Old Faithful

Sydney Morning Herald

Monday December 5, 2005

Greg Borrowman. Greg Borrowman is the editor of Australian Hi-Fi magazine.

Pick the right speakers and this valve amplifier will serve you well, writes Greg Borrowman.

Electronics engineers are baffled by the popularity of hi-fi amplifiers that use old-fashioned valves rather than state-of-the-art bipolar devices or field effect transistors (FETs). One engineer told The Guide that valves' performance may have equalled transistors in the 1960s, when transistor technology was still in its infancy,

but modern transistors and FETs were now superior in every respect. They deliver more power across a wider range of frequencies than any valve amplifier, have virtually no measurable circuit noise and do not introduce distortion to the music signal.

What our engineer informant overlooked is that only electrical engineers will buy an amplifier because its circuit noise is too low to be measured or because of an extended frequency response. Conventional consumers buy hi-fi amplifiers to listen to music and if one amplifier makes that music sound better than another, that's the amplifier they're likely to prefer no matter what its technical deficiencies. The difficulty with this subjective approach to buying hi-fi is that it's possible for an amplifier that sounds great with one brand of speakers to sound completely different when connected to another brand.

PrimaLuna's ProLogue One valve amplifier (pictured) is a perfect example of this. Technically, its performance is excellent for a valve amplifier, with a frequency response extending from 3Hz to 64kHz, a signal-to-noise ratio of 100dB and distortion of less than 0.08 per cent at ordinary listening levels. The problem is that the ProLogue One's frequency response depends on the speakers connected to it. Hook up a pair of Magnepan speakers and the ProLogue One's frequency response remains flat, so that all frequencies are reproduced at equal volume. Substitute a pair of Diaspora IV speakers and the ProLogue One will emphasise the lowest and highest frequencies, making them nearly 3dB louder. Depending on the speakers, the parts of the audio spectrum that will be boosted will vary, as will the degree of emphasis, making it impossible to predict how this amplifier will sound with any pair of speakers.

The ProLogue One's circuit also has a low damping factor, with only a limited ability to control any unwanted movement of a speaker's bass driver. As a result, the tone

of the bass will vary depending on the size of the driver cone and whether the speaker cabinet has a bass reflex vent or is completely sealed.

Finally, there's the matter of power output. Rated at 35 watts a channel, we found the ProLogue One delivered this power only at mid-range frequencies. At low frequencies, output fell to just 10 watts a channel. These low wattages mean the ProLogue One delivers high, undistorted volume levels only when connected to speakers with sensitivity ratings of 90dBSPL (decibels sound pressure level) or higher.

Connected to compatible speakers and operated within its output capabilities, we found the sound quality of PrimaLuna's ProLogue One as engaging and musically satisfying as that of any valve amplifier we've heard recently, as well as being richer and warmer than most solid-state amplifiers. It certainly made the music sound fabulous.

As to whether what we heard was true to the original recordings, that's another matter entirely.

Infofile

PrimaLuna ProLogue One Integrated Amplifier

RRP: $2495

Reference Audio Visual Pty Ltd

PO Box 171, Park Orchards, VIC 3114

1800 133 135

info@referenceav.com.au

www.referenceav.com.au

© 2005 Sydney Morning Herald

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