Integrated Amplifiers

Based in Treviso, Italy, Unison Research has long specialised in making very traditional looking tube amps with polished wooden chassis and rows of glowing bottles on display. At the same time its Unico series has adopted a more mainstream aesthetic and includes valve-based amplifiers that, well, don't really seem like valve amplifiers. Despite an outward appearance suggesting a completely conventional integrated amp, the Due – which sells for £2500 in standard silver with black available at a £100 premium – is very definitely a valve amp, or at least half of one.

In fact, this hybrid design aims to bring the user the best of both worlds: the character of valves, thanks to one ECC83 double triode per channel in the preamp stage, plus real-world speaker-driving ability thanks to a MOSFET-based power amp claiming 100W per channel, and designed for ultra-low distortion to let all that valve character through. This, then, is the valve amp tamed, made domestically acceptable, easy to use and fully compatible with a wide range of loudspeaker types. Plug it in, and given a bit of time for the whole caboodle to warm up, you're ready to play music.

And Digital Too
However, there's more to the hybrid thing here than just the valve/solid-state combination. In practice this is basically an analogue input amplifier, including a phono stage, but it also has an onboard DAC, albeit with just one input, on a USB-B socket, to allow a computer to be connected. However, even here the design is unusual, as the DAC has its own line output as well as being connected to the preamp, so should you want you can use the Due as a standalone DAC, for example straight into a headphone amplifier.

Using the 'OSB' button on the amp allows this DAC output to be used while the power amp output stages are in standby, this also being a handy facility for keeping the Unico Due ready for more rapid use, as the valve preamp stage is kept powered with this setting. The DAC itself is one of those ubiquitous ESS Sabres, in this case an ES9018K2M that can handle file formats up to 384kHz/32-bit and DSD256, which should be more than adequate for almost any 'computer audio' need.

Meanwhile the amp has two analogue line-ins and a tape loop – remember those? – and as well as two sets of speaker terminals to facilitate bi-wiring there's also a stereo subwoofer output for use with active subs, also under the control of the main volume adjustment. The MM phono stage module comes as standard, but can be reconfigured for use with moving-coils. Moving from vinyl playback to AV, it's also possible to set one of the line inputs to a fixed gain (user selectable) for use when connected to an AV processor or receiver's front left/right pre-outs. Only confusingly, this mode is chosen, once set up, by pressing a button on the remote amusingly labelled 'push'. Tempting, isn't it?

Complete Control
The fascia layout is fairly self explanatory, with one rotary selector for input, also accessing the tape – or 'monitor' input when pushed, while pushing the volume control mutes the output. Unless you push and hold it, that is, in which case the volume knob turns into a balance control. So this is one seemingly simple amp where you really need to read the manual to exploit all its facilities. The volume control uses a switched resistor array and works over a very wide 120dB range in 0.5dB steps, while input selection is via sealed relays for low noise and reliability.

Designed as a replacement for the company's Secondo integrated, a design so long-running the new model might be described as having been 'over-Due', the amp is the result of what Unison Research describes as 'key improvements… that are nothing short of ground-breaking'. In fact, what's been done is all pretty sensible stuff: the power supply has been beefed up with a new shielded and encapsulated transformer, and an increase in filter capacitance, while the valves for the preamp stage, configured as a gain stage with a cathode-follower driving the power stage directly, were chosen in the only sensible way – by listening tests.

No fewer than ten separately regulated power supplies are employed ranging from 15V all the way up to the 300V for the valves, and the circuitboards use thick tracks, with almost a quarter of the entire board real estate in the amp being used to supply power to the output devices. Other design touches extend to gold plating on the input and speaker sockets, as well as the valve holders, and selected components including Mundorf capacitors, while microprocessor-controlled protection will reduce the output level if the amplifier is run too hard for too long.