Audio Research SP20In my youth, in audio’s dark ages, when LPs were the primary format for recorded music, a preamplifier was a single box housing a line stage and a phono stage. Today, however, preamplifier is often used as a synonym for line stage. If you’re a vinyl fan, there’s a good chance your phono stage is a separate component with its own power supply -- a phono preamplifier. That makes economic sense; despite the resurgence of interest in vinyl, many of today’s audio systems have only digital sources, and the surge of interest in computer audio will probably only increase the popularity of all-digital systems.

Audio Research Corporation’s product lineup has always included classic preamplifiers, but with the SP16 and SP17, they became ARC’s entry-level products. Given the excellence of ARC’s separate line stages and phono preamps, I speculated that the SP17 might not have a successor.

Boy, was I wrong. With the subject of this review, the SP20, ARC has not only reaffirmed its support for the preamplifier of yore, but has improved its circuitry to mirror the designs in its separate LS27 line stage and PH8 phono preamp ($7500 USD and $7000, respectively). And to support the skyrocketing interest in headphones, the SP20 includes the first headphone jack in ARC’s history.

The SP20 has other features new to ARC. These include knobs that actually fully rotate, a color touchscreen to replace the physical buttons on earlier preamp and line-stage models, and perhaps the biggest surprise of all: no rack handles on the front panel! And new to me, at least, was the all-metal remote -- all the ARC remotes I’d seen had been plastic and metal. (That’s not a complaint; I’ve dropped them on my coffee table often enough to be grateful that the plastic doesn’t scratch.) The changes to the SP20 carry a substantial price increase: $9000 for the SP20 vs. $3495 for the SP17, which was recently discontinued.

Available in Natural (silver) or Black, the front panel is simple: the 4.3” LCD touchscreen is flanked by knobs reminiscent of those on early ARC preamps such as the ground-breaking SP3 -- except that the SP20’s knobs are all metal, not plastic. In another departure from ARC convention, the right knob is the volume knob, the left the input selector. As is the norm with ARC gear, a comprehensive, easy-to-read owner’s manual is provided.

Audio Research SP20

The touchscreen provides lots of controls: Phono Cartridge Load, Balance, Mute, Screen Brightness, Input Name, Input Gain Offset, and Tube Hours. The last feature is neat; when the tubes have logged 4000 hours of use, the Settings icon turns red to remind you to replace them. There’s also a control for resetting the hour counter when you’ve installed your new tubes -- without having to poke around inside a powered-up unit, as is necessary with my LS27 line stage. There is no control to turn off the tubes in the phono section, so those tubes will wear out as fast as the line-section tubes. While the touchscreen presents a lot of information, some of the displays are rather small, and hard to read from my listening position, about 10’ away.

Duplicating the touchscreen, the remote lets you choose among different cartridge loadings: 50, 100, 500, 1000, and 47k ohms -- you can sit in your chair and listen to the effects of different loads. (Yes, there were differences.) The phono section’s gain is 58dB, which, together with the line section’s 13.8dB of gain (through the balanced output), means the SP20 will work with “moderately low output moving coils.” My medium-output (0.65mV/channel) van den Hul Frog cartridge was a terrific match for the SP20. The phono section uses low-noise JFET inputs and four Sovtek 6H30 output tubes, two per channel, in a configuration also used in the line section -- and in ARC’s Reference line stages and phono preamps. The phono section’s claimed frequency response is 5Hz-80Hz, ±0.4dB.

I’ve heard complaints about ARC phono preamps that offer only a single gain setting (58dB) for both moving-coil and moving-magnet cartridges: 58dB gain will be very loud if used with a MM cartridge, and could overload some line stages. Fortunately, the SP20 lets you adjust the gain for each input separately, to keep the phono preamp from being too loud.

Audio Research SP20

The SP20’s circuitry is class-A, zero-feedback, and fully balanced throughout, even though the phono section has only an unbalanced (RCA) input. Besides the phono input, there are four other unbalanced line-level inputs, two balanced (XLR) inputs, and separate unbalanced Monitor In and Record Out jacks. Finally, there are two pairs of balanced and a single pair of unbalanced output jacks. A 15A IEC connector is provided for the power cord. ARC provides a typically hefty cord whose sound is a cut above the flimsy cords included with most components.

Does it seem odd that the SP20 has the first headphone jack ever on an ARC preamplifier? Not to me; these days, headphones are usually used in small systems consisting of a headphone amp, a source (often a computer), and perhaps a DAC; not a full audio system with speakers and a power amplifier. But if you listen into the wee hours and don’t want to disturb others, being able to plug in headphones and listen to music may preserve domestic tranquility. A front-panel Headphone button switches off the SP20’s line outputs. ARC claims that the headphone jack, with a maximum output of 6V RMS into loads of 30 to 300 ohms, will drive a wide variety of headphones.

The SP20 measures 19"W by 5.25"H by 16.5"D and weighs 17.8 pounds. The rest of this paragraph summarizes ARC’s published specifications for it: The line-level input impedance is 120k ohms balanced and 60k ohms unbalanced, neither of which should be a problem for any source you might connect. The output impedance is 500 ohms balanced, 250 ohms unbalanced -- low enough to drive most power amplifiers except those with very low input impedances. The headphone amplifier has an extremely low output impedance of less than 0.05 ohm, thanks to a solid-state output buffer. That means it should be able to drive even headphones of very low impedance. The specified signal/noise ratio is incredible through all inputs: more than 125dB through the line stage, better than 94dB through the phono section, and greater than 110dB through the headphones. That’s quiet!

No one has ever accused me of having good taste, but to my eye, the SP20 is the most attractive component ARC has ever made, and by not a small margin. The amount of bling you prefer in your hi-fi gear is a matter of personal taste, but I’ve always thought that if you pay this kind of price for your equipment, you should be able to take pride in its appearance. I am not saying that earlier ARC gear has been ugly; my equipment rack is full of ARC components, which I chose for their sound quality. But next to the SP20, older ARC models look somewhat industrial.

Setup and use

ARC separately boxes the SP20’s tubes, cushioned in blocks of foam -- the first thing I had to do was remove the preamp’s top panel and insert the tubes in their sockets. As usual, I used the manufacturer’s stock power cable, plugged directly into the wall (I’m lucky to have clean power). My digital-to-analog converter was MSB Technology’s very fine Analog DAC; although the MSB was designed to be used as a system line stage, I was reviewing a preamplifier, so I plugged the Analog’s unbalanced output into the SP20’s SE2 jack. I also set the label on the SE2 input to read “DAC” on the display. Of course, that made the input display and the remote button for the same input read differently. My Linn LP12 turntable was connected to the phono input via Crystal Cable CrystalConnect Micro Phono cables. After trying other values, I set the cartridge loading to 1000 ohms. A Sony XDR-F1HD (Radio X modified) tuner was connected to the SE1 input with Crystal’s Piccolo unbalanced interconnects. I changed the SE1 display to read “Tuner,” which displayed as “TUN.” High Fidelity Cables CT-1 unbalanced interconnects connected the SP20 to my David Berning ZH-230 amplifier.

Because the huge Teflon capacitors ARC uses take so long to burn in, they specify a burn-in period of 600 hours for everything they make. Fortunately, the review sample of the SP20 had been used at the 2014 Consumer Electronics Show and already had nearly 600 hours on it, per the Tube Hours clock. The headphone amp, which presumably had not gotten so much use, at first sounded flat and a bit wimpy, but a couple hundred hours of break-in with headphones plugged in brought it to life. The line section had a gain of 13.8dB via the balanced output, which meant I had to use higher volume settings than I normally do with my LS27 line stage, which provides 24dB of gain.

I tried the SP20 with several headphone models: HiFiMan HE-400 (35 ohms), AKG K712 Pro (62 ohms), and Sennheiser HD 650 (300 ohms). While none of those is anywhere as difficult to drive as, say, HiFiMan’s HE-6 (which demands several watts of power), the nearly tenfold spread in impedances could pose a challenge to the SP20.

The two knobs on the faceplate rotate freely, with no stops or detents. The faster you spin the Volume knob, the faster the volume changes -- quite handy when the volume is set at a pretty high level. But without detents, it was difficult to know how far to turn the Source knob to switch sources. I had to turn it a long way -- 180 degrees or more -- which I found annoying. I’d never used a line stage or preamp whose source-selection knob lacked positive positions, and I never got used to it. Fortunately, the remote lets you change sources by simply pushing a button.

Sound: speakers

I began with digital sources, since they provide a familiar, repeatable baseline. First up was The Best of Eva Cassidy (16-bit/44.1kHz AIFF, Blix Street). Cassidy’s early CDs sounded a bit raw, while her first “best of” album, Songbird, sounded rolled-off and overprocessed, which smoothed out the sound. Containing no new material, The Best of comprises remasterings of previously released tracks. In her cover of Cyndi Lauper’s “Time After Time,” Cassidy’s voice is smooth and expressive, although I thought I heard a brief breakup. The SP20 presented Cassidy’s voice with tons of detail, but it never sounded etched or peaky. When I say detail, I include harmonic and microdynamic detail, which made Cassidy’s expressive phrasing easy to follow.

When I played my fave test track, Folia Rodrigo Martinez, from Jordi Savall’s La Folia 1490-1701 (16/44.1 AIFF, Alia Vox), I could easily make out the cascabels (sleigh bells) and castanets, even when they were played softly while the entire ensemble was also playing. Sometimes they tend to blur into the background. Horizontal placements of instruments on the soundstage were precise. Bass was deep, powerful, and well defined -- all characteristics of the MSB Analog DAC that the SP20 did nothing to degrade.

I got similar results with the Tallis Scholars’ recording of Allegri’s Miserere (24/96 FLAC, Gimell): The SP20 made it easy to hear the instrumental details in this information-rich recording, as well as the precise positions of singers across the soundstage. The ARC also depicted, with unusual precision, the sense of depth of the small solo group behind the main chorus; I almost felt I could see the space between the groups. Most line stages I’ve heard smear the depth dimension or, even worse, flatten it.

Audio Research SP20

With “The Briar and the Rose,” from Holly Cole’s Temptation (DSD64/DSF, Acoustic Sounds), the SP20 painted the horns with fully fleshed-out harmonics. The expressiveness of Cole’s voice bespoke excellent timing precision.

The SP20 reproduced “Shenandoah,” from guitarist Alex de Grassi’s Special Event 19 (DSD64/DFF, Blue Coast), with rich harmonics and transient information. This is one of the best recordings of acoustic guitar I’ve heard, and the SP20’s reproduction of it was unforced and smoothly natural.

With Dance of the Tumblers, from Rimsky-Korsakov’s The Snow Maiden, conducted by Eiji Oue on Exotic Dances from the Opera (24/176.4 WAV, Reference HRx), the SP20 reproduced the Minnesota Orchestra with plenty of low-end weight and burnished low strings. Harmonics were rich throughout the audioband, and the opening trumpet sounded very realistic. Dynamics were unconstrained.

Since the digital version of The Best of Eva Cassidy had sounded so good, the first analog disc I tried was the same track from the same album (LP, Blix Street G8 10206). Ha! “Time After Time” was flaming gorgeous. Cassidy’s voice was sweeter and more human, and the guitar was smoother, but the breakup I’d heard in the digital file was also present on the LP -- it must be on the master tape. Unexpectedly, the LP’s bass was slightly more pronounced, giving the music additional underpinning. The differences weren’t huge, but generally favored the LP. And this pressing’s silent surfaces certainly didn’t hurt the sound.

Cueing up the same Rimsky-Korsakov track from Exotic Dances from the Opera, this time on LP (Reference RM-1505), I expected the high-resolution digital version to stomp the vinyl. Again, Ha! The 24/176.4 file sounded slightly more murky -- not a huge difference, but there it was. Maybe digital hasn’t come as far as we’d hoped. Wonder what the DSD version sounds like . . .

Sound: headphones

Switching to the SP20’s headphone output, I discovered that the ARC’s volume had to be cranked rather high to achieve satisfactory loudness -- and I’m no headbanger. All three headphones needed a volume setting in the range of “70” to “80” (of a maximum of “103”) to sound realistic. But once I’d found the right volume, the SP20’s headphone amp really sang. Luckily, the SP20 remembers the line-out and headphone volume settings, and automatically switches to them when you switch to or from headphones, so you won’t get blasted by your speakers.

I began with my go-to headphones, the AKG K712s. The Rimsky-Korsakov had superior highs and midrange and sounded quite accurate, with very deep, detailed bass. The HiFiMan HE-400s have planar-magnetic drivers (think Magneplanar speakers), and their bass was even deeper. Highs were rolled off, but that’s a characteristic of the headphones, not the SP20. On another track from Exotic Dances from the Opera, the Polonaise from Dvořák’s Rusalka, which has deeper bass, the HE-400s were absolutely subterranean. The biggest surprise were the Sennheiser HD 650s; I’m not their biggest fan, but the SP20 made them sound listenable, with audible highs and pretty deep bass. Once I got used to the high volume setting, the SP20 proved to be a wonderful headphone amp that made all of my headphones sound better than I’d heard them before.

I wouldn’t expect anyone to buy an SP20 to use only with headphones -- there are too many superb headphone amps out there at far lower prices. But if you do a good bit of listening through headphones, it’s nice to know that the SP20’s headphone amp is top-notch.


I compared the SP20 with two other ARC products: my LS27 line stage ($6995) and PH5 phono preamplifier ($1995 when first produced). That would appear to be a very close match, on the basis of price: the LS27 and PH5 together cost $8990, only $10 less than the SP20’s $9000. But it’s not that simple -- a complete comparison would have to include $1400 for the 1m pair of Clarity Cable Organic unbalanced interconnects that connected the PH5 to the LS27. Another way the SP20 saves the buyer money is in the cost of your equipment rack: It takes up half the space of a separate line stage and phono preamp.

Comparing the line stages of the SP20 and the LS27 was a challenge -- they sounded much more alike than different. Both had deep, forceful bass, and their depictions of the bass drum in Folia Rodrigo Martinez were indistinguishable. But the LS27 produced a slightly greater sense of dynamic impact. Through the SP20, percussion instruments seemed to remain a bit more distinct throughout this piece; with the LS27, they tended to fade into the background a little. Both produced splendid soundstages. The SP20 produced slightly more focused depth of field with Allegri’s Miserere, so that the distant solo group sounded more realistic. The impression of the separation of the two groups was slightly more tangible.

While the SP20’s portrayals of the harmonic structures of the sounds of instruments were rich and full, it had, by a very small amount, less tube “juiciness” than the LS27. I’m tempted to say that the SP20 sounded just a bit more like a solid-state preamp. To be fair, I was using the LS27 with an aftermarket power cord and some Black Ravioli footers, which, to my ears, improved the sound.

Comparing the phono section of the SP20 to my ARC PH5 phono preamp was not a challenge. The PH5, a ten-year-old design based on JFETs and four 6922 tubes, has virtually the same gain as the SP20’s phono section: 57.5 vs. 58dB, respectively. Listening to “Time After Time” on vinyl, the first thing I noticed was that the bass was less robust -- there was less underpinning to the song. While the sound was pleasant, it was less open, and the harmonic structures of voice and instruments were not as well developed. The PH5’s soundstage was smaller and less open with Rimsky-Korsakov’s Dance of the Tumblers -- not unpleasant, but the SP20 opened up the sound, clearly outclassing the PH5.

There’s little point in comparing the SP20’s headphone performance with that of my iFi iCan headphone amp. Although at $259 the iFi is an amazing bargain that can drive all of my headphones to much higher volumes than I would ever want to hear, it was no match for the SP20. I may soon upgrade my headphone system.

Bottom line

With the SP20, Audio Research Corporation strides surefootedly back into the market of high-end preamplifiers. While not at the rarefied level occupied by ARC’s Reference components, it’s a big step up from the SP16 and SP17, and enters the territory occupied by ARC’s best non-Reference phono and line stages. According to Dave Gordon, ARC’s managing director of sales, the SP20 “has a phono section comparable to a $7000-ish phono stage, with a line section comparable to a $7000-ish line stage, with a headphone output comparable to a $1500-ish headphone amp, utilizing a new touchscreen display.”

Do the math: For $9000, you get a preamp roughly equivalent to $15,500 in separates. More important, it sounds wonderful. I didn’t have a PH8 phono preamp to compare, but in most respects the SP20 did sound slightly better than my LS27 line stage, and its controls are easier to operate. The frosting on the cake is that all of this quality and value are packed into a case whose beauty rivals almost anything on the market. What’s not to like? I’m buying the review sample.

. . . Vade Forrester

Associated Equipment

  • Speakers -- Affirm Audio Lumination
  • Amplifier -- Berning ZH-230
  • Preamplifier -- Audio Research LS27
  • Phono preamplifier - Audio Research PH5
  • Sources -- Linn LP12 turntable on custom isolation base, Graham Engineering 2.2 tonearm, van den Hul Platinum Frog cartridge; Sony XDR-F1HD tuner (Radio X modified); Hewlett-Packard dv7-3188cl laptop computer running 64-bit Windows 7 Home Premium and JRiver Media Center 19; MSB Technology Analog DAC
  • Interconnects -- Audience Au24 e balanced, Clarity Cables Organic, Crystal Cable CrystalConnect Micro Phono, Crystal Cable CrystalConnect Piccolo
  • Speaker cables -- Clarity Cables Organic
  • Power cords -- Audience powerChord e, CablePro Freedom, Clarity Cables Vortex, Purist Audio Design Venustas
  • Digital cable -- WireWorld Platinum Starlight USB
  • Headphone amplifier -- iFi iCan
  • Headphones -- AKG K712, HiFiMan HE-400, Sennheiser HD 650

Audio Research SP20 Preamplifier
Price: $9000 USD.
Warranty: Three years parts and labor to original purchaser; tubes, 90 days.

Audio Research Corporation
3900 Annapolis Lane N.
Plymouth, MN 55447-5447

Phone: (763) 577-9700
Fax: (763) 577-0323