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Line / phono preamplifier


Audio Research

Manufacturer: Audio Research Corporation
Price (in Poland): 39,800 PLN

Contact: 3900 Annapolis Lane North ǀ Plymouth
Minnesota | USA | 55447-5447
tel.: 763-577-9700 ǀ fax: 763-577-0323


Product provided courtesy of: Fast

ny of the audiophile/music lover visitors to the Audio Show when asked about their first association with the name Audio Research would answer without hesitation: vacuum tubes. And rightly so - in 1970, when William Z. Johnson presented his first product under this brand, the Dual 100 amplifier, in Plymouth, Minnesota, it was filled to the brim with tubes. The amplifying circuit and power supply together could easily warm up a living room and fared no worse than a medium-sized fireplace. The accompanying SP-1 preamplifier, also vacuum tubes-based, looked like another incarnation of McIntosh components as Audio Research has yet to come up with its own characteristic visual identification, so to speak. For a long time, Mr. Johnson’s amplifiers looked like measuring equipment lugged out of a laboratory, mostly due to their distinctive control knobs and the use of characteristic voltmeters for output power indicators. One look at the pictures available on "Audio Research Database" speaks volumes. It was not until 1980 and the D60 power amplifier that the manufacturer developed its own characteristic external design. The preamplifier design as it is known today developed much faster. The SP3 from 1972 still liked like a McIntosh, but the SP4 launched in 1976 had almost all of the details that justified calling it "Audio Research." This primarily included characteristic control knobs (incidentally, they referred back to the first Mark Levinson components), toggle switches and handles on both sides of the front panel. Perhaps this is why the external design that the company adopted and that was consolidated over the following years has been since uniquely associated as "vintage 1970s look".

The launch of the SP20 preamp brought the first major change of this paradigm. The new one involves two large control knobs on both sides of the faceplate and LCD touch screen in the center. The whole fascia is reminiscent of car radios from the 1970s, and is actually a combination of two stylistic approaches, separated by 40 years: preamplifiers from the early days of the company and its latest products under the aegis of Fine Sounds SpA, an Italian company owned by Quadrivio investment fund. Which, by the way, is the owner of both AR and - already mentioned - McIntosh.
Such a mix of the past and present, of modernity and tradition has always been characteristic for William Z. Johnson’s company, but not always so explicit. Take, for example, vacuum tubes - nearly synonymous with AR. Yet the same Audio Research also offers class-D power amplifiers that have nothing to do with vacuum. And how about preamps? One of the best AR designs, the Reference 3 preamplifier from 2004 employed FETs and a large display. While the transistors only worked as current sources and hence weren’t directly included in the signal path, the amplifier paved the way for the Reference 5 that can be called a hybrid design, with a transistor-based input stage and tube-based gain and buffer stages.

The SP20 seems to be a direct descendant of this particular unit. Conceived as an upgraded version of the SP17, it is really a different preamp, both from the outside and inside, although the basis - naturally - remained the same. The input stage features FET transistors followed by tubes. The circuit is fully balanced and all stages operated in class A with zero feedback. Inputs and outputs are, however, available both as balanced XLRs and unbalanced RCAs and so the functionality of the SP20 is better than that of other AR components that only offer XLR connectors. In addition to five RCA and two XLR line inputs there is also a variable load MC phono input with gain of 58 dB. The SP4 input can additionally be switched to unity gain. There is also a feature that we see for the first time in the preamplifier from this manufacturer – a dedicated headphone output with a separate headphone amplifier boasting an ultra-low output impedance of < 0.05 Ω. The amplifier design is based on solid state components that include input transistors but also tube buffers.

Audio Research in “High Fidelity”
  • REVIEW: Audio Research REFERENCE CD9 – Compact Disc player, see HERE
  • REVIEW: Audio Research REFERENCE 5 SE – line preamplifier, see HERE
  • AWARD OF THE YEAR 2012: Audio Research REFERENCE 75 - power amplifier, see HERE
  • REVIEW: Audio Research REFERENCE 75 – power amplifier, see HERE
  • Albums auditioned during this review

    • Rachmaninoff Plays Rachmaninoff, RCA Red Seal/Sony Music 8697-48971-2, “Zenph Re-Performance”, CD (2009).
    • Anita Lipnicka, Vena Amoris, Mystic Production MYSTCD 244, CD (2013).
    • Arimasa Yuki & Hisatsugu Suzuki, Duet, Una Mas Jazz UNACD-10-01, XRCD24 (2010).
    • Clifford Brown, All Stars, EmArcy/Mercury M.E. PHCE-3063, “2496 Spectrum Rainbow CD”, CD (1954/1996).
    • David Crosby, Croz, Blue Castle Records BCR1142-1, CD (2014).
    • Depeche Mode, Policy of Truth, Mute CD BONG 19, singiel CD (1990).
    • Dinah Shore, Vivacious, RCA/BMG Japan BVCJ-37260, “RCA. 100 Years of Music”, K2 CD (1960/2002).
    • Ella Fitzgerald, Clap Hands, Here Comes Charlie!, Verve/Victor Entertainment VICJ-011-4052, XRCD24 (1961/1998).
    • Elvis Presley, Elvis is Back!, RCA/BMG Japan BVCM-37088, “Living Stereo”, CD (1960/2002).
    • John Coltrane, Coltrane’s Sound, Atlantic/Rhino R2 75588, CD (1964/1999).
    • Miles Davis, Bags Groove, Prestige/JVC JVCXR-0046-2, XRCD (1955/1987).
    • Muse, The Resistance, Warner Music Japan WPZR-30355-6, CD+DVD (2009).
    • The Doors, The Doors, Electra/Warner Music Japan WPCR-12716, CD (1967/2007).
    • The Rolling Stones, Exile on Main St., Atlantic/Universal Music Company (Japan) UICY-40001, Platinum SHM-CD (1972/2013).
    • Włodzimierz Nahorny, Jej portret, Polskie Nagrania Muza/GAD Records GAD CD 006 (1965/2013).
    Japanese editions of CDs and SACDs are available from

    Musically, this year started off fantastic. And February surely surpassed itself. I ordered tickets for three concerts of the Misteria Paschalia Festival, GAD Records announced the release of Show Band’s album Punkt styku, both on CD and LP (I ordered both versions), Mr. Krzysztof Duda, author of the album Altus that I reviewed in the February editorial (see in the archive section), contacted me and we arranged an audition of recordings straight from him (there was a mastering fault in the first release that is supposed to be corrected in the second release), Sony Music announced the release of the entire Depeche Mode catalog on mini LP, its mastering and Blu-spec 2 (I already ordered the whole set from CD Japan), and David Crosby released his new album. I will dedicate separate articles to each one of them, but let me now say a few words about Crosby.
    His new album Croz has been recorded in several different studios, and most of the guest musicians recorded their parts "remotely" in still other places. This is what recording an album looks like these days and there is nothing to get offended about. You need a lot of experience to mix it all as good as on the new album from The Byrds’ musician. The album’s sound is coherent and good. There are better and worse recorded tracks, as each of the studios involved has left its "mark". It shows, among others, in a decreased sound volume of the leading vocal and guitars on some tracks, as well as a decrease in guitars’ sonority and "presence". On the best recorded tracks, e.g. The Clearing, everything is in place and fits perfectly.

    While these are not major changes, they are audible on quality audio gear and affect our perception of music. They are even more pronounced on top audio components, but their impact on the reception is smaller - another audio paradox. The reason for that is that a good system is capable of going over the music production layer and get straight to the performance layer. Not by negating the former but rather by showing it as something separate, something "next" to music, like a turntable crackling and travel noise. For that to be possible, we need high resolution, good selectivity and above-average micro-dynamics. But the most important is timbre differentiation.
    Audio Research SP20’s behavior seemed extremely interesting in this context. The official trademark Audio Research catchword featured on all its components is "High Definition". This can be explained in different ways, but the basic meaning is probably that of 'high resolution'. Given the sound of all recently reviewed AR components combined with my impressions after auditioning the SP20, I would rather say that their trademark is something else: "Warm Definition". That, in my opinion, includes the whole of what these components are and what they are not.
    The point is that the sound of the preamplifier under review is saturated and full. It’s a truism, as this is true of all AR components. The sound is palpable - another truism. But there is no sense of a slight roll-off on the edges of the frequency range, which is something I hear for the first time. The thing is that all the AR products from the Reference Series offer a charming and incredibly saturated midrange. The top and bottom ends are rounded, although they are strong. Listener's attention is drawn away from them, however, as what dominates is the frequency range that includes vocals, guitar, violin or cello, and also because of the method of shaping the attack transients. Bass and treble are present, too, but the first impression is different.

    SP20’s sound is shaped differently. The bass is not as deep as that of the Reference 5SE or the best preamplifiers I know, including the Dan D'Agostino Momentum Preamplifier and the Ayon Audio Spheris II (I am yet to audition the Spheris III). The treble is not as strong and high. And yet it seems that both SP20’s bass and treble are much more pronounced than in all the AR components mentioned above.
    It seems that the manufacturer has attempted to adjust the SP20’s sound to fit the systems in which it is likely to operate - pragmatism is a valuable quality. Stronger than usual frequency edges - not objectively strong but in comparison to other AR components - are built by bringing the phantom images closer to the listener and focusing the sound in the dense space on the speaker line. It is full of emotion and music information.
    At the same time, the preamplifier sounds very "harmonic". By this I mean the ability to convey the harmony of vocals and instruments that sound together like a single large source, while individual tones are still clear. The SP20, like other components from this manufacturer, is not particularly selective, hence there is no use expecting a clear separation and isolation of sound sources. Its value and advantage over many other excellent preamps is based on unity in diversity. Crosby's vocals were mixing perfectly with other supporting vocals, but it was not possible to confuse that with a chorus effect on a single vocal line. It was a true harmony, a trademark and a gift that God or someone (if you believe in something/someone else) put in the throat of this former drug addict, alcoholic and at the same time - as it happens - a phenomenal musician.
    I have lingered on the new album from the former member of The Byrds because it’s been a pleasant surprise for me. Yet it is not the only record that will show what I’ve just described. The preamplifier under review will treat each album with attention and concentration. It was true with Anita Lipnicka’s Vena Amoris as well as with dirty produced The Resistance by Muse. Listening to Uprising from the latter album was particularly instructive, because despite the poor selectivity of vocals and rather poor stereophony of this recording, it showed great rhythm, without the sounds merging into one or trailing between the speakers.

    SP2The SP20 and the headphones

    The preamplifier sounded great on speakers. Despite that, it is "the SP20 and the headphones" that seems to me the central motif. Paired with the best available headphones, the Audio Research retains the basic sonic characteristics of the Reference series preamplifiers. These include a thick midrange, palpable and warm tonality and exceptionally refined internal differentiation of colors and dynamics. It adds to that stronger frequency band edges, which opens the door to much more audio systems. Hence, perhaps somewhat paradoxically as we are talking here about the high-end for sensible money, it is the most versatile components of this type in AR offer that I know of. It also takes the lead in terms of functionality, because in addition to line input it also sports a very good phono stage (which I didn’t listened to long enough to make a separate review, but it was a really great and dense sound) and headphone amplifier. Let me now focus for a moment on the latter.
    Headphone amplifiers implemented in preamplifiers are, to some extent, a pleonasm. For many designers, the difference between one and the other is small and reduced to the output stage design, and often simply the change of its gain level. I think that is the reason why there are no good preamps that at the same time make for good headphone amplifiers. In my experience, only specialized products - either a preamplifier or headphone amplifier - are capable of high quality sound. Hence, I treat the presence of headphone jack in preamplifiers with a pinch of salt, seeing it as another functionality but not one really worth my attention.

    The sound I got from the SP20 paired with the difficult to drive HiFiMAN HF-6 magnetostatic headphones was a real surprise for me. From the first track it was clear to me that we’re talking here about a very mature sound. It took me quite some time, however, to properly assess its caliber and compare this component of the Audio Research preamp against the reference Bakoon HPA-21 headphone amplifier.
    Repeated tests proved that the Korean unit still came up tops. It exceeded in terms of the depth of sound and resolution. Its bass definition was also clearly better. Except that the same arguments for it may be cited when the HPA-21 is pitted against any other headphone amplifier. As a matter of fact, the SP20 sounded so good that if I had it in my system I wouldn’t think of buying the Bakoon, even though, objectively speaking, the latter one is better. What the American preamplifier offers is actually so good, so complete and so satisfying that it leaves us listening to music with pleasure, without wondering whether "it could be better."
    The depth and lightness of conveying the music information are impressive. I don’t mean here the tonal lightness, for this is a deep and dense. The soundstage – or actually headstage, limited by headphones’ design - is fantastic, even better than what you hear through the speakers. Not to mention that the SP20 is capable of driving basically any headphones. Way to go!


    Ken Kessler, an admirer of Audio Research products in his the review of the SP20 published in the February issue of "Hi-Fi News & Record Review" says that “the subtleties between the SP20 and the REF 5SE can all be ameliorated or even eliminated by a variable we must never undervalue: system synergy” ("Hi-Fi News & Record Review", February 2014, Vol. 59, No.02, p.23). All I can say is amen brother, I fully agree but on a completely different matter: the value of the Reference 5 MkII and the SP20 is the same; I would even venture to say that the sound quality of both is on the same level. This is a remarkable achievement. However, they significantly differ in their sonic characteristic and the difference is audible irrespective of an audio system in which each preamp will be auditioned. Ken is right to turn our attention to the context in which the unit will work, but in my opinion we cannot talk about the "equivalence" of sound of these two preamplifiers.
    The SP20 presents a more universal and more open sound, with most of the events - and there are really lots of them - taking place in the foreground. Hence, the top end and bottom are clearer and more "present". We get outstanding rhythm and beautiful tonality. Resolution is exceptional, although it doesn’t go hand in hand with selectivity, the latter not being a particularly strong point of components from Plymouth. Hence, sound definition is not very clear, which can also be said of the differentiation of sonic texture and body.
    However, those looking for the latter should listen to the SP20 to know what they are missing. They will be met with a fantastic saturation and density as well as excellent tonality - slightly warm, saturated and tangible. That is exactly what the term "Warm Definition" intends to describe: a fantastically defined, warm tonality. The SP20 is just that - no less, no more.

    Tube preamplifiers are sensitive to the type of surface they sit on. Although there are various ways to minimize tube microphonics, it can’t be completely eliminated. Other components such as relays, PCBs, capacitors or power supplies are also subject to microphonics. Hence, you need to be careful where you put the SP20. In my case, it was seated on the Acoustic Revive RST-38H air board on top of my Finite Elemente Pagode Edition rack. You can also think of adding isolation feet. The unit was powered by the Harmonix X-DC350M2R Improved-Version power cord. The SP20 was compared against my reference Ayon Audio Polaris III [Custom Version] preamplifier and directly to the variable output of my Ancient Audio Lektor Air V-edition CD player. For a while, I also had the opportunity to listen to the SP20 phono stage using the TechDAS Air Force One turntable (with the Dynavector XV-1 cartridge).

    I talked about the Audio Research tube legacy, and not without a reason. The SP20 sports no less than four 6H30 dual-triodes, also known from BAT amplifiers, Ancient Audio and Loit CD players, as well as Ayon Audio preamplifiers. The faceplate looks very "modern", though. The 1970s were the time when vacuum tubes were considered the height of anachronism, and yet the unit looks like it was taken straight from that time, while audio products from the second decade of the 21st century are more and more often equipped with touch screen displays, only to mention the two-piece Alluxity (see HERE) amplifier. Two knobs are used for volume control and input selection. The front display shows the current active source and the volume level. The latter is set in the 0-103 range, in 1dB steps. The 4.3-inch LCD touch screen allows to control various menu settings. We can read out tube service time, change display brightness, set gain for individual inputs as well as change their name, adjust a preferable power-up volume level (separately for speakers and headphones), and set cartridge load for the phono input (100, 200, 500, 1000 Ω and 47 pF kΩ/200). There are also settings for the absolute phase, mono or stereo mode and channel balance. Below the knobs are small push buttons to turn on the unit, activate the mute mode, and route the signal either to the regulated outputs on the rear panel or to the 6.3mm headphone jack on the front.
    The rear panel connectors are all high-quality. The RCAs seem to come from Cardas or CMC. The gold-plated XLRs are from Neutrik. There are 6 RCA inputs, including the phono input, and 2 XLR inputs. The outputs are a single pair of RCAs and two pairs of XLRs. There is also an unbalanced tape output. The unit can be controlled via a RS-232 port and Remote IR input and also features a 12-volt remote trigger port. The enclosure is fully made of aluminum. While the faceplate is a thick aluminum panel, the rest of the enclosure is made from bent aluminum sheet – the top and sides are quite thin and flexible. It’s worth thinking of something that could weigh down the top without blocking the air vents. The supplied small rubber feet look a bit silly, too. The remote control unit is a well-known affair and has been used by AR for years. The only difference is that it now comes in an aluminum rather than plastic housing.

    The preamplifier sports a fully balanced topology and operates in pure class-A with zero feedback. The line and phone stages feature JFET transistors in the input and 6H30 triodes in the output. Both stages also use high quality coupling and bypass capacitors. The whole electronic circuit is mounted on several PCBs, with the main board occupying the entire bottom. The input FETs are housed in transparent plastic cups filled with a kind of silicone. It is probably to minimize microphonics and is also used for temperature compensation of the transistor in both halves of the signal. Cartridge load is set via precision resistors switched by reed relays. The inputs are selected via relays. The next stage is tube-based and features two 6H30 dual-triodes with rubber rings to minimize microphonics. The output stage looks similar, although it is much more complex and it is here that the largest coupling capacitors are. The headphone amplifier is mounted on a separate board. It is fed the signal that is taken after the input tubes (and FETs), which is amplified in the LME47920 integrated circuits from Texas Instruments followed by the LME49600 high-performance buffers from the same manufacturer.
    A significant part of the interior is occupied by the power supply unit. Its base is a large R-core transformer with three secondary windings. Voltage filtering and regulation is in six cascaded stages, and the components include capacitors from Nichicon, Wima, Rel-Cap and MultiCap. The preamp circuit features precision resistors throughout.

    This is professionally designed audio component from a manufacturer that knows its stuff and that is large enough for its products to be consistently reproducible and small enough to control every stage of production. The more so that all its products are made in the USA. Let’s add that the preamplifier comes with a very well put together and really helpful instruction manual.

    Technical Specifications (according to the manufacturer)
    Frequency Response
    Line: +/- 3dB 2 Hz to 80 kHz; -3dB 0.8Hz to 220 kHz
    Phono: +/- 0.1dB of RIAA 10Hz to 20kHz; +/- 0.4dB 5Hz to 80kHz
    Headphone: +/- 0.05dB 20Hz to 20kHz; -3dB 0.8Hz to 220kHz

    Line: <.003% at 2V RMS, Balanced output (XLR)
    Phono: <.005% at 3V RMS output, to Record output
    Headphone: <.009% at 1V RMS output

    Line: 13.8dB, Processor: 0dB
    Phono: 58dB @ 1KHz to Record output
    Headphone: 11.3dB

    Line: <-101dBV volume at max.
    Phono: <-77dBV to Record output 
    Headphone: <-88dBV volume at max.

    Channel Separation
    Line: > 105dB Balanced output
    Phono: >76dB to Record output
    Headphone: >62dB

    Signal to Noise Ratio
    Line: >125dB Balanced output
    Phono: >94dB to Record output
    Headphone: >110dB

    Rated Outputs:
    Line: 2V RMS (1V RMS SE) into 200k ohms balanced load (maximum balanced output capability is 18V RMS at less than .5% THD+N at 1kHz)
    Phono: 0.5V RMS into 100k load at Record output (maximum output capability is 25V RMS)
    Headphone: 6V RMS maximum into 30 to 300 ohm load

    Input Impedance: 120k ohms Balanced, 60k ohms SE; Phono impedance programmable (100, 200, 500, 1000 or 47k ohms w/200pf unbalanced)
    Output Impedance: 500 ohms Balanced, 250 ohms SE; 1000 ohms Record Out SE; <.05 ohms Headphone SE.
    Power Consumption: 77 W (max ) / standby 2,7 W
    Dimensions (W x H x D): 480mm (19”) x 134mm (5.25”) x 420mm (16.5”)
    Weight: 17.8 lbs. (7.4 kg) Net; 27.8 lbs. (10.5 kg) Shipping



    - Turntable: AVID HIFI Acutus SP [Custom Version]
    - Cartridges: Miyajima Laboratory KANSUI, review HERE | Miyajima Laboratory SHILABE, review HERE | Miyajima Laboratory ZERO (mono) | Denon DL-103SA, review HERE
    - Phono stage: RCM Audio Sensor Prelude IC, review HERE
    - Compact Disc Player: Ancient Audio AIR V-edition, review HERE
    - Multiformat Player: Cambridge Audio Azur 752BD
    - Line Preamplifier: Polaris III [Custom Version] + AC Regenerator, regular version review (in Polish) HERE
    - Power amplifier: Soulution 710
    - Integrated Amplifier: Leben CS300XS Custom Version, review HERE
    - Stand mount Loudspeakers: Harbeth M40.1 Domestic, review HERE
    - Stands for Harbeths: Acoustic Revive Custom Series Loudspeaker Stands
    - Real-Sound Processor: SPEC RSP-101/GL
    - Integrated Amplifier/Headphone amplifier: Leben CS300XS Custom Version, review HERE
    - Headphones: HIFIMAN HE-6, review HERE | HIFIMAN HE-500, review HERE | HIFIMAN HE-300, review HERE | Sennheiser HD800 | AKG K701, review (in Polish) HERE | Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, version 600 - reviews (in Polish): HERE, HERE, HERE
    - Headphone Stands: Klutz Design CanCans (x 3), review (in Polish) HERE
    - Headphone Cables: Entreq Konstantin 2010/Sennheiser HD800/HIFIMAN HE-500, review HERE
    System I
    - Interconnects: Acrolink Mexcel 7N-DA6300, review HERE | preamplifier-power amplifier: Acrolink 8N-A2080III Evo, review HERE
    - Loudspeaker Cables: Tara Labs Omega Onyx, review (in Polish) HERE
    System II
    - Interconnects: Acoustic Revive RCA-1.0PA | XLR-1.0PA II
    - Loudspeaker Cables: Acoustic Revive SPC-PA
    System I
    - Power Cables: Acrolink Mexcel 7N-PC9300, all system, review HERE
    - Power Distributor: Acoustic Revive RTP-4eu Ultimate, review HERE
    - Power Line: fuse &#8211; power cable Oyaide Tunami Nigo (6m) &#8211; wall sockets 3 x Furutech FT-SWS (R)
    System II
    - Power Cables: Harmonix X-DC350M2R Improved-Version, review (in Polish) HERE | Oyaide GPX-R (x 4 ), review HERE
    - Power Distributor: Oyaide MTS-4e, review HERE
    - Portable Player: HIFIMAN HM-801
    - USB Cables: Acoustic Revive USB-1.0SP (1 m) | Acoustic Revive USB-5.0PL (5 m), review HERE
    - LAN Cables: Acoustic Revive LAN-1.0 PA (kable ) | RLI-1 (filtry), review HERE
    - Router: Liksys WAG320N
    - NAS: Synology DS410j/8 TB
    - Stolik: SolidBase IV Custom, read HERE/all system
    - Anti-vibration Platforms: Acoustic Revive RAF-48H, review HERE/digital sources | Pro Audio Bono [Custom Version]/headphone amplifier/integrated amplifier, review HERE | Acoustic Revive RST-38H/loudspeakers under review/stands for loudspeakers under review
    - Anti-vibration Feets: Franc Audio Accessories Ceramic Disc/ CD Player/Ayon Polaris II Power Supply /products under review, review HERE | Finite Elemente CeraPuc/ products under review, review HERE | Audio Replas OPT-30HG-SC/PL HR Quartz, review HERE
    - Anti-vibration accsories: Audio Replas CNS-7000SZ/power cable, review HERE
    - Quartz Isolators: Acoustic Revive RIQ-5010/CP-4
    - FM Radio: Tivoli Audio Model One