Audio Space Reference 2 Linestage Preamplifier

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Tubed power amplifiers
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Audio Space Reference 2
Audio Space Reference 2 Linestage Preamplifier

The Audio Space Reference 2 from Hong Kong audio engineer Peter Lau is a genuine rara avis—a fullfunction, fully balanced preamplifier that uses two matched pairs of 300B directly heated triode tubes in its output stage.

Yes, you read that right: 300Bs. While there are plenty of 300B-based amplifiers—single-ended and pushpull—on the market, outside of David Manley’s “Neo-Classic,” which isn’t a balanced design, and a few oddities from DIY companies, I know of no other 300B preamp.

There are reasons for this. As Audio Space itself notes, the 300B is “extremely microphonic and highly susceptible to RFI and EMI.” On top of this it is a lowmu (low-gain) power tube, which, coupled with its vulnerability to noise, would seem to make it unsuitable for boosting the tiny signals that a preamp has to cope with.

As David Manley did, Lau has gotten around some of these inherent problems by using two cascaded gainstages: first, two 6SL7 dual-triodes to boost the lowlevel signals from phonostages and CD players, and second, two matched pairs of 300Bs to amplify the voltage and current of the 6SL7s to line-level.1 (Two more 6SL7s are used as cathode-followers to buffer output, making the Audio Space suitable for use with solid-state as well as tube amplifiers.) Beyond their similar dualgainstage topologies, the Manley Neo-Classic and the Audio Space don’t have much in common, as the $9.9k Reference 2 is one of those ultra-high-end flagship designs—the product of many years of research and development—in which no expense has been spared.

For instance, to isolate tubes from noise and vibration Lau houses his circuit in a forty-six-pound(!), double-layered chassis of thick metal alloy and top-grade stainless steel, with additional shielding provided by heavy-gauge anodized aluminum plates at the front and rear of the unit, heavy-gauge anodized aluminum pipe on either side, and spiked aluminum feet on its bottom. To further isolate the tubes from vibration-induced microphonics, the 300Bs are seated in what Audio Space calls “Floating Sockets” made from “the same patented rubber material that is used in earthquake prevention in the construction industry in Japan.” It goes without saying that all circuit parts are first-class (custom-made metal-film capacitors from TOPCap of Germany, custommade low-leakage power transformers, pure silver wiring, ALPS controls, RS switches from Great Britain, TopLine WBT terminals, etc.), and that wiring is point-to-point. The tube complement, which in addition to the tubes already mentioned also includes two 12AX7s (for the moving-magnet phonostage of the Reference 2—remember, I said this was a full-function preamplifier) and two 6922s (for the moving-coil phonostage), are highly select Chinese numbers.

So…what we have here isn’t just odd; it’s ostentatiously odd. A 300B preamplifier built like a Vacheron Constantin watch that includes moving-magnet and moving-coil phonostages in addition to a fully balanced linestage and boasts eye-rubbing bandwidth and distortion numbers. (Audio Space claims frequency response out to 100kHz ±1dB, a signalto-noise ratio in the linestage greater than 88dB, and overall noise lower than 0.15mV at minimum and maximum volume settings—from a 300B preamp!)

Of course, none of this overkill addresses the core question of why anyone would want to build a 300B preamplifier in the first place. To answer that you’ll have to give the thing a listen, as I did.

Rather than keep you guessing, let me say at the start that as a linestage in my reference system—Walker Proscenium Black Diamond record player, Air Tight PC-1 cartridge, ARC PH7 phonostage, ARC 610T monoblock amplifiers, MAGICO Mini/Wilson-Benesch Torus “supersystem,” and Tara Labs “Zero” interconnect and “Omega” cables—the Audio Space Reference 2 sounds in the midrange less like hi-fi and more like the real thing than virtually any other preamp I’ve auditioned.

A large part of the Reference 2’s extraordinary midband naturalness has to do with the way it “disappears” as a sound source (and allows the components it feeds—both amps and speakers—to more fully disappear). Many of the telltale signs that alert us to the fact that we are listening to and through electromechanical devices simply aren’t there with the Audio Space—or not there in the usual abundance. I attribute this to three salient virtues.

First, there is the Reference 2’s lack of grain. The slight rough burr on the edges of transients, the faint granular noise in the silences between notes or in the air of the recording venue, the specular electronic sheen that overlies voices and instruments the way the glass of a direct-view TV overlays the picture have been virtually eliminated. Second, and combined almost inextricably with this, is the preamp’s neutrality. Usually when one thinks “300B,” one thinks of a warm, gorgeous, euphonically colored sound, rich in second harmonics. Here the sound is beautiful, of course, but utterly natural—non-colored, non-electronic. Gone, or seemingly so, are the slight persistent darkness or brightness, the artificial warmth or coolness (or warmth and coolness combined), the exaggerated roughness or smoothness that are typically part and parcel of the stereophonic reproduction of timbres. In the midband, the Reference 2 isn’t just a clear window on the music; it is very nearly an open window. Third, and once more closely allied to its grainlessness and neutrality, is the Audio Space’s unusually realistic midrange presence. Instruments, solo and ensemble, are naturally sized, highly dimensional, more fully “there.” Minus the usual haze of electronic grain and coloration, they hang in space—freestanding, full, lifelike—with little of the customary sense that they are being projected by amps and loudspeakers. Their colors and dynamics seem to unfold in natural swells and gradual subsidences—continuously, rather than in a series of sharp, discrete steps—and those colors and dynamics are more completely “filled in,” more solidly present, than they are with other preamps.

With really good recordings the sonic results are magical. Whether it’s a solo voice, like Joan Baez’s sweet, joyous the close of the “Jocul cu bata” section of the Rumanian Dances, sounds every bit as electrifying as it does through the ARC Ref 3 or MBL 6010D. Ditto for the timp strikes on the fine Columbia recording of Lutoslawski’s Les Espaces du sommeil.)

Nowhere does the Audio Space lack for air, size, and bloom. This is a big sounding preamp, with life-sized images on a huge, airy soundstage that is impressively deep and wide and tall (though not as wide and deep as that of the ARC Ref 3).

Thus far I’ve talked about the Audio Space Reference 2 as a linestage preamplifier, but it also includes, as noted, sophisticated moving-coil and moving-magnet phonostages, with front-panel controls that allow you to adjust gain, loading, and other parameters. Alas, in my room, the mc phonostage wasn’t fully listenable due to RFI and hum. Note that the Audio Space is not entirely to blame for this noise problem; every phonostage I’ve tried in my room is plagued to some extent by RFI and hum. This problem can generally be ameliorated or eliminated by relocating the component, but, in this case, due to the presence of other gear and thesheer size and heft of the Reference 2, I couldn’t situate it in a less noise-prone spot. When I’ve cleared some space, I will reposition the Audio Space and report more completely on what I hear.2

However, on the basis of what listening I was able to do I’d have to say that, like the linestage, the phonostage is big, bloomy, liquid, and beguilingly lovely sounding, quite detailed and dynamic, with good bass—a very respectable performer. That said, it did not have the purity, naturalness, and transparency that the linestage has when driven by the ARC PH7 phonostage. To my ear (and once again bear in mind that this is complicated by the way RF and noise modulated the signal), the phonostage was noticeably darker and more (warmly) colored in balance; in other words, it had more of an audible electronic signature than the brook-clear linestage. I think most music lovers could live with it happily, but I also think there are better phonostages to be had (most obviously, the ARC PH7 with which the Audio Space makes such a grand match).

1 I presume that two matched pairs of 300Bs allow the signal to be split for balanced output, with the positive signal going to one pair of tubes and the negative to the other.

2 Shortly after I finished this review, Alfie Lew, U.S. distributor of Audio Space, informed me that Peter Lau developed a simple fix for the movingcoil phonostage’s RFI problem: “All it took was two 120pF bypass caps, one at the cathode input of each of the two tubes of the phono section.” The fix is now standard on all Reference 2s.

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