Audio Space Reference Two Preamplifier Quick Manual

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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."

Value "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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SoundStage! Equipment Review - Audio Space Reference Two Preamplifier (4/2008)

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