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Home Audio

Equipment Review

April 2008

Audio Space Reference Two Preamplifier

by Ken Choi

Even though I usually favor a simple

tumbler of house plonk, I enjoy

reading the occasional wine review.

Unlike audio reviews, wine reviews

are near-ubiquitous, appearing as

they do in the weekend newspapers

and even on the all-news radio

station I listen to during my daily

commute. Like audio reviews, an

elaborate, descriptive vocabulary has

evolved that allows the reader to

savor secondhand the subject under

review – assuming, in this instance,

that his palate is intimate with the

flavors of gooseberry and buttery

oak. Interestingly, while they

probably exist, I’ve not seen reviews

of bottled waters, despite the wide

choices available, with some of

these in "fine" restaurants and

costing more than the wine I usually

order. Variously sourced or

processed, waters clearly differ in

taste, but putting these differences

into words would present an onerous

task, at least to me.

In theory, the preamplifier is audio’s

drinking water, but some are more

like wine. The preamp ideally serves

as a totally transparent conduit,

allowing the source signals to pass

largely unadulterated on their way to

the amp-speaker unit. But in practice

we all know that a preamp can exert

subtle or not-so-subtle and pervasive

effects on the system’s overall

sound, which is why so many are

available using diverse technologies

to provide the critical first stage of

gain.

The $9900 USD Reference Two is

Hong Kong-based Audio Space’s

entry into the ultra-high-end

preamplifier sweepstakes. Released

at the beginning of 2007, it is the

second product in Audio Space’s

Reference series heralded by the introduction of the Reference One monoblock power

amplifiers, which I reviewed earlier. Built and voiced to standards aimed at competing in the

upper end of the worldwide marketplace, the Reference series has now grown to include the

Reference Three mono amplifiers and the Reference 3.1 integrated amplifier, both of which

offer the user a choice of output tubes.

The Reference Two is a full-function tube preamp that features preservation of the signal in a

fully balanced fashion from input to output. A pair of 6N9P high-gain octal tubes do duty in

an input/driver stage, and a pair of 300B tubes per channel serves in an output stage. Another

pair of 6N9Ps act as cathode followers, allowing for driving long cable runs and solid-state

amplifiers with low input impedance. The phono stage, which is not balanced, uses a pair of

more pedestrian 12AX7s for moving-magnet gain. Instead of requiring step-up transformers,

moving-coil signals are processed by 6922s in a gain stage that features adjustable input

impedance. Another 6922 is used as an output buffer to maintain signal strength. As with the

Reference One amplifiers, all tubes are culled from the cream of Shuguang’s crop. The

Reference Two is the world’s only truly balanced, 300B-based line driver.

The preamp’s output impedance is less than 2000 ohms. The line stage provides 18dB of

gain, and the moving-magnet phono stage 37dB. Moving-coil gain is an additional 20dB, for

a total of 75dB. Two additional 1.5dB steps of moving-coil gain are user selectable via a

front-panel knob. A front-panel knob also selects loading for moving-coil cartridges.

Review Summary

Sound "Allowed the music to breathe with utter ease

and naturalness," "created a remarkably open

and spacious sound" and reproduced voice

"with a kind of clarity that is a little difficult to

describe." "The soundstage expanded in all

dimensions but did not seem exaggerated.

Depth and layering were especially

impressive, with instrumental and vocal

images rendered with increased separation

and enhanced spatial resolution."

Features "The Reference Two is a full-function tube

preamp that features preservation of the

signal in a fully balanced fashion from input to

output. A pair of 6N9P high-gain octal tubes

do duty in an input/driver stage, and a pair of

300B tubes per channel serves in an output

stage. Another pair of 6N9Ps act as cathode

followers, allowing for driving long cable runs

and solid-state amplifiers with low input

impedance." "The line stage provides 18dB of

gain, and the moving-magnet phono stage

37dB. Moving-coil gain is an additional 20dB,

for a total of 75dB."

Use "I did have one operational issue with the

Reference One: Tube microphonics were

evident and a distraction at times. However, if

my experience with the Reference One

amplifiers is any indication, the ingenious

folks at Audio Space will come up with a

solution to this problem."

V

alue "I would urge anyone shopping for a world-

class preamp to use with digital sources or a

separate phono stage to give the Reference

Two a serious listen, because its line stage is

seriously good."

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