Tube Preamp Reviews

That's the line long uttered by the most dreaded members of my family, and their friends, whenever they tried to pry into my personal affairs. Often the last word, "happy," was uttered with a downward cadence and accompanied by a shrug.

Then came the kicker. "You are happy, aren't you?" said with eyes boring into my soul. "Well, as long as you're happy."

Cue the telltale shrug. With disapproval voiced and points scored, it was time for the obligatory peck on the cheek, handshake, or—worse—mutual male hug disguised as burp assistance.

Thus were the seeds of doubt planted by those who used words and looks in place of cordless leashes and electroshock. Was I truly happy, or was I masking deep-rooted existential disease? What does it mean to be happy? Is contentment good enough, or is it merely a convenient compromise?

Irony of ironies, here I am decades later asking myself the same question. Except, whereas before the mandate to probe my emotions was intrusive and unwelcome, now it's something I'm paid to do as I listen to audio equipment and recordings. Just what are you really feeling while you're listening, Serinus? You are happy, aren't you?

Questions asked become questions owned. Karma and dharma united in a macabre dance, à la Shostakovich.

Which brings us, in ways that will hopefully become apparent, to the latest piece of gear to fall within the Serinus reviewing sights, Audio Research Corporation's new, top-of-the-line single-chassis line-stage preamplifier (footnote 1), the Reference 6SE ($17,000), ARC REF 6SE for short. An updated version of the discontinued REF 6 ($15,000), which was released in 2015, its changes include new capacitors and a lot of new wiring. Otherwise, the preamp's fundamental design, housing, and specs remain the same. Current REF 6 owners can upgrade to the 6SE for $3000. All new parts are installed by hand in a changeover that requires a full day.

According to Audio Research Corporation's extremely knowledgeable and articulate national sales manager and brand ambassador, David (Dave) Gordon, who has been with the company for more than 31 years, the REF 6SE was made possible by the many years of development and research that produced Stereophile's 2018 Joint Amplification Product of the Year, the 160M monoblock amplifier, reviewed by yours truly, and the 160S stereo amplifier, reviewed by Jim Austin. The engineers who worked on those amplifiers were responsible for the development of the REF 6 and the REF 6SE.

"In the final stages of developing the REF 6, we spent a year working on capacitors, especially coupling caps, because they made such a big difference," Gordon explained by phone. "We listen to the distinctive sound of all the caps we get, and change wraps and materials (eg, foil, quality and amount of copper, dielectrics, soldering) as necessary because they always make a difference. It's like making a fine dish. A good cook will sample along the way and add a little more spice or salt to taste. That's what we do with our circuits. We know what our products sound like, and we're looking to get better sound without trade-offs."

Eager to apply what they'd learned in developing the 160S, ARC's engineers first tried changing some of the REF 6 preamp's capacitors. Then they focused on hook-up wiring, incorporating wire from two different manufacturers and experimenting with different dielectrics. Finally, they put the two together and tweaked until everything worked synergistically and the company's "ears," Sonic Evaluation/Materials Engineer Warren Gehl, signed off.

"We know that we can hear things we can't measure," Gordon told me. "Bill Johnson, who founded Audio Research in 1970, always made a point of saying that we measure statically but listen dynamically. When we measure, we cut off the signal in time; when we listen dynamically, the music flows. We just don't have enough measurements to describe what we're hearing. Something can measure well and sound bad. Skilled engineers learn how to tweak the circuit and parts to produce the sound they want. That's where the art lies."

What it is
The REF 6SE is a fully balanced, class-A design with zero feedback. To quote the late and great Art Dudley, who authored the REF 6 preamp entry in the fall 2019 edition of Stereophile's Recommended Components, "The audio circuits include three 6H30 dual-triode tubes per channel, while the power supply has one 6H30 and one 6550WE tube. The eight pairs of line-level inputs are evenly divided between single-ended (RCA) and balanced (XLR), alongside three pairs each of single-ended and balanced outputs. Among the Reference 6's electronically controlled functions are its 103-step volume control, signal-polarity inversion, and a mono switch. [Michael Fremer] noted the Reference 6's unimpeachable specs and reported that while listening to favorite recordings through it, he heard 'intense surprises that I'm sure can't be measured. Record after record, I found that the Reference 6 greatly increased my understanding of very familiar recordings.' In measuring the Reference 6, JA noted 'superb channel matching, 'inconsequential AC-supply noise,' and, overall, 'little hint of the presence of tubes in the circuit'—that last observation intended as a compliment."

When, at Gordon's suggestion, I used the REF 6 preamp in my review of the 160M monoblocks, I found that it enhanced air and depth as well as midrange beauty. Once I replaced my DAC's volume control with the REF 6, "the sound of the horns was to die for, and bass lines were well defined," I wrote. "Everything sounded more substantial and gained in emotional impact. ... The bloom [my friend Gary and I] heard with the ARC pairing of Reference 160Ms and REF 6 sounded heavenly to our ears. Forget the oft-invoked 'It's all good'—what we heard was much better than that." The REF 6's relatively modest touches of warmth and roundness, which were quite pleasing, left me eager to discover how its REF 6SE successor would sound.

Easy Easy
Even without grasping its front handles, it was a cinch to hoist the 37.5lb REF 6SE preamp onto the top shelf of my four-shelf Grand Prix Audio Monza rack. To connect the 6SE to the D'Agostino Momentum monoblocks, I chose whichever of the REF 6SE's balanced outputs best allowed me to avoid crossing or touching other power cables. (The REF 6SE, like its predecessor, requires a 20-amp power cable, whose component-end termination differs from that on a 15-amp power cable. There's one in the box of course, but I maintained sonic consistency by using a 20-amp version of the Nordost Odin 2 power cables I use elsewhere in my system.) When cables did cross, I used extremely rare, imported-at-great-risk Portuguese Styrofoam blocks, available in lurid, quasi-dayglo green and laidback charcoal colors, to separate the cables. Despite the markedly different emotional responses those colors elicit, I found that as long as I didn't shine a spotlight on the green ones, their colors did not affect sound quality (footnote 2). What did affect sound quality was the choice of supports between the REF 6SE and the rack's bamboo shelves. More on that follows.

Throughout the review, I stuck with the dCS Rossini DAC/Rossini Clock combo fed by the Roon Nucleus+ music server with outboard HDPlex linear power supply. While I could have also used the EMM Labs DV2 Integrated DAC, I figured that the extreme openness, transparency, and resolution of the dCS combo, as well as its extended, lively top, would be most conducive to discerning differences between the 6SE, my aural memory of its predecessor, and other preamps I might invoke for comparison.

Given the 6SE's balanced design, I also used balanced interconnects between the Rossini DAC and the REF 6SE. When I briefly tried the 6SE's single-ended inputs, I was not convinced that they transmitted equally transparent sound.

Not so easy
All that sounds simple, doesn't it? Alas, as alluded to in the intro, the simple and direct path to happiness is not the Serinus way. Thus did Yours Truly complicate matters by asking Editor-in-Chief Jim Austin and Technical Editor John Atkinson to send the loaner Benchmark LA4 ($2599) and MBL Noble Line N11 ($14,600) preamplifiers they had on hand so that I could compare them, as well as my reference D'Agostino Momentum HD preamp ($40,000), with the ARC REF 6SE. The three other preamps use 15A cords. The D'Agostino offers only balanced inputs and outputs. Because I only had room for three preamps on my eight-shelf rack, the Benchmark warmed up on the floor until I finished listening to the MBL. I used the Rossini's 2V output throughout the review.

Do not begin to think what it was like to keep 12 power cables and an obscene number of interconnects and grounding wires separate, let alone match volume as I moved between four preamps and the Rossini's own volume control. Happy to say, I didn't once put the integrity of the tweeters of my Wilson Audio Alexia 2 loudspeakers (or my ears) at risk by forgetting to turn the Rossini's volume down from its maximum 0dB setting whenever I switched from one of those four preamps' volume controls back to the Rossini's.

Gordon suggested I give the already–broken-in REF 6SE two days to settle in before beginning serious listening. The unexpected treble edge I heard when I snuck in an immediate "I can't resist" listen confirmed the wisdom of his counsel.

Now you hear it, now you don't
Two nights later, I began my first serious audition. "Am I really getting paid to do this?" I wrote in my notes as my speakers poured forth some of the most polished, transparent, and arresting sound I'd heard from my system. The absurdity of calling such pleasure-inducing happiness "work" left me smiling.

Footnote 2: Am I being serious? Well, even though my surname is Serinus...