LS27 Line Preamp

Audio Research LS27 Preamplifier

Written by Howard Kneller

Category: Full-Length Equipment Reviews

Created: 01 October 2011

Preamplifiers are strange creatures. If your gear doesn’t suffer from impedance mismatches and you don’t use a turntable, you don’t really need one. Do you need a separate box for volume attenuation? Many of today’s D/A converters and CD players have volume controls. Of course, a simple potentiometer will also do the trick. Do you need source selection? Just add a simple switch. Indeed, some audiophiles assert that, in the age of computer-based audio, the optimal sound will be achieved with no preamp at all.

Yet, for the sake of convenience, not to mention tradition, most audiophiles are reluctant to do without a preamp. If that’s how you feel, whether or not to get a preamp is only the first decision you’ll have to make. You next have to figure out which preamp to buy, and that’s where it gets tricky. A preamp can have an enormous impact on a system’s sound. And unlike, for example, some source components, a preamp can be devilishly difficult to match to your system.

So after experimenting with a few preamps in my system, all of them from reputable audio manufacturers, I decided that the subject of this review would be a preamp made by a company known for building great ones -- and Audio Research Corporation couldn’t be a better example of such a company. Not that it doesn’t make fine power amplifiers, disc players, and DACs (I own an ARC DAC8), but when you think of Audio Research, you first think of preamps, particularly tubed preamps.

Not too long ago, Audio Research introduced the LS27 preamplifier, to replace the outgoing LS26. The LS27 comes below the company’s Reference 5 and above the LS17. If you’re interested and/or very wealthy, ARC stopped taking orders for the limited-edition Reference Anniversary preamp ($24,000) in April.

Features

The LS27 weighs 16.3 pounds, measures 19"W x 5.25"H x 13.3"D, and comes with a three-year limited warranty (90 days on the tubes). The front panel has two microprocessor-driven rotary controls: with the first, the volume can be adjusted for both channels simultaneously; the other knob selects among the LS27’s six inputs: CD, Video, Auxiliary 1 and 2, Tuner, and Phono. The front panel and remote control both have buttons for power on/off, mute, processor pass-through (which lets you use an external home-theater processor), volume up/down, balanced or single-ended inputs, mono/stereo, and monitor (which routes the monitor input signal to the main outputs).

Via only the remote, you can adjust the LS27’s display to one of nine brightness levels, adjust the levels of the left and right channels, keep track of how many hours the tubes have been used, adjust the gain for each of the six pairs of discrete inputs (high, medium, low), and invert the absolute phase of the output signal.

The rear panel has eight pairs each of balanced and single-ended connectors for the aforementioned inputs, as well as the monitor and processor inputs. There are also two sets each of balanced and single-ended main outputs, a tape record output, a 12V trigger, a 15A IEC connector, and a fuse bay.

The LS27 is a pure class-A design with zero feedback and a fully regulated power supply. The internal circuitry and connections are differentially balanced. Gain is provided by a hybrid audio circuit that includes JFET transistors and two 6H30 triode tubes, the latter rated by their manufacturer to last for 10,000 hours of use. Dave Gordon, ARC’s director of sales, states that the optimal dynamic performance can be had for 5000 hours. However, he generally recommends replacing the tubes at somewhere between 4000 and 5000 hours. Replacement tubes cost about $130/pair.

The LS27 is specified as having a frequency response of 0.2Hz-160kHz, +0/-3dB, at its rated output (balanced, 200k ohms load), and distortion of less than 0.01% at 2V RMS though its balanced outputs. Its output impedance is 700 ohms balanced, 350 ohms single-ended, 20k ohms minimum load; and the selectable gain for each input is 18, 12, or 6dB single-ended, and 24, 18, or 12dB balanced.

According to ARC’s website, the LS27 sounds a lot like the Reference 5, albeit on a slightly smaller scale. ARC further states that many changes were made between the LS26 and the LS27, including a new power transformer, new output and bypass coupling capacitors, a new microprocessor for the function controls, and an improved power supply.

Setup

Setting up a preamp is typically not difficult, and the LS27 was no exception. As with many tubed products, the LS27’s tubes were delivered uninstalled. Audio Research inserts them in a protective block of foam, which it tapes to the inside of the LS27’s case. To install the tubes, you use a heavy-duty Phillips-head screwdriver (provided) to remove the LS27’s top plate, insert the tubes in their sockets, and screw the plate back into place. Hook up your signal cables and power cord, and you’re just about ready to start listening.

I say “just about” because, for about 50 seconds after startup -- or any interruption of power -- the LS27 puts itself in mute mode. After that, it remains muted until you press the Mute button on the front panel or remote control. According to ARC, this feature helps protect the LS27 from power interruptions or a severe drop in voltage.

Even before I received my review sample, ARC sent me a “reviewer’s note” requesting that I first use the LS27 without a power conditioner, isolation device, or aftermarket power cord. In some cases, the note said, such products could degrade one or more aspects of the LS27’s sound. I was also advised that the LS27 requires 100-200 hours of use to be fully broken in, after which it will, according to the note, “continue to improve incrementally.”

Being that my mama didn’t raise no fool, I knew enough to request that the unit be sent to me with some burn-in time already on it. When it arrived, its tube hour display informed me that ARC had run it in for about 200 hours.

I did my initial listening without any of the above-mentioned isolation or AC devices, and used the power cord provided by ARC. Later, however, after some 100 hours of listening, I replaced ARC’s stock cord with Synergistic’s Tesla’s T2 cord plugged into my Synergistic Research Powercell 10SE Mk.II power conditioner, and placed Synergistic MiG isolation cones under the LS27; the combination of these made substantial improvements in the sound, with no downsides. So did my Bright Star Audio Reference isolation platform. From that point on, I used them all.

Dave Gordon advises that, for maximum performance in a fully balanced system, XLR cables be used with the LS27. My system is not balanced, so I used my reference single-ended cables. Also per ARC’s recommendation, I selected the LS27’s highest gain setting.

Performance

As someone with an interest in making electronic music, I’ve been toying with the idea of purchasing a vintage Roland TR-808 drum synthesizer. The 808, as this instrument is popularly known, is easily the most popular drum machine of all time, and has been deeply influential in many musical genres, including pop, rap, R&B, blues, house, and electronic music. Discontinued in 1984, the 808 sounds significantly better in many ways than its replacement, Roland’s TR-909.

Although each TR-808 sounds slightly different from other TR-808s, all share the same superclean, transparent sound, and the instrument’s bass drum goes almost insanely subsonic -- so low that it has blown out more than a few studio monitors over the years. However, the 808’s unique characteristics are lost through many audio systems, even some expensive ones.

So when ARC’s LS27 showed up on my doorstep, I was looking forward to hearing how well it could convey the 808’s singular sounds. I was also eager to hear what the LS27 could do with my MartinLogan Summit X electrostatic speakers. As many audiophiles know, the marriage of electrostats and tubes can often produce heavenly results.

I began my listening using, as a source, a Marantz UD9004 Blu-ray player modified by Tube Research Labs. However, it soon became apparent that there was a possibly significant problem: inexplicably, the LS27 kept shutting down. My first thought was a reasonable enough one: the LS27 was somehow defective. However, within a few minutes, I realized that the frequencies for certain functions of my UD9004’s remote control overlapped with those of some functions of the LS27’s remote. Pressing the skip forward or back button on the Marantz’s remote turned off the ARC. Pressing other buttons on the UD9004’s remote made the LS27 do a variety of other things I didn’t want it to, such as select a different input. The next day I called Dave Gordon, who told me what I already suspected: This was a very rare problem for which nothing could be done. Obviously, this did not, over the next few months, make my life any easier.

I looked around for recordings I had that featured the Roland 808, and the first one I cued up was “Sexual Healing,” from The Very Best of Marvin Gaye (CD, Motown 530 292-2). Vocals excepted, this song was performed entirely on an 808. It was readily apparent that the LS27 could throw a large soundstage characterized by depth of field and very solid images. Moreover, I could clearly identify the 808’s trademark drum rhythms. The hazy, superfluous electronic grunge that, through some systems, makes the 808 sound less transparent and more like a 909, was virtually absent. Right from the start, the LS27 proved that the Beastie Boys were right when they rapped, in “Super Disco Breakin’,” “make no mistake, nothing sounds quite like an 808.”

Also, with “We Belong Together,” from Mariah Carey’s The Emancipation of Mimi (CD, Island B000578402), the LS27 wonderfully brought out the unique sound -- synthesized, metallic, perhaps unnatural -- of the 808’s hi-hat cymbal. Those traits came through on this track, revealing that the LS27 was one tube preamp that was transparent and timbrally discriminating. That it managed to do this while maintaining a liquid, refined midrange was demonstrated by its velvet-smooth and textured portrayal of Carey’s voice.

I next turned to Kanye West’s appropriately titled 808s & Heartbreak (CD, Roc-A-Fella/Def Jam 1791341). Obviously, by the time a track finds its way onto a pop CD, its dynamics have been crunched significantly in the production process. However, with the LS27, the 808’s distinctive, super-low-octave bass drum in “Love Lockdown” was extended and more authoritative than I’d expected. Low levels of noise and high levels of detail retrieval may not be historical strengths of tubed preamps, but the LS27 was so quiet and resolving with 808s & Heartbreak that I could even hear how much decay had been dialed in.

I next listened to the acoustic version of “Prayer for the Dying,” from Seal’s Best: 1991-2004 (CD, Warner Bros. 48882-2). Immediately noticeable was the stunning cymbal decay. In fact, the LS27 let me hear this decay in parts of that song that I’d previously thought to be silent. In Seal’s “Killer,” the upper-end extension of xylophone notes was detailed and resonant, with no fatiguing sharp edges. And throughout this compilation, detail was exceptional. For example, I could hear the most subtle details of the acoustic guitar, including the sounds of hands on the instrument’s body, fingers on strings, and strings on frets. Massed strings were beautifully unmuddled.

On any of a number of tracks of Eric Clapton’s Clapton (CD, Reprise 9362-49635-9), including “Autumn Leaves,” the strings of the London Session Orchestra sounded sweet and silky smooth. But the LS27 also proved the audiophile adage that tubes love horns. In “Tenderly,” from Ella Fitzgerald and Louis Armstrong’s Ella & Louis (Verve/First Impression Music FIM UDH 045), expertly remastered at 192kHz by Winston Ma’s First Impression Music, Armstrong’s trademark trumpet was rich, lush, and brassy.

Of course, like any audio component, the LS27 is not perfect. For example, like many tube models, the LS27 wasn’t the last word in transient impact. In Seal’s “Killer,” for example, the sound of the xylophone, while neither etched nor peaky, lacked a bit of the bite that some other preamps offer. If your tastes lean more toward Metallica and Iron Maiden, you might want to consider a different preamp.

Also, some solid-state preamps, and some much more expensive tube models, offer a bit more high-frequency extension and air, and even more bass control, than the LS27. Of course, the solid-state models that have these abilities often lack one or more of the romantic charms possessed by the LS27. And the tube models that do -- such as ARC’s own Reference 5 -- typically cost well over $10,000.

Comparison

I compared the ARC LS27 with my reference solid-state preamp, a NuForce P-9 ($3150). In past reviews, I’ve said ad nauseam that the P-9 outperforms preamps at more than twice its price, and it does -- just not this one. The LS27 was a more honest, more articulate, more dynamic, and cleaner-sounding sonic machine.

That didn’t mean that the LS27 kicked preamp booty in every respect: the P-9 sometimes rendered voices in a slightly more solid manner. In “We Belong Together,” for example, the P-9’s lock on Mariah Carey’s voice was a touch tighter than the LS27’s. The same was apparent in the acoustic version of Foreigner’s “Jukebox Hero,” on Foreigner 4 (CD, Atlantic/Rhino R2 78275). However, with any track from Seal’s Best, the imaging contest was too close to call.

Also worth noting is that the P-9 generally brought more heavy wood to the ballgame. For example, the P-9 mustered more low-level transient slam for the percussion instruments in the excerpt from Rachmaninoff’s Symphonic Dance No.1 on Winston Ma’s This Is K2 Sound! (CD, K2 HD FIM UDC 078).

All told, though, the LS27 had so many significant strengths that the very few ways in which the P-9 outdid it were of fairly little consequence. Moreover, the areas in which the P-9 can’t hold a candle to the LS27 are in the ARC’s refinement and sheer sonic beauty. The LS27 managed to do such things as excel at the retrieval of inner detail, while at the same time sounding wonderfully flowing, refined, and musical. Neither the P-9 nor any $3000 preamp I have heard can do that.

While the P-9’s home-theater bypass can be used while the P-9 is turned off, the LS27 must be left on while its version of this feature is engaged. This would be an all but insignificant inconvenience were it not for the fact that the LS27 uses tubes. However, this wouldn’t be a deal-breaker for me, since my main priority has always been two-channel listening. A few extra hours on the tubes in exchange for having a great two-channel preamp seems more than a fair exchange.

Also, the LS27’s large, bright LED display is easy to read from the listening chair -- unlike the P-9’s small, dark LCD display, which provoked a whole lot of eye squinting on my part. Finally, as I’ve described in other reviews, the P-9’s hexagonal remote control is world-class -- a perfect blend of art and functionality. The LS27’s workmanlike remote, standard issue for ARC, won’t win any design awards, but it worked well and was easy to use.

Conclusions

In this new digital age, isn’t the preamp dead? I don’t think so -- certainly not for someone like me. Although I’m unwilling to commit to a tubed amplifier, I love the warm, rich sound that tubes bring to my solid-state electronics and electrostatic speakers.

Lacking serious sonic faults and exceeding my expectations for its price, the Audio Research LS27 is one of the very best preamps I have had in my system. It not only provided me with the conveniences of a preamp, it infused my system’s sound with some needed tube goodness while not degrading that sound. Indeed, I know of many solid-state systems -- even many that include speakers with traditional dynamic drivers -- that could greatly benefit from such a pairing.

The LS27 will thrill most audiophiles. It raises the bar for what should be expected from a preamp in its price class. Moreover, it may convince all the digital junkies and audio minimalists out there that they really do need a preamp after all. The fact that I’m giving the LS27 a Reviewers’ Choice award may not be entirely surprising, given that it’s made by Audio Research -- a company known for making great preamps.

. . . Howard Kneller

howardk@soundstagenetwork.com

Associated Equipment

• Amplifier -- Bryston 6B SST²

• Preamplifier -- NuForce P-9

• Sources -- Marantz UD9004 universal Blu-ray player modified by Tube Research Labs, Audio Research DAC8

• Interconnects -- Synergistic Research Tesla Apex, Precision Reference, Synergistic Research Galileo MPCs on all signal cables and power cords

• Speaker cables -- Synergistic Research Tesla Apex

• Power cords -- Synergistic Research Tesla Hologram A (amplifier) and D (source); Precision AC (speakers, Powercell 4 power conditioner), AC SE (Powercell 10SE power conditioner), T2 (preamplifier)

• Power conditioners and distribution -- Synergistic Research Powercell 10SE (power and analog) daisy-chained to Powercell 4 (digital), Synergistic Research QLS 6 and 9, DIY parallel filter

• Isolation devices -- Silent Running VRfp Isobases, Synergistic Research MiGs, Mapleshade Heavy Hats, DIY amp stands

• Misc. -- Synergistic Research Galileo Universal interconnect and speaker cable cells

Audio Research Corporation

3900 Annapolis Lane N.

Plymouth, MN 55447-5447

Phone: (763) 577-9700

Fax: (763) 577-0323

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Audio Research • LS27 Preamplifier

New, improved and "surely one to beat in its price range."

by Dennis Davis | March 30, 2011

othing should be simpler than comparing a new version of an existing product to its predecessor, as it makes the "all other things being equal" rule child’s play to follow. Audio Research’s LS27 line stage is just one digit removed from the extremely successful LS26, which I used in my system for two years -- until the Reference 5 took its place. I’m not adverse to easy assignments when the menu includes something as tasty as an Audio Research line stage. A component that’s pure plug-in-and-play, with no toe-in or leveling or break-in, leaves only the exercise of typing the review as a chore. With the LS27, everything preceding those keystrokes was pure pleasure.

The LS27 is Audio Research’s middle-range line stage, sitting between the LS17 and the Reference 5. The LS27 is a serious component that a regular audiophile can aspire to owning without robbing a bank. It updates the cosmetic look of the LS26's front panel, switching out black for silver handles (though the black are still available) There is also a Darth Vader version: black in all but the buttons. The LS27 also replaces the older square-button array with a new set of round buttons, a cosmetic touch first seen on the Reference Anniversary.

Under the hood, things look very similar to the LS26, until your eyes stray to the back of the circuit board and you notice that the unit has become almost an inch and a half deeper. This is not surprising, as the LS26 was already packed full of components, and the LS27’s upgraded parts required additional breathing space. Bulk power-supply storage has been increased. A new power transformer along with new output and bypass coupling capacitors account for the added real estate. Despite these changes, the LS27 weighs in a few ounces lighter than its predecessor. The stated specifications of the LS27, except for weight and dimensions, are identical to those of the LS26.

Like the LS26, its replacement remains a pure class-A design with zero feedback. It has a fully regulated solid-state power supply and a hybrid JFET/tube audio circuit using two 6H30 dual-triodes in the analog stage. As with the LS26, it has three selectable level settings for each input, with a recommendation that the highest setting be used for best performance. I found this to be too high for any of the cartridges I use, but the lower settings adjust for any phono stage/cartridge combination.

The LS27 also sports a choice of balanced or single ended inputs and outputs, with a total of eight input choices. Unlike with most line stages, a right-left balance control, a phase inversion switch, a mono/stereo switch, and a tube-hour counter are also included. For me, a balance control is essential, and I suspect most audiophiles do not have custom-built listening rooms that need no tweaking of right-left balance.

All of these functions may be controlled with the ubiquitous Audio Research remote. The LS27 also includes a processor pass-through for home-theater use. Audio Research states that all of these functions are controlled by a new microprocessor, although I could not detect any difference in application. Indeed, with the exception of the tube-hour counter, I could control all other functions whether I was using the LS26, LS27 or Reference 5 remote. That is to say that they all worked flawlessly and intuitively.

Audio Research long ago dispensed with attached power cords, and the LS27 has a 15-amp IEC inlet. A high-quality power cord ships with the unit for those not inclined to buy an add-on power cord.

The line stage arrived from Audio Research with about 200 hours logged on. Before listening to it, I ran it in another 50 hours or so using a burn-in CD. Audio Research now packs all of its tube electronics with a notice that the device continues breaking in until somewhere around the 600-hour mark. I suspect that this varies by unit, with the more expensive models and their larger capacitors breaking in more slowly. I have listened to other Audio Research models starting from scratch and know that the biggest changes occur in the first couple hundred hours, so I felt confident that this unit was good to go at 250 hours. After the additional break-in time, I listened to a wide range of music before comparing the LS27 to its predecessor.

udio Research line stages all share a very strong family sonic resemblance. They are also the products of one of the industry’s most consistent trickle-down programs. Each new Reference line stage is eventually followed by a new version of the LS line stage, with those advances from the top model scaled back and incorporated into the mid-level model. So those audiophiles who refrained from mortgaging their home during the real-estate bubble to spring for a Reference 3 waited for the release of the LS26. Now the LS27 holds out promise that the Reference 5 advances have trickled down to it, notching it up near the performance of the Reference 3 (there was no 4, as it is considered an unlucky number in the Far East).

Among their consistent strong points, Audio Research line stages have an uncanny ability to organize musical information into a deep, wide soundstage, especially with the best of both stereo and mono recordings. The solidity and "you are there" qualities of the instruments within that stage are equally remarkable, and they have done nothing but get better both within the Audio Research range of products and viewed over time as each new generation of a particular model appears. The LS27 is no exception to this rule. Whether it’s reproducing large-scale orchestral works such as Stravinsky’s Firebird on Mercury [Mercury SR90226] or small-scale jazz ensemble as exemplified by the stunning mono reissue of Kenny Dorham’s Afro-Cuban [Blue Note/Music Matters MMBLP-1535], the preamp will throw as large and realistic a soundstage as your cartridge and phono stage can pass on to it.

It’s the solidity and focus of images within that soundstage, however, that really separate the very expensive units, with massive power-supply parts and ultra-spendy capacitors, from more affordable line stages. The LS27 does not match what the Reference 5 achieves in this regard, nor does any other preamplifier in this price range. The very best units can cast extremely convincing three-dimensional images, in the same way that adjusting the depth of field of in a camera viewfinder will cause the image to "pop" and take on a three-dimensional quality. You can’t make as good an image with a cheap Tokina lens as you can with top Leica glasswork, and the same limitations apply to preamplification. Audio Research does not make any Tokina-level products, and the LS27 is like a good Leica lens, but not the fastest-aperture version of a particular size. It can produce very stable images within the soundstage, if not achieve the divine results that a Reference 5 can pull together. However, the LS27 gives you an awfully close approximation of what Audio Research’s much more expensive Reference line stage can do under most circumstances. On less-complex recorded material, the differences can be subtle indeed.

The LS27 performed beautifully in the frequency range of string instruments. I spent a good deal of time listening to the new Coup d’Archet set of violinist Johanna Martzy's recordings, The EMI Recordings [COUP 16-23], and the LS27 performed brilliantly. It reproduced Martzy's unique tone, which is on the cool side, without ever sounding harsh. It captured that coolness while at the same time placed enough air around the instrument to make these refurbished early EMI recordings sound almost modern. I played some of this music for a friend and didn’t tell him that he was listening to the LS27 instead of the Reference 5. He was agog at the beauty of the recording and gave no thought to the equipment.

The LS27 was also accomplished at revealing small or large changes in other equipment in the chain. It accurately captured the differences in string sound between Lyra and Koetsu cartridges, and I used it to discern and evaluate the differences between VPI’s Super Platter and standard-issue aluminum platter, and then the differences between the aluminum platter bare, with a rubber mat and with a paper mat. The LS27 did not obscure in any way the differences among these variations.

It also was a champ at reproducing the best of Rudy Van Gelder’s Blue Note recordings. The earliest of these are in mono, and an exceptional line stage can present an almost stereo-like image with none of the drawbacks of early stereo. Kenny Dorham’s Afro-Cuban sounded alarmingly real. Like the Dorham 45rpm set, Acoustic Sounds’ remake of Nat King Cole’s great mono album After Midnight [Capitol Records/Analogue Productions AAPP 782-45] also threw an incredible mono soundstage that lacked nothing with the LS27. That’s not to say that it doesn’t show up the imbalances of poor stereo. It certainly didn’t gloss over these details, and it likewise didn’t tamp them down, as some less-stellar line stages can do.

ompared to the LS26 ($5995), the LS27 is definitely a move up the spectrum, making that thousand-dollar increase in price, along with the improved power supply and more expensive parts, wholly justifiable. I expected the improvement in soundstaging solidity, but I wasn’t prepared for a jump in tonal quality and bass definition. However, within minutes of a side-by-side comparison of the two units, my listening panel was like a group of Olympic judges, declaring a clear win for the LS27 because of these improvements. Shelby Lynne’s "Just a Little Lovin’," from the CD of that name [Lost Highway 1744825], made it clear that the LS27 had tightened up the LS26's bass and refined its highs. I never considered the LS26 lacking in these areas until this comparison. Extended listening to the two units confirmed this finding, but showed it was more pronounced with some recordings, as I could not reproduce the significant differences with most material. On one of my favorite test LPs for the quality of the upper frequencies, Salvatore Accardo’s Diabolus In Musica [Deutsche Grammophon DGG 477 6492], the differences between the way in which the two units interpreted the violin, cymbals and triangle were subtle, confirming that the LS26 was no slouch in this department. But with a few modern digital recordings, such as the Shelby Lynne, the improvements in the new unit were obvious.

Similar subtle enhancements were detected in areas where the LS26 was already quite strong. Both units have a very low noise floor, and this gives rise to acute retrieval of low-level detail and notable clarity. Like the prior model, the LS27 sounded unforced and delivered an natural entrée to the flow of recorded music -- an uncommon ability for all but a few line stages in this price range. While I had the benefit of auditioning the LS27 with a much more expensive phono stage, I suspect that the LS27 along with Audio Research's new PH8 will be a match made in heaven.

o if you can’t afford to invest more money in your hi-fi system than you have tied up in your Maserati, the LS27 may well be the ideal heart of a system you can live with for the long haul. It’s an extremely versatile and musical line stage that is surely one to beat in its price range. Audio Research continues to pull one rabbit out of the hat after another.