Audio Research • Reference Phono 2 Phono Stage

A technological admixture creates an "instant classic."

by Tim Aucremann | August 13, 2010

hanks to the likes of Radiohead, Blue Note Records and the late Michael Jackson, vinyl sales in 2009 were up roughly 30% over 2008. Nonetheless, amid digital downloads and (plummeting) CD purchases, last year’s new vinyl accounted for a tiny 1% of total album sales. Despite a steady uptick in LP sales over the past five years, many more new records have been sold than ever will again.

Here in 2010, vinyl abides. Ask a newbie convert or veteran vinylista about its appeal and you will hear a case as clear as always: records played on today’s analog gear sound better than ever. The groove -- "the bright and sinuous rill," to borrow from Coleridge -- yields her treasure over time, the technology enticing us to mine for more. How much information is in the groove? With a good analog rig, you just want to keep playing music -- one record after another, which is why many of us got into this avocation in the first place. Every link in the analog chain keeps getting better, from the stylus to the cantilever to the armature to the housing to the headshell to the phono stage.

Which brings us to Audio Research, high-end bedrock whose 40 years of enthusiasm for the vinyl medium continues unabated by the vicissitudes of sales. Since 1998 alone -- into the heart of the vinyl downswing -- Audio Research released five dedicated phono stages. Number six is the company's most ambitious yet.

As suits its appellation, the Reference Phono 2 has the flexibility to work with any vinyl front-end. It packs a host of user-convenience features, all selectable from its front panel and lightweight remote. Design goal? "It aims to be the best phono stage possible," said Dave Gordon of Audio Research, "one that can musically outperform any other phono stage, regardless of price." That alone earns it a closer look.

Inside-the-box thinking

our typical phono cartridge is an inherently balanced device, with separate outputs for positive and negative for each channel. Audio Research has long held that a fully balanced audio chain will deliver the best sound. Most phono cables come with RCA connectors, and the Reference Phono 2 won’t ask you to re-terminate your existing cable or buy a new one to take advantage of its balanced circuitry. It offers a proprietary input stage designed by company founder William Z. Johnson that allows balanced output via the convenience of RCA jacks. And vinylists blessed with two turntables or tonearms will be happy to find dual RCA inputs, each with discrete settings for gain, impedance load, and equalization, all of which the Reference Phono 2’s microprocessor remembers.

Gain aplenty and a whopping 250mV of input headroom suggest the Reference Phono 2 is ready for virtually any moving-magnet or moving-coil cartridge. When its balanced outputs are used, the unit offers front-panel and remote selectable gain of 51dB (low) or 74dB (high), with 45dB (low) and 68dB (high) for single-ended output. This 23dB swing is considerable, so the phono stage thoughtfully places itself into Mute when switched from low gain to high.

Continuing with a feature introduced with Audio Research's PH7 phono stage, the Reference Phono 2 offers listening-chair convenience from push-button impedance loading. I found myself using this feature to tamp down high-frequency cartridge resonance on overly bright-sounding Deutsche Grammophon records. Preset values include 50, 100, 200, 500, 1000 and 47k ohms. In fact, the Reference Phono 2 goes the PH7 one better by allowing you to install your own load, or Audio Research will do it for you at the factory. A Custom button on the remote gives easy access to this.

Known for years as champions of vacuum-tube gain circuits, Audio Research has never hard-soldered itself to a particular technological orthodoxy. The first Reference Series phono stage, released in 2000, used eleven 6922 tubes to amplify low-gain input. Since then, and perhaps more fervently than with any other high-end manufacturer, the design focus for Audio Research’s top-line Reference products has been on the integration of tubes with solid-state devices. Thus, the Reference Phono 2 is a fully class-A tube-transistor hybrid. The first stage in its low-gain circuit is FET-based; the second uses two Russian 6H30 dual-triode tubes per channel. Audio Research opted to swap a handful of 6922s for a couple 6H30s based solely on listening, not economy. The 6H30 has sufficiently high transconductance that it easily substitutes for multiple 6922s; however, high-current demand on heater supplies means it is no less expensive a tube to implement.

While the 6922 and the 6H30 have their sonic signatures, to my ears the four 6H30s in the Reference Phono 2’s implementation are quieter and evince lower grain than the four 6922s in the PH7, let alone the 11 found in the original Reference Phono. The low-gain section of the Reference Phono 2 is very quiet. How quiet is it? It is so quiet that at my listening seat I heard more noise caused by blood pulsing in my ears than I did from tube rush. Not by accident, Audio Research’s Reference 5 line stage uses this same gain circuit.

To amplify the signal of an ultra-low-output moving-coil cartridge without adding coloration or noise is a challenge for any phono-stage designer. Does he choose a transformer to step up voltage or an active device to increase it? Passive step-up transformers are dead quiet, reduce circuit complexity and tend to be less costly to implement; however, inductive ringing and inevitable transformer hysteresis loss distort tiny signals and mask high-frequency detail. No downstream circuit will restore lost information. Nowadays .2mV-output moving-coils are no longer an oddity, so there is even less signal to lose.

For the original Reference Phono, Audio Research opted for expensive Jensen step-up transformers in the high-gain circuit. Those Jensens had an impedance of 280 ohms. If your cartridge preferred a 400-, 500-, or 1000-ohm load, you were out of luck, because the Reference Phono could lower its impedance but not increase it. Today, the active high-gain circuitry in the Reference Phono 2 uses rigorously graded, ultra-low-noise FETs, which are more expensive than the Jensen transformers, to deliver that 23dB of additional gain while accommodating a precise cartridge load. Audio Research claims this active approach delivers superior sound quality across a wider bandwidth.

Dave Gordon spoke with quiet confidence about his company’s in-house transformer design. They’ve been at it for decades. Off-shore outsourcing at lower cost was considered for units meeting their stringent specs; however, again based on listening comparisons, Audio Research choose to keep building transformers in the United States. The gain sections of the Reference Phono 2 get their own dedicated R-Core type transformer. R-Cores accommodate proximity to sensitive audio circuits because they tend toward lower mechanical vibration with less magnetic-flux radiation. The Reference Phono 2 avoids spurious noise feedback into the signal path by using a second separately circuited R-Core for its tube heaters, microprocessor, and other non-audio needs.

The Reference Phono 2’s power-supply circuit is the same found in the Reference 5 line stage. It has eleven stages of regulation and uses a fifth 6H30 to control a 6550C pentode tube. Vacuum-tube power supplies are costlier to implement, but Audio Research told me their listening tests again convinced them that tubes are sonically superior to solid state. Damping rings are included for all 6H30s.

The features just keep coming. The Reference Phono 2 has Columbia and Decca equalization curves along with the RIAA standard. Today, variable equalization is used for only a handful of phono stages (mostly high-dollar exotics such as those from Zanden and FM Acoustics); however, it was common for preamps made before 1960 to require their user match a playback curve with a proprietary recording spec used by a given record label. To gather enough music on a side to make a 50+ minute LP, manufacturers cut records with reduced low-frequency amplitudes and increased highs. This yielded a narrower groove and more music per side. During playback, the preamp must decode what recording hath wrought to obtain a flat frequency response, and to this day all phono sections implement equalization circuitry to boost bass and cut treble. Not until the arrival of stereo did recording labels begin widespread adoption of the standardized equalization metrics laid down by the RIAA.

Equalization curves are typically described with two numbers: the turnover number is the frequency that is +3dB from the 0dB reference portion of the playback curve, below which bass must be boosted on playback; the roll-off number is the rate in decibels of treble attenuation applied at 10kHz. For example, if you use a phono stage that only decodes the RIAA curve (turnover 500Hz, roll-off -13.7dB) to play a 1953 Columbia two-eye LP (turnover 500Hz, roll-off -16dB), you will not harm the record, but it will sound overly bright. Experiments with a few old Columbia Masterwork LPs proved to my ears that proper equalization made them far more listenable. By implementing the Decca and Columbia curves, the Reference Phono 2 allowed experimentation at the push of a button.

Sporting muscular silver rack-mount handles on a silver faceplate, the Reference Phono 2 looks modern yet iconic. (Black is an option, but is it really Audio Research if it is black?) A couple inches taller than the PH7, this Reference-sized box went on my top shelf. The extra height allows vertical mounting of its 6550C and gives room for a fluorescent green display large enough to serve as a drive-in theater for a family of hamsters -- which meant I could see it from across the room. The review unit arrived after working CES in Vegas. It was wearing its laser-cut acrylic top -- a smoky negligee available as a no-extra-cost alternative to the full-metal jacket. It looked sharp. Audio Research claimed its resonance characteristic means better sonics.

Front-side buttons cycle through options shown on the display; each is also on the remote: Power, Input, Gain, Load, RIAA (EQ curves) and Mute. Power-on takes 40 seconds to deliver the unit into Mute. Happily, the Ref Phono 2 positions the Mute button beneath its indicator on the display, correcting an ergonomic beef I had with the PH7. There are no Standby, Mono or Phase switches, the latter two properly located to the preamp. The Reference Phono 2 does not invert phase.

The remote adds additional control over the display’s six degrees of brightness. You can also turn the display off, leaving nine lonely pixels to indicate power. The Hours button on the remote reveals total operating time, useful for tracking tube life. You can reset the Hours when you change tubes.

Along with those dual RCA inputs, the backside offers a ground-lug and RCA and XLR outputs. The IEC socket takes a 20-amp termination only, which makes for a sturdy connection. Note this termination if you are plan for an aftermarket power cord. I found the Shunyata Research Python CX an excellent match.

The review sample showed 424 hours on its counter, so I assumed the unit was broken in -- the manual did not speak to this, however. It sat for 24 hours of power-on settle-in prior to listening. Even then, I sensed the unit acquired an increment of what I’ll simply call smoothness after another 100 hours of use. I started taking notes after that. According to the manual, an hour of warm-up yields "maximum sonic performance."

Living la vida vinyl

y analog-reviewing ritual dictates that I always play side two of Paul Simon’s Graceland [Warner Bros. 25447-1] to kick things off. I listen for the syncopation of the drums and accordion during the funky, quick-time Zydeco riff at the start of "That Was Your Mother"; the subtle differences in ambience during the Ronstadt-Simon duet on "Under African Skies" that tell me each sang from his or her own booth; the speaker-to-speaker arc laid out by Ladysmith Black Mambazo and Simon singing "Homeless" a cappella -- a performance flecked with subtle throat and lip chirrups and trills; the faint background strumming of acoustic guitars from Los Lobos' David Hidalgo and Cesar Rosas as they double Simon on "The Myth of Fingerprints."

Here was an upbeat album with lots of musical cues for making early impressions. I heard them all and more, but the only note I wrote during my first reviewing session with the Reference Phono 2 echoed the conclusion I ended with months later: "music amplified through the Reference Phono 2 simply unfolds in a natural way." That’s all she wrote. Cut. Print. Let’s eat.

I’ve heard diva components strut their stuff in exciting ways, grabbing attention from the opening bar. "Wow, listen to that bass." "Wow, that’s really fast." "Wow, warmth and clarity together at last." But the Ref Phono 2 was no wowzer -- no sonic shock and awe shook my cochlea, no uff da moment punctuated my listening time. My reviewer noodle had clocked out, but, by the end of the first side of Graceland, I had a silly grin on my face. At limbic level, I knew one simple truth: I really wanted to play another record. What better gauge is there of your ear’s synergy with a piece of gear than its leaving you with the desire to take another hit? Getting to know the Reference Phono 2 was as much about gaining new insight into my music collection as it was about analyzing its sound. I found listening to music though the Reference Phono 2 engaging, relaxing and effortless.

But analysis you expect, and you shall have it. The Reference Phono 2’s tonal character was inseparable from its 6H30 tubes, but it did not sound particularly tubey. Taking the best of what tubes and transistors have to offer, Audio Research seems to have found that sweet spot of admixture that yields a sound overtly like neither technology. It avoided the grain and slosh of tubes without sacrificing the body and harmonic density they bring. Its character reflected the best of the Audio Research house sound: clear and open with that confident smoothness that is a hallmark of the modern Reference lineup.

Tonal balance was linear and coherent; it held steadfast up and down the frequencies without any attention-getting boost to the upper or lower midrange. If you are looking for a phono stage that injects copious warmth or tubey sweetness, the Reference Phono 2 may not be your answer. When I heard overt warmth or frequency emphasis, it came from the record. Though I listened hard for it, there was scant trace of that silvery forwardness I have known from pre-21st-century Audio Research products.

"Neutral" is an overused attribute in the reviewing lexicon. It is ultimately subjective and without a true baseline -- live music is never outside a venue that imbues itself upon the performance within it. But how to describe a chameleon whose resulting reproduction is a more the product of musical context and recording technique than component character? Every piece of gear has its own tonal flavor, but the Reference Phono 2 never drew attention to itself. It did not sound like anything.

If a component’s personality layers a coloration upon the music, the lack of such bodes well for reproducing instruments and vocals as recorded. The Reference Phono 2 consistently resolved the nuanced harmonic structure that allows the ear to differentiate discrete instrumental and human voices within complex musical passages. Listening to the Lyrita recording of Gerald Finzi’s Intimations of Immortality with soloist Ian Partridge and the Guilford Philharmonic Choir and Orchestra conducted by Vernon Handley [Lyrita SRCS 75], I heard fine-spun differences in pitch from members of the large choir in a way that told me about the contributions of individual choristers as they sang together. Striking was the way the Reference Phono 2 resolved combined singers all hitting the same note. Here the choir mimicked the shimmering effect I have heard as a harmonic cloud hovering over massed strings in the live concert hall -- very realistic and simply gorgeous.

When the choir, orchestra and soloist were all going at it, there was no collapsing of basses into cellos into violas into fuzzy harmonic soup. The Reference Phono 2 delivered each section clearly intact, refusing to blur overtones from the combined performers. As called for by the arrangement, soloist Partridge was discrete from the choir or integrated with it, neither spot lit nor washed out. Lyrics from each were clear. A leitmotif throughout my notes said that the Reference Phono 2 consistently conveyed the clearest lyrics I have heard from any piece of audio gear -- no small praise.

Unlike Audio Research’s excellent PH7, which dispenses harmonic texture in airy, burst-from-a-seed-pod blooms, the Ref Phono 2 was less pixilated and a wee bit drier, with a tight sonic weave that was rich, clear and very, very solid. Image outlines were refined with articulate placement and excellent separation. Individual instruments were more in high bas-relief than displaying the three-dimensional effect I’ve heard from all-tube components -- with nicely rounded images but fuzzier about their edges.

Ambience retrieval was abundant and soundstage depth varied appropriately with each recording. From damped-down studio work, to large reflective halls or intimate small clubs, the Reference Phono 2 gave me a clear aural picture of performers relative to one another within their space. It had an uncanny way of folding tiny details into the big picture. It did not shout its high resolution, yet detail was abundant wherever I chose to place my focus.

Hear how sustained roiling cymbals hit with soft timpani mallets decay behind Ian Partridge, as their sound wafted up and out after the percussionist stopped. As he sang "I love the brooks which down their channels fret," listen for the ever so faintly burbling flute that represented the brook. Who knew this was there? Here were but a couple of the countless slices of small discovery I had with the Reference Phono 2 that gave me delight and added insight into a familiar composition. Venue noises, musicians’ bowings, shufflings and instrument movements evoked the ambience and human context of music-making.

When a 23-three year old Finnish violinist brought down the house to win the first Herbert von Karajan Conducting Competition -- 1970's version of Conducting with the Stars -- Herbert handed his preisträger a recording contract and the keys to the Berlin Philharmonic Orchestra ("Ja ja, take her out for a spin"). Okko Tapani Kamu promptly recorded Sibelius’s first three symphonies, all included in von K’s second (and to my ears, best) Sibelius cycle. Kamu’s recording of the Second [Deutsche Grammophon 2530 021] belied his lack of formal conductorial training. Like Hans Stuck in a big Bimmer at the ‘Ring, Kamu drove the BPO with a deft and daring throttle, impelling strings and brass late into the curves before lifting. The orchestra had such controlled power that Okko got away with it time and again.

It was here I heard the Reference Phono 2 make its case to be considered a special piece of audio gear. It melded subtle changes in loudness with the smallest shifts in tempo to resolve musical motifs into phrases and phrases into melodies with vitality, nuance and authenticity. Arpeggios crossed frequency boundaries with clarity and coherence as they moved from one section to the next. Bass was not always über firm in the lowest lows, but never wooly and always tuneful. Transients had startlingly clean delineation with inertia-less jump, all without the faintest whiff of hardness. Notes could stop on a dime or ember-fade. I gained a new appreciation for Kamu’s unique interpretation as he gathered shifting fluid patterns of tension and release. From the softest degrees of fading woodwind pianissimos to sforzando attacks of trombones and timpani, music evinced a liveliness and immediacy that took me tantalizingly closer to the concert-hall experience.

The Reference Phono 2 offered realistic flow in seemingly limitless gradations of rhythmic and dynamic combination. Kamu’s finale speaks of both joy and warning, not the rushed Finlandia-like boisterousness you get from some. He let the upper strings soar, and through the Reference Phono 2, the BPO delivered like Valküren on fire. Among standalone phono stages I have reviewed, the Reference Phono 2 was the most lifelike I have heard to date.

Where’s that bee and where’s that honey?

ew perceptions gain relevance compared to what we know. We swap boxes in our systems and listen. On hand were the Reference Phono 2’s older, smaller brother, the PH7 ($5995) and the Atma-Sphere MP-1 Mk 3 preamp ($12,900) with its internal phono stage.

First, a couple usage notes. My Transfiguration Orpheus cartridge sounded best through the PH7 loaded at 100 ohms, and at 120 ohms through the MP-1. Surprisingly, the Reference Phono 2 sounded optimal with the Orpheus loaded at 47k ohms; there, aural images took on better definition against the background, yet without any high-frequency sparklies. Unlike the other units, the Reference Phono 2 made me keenly aware of the polarity of individual recordings relative to my phase-correct system. I never realized how sensitized my ears were to the effect until the Reference Phono 2 made it obvious. The MP-1’s normal/inverted switch made adjustment simple.

Comparing the PH7 with the Reference Phono 2 confirmed what an excellent value the PH7 is, while acknowledging that, at twice its price, the Reference Phono 2 had the sonic chops to warrant it as no poster child for the high-end’s law of diminishing returns. I heard no order-of-magnitude difference for any single sonic attribute, yet in sum the Reference Phono 2 was clearly the more refined product on every level.

On the first Nora Jones album, Come Away with Me [Blue Note/Classic Records JP5004], the Reference Phono 2 delivered unmatched intimacy and dynamics. It really drew me in to the dusky seductiveness of Nora’s voice. Through the Reference Phono 2, I heard better separation of vocal lines when she doubled herself via over-dubbing.

With Thus Spake Zarathustra with Reiner and the Chicagoans [RCA/Classic Records LSC 1806], the PH7 delivered nice venue context with gobs of air and presence, yet, by direct comparison, its images had a certain diaphanous quality, lacking the solidity of those from the Reference Phono 2. I heard slightly purer pitch on upper-octave trumpets from the Reference phono stage and plenty of small sonic details, such as oboist Ray Still’s attack on his reed -- details faintly muffled (or simply missing) with the PH7. Overall, the Reference Phono 2 offered a greater sense of transparency, quicker transients and better low-end weight.

The phono stage of the fully balanced, all-tube Atma-Sphere MP-1 Mk 3 had considerably more tube rush than the Reference Phono 2. With the Sibelius Second, both units offered rich tonal texture and nuance, with the MP-1 Mk 3 being a teeny bit sweeter. The Atma-Sphere phono stage delivered slightly more air, and its aural images had a nice dimensionality. Compared to the definition, separation and resolution of the Reference Phono 2, the MP-1’s images were similar though larger -- more third-row than mid-hall -- and a touch scattered or diffusive at their outlines.

On "Cecilia," a lively rocker from NRBQ’s All Hopped Up [Red Rooster LP101], the MP-1 Mk 3 delivered slightly crisper leading edges with slightly more tonal weight from the stand-up bass. The Reference Phono 2 was more articulate in the mids and highs. Through the Reference Phono 2, the sax solo had just the right amount of wet, reedy grunt and saxy overtones, and it was neat to hear the raspy punch of notes from the horn section expand outward from their instruments' bores. Clarity from the Reference Phono 2 matched the MP-1 Mk 3’s transparency -- a first in my system -- as both reproduced this dynamic roadhouse tune with the gusto and jump of a live performance. By way of contrast, music from the Atma-Sphere phono section was visceral, imminent and faintly darker, a Jack Nicholson to the solidity, refinement and quiet strength of the Reference Phono 2s Humphrey Bogart.

True joy is a serious thing

he Reference Phono 2 managed to do for me what no other phono stage has done: demonstrate the merit of coupling an active solid-state low gain stage with the virtues of modern vacuum-tube circuitry and thus make moot the debate about solid state versus tubes. Through careful parts selection, design and implementation, Audio Research engineers have achieved a balance of technologies that avow genuine sonic realism. Appropriate to the quality of each LP’s recording, the Reference Phono 2 preserved music’s rhythmic life, detail, and dynamic flux. Previously obscure lyrics became clear. Harmonic insight, texture and pitch accuracy earned top marks.

Audio Research continues to carve away at what stands between sonic reproduction and the sound of live music. The Reference Phono 2 shows the company to be at the top of its game. And so it ends where it began: "music amplified through the Reference Phono 2 simply unfolds in a natural way." Here is an instant classic. Here is a component with which to complete your analog front-end.