It probably took a bit longer to grow the wood which forms the Mystery One's case. All I know is that nearly a year has passed since I first took delivery of the prototype, and enough detail changes occurred between 'pre-production' and 'shop-ready' to require the loan of a fresh sample. But it was worth waiting for a pre-amp to match the Unison Research Smart 845.

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Whatever the wizards in Italy did to that early Mystery One, as seen at the 1995 Hi-Fi Show and still serving as the demo sample 'on the road', it wasn't a simple retrofit. The rather large, garish metal name-plate on the top has been replaced by one you needn't measure by with surveyor's tools, and the top-plate is now held by four quick-release screws. But those of you who recall the swoopy wood, the long, slender rotary controls and the chic charcoal cover will be pleased to hear that it looks just the same as before: drop-dead gorgeous. Unison Research has cornered the market for sexy woodwork in amplification, in the way the Sonus Faber has the same for speakers, and there are probably enough customers out there who'd covet the Mystery One for its looks alone. So let's get that bit out of the way.

Like every other product to emanate from the Unison Research factory, Mystery One is styled like nothing else on the market. It measures a large 490x430x160mm (WDH, including knobs and earthing post), so an ample shelf is needed. I was pleased to find that it fit perfectly in the Hi-Fi Newsstand, but I suspect that its iconoclastic appearance might cause problems for those hoping to slot it into a space which previously held a metallic, cubist device. Carlo Chiarello has created an organic look consisting of a sculpted, solid cherry frame, with a chunky front panel slotted for both ventilation of the valves and egress of the rotaries. The curve of the end-cheeks lends them carrying handle status and a forward crouch. While a collection of four knobs suggests that you're looking at some kind of hi-fi equipment, the effect is still more in keeping with a modernist's idea of a rustic cigar humidor or jewellery case. Or maybe a horizontal knife rack...

Peering through the upper slot allows you to see the glow of the three double triodes (two ECC82s and one ECC83) and the EZ81 double diode rectifier which form the heart of this Class-A line level pre-amp. The lower aperture houses the controls, the on/off rotary at the extreme left with the trio grouped at the right consisting of the source selector, the tape monitor/source selector and the volume control. At the back, all is conventional: gold-plated inputs for four sources plus tape, outputs for tape and two power amps and an IEC mains socket. The one teensy exception to the norm is a multi-pin connector to power a Simply Phono, Unison Research's £495 optional external phono section. Note, however, that it's only the power source for the phono stage; the phono signal is fed separately to the input marked aux/phono rather than through the multi-pin socket.

Release the four screws to remove to cover and you'll see why this sucker weighs a power-amp-like 15kg. The power supply fills the left-hand third of the case, the rest of the space occupied by a motherboard containing a daughterboard for the EZ81 rectifier. The socketry is soldered directly to the main PCB, as are all of the main components, the other three valve bases and the volume control. The source and tape selectors are connected to a second daughter board at the back of the main PCB. Despite the presence of secondary PCBs, the layout is tidy and the build quality impossible to criticise.

It's a clean, minimalist design making use of the extra acreage by spacing the components as far apart as is beneficial, preventing unwanted interaction without adding too much length to the signal path. Then again, the PCB traces are wide and substantial, so signal fragility doesn't seem to be a by-product of the longer path. And then you see the secret weapon, designer Giovanni Sacchetti's little twist: a row of four CR2032, 3V lithium batteries providing the pure DC supply for the valve grids.

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