October 2007Audio Space Reference One Mono Amplifiers
by Ken Choi
Could anyone but an audiophile have written this? Scenes such as this provide a small validation for our hobby -- a pastime often marginalized by non-audiophile friends and family.
Movies aside, Hong Kong-based Audio Space is a very real company that has been building and refining its line of tube-based audio electronics for over 15 years. It's a brand that has enjoyed considerable growth in the Far East. About two years ago, Audio Space doubled the size of its production facilities and moved them from Hong Kong to the modern, industrialized city of Zhuhai in southern Guangdong province, just across the border from Macau. Some of the earlier Audio Space products, produced under the Houston Audio label, had previously made it to North American shores, and, at least in my area, they were found in shops that you would not typically associate with high-end audio. Over a year ago, stable distribution through Gini Systems in the United States and Charisma Audio in Canada was secured, with these companies committed to supporting and servicing the Audio Space brand locally.
Like many Chinese audio concerns, Audio Space is probably best known for producing good quality gear at attractive price points, although Westerners might consider the equipment to fall a notch or two below European and North American standards. I suspect that these sentiments, whether justified or not, motivated Peter Lau, Audio Spaces owner and chief engineer, to conceive and produce his "no holds barred" Reference products. These include the Reference One amplifiers first introduced in 2004 and under scrutiny here, along with the Reference Two preamplifier, which debuted earlier this year.
Nuts 'n' bolts
At a list price of $19,900 USD per pair, the Reference Ones won't become Audio Spaces bread-and-butter product. Rather, they serve as a statement for what the company can produce with cost being no impediment. For such coin, you will get two massive dual-layer stainless-steel chassis that are flanked by heat sinks machined out of heavy-gauge aluminum pipe. Each amp measures roughly 19 1/2"W x 11"H x 26"D inches weighs 121 pounds. Power-supply and output transformers are wound in-house, and the amp's "Magic Power" power-supply capacitors are custom made. I did not examine the amps innards. However, I have no reason to doubt the manufacturers claim that highest-quality parts are used throughout. It took the designer over five years of development and tweaking before the amps could be released commercially.
Each Reference One monoblock utilizes a pair of 845 output tubes operating in a triode, class-A, push-pull fashion to produce a reported 75 watts. The circuit features true balanced operation from input to output. A 6N9P is used for the input and a 6N8P does duty in the buffer stage. Lau appears to be a proponent of the 300B, as he uses them here to drive the 845s. Even more unusually, 300Bs are used to provide gain in the companion Reference Two preamplifier. All tubes are sourced from Chinas Shuguang factory, subject to careful selection, and subsequently labeled by Audio Space.
Certainly from the exterior, the Reference One appears as well put together as any component that has graced my listening room. From the thick anodized aluminum front and rear panels and integral adjustable spiked aluminum footers to the silky-smooth operation of the on/off and bias-selector knobs, the Reference One exudes a sense of superior quality. The front panel features a blue backlit meter that reflects the output signal level. This can be toggled to allow for bias adjustment of the 300B and 845 tubes, which is done via pots easily accessible on the top surface of the amp. Hum-balancing pots for each of the big triodes are reached in a similar way. The amp has a user-adjustable feedback loop where you can choose between 0 and 2dB of negative feedback by means of a toggle switch on the front panel. The back panel has provision for RCA and XLR input as well as a standard 15-amp IEC mains receptacle. Separate binding posts are provided for 4-, 8- and 16-ohm loads.
The review pair of Reference Ones were dealer demos and, as such, had considerable run-in time. I auditioned the amps mostly with Wilson Audio WATT/Puppy 7 speakers, although the Sonus Faber Guarneri Homage minimonitors made it downstairs for some listening as well. I used my 845-based Nagra VPA mono amps for comparative purposes. The bulk of the listening was done with my Convergent Audio Technology SL-1 Ultimate Mk 1 preamp, which generally proved to be a fine match with the Reference Ones, whose input impedance is 68k ohms. Audio Spaces own Reference Two preamp was also on hand for some listening. Sources included the original EMM Labs CDSD and DCC2 combo and a Koetsu Onyx / SME V/ Oracle Delphi V vinyl setup. I ran the Koetsu cartridge straight into the preamps, bypassing the step-up transformer that I often use. Speaker cables and interconnects were Purist Audio Designs Venustas.
When the Reference Ones were plugged directly into the wall with Purist Audio Venustas power cords, I noted some ground-loop hum, but powering the amps along with the rest of the equipment through a Shunyata Hydra Model-8 power conditioner completely eliminated it. The Model-8 was fed from a dedicated power line via a Shunyata Anaconda power cord and Acme Audio Labs wall outlet.
Beauty and the beast
Sonically, the Reference Ones did the things that good tube amps do, and they did them very well. They produced an enveloping soundfield and captured the ambience of each recording quite nicely. The imaging was dense, almost thick, and palpable. A rich tonality pervaded whatever music I played. I have not heard a solid-state amp that can come close to reproducing the natural warmth of acoustic instruments the way the Reference Ones did.
If I were to thin out my record collection, at the top of my "keepers" pile would be Oscar Peterson Plays the Cole Porter Song Book [Verve UMJ 3117], John Lewiss The Wonderful World of Jazz [Atlantic 1375] and Gerry Mulligans Night Lights [Philips EXPR 1037]. This is music I enjoy after a hard day at the salt mines -- mellow, moody, and melodic. The Audio Space amps did more than justice to these recordings. Jim Halls guitar on "Two Degrees East, Three Degrees West," from the John Lewis album, was captured with remarkable depth and purity of tone. Hall reappeared in this mini-set on "In the Wee Small Hours of the Morning" from Night Lights. But the highlight of this take on the woeful Sinatra classic was Mulligans warm, rich, sonorous baritone sax. The sound here made me want to recant a comment I made in a previous review about the cello being the most expressive instrument. I suppose there is no room for absolutes in audio reviews.
The Oscar Peterson album is one of my absolute favorites. Musically, its hard to beat Petersons confident covers of these standards, which also feature Ed Thigpens understated percussion and Ray Browns tuneful lines. The Reference Ones did nothing to detract from the natural and balanced sound of this recording; they introduced no coloration or artifact. They captured this recordings remarkable three-dimensional quality and convincingly suspended the instrumental images in space.
The Reference Ones really showed their mettle when I moved on to more dynamic material. They put out 75 watts of serious drive and at no time showed any sign of strain or compression. They exerted such grip and control that it seemed their power rating had been underestimated fourfold. They simply energized the speakers, resulting in a sense of immediacy that was apparent throughout the audio band.
These amps produced a most impressive bottom end. "In the Still of the Night" from the aforementioned Oscar Peterson album is a cut Ive listened to many times, and I often use it when fine-tuning cartridge setup. Ray Browns bass has never sounded fuller and at the same time more dimensional and defined than with the Audio Space amps, which gave a better appreciation of the nuances of his playing. While bass of this nature is rather subtle overall, headbangers will not be disappointed. Frou Frou makes electronic music that features a female vocalist, Imogen Heap. Several tracks on the band's one and only recording, Details [Island 5869962], contain pounding percussion and bass lines generated, I assume, from chips rather than skins or strings. The Reference Ones rendered the depth and force of this bass surprisingly well. Sure, solid-state bruisers might provide a little more tautness, but the sound here was remarkably controlled and not at all soft or mushy.
My half-speed-mastered version of Bruce Cockburns Dancing In The Dragons Jaws [True North APH(T)-5008] contains a lot of detail and energy in the treble region. This music sounds just as fresh now as it did almost 30 years ago, when I used it to help me build my first high-end system. On "Hills of Morning," the steely sheen of Cockburns guitar along with some particularly extended cymbal crashes were vividly reproduced without any stridency. Extended decay of piano notes and snare-drum thwacks was indicative of superior high-frequency resolution, as was the airy, detailed quality of the brush strokes on "Be-bop" from Dizzy Gillespies Something Old Something New [Mercury 6336-304]. "Be-bop," by the way, is characterized by such a frantic tempo -- the Reference Ones conveyed the pace and drive of this music with vigor -- that I could easily feel exhausted after listening intently to it.
The midrange was similarly infused with this intense energy. On quieter passages this manifested as an eerie sense of presence. Rickie Lee Joness Pop Pop [Geffen GEFD-24426] contains a wealth of tonally rich material that is wonderfully recorded. On "Ill Be Seeing You" Jones materialized between the speakers, the purity of her voice and her idiosyncratic phrasing presented with a tangible quality. This drew me into the music, allowing the considerable emotion she put into this performance to be made much more evident. The warm, resonant tones of the accompanying clarinet and nylon-stringed guitar were icing on the cake. Taken together with the immediacy of Joness vocals, the sound here made for an immersive listening experience.
When the music became louder and more dynamic, however, this energetic presentation could make itself apparent as a hardening of the upper midrange that can range from almost unnoticeable to unpleasant. On "Be-bop," the harder Dizzy blew the more the sound of his trumpet glared. This quality was apparent on more than a few recordings, with piano crescendos, horns, massed strings, and even spirited vocals being subject to some degree of audible distortion when the material was closely miked and the going got loud. The effect was somewhat reminiscent of a super-sensitive horn loudspeaker pushed by an amplifier that's too powerful for it.
I decided to take some corrective measures. I spent a fair bit of time trying to sort this out. I did most of my listening to the Reference Ones with no negative feedback. Toggling in 2dB of negative feedback ameliorated this hardening, but did not eliminate it. This came at the expense of losing some of the presence the amps produced when run without negative feedback. With the WATT/Puppy 7s, I slightly preferred the sound of the amps through their 8-ohm taps, but the hardness was still there when the speakers were connected to the 4-ohm taps.
While listening to Benny Carters Jazz Giant [Contemporary Records OJC-167], I proceeded to swap equipment around. This is unquestionably a fine-sounding album but in my reference system the Audio Space amps lent an edgy quality to Carters closely miked alto sax and trumpet solos that I had not previously noted. This was made considerably less evident when Audio Spaces own Reference Two preamp was inserted in place of my CAT preamp. When the Sonus Faber Guarneri Homage speakers were added, I perceived some of the hardness with the CAT preamp in the chain. With the Audio Space combo driving the Guarneris, forward and dynamic material was just that, with no edge at all.
Perhaps the Audio Space electronics work particularly well together. The CAT preamp and Wilson Audio speakers are not terribly forgiving of associated equipment, but the Sonus Faber speakers are far more accommodating. Does this mean that the Sonus Faber speakers are superior? Does a flaw reside within the CAT preamp or Wilson speakers, or is the associated equipment at fault? These types of questions have no correct answer, but they do provide nice fodder for audio discussion boards. Suffice it to say that the Reference One amplifiers require careful consideration with respect to system matching.
Apples to apples?
Comparing the Audio Space amps to my reference Nagra VPA monoblocks ($19,995 per pair) helped me get a better handle on the performance of both. Like the Reference Ones, the VPAs are a class-A, push-pull design based on 845 output tubes, which in this case produce 50 watts. For the past two years I have been using metal-plate 845M tubes from Shuguang. Over the years I have also replaced the small signal tubes in these amps. Presently they are E182CC (Philips Miniwatt) in the input stage and a pair of 12AX7s (Ei Elites) as drivers. Each VPA weighs in at 30 pounds -- that being about one-quarter the mass of the Audio Space amp. Both amps generate a similar amount of heat, which is considerable.
On standby, the Audio Space amps are dead quiet, while the Nagras display some inherent noise to which Ive become acclimated but which I still wish was not there. The Reference Ones are clearly the more powerful-sounding of the two, with a seemingly infinite amount of headroom and a presentation that is visceral. Dont be misled by the diminutive size of the Nagra amps, however; they produce more-than-satisfying drive and punch, especially at my normal listening levels. When I cranked up "its good to be in love" from Frou Frous Details, however, the VPAs just couldnt keep up, gently running out of steam at the point where the Reference Ones soldiered on in an unflappable fashion.
The Audio Space amps are characterized by a dense, muscular sound, whereas the Nagras appear somewhat more lithe and quicker by comparison. Both amps are superbly expressive and excel at portraying the harmonics, textures and details present in the music, but they present these rather differently. Through the Reference Ones, the music arises from a deep, dark backdrop; the illusion that the performers are present in my room was readily created. In contrast, the Nagra amps' background appeared more brightly lit and open. It was easier to hear through the performance and into the surrounding space -- the illusion was that of being transported to the recording venue.
In summary, the Nagra amps are more transparent, while the Audio Space amps sound more vivid. Two obvious conclusions: Listener preference will dictate which presentation is superior, and if you're shopping in the $20,000 price range, both amps are worthwhile auditions.
I reviewed the Reference Ones "as is," with a minimum of tweaking. Stock power cords were not supplied with the demo amps, so I used the cords I normally use with my Nagra amps and did not experiment further. Certainly, replacing the stock tubes, even with other current-production offerings, would be expected to change the sound of the Reference Ones, and perhaps bring me closer to sonic bliss.
Connecting amplifiers to a given set of speakers is also a way of using them "as is." The match may or may not be optimal, and in the case of the Reference Ones and the WATT/Puppy 7s, the pairing was not completely felicitous. While there was little to fault when the amps were used with the Sonus Faber Guarneri Homage speakers, the Wilson Audio speakers did a much better job of revealing the considerable strengths of the Audio Space amps. I am apt to conclude that they were also better at exposing their weaknesses.
I relished the time I spent with Audio Spaces statement amplifiers and found their build and functionality to be beyond reproach. However, I am left with a sense of disappointment about the upper midrange, which seemed to overshadow all of the things these amps did so well. Obviously, amps of this cost and caliber need to be carefully evaluated in any prospective owners system. In my system, the potential of the Reference Ones was clearly apparent, but it was not fully realized.
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