Denon POA-S1 ($40K), Jadis JA-500 ($35K) Krell Audio Standard ($35K) and, last but not least, the Audio Note Gaka-On ($250K).

Bogolu Haranath's picture

You are missing the whole point ........ The fundamental idea of a tube amp is not to measure and sound like a transistor amp :-) ........

Ortofan's picture

... measure and what should it sound like?

Bogolu Haranath's picture

Even the best and experienced audio reviewers (and measurers) don't know the answer :-) .......

Ortofan's picture

... Hafler type straight wire differential tests - with the amp under evaluation connected to Stereophile's standard simulated loudspeaker load.

The amp which achieves the best measured null on that test will then be the "best" amp.

If two, or more, amps should happen to exhibit similar performance on the null test, then move on to blind, level-matched comparisons.

Otherwise, the reviewers can keep on performing uncontrolled listening tests on different amps, in different systems and with different music all the while trying to select the one that sounds to them to be the most pleasant - in spite of audible levels of distortion and frequency response that varies with load.

Jack L's picture


"..... amplifiers to allow switching between triode and Ultralinear operation." quoted Jim Austin.

VTL got its tetrode power amps with switchable triode & tetrode operation decades back. How come ARC took so long to do so until now?

Likewise, I consider I have done the best ever sonic upgrade of my vintage Dynaco ST-70 35W+35W power amp by converting it to triode/pentode ultra-linear switchable over a decade ago.

That said, we should know the sonic downside of trioded pentode/tetrode by strapping the screen grid to its plate with a low-resistance resistor, a conventional way used by brandnamed amp manufacturers & DIYers alike since day one decades back. So the grid screen is working at a voltage almost the same as the plate.

I have read many reports criticizing such simple trioding method causing the sound somewhat soft, weak & punchless vs its original pentode/tetrode configuration. Unacceptable to my critical ears, to say the least.

To fix such sonic 'problem', I set the operating voltage of the screen grid, STABILIZED, LOWER than the plate as it were working as a pentode/tetrode. Ite is done by connecting the screen grid to the plate with a circuit of diodes, fast quality capacitors, & resistors.
I would label it as: "plate/screen grid split potential topology".

The key issue is: what is the proper voltage difference between the plate & the screen grid to get the best sound.

After enough trial & error, I finally get the right potential difference between the screen & the plate. It works like a chime: it sounds
fast, punchy & forceful like a pentode/tetrode & beats the latter by being more defined, smoother, & transparent like a real triode.

I have used it first in trioding my Dynaco ST-70 power amp & my ALL other later power amp projects. The trioded Dynaco sounds so good that I have left it switched to triode mode for ever.

Added merit: Such split potential triode conversion does not sound noticeably lower than its pentode mode though its output power is rated only half of its pentode operation !

Listening is believing

Jack L

JRT's picture
Jack_L wrote:

"To fix such sonic 'problem', I set the operating voltage of the screen grid, STABILIZED, LOWER than the plate as it were working as a pentode/tetrode. Ite is done by connecting the screen grid to the plate with a circuit of diodes, fast quality capacitors, & resistors"

Or instead of modifying a Dynaco/Dynakit, build an amplifier using a better output transformer with a separate center tapped winding for the screen grids, better providing for lower subregulated nominal voltage well below the B+ rail voltage powering the anodes. And you can get that output transformer with cathode tapes, separate windings for the cathodes.

The old Audio Research VT 150 SE had all of that. Not sure about the amplifier under review here.

Your old Dynaco/Dynakit amplifier was built to sell at a much lower price point and did not have those features, rather saved on build cost with only two windings, primary and secondary, with multiple taps.

If you want to DIY, consider using Menno van der Veen's VDV-2100-CFB-SSCR-PPS.

Jack L's picture

....... a better output transformer.." quoted JRT.

You are comparing apple to orange, my friend!

I said "UPgrade" but you meant to say "Rebuild". We are in different wavelengths.

Tons of so called "upgrades" (which were actually "rebuilds) of Dynaco
since day one half a decade back. It involved rebuilding the entire driver board with different tubes, replacing the original output & even power transformers, etc etc. So such drastic rebuild made Dynaco sounded
like something else. Gone was the original famous award-winning Dynaco sound.

What I have done to my Dynaco was to maintain its original sonic signature by keeping the major crucial components, e.g. driver board, output & power transformers.

The most substantial sonic improvement was to convert the Dynaco ST-70 to triode & pentode switchable using my unique design/built "plate/screen grid split potential topology". Triode sound is always much better than pentode sound even using the very expensive brandnamed ultra-linear output transformers. I achieved the sonic improvement yet saved a bundle.

Any other upgrades I also did would be icing on Dynaco's cake, e.g. replacing all passive parts, e.g. now using polypropylene metal-film coupling capacitors, film resistors, fast recovery silicon rectifiers, HV motor-run OIL filter caps (replacing the vintage HV multi electrolytic cap) etc.

Much improved sound the Dynaco style without need to spend a bundle to replace major items.

Listening is believing

Jack L

tonykaz's picture

...those see thru Meterings.

I've owned large ARC Amps, they look & give off the "I'm a certified audiophile" feeling with publicly claiming "ARC ownership" a Statement of audiophile authenticity but it might be more bluster than ultimate performance. I've heard a few ARC Electronic Based Systems that didn't perform as hoped or expected.

It might be simpler to build around KRELL or PS Audio or PASS gear because they lack tubes. ( and solid state devices last forever-- as claimed by Nelson Pass )

Tube life of 3,000 hours seems rather hopeful. 3,000 hours could equate to a Decade or likely less than 2 years of 5 hour listening days. So, a spare set of Tubes needs standing-by. My experience would predict less than 1,000 hours.

Tube Amp buyers are Brave, I have to hand it to them, especially if they are running those pricy KT150s.

Tony in Venice

ps. those Glass Meters are gorgeous Impulse buyer magnets & so are the Diavialet Amps with their remote control and wall mounting.

Jack L's picture

.......Tube life of 3,000 hours seems rather hopeful. 3,000 hours could equate to a Decade or likely less than 2 years of 5 hour listening days"

"Tube Amp buyers are Brave, I have to hand it to them, especially if they are running those pricy KT150s." quoted tonykaz.

First off, how long you owned yr tube gears before you switched to sold states ?

You worry about vacuum tube lifespan?

Let me tell you, the 60-year-young vintage Telefungen ECC83 tubes still work perfectly in my design/built phono-preamp, excellent sounding. It renders me timeless pleasure on my 1,000+ vinyl collection !

Yes, transistor amps may last "for ever" if you are lucky. But so what?
My critical ears can't tolerate the clinical sonic of any solid state amps, sorry !

Listening is believing

Jack L

tonykaz's picture

I've owned and maintained Tube Gear since the 1950s . I've owned Macintosh Tube gear that went thru tubes on a 6 month basis.

Tubes are our finest sounding Audio Amplifiers, which is why we still bother with them. They all tend to have differing sound qualities and can have magnificent singing "voices" ( my opinion ).

I do worry about Tube Life because they are so dam hard to find and tend to have such short "peak" lives, whilst great SS gear never seems to cease. ( I have seen recent unserviceable NAD SS gear fail and get tossed into Waste Management's infinite mountain)

People that achieve outstanding Sound Quality with factory serviceable Solid State Designs deserve the accolades they get.

Tony in Venice

ps. You have good fortune in the ECC83s you own ( maybe it's because you live in a humane Canada ) , great sounding ones will cost mucho dinero today. ( but they are out there as are great sounding SS gear )

ps.2) I know folks that have owned Tube gear only, no SS. They miss out on headroom but live a pleasant midrange life. ( my opinion )

Jack L's picture

..... out on headroom but live a pleasant midrange life. ( my opinion )"
quoted tonykaz.

Only your opinion is OK.

Yet I would like to change yr opinion on good tube amps.

This is what happened just a couple of weeks ago with my curious audio fans came by my home basement audio den, to audition first time how my home-brew 9W+9W SET (single-ended tube) power amp using 2x2A3 direct-heated triode power tubes would perform.

Making miraculous illusion like David Copperfield using a small 9W+9W tube power amp ?

It is real ! All I did some years back was to install 3x100W active subwoofers to L, R & L+R channels of my stereo system, all hooked up to my design/built stereo phono-preamp !

Here how my little "David" killed "Goliath".

I tried out the Tchaikovsky 1812 Overture on CD, with my 9W+9W amp + 3 subwoofers on. We could virtually feel the thouderous battlefield effect, with cannon cells virtually flying upfront right over & well beyond our heads. My audio fans dropped their jaws bigtime.

My wife came down to find out what was happening, saying:"The floor above was shaking!!!!"

Can a thousand watted solid state power amp produce such convincing climax effect ???

Listening is believing

Jack L

tonykaz's picture

I didn't realize that you are that differing type of old school DIY system builder able to extrapolate out and achieve your greatness.

There are only a small few of you advanced souls. You inhabit a unique world.

I am living in the world of "Pocket" systems but I know the delights of your pursuits. You'd be a gourmand if you we're a food guy. We should have a special name for y'all like we do for Ham Radio people that prefer ultra low power ( QRP )

Well, Mr. Jack, nice reading and writing to you here at the Stereophile's Campfire, I hope Mr.Dudley does a Story about you.

Tony in Venice

Jack L's picture

..... old school DIY system builder able to extrapolate out and achieve your greatness..." quoted tonykaz.

Thanks yr complement.

MY way: "Think OUTSIDE of the box !"

Jack L

Ortofan's picture

... tossed really unserviceable, or was the repair cost simply deemed too high relative to the price of a new replacement unit?

Also, a repair shop used to working on point-to-point wired tube equipment or solid-state products with through-hole circuit boards might take one glance at a unit populated with surface-mount devices and declare that it's unserviceable. However, just because they might not be equipped to fix it doesn't mean that no one can.

tonykaz's picture

I have/had a Servicemen : Morel TV in Farmington Michigan that is a critic of "modern" manufacturers selling gear that cannot be serviced. He is not alone, there are Youtube videos by Service Techs that clearly illustrate and Show how our electronics are sealed by the factory.

I'm asking Stereophile Editors to establish Serviceability as part of their review process.

Morel has a back room with stacks of Consumer Audio Gear that is unserviceable with owners not returning to collect their broken pieces.

Of course, some gear could be too costly to service but that is not what I'm referring to.

Some outfits ( Apple, I'm told ) attempts to block anyone from servicing their gear ( including legal blocks in Court Rooms ).

My point, my rant is that we should be allowed to know about service before we invest.

Sales outlets offer extended warrantees, for a stiff price but those warrantees get the owner a NEW box, not a repair. ( I think )

Are ALL NAD products serviceable? I don't think so.

Be careful about this.

This entire issue revolves around Chinese sourced products.

Tony in Venice

Ortofan's picture

... that you and/or the TV repair shop consider to be unserviceable?

NAD has been sourcing most, if not all, of its electronic product line from China for quite some time.

Looking at a few of the sites that have service manuals available for download, manuals are shown for many of those made-in-China NAD products.
One example is for the C368 integrated amp from the current product lineup:

tonykaz's picture

I'm not a NAD watchdog or watching any other brands ( for that matter ).

My concerns revolve around the trend of Manufacturers to block their products from the 3 Billion Dollar aftermarket Service industry and from their customers knowing about the unservability of their wonderful creations.

I am encouraging Stereophile's Management to include Service as part of the review process.

Some outfits : Schiit, PS Audio, Audio Research ( ARC ) are recognized for featuring Serviceability as part of their ownership experience. ( Apple doesn't seem to even allow their Schematics to be known )

On the plus side, our reviewers have mentioned that a reviewed device had defects needing attention ( sometimes considerable attention ).

Tony in Venice

David Harper's picture

The notion that the value and enjoyment of music has anything to do with the expense or sound quality of your playback system is the same as the notion that the value and enjoyment of a movie like "The Godfather" has anything to do with the expense or the resolution of the TV picture that you're watching it on.

Bogolu Haranath's picture

JCA could also review the conrad-johnson ART 150 stereo amp ($19,500) ........ About the same power output and about the same price of ARC 160S :-) ..........

Archguy's picture

From the review:

For a company to design its own internal parts was unusual—and remains so—as was the notion that specific capacitor and wiring choices sound quality. And yet, even though transistors were not could affect the sound of an amplifier.

Two consecutive sentences. Does anyone actually read these?

Jim Austin's picture

>>Two consecutive sentences. Does anyone actually read these?

Apparently they do--otherwise, how could you have noticed the errors? We call it beta testing. :-)

Seriously, it was perfect in print. Sometimes errors are introduced when copy is prepared for online publication. I'll fix it now.

Jim Austin, Editor