Reviewers' ChoiceA little less than two years ago, I reviewed Audio Research’s Reference 6 preamplifier ($15,000, discontinued; all prices USD). Little more than a day of listening later, I’d decided I wouldn’t be sending my review sample back, and ever since, the Ref 6 has been my reference preamp. Asked to review the Ref 6’s successor, the Reference 6SE ($17,000), my answer was a no-brainer: Yes.

Sound engineering

To look at them, the Reference 6 and Reference 6SE are identical, other than the “SE” appended to the latter’s name on the rear panel. Otherwise, the Ref 6SE carries forward the Ref 6’s aluminum case, top and bottom acrylic panels, 37.5-pound weight, and dimensions of 19″W x 7.8″H x 16.5″D. Most of what’s inside, too, remains unchanged, as do ARC’s specifications. So why does the Ref 6SE cost $2000 more?

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I put that question to ARC’s managing director, Dave Gordon, who generously provided me with so much information that I prepared the way for this review with a short article about what “SE” means to Audio Research. The gist of that article is that Audio Research does not take adorning their products with these two letters lightly; in fact, quite the opposite. Gordon said that whenever ARC releases a MkII, MkIII, or Special Edition, the improvements made have been substantial enough to qualify the new product as a new model, not just a revision.

“We only offer a completely new model when we have a new circuit design, along with numerous other improvements, that do not allow us to update the previous model. For example, the Ref 6 was fundamentally different than the Ref 5SE; it used six 6H30 tubes in the gain stage, new transformers, new chassis design, etc.—that simply could not be retrofitted in the Ref 5SE, so we introduced an entirely new model.”

It wasn’t until ARC had completed work on the Reference 160 stereo amplifier that they felt they’d accumulated enough technological advances to warrant an upgrade of the Reference 6. The SE version includes numerous upgrades of passive components, 18 new capacitors, and all new internal wiring. If you own a Ref 6 and want to have it updated to SE spec, you’ll need to call ARC to reserve an upgrade timeslot, pay them $3000 (if you live in North America), then ship your Ref 6 to ARC—this upgrade can’t be done by an ARC repair center, certified or uncertified. In addition to the upgrade, all units will get a new 6550 tube installed for the power supply, and a one-year warranty or extension of current warranty. Gordon told me that it takes a full day to upgrade a Ref 6 to 6SE status, and once that’s done, the revised unit is evaluated in ARC’s reference system before being shipped back to the customer. I appreciate so thorough an approach to quality assurance.

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While discussing the upgrade’s sonic benefits, Gordon noted that while ARC ensures that every component installed in an ARC product measures very well before being installed, the process is not complete without fine-tuning by ear. Despite there being no measurable differences between the technical performance of the Refs 6 and 6SE, after only a few minutes of direct A/B comparisons the differences in sound were clear to me, and anything but subtle. I won’t go too deeply into the technical design of the Reference 6SE, which is, despite the changes Gordon mentioned, basically the same as outlined in my review of the Reference 6. The Ref 6SE uses the same tube complement of six 6H30P dual triodes driving the analog section, with a 6550WE and a 6H30P feeding the power supply. The circuit path is fully class-A and balanced from input to output, and no feedback is used. The Ref 6’s volume control, based on a resistor-ladder network, is carried forward with its 103 steps of attenuation. The connections, too, remain unchanged: four balanced (XLR) and four single-ended (RCA) inputs, three balanced (XLR) and three single-ended (RCA) outputs, an RS-232 control port, an IR input, a 12V trigger input/output, a fuse bay, a 20A IEC power inlet, and a surprisingly high-quality power cord.

I was glad to see that the volume, mute, and polarity adjustments, source selection, and display brightness can all still be configured using the supplied infrared remote control—but I uttered a choice selection of four-letter words of disappointment when I discovered that the Ref 6SE comes not with the Ref 6’s beautifully made, solid-aluminum remote handset, but with a cheap plastic knockoff that feels completely unsuited to a $17,000 preamp. The Reference 6SE is warranted for three years, parts and labor; its tubes are warranted for 90 days.


I knew exactly what to expect when the Reference 6SE arrived: big box, substantial packaging, an inner box containing all eight tubes, a manual, and an instruction sheet indicating in which socket each tube was to be inserted. The tubes so socketed, I set down the review sample next to my Reference 6, atop an isolation shelf. Connections to my PS Audio DirectStream DAC and Classé Delta Mono amplifiers were made with Kimber Kable Select KS-1116 interconnects, and to my Paradigm Persona 7F speakers with Kimber KS-6063 speaker cables. Analysis Plus USB links tethered my Intel NUC computer running Windows 10 and Roon. Clarus Crimson power cords delivered AC to each component from a Torus AVR 20 power conditioner. The Reference 6SE’s own beefy power cord easily held its own against the considerably costlier Clarus Crimson.

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A refined new voice

Per the Reference 6’s handy onboard tube timer, since purchasing my review sample 18 months ago I’ve logged 1084 hours of listening on it—just under a third of that time spent breaking it in. So when the Reference 6SE arrived, I made sure to put at least 300 hours on its tubeometer before doing any serious listening.

Familiar with the vast improvements made over the Reference 5 by the Ref 5SE—better-controlled bass, more top-end detail, bigger soundstages, a more neutral midrange, etc.—I was hoping to hear similar improvements from the Ref 6SE over the Ref 6.

I did. In fact, it took me a little while to acclimate to the Ref 6SE’s decidedly different sound, which shares much with good solid-state sound. For example, the Ref 6SE reproduced aural images with more sizzle than the Ref 6, while also sounding a wisp more polished. Image specificity was better no matter what recording I played, and the tonal colors of instruments and voices seemed a degree cooler. The Ref 6SE also trumped the Ref 6 in transparency: the sound had a vividness the Ref 6 doesn’t offer, and part and parcel with that came less constraint in dynamics. The combination of these newfound qualities culminated in a cleaner, clearer, more realistic picture, but also laid bare more flaws in the recordings themselves than some might like. Basically, the Ref 6SE gave up slight measures of warmth and liquidity in favor of greater insight. As enticing as I found this difference, at first I wasn’t sure I liked it—while the Ref 6SE’s sound was technically of higher fidelity, warmth and liquidity are, after all, two of many reasons some prefer tubed gear in the first place.

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Throughout my listening sessions, I found that whether or not I preferred the Ref 6SE over the Ref 6 depended on the quality of the recording played and, to some extent, what type of music it was. Take “Tea in the Sahara,” from a high-resolution edition of the Police’s final album, Synchronicity (24-bit/96kHz FLAC, A&M). Through the Ref 6SE, Sting’s meticulously plucked electric bass was projected into my room with slightly more articulation and fortitude than I’d come to expect from the Ref 6, while adding a measure of texture. Sting’s voice, appearing as expected dead center on the soundstage, was pushed farther back on that stage with a sound undeniably more cool and vivid, and less veiled, than I’m used to from the Ref 6. Remarkably, before comparing the Refs 6 and 6SE back to back, I never would have described the Ref 6 as sounding “veiled” in any way—but there’s no question that the Ref 6SE let me “see” music through a clearer aural lens. Stewart Copeland’s tapped cymbals sounded livelier and more crisply defined on an airier soundstage, while giving up none of the delicacy I’ve learned to love through the Ref 6. As the track progressed, the Ref 6SE’s better dynamic range and longer decays let the sounds of percussion instruments, particularly the triangle, come to life more easily.

The greater transparency of the Ref 6SE allowed the opening seconds of “Slow Burn,” from Kacey Musgraves’s quadruple-Grammy-winning Golden Hour (24/96 MQA, MCA/Tidal), to really bloom in my room. I could better hear nuances of acoustic guitarist Todd Lombardo’s playing, such as the sliding of his pick, that the Ref 6 struggled to communicate—and I could more easily pick out elusive textural details, such as string resonances, that I can’t hear at all through the Ref 6. Likewise for Lombardo’s banjo, which subtly enters at left shortly before Musgraves begins singing—there was a wonderful sense of space around the instrument that helped highlight the quick transient of each pluck. As the track progressed, Daniel Tashian’s bass guitar chewed its way onstage in tandem with Ian Fitchuk’s drums—the combination punched hard, reminding me on each beat that the Ref 6SE was doing nothing to constrict their impact, including Fitchuk’s dynamic intent, that informed each thwack of skins.

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An interesting thing about Golden Hour that I hadn’t noticed until I listened to it through high-end gear is that Musgraves’s voice has been punched up ever so slightly, to ensure that she’s consistently heard above everything else in the mix. The Ref 6SE did nothing to hide this, reproducing her voice at dead center and about 1ʹ in front of my speakers, replete with as much microlevel detail, breath, and nuance as I could ask for. Unfortunately, the Ref 6SE’s clean-glass demeanor sometimes brought Musgraves a little too far into my room—I found myself sitting front-row center. Some listeners might enjoy that, but I prefer the middle of the fifth row, particularly for music performed at higher volumes. Golden Hour was the only album with which I experienced this level of forwardness; Musgraves’s other records sounded just fine. Had I not had the Ref 6 on hand for comparison, I might not have noticed it at all.

As I swiped through pages of albums on my iPad, looking for something engaging, I landed on what has recently become one of my favorite albums: London Grammar’s If You Wait (24/44.1 FLAC, Ministry of Sound/Tidal). I find every track on this album evocative—each elicits a mood, through its lyrics and/or the way lead singer Hannah Reid soulfully infuses those words with feeling. When I listened to “Strong” directly after playing Musgraves’s “Slow Burn,” Reid’s voice soared, but with better senses of scale and location. Properly placed deeper on the soundstage, Reid’s voice sounded velvet-smooth, and wonderfully balanced among the various electronic instruments. Both the Ref 6 and 6SE can seem to push back the walls of my room, and make soundstages and the instruments and voices on them image well beyond the confines of my speakers. With “Strong,” the sizes of the soundstages projected by both preamps were similarly expansive, as were the depth and impact of the timpani. The Ref 6SE provided the best reproduction of this track I’ve heard in my room and system. The resonances of Reid’s emotionally expressive voice reached deep into the soundstage, accentuated by rich, fluid notes emanating from a soulfully played electric guitar. I was also able to more easily hear the individual beads of the cabasa being shaken toward center left.

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Kicking things up a notch, I cued up Supertramp’s Crime of the Century (24/192 FLAC, A&M), intending to first listen to a few tracks before choosing one for my comparisons. I got no further than “School” before feeling compelled to put fingertips to keyboard. Listening to the “Red Book” (16/44.1) version of this track back to back against the hi-rez file, I heard differences akin in many ways to what I heard when playing only the hi-rez file through the Ref 6 and the Ref 6SE, if to lesser degrees. Detail and dynamics on both the micro and macro levels were better fleshed out through the Ref 6SE, making the sound livelier, clearer, more arresting. Roger Hodgson’s voice appeared solidly, just above and about 3′ in front of Rick Davies’s more holographic-sounding harmonica. As instruments entered one by one on either side of the stage, I got a clear impression of the soundstage’s dimensions, which were, overall, comparable to what I heard from the Ref 6: instruments appeared at least 2ʹ outside the speakers. Focusing on Dougie Thomson’s bass, I heard a hint more textural detail in the lows, but no improvement in low-frequency articulation, weight, or impact. That’s not to slight the Ref 6SE—the Ref 6 is outstanding in this regard.

Summing up

Audio Research’s Reference 6SE preamplifier is a big step forward from their Reference 6 in terms of transparency, and thus in terms of all the sonic nuances that a superior preamplifier can communicate. Partner that with a slightly cooler tonality, better dynamic fortitude, chiseled as opposed to holographic imaging, and a subtle tilt more toward the vivid than the rich, and you have a preamplifier whose sound can’t be mistaken for that of its immediate predecessor. To say that the Reference 6SE is better than the Reference 6 would be a subjective statement; the fundamental designs of both are very similar, and after all, some might buy a tubed preamp because its sound is warmer, all else being equal, and for its holographic imaging. I prefer to describe the Reference 6SE as a variation on the theme established by the Reference 6 but executed with higher-quality parts, a variation that pushes that original theme a big stride closer to solid-state sound while sacrificing very little of its tube charm.

The Reference 6SE is the second Audio Research preamp I’ve reviewed. It will now be the second Audio Research preamp I refuse to return.

. . . Aron Garrecht

Associated Equipment

  • Speakers: Paradigm Persona 7F
  • Subwoofers: JL Audio Fathom f112 (2)
  • Amplifiers: Classé Audio Delta Mono monoblocks (2), Parasound Halo A 51 (five-channel)
  • Preamplifiers: Anthem AVM 60, Audio Research Reference 6
  • Digital-to-analog converter: PS Audio DirectStream
  • Sources: Oppo Digital BDP-103 universal BD player; Intel NUC computer running Windows 10, Roon
  • Interconnects: Analysis Plus (USB, S/PDIF), Kimber Kable Select KS-1116 (XLR)
  • Speaker cables: Kimber Kable KS-6063
  • Power cords: Clarus Crimson
  • Power conditioner: Torus AVR 20

Audio Research Reference 6SE Preamplifier
Price: $17,000 USD.
Warranty: Three years parts and labor; 90 days, tubes.

Audio Research Corporation
6655 Wedgwood Lane N., Suite 115
Maple Grove, MN 55311
Phone: (763) 577-9700