Unison Research SR1 Tube Amp Reviewed

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Think 'Unison Research' and, if the brand is known to you, you'll picture groovy wood and single-ended triodes. Trouble is, the new century has been celebrated by the firm with a change of the company structure, new partners and a revised view of the market, so that image must be altered. While S.E.T.s remain the core business, radical new lines are planned which should create an appeal for the products beyond the hardcore stereo tube crowd. The SR1 reviewed here is but a hint of what Unison Research has in store, and it encapsulates the new thinking. For the SR1 is a tube/transistor hybrid...

Additional Resources
• Read audiophile power amp reviews from the likes of Krell, Mark Levinson, Audio Research, Linn, Naim, VAC, VTL, NuForce, Pass Labs and many others here.
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Personnel in Italy told me it was best not to use the Italian word for hybrid - 'ibrido' - as it has a connotation at street level relating to sexual ambiguity. Er, oops. For audiophiles everywhere else, 'hybrid' means a mixture of solid-state and valves, typically with transistors serving as the output stages - precisely what constitutes the SR1's layout. The SR1 features a pure triode input stage followed by second triode driver stage with active bias control; the two matched ECC82 double triodes which constitute the valve element are positioned proudly at the front of the amplifier in the classic Unison Research manner. The output stage? A complementary pair of power MOSFETs, symmetrical and operating in what is called Dynamic Class A mode.

Along with the aforementioned evolutionary changes to Unison Research, the company has collaborated with Prof. Leopoldo Rossetto of the Applied Electronics Department of the University of Padua, hence a circuit which seems like such a departure from their norm. The most obvious manifestations are the modular internal construction, sophisticated protection circuitry, an unusual type of remote volume control, assorted warning lights and more. The result is a deliciously modern amplifier masquerading as a be-tubed anachronism. And all is revealed just by switching on.

Competition and Comparison
You can compare the Unison Research SR1 against other tube amplifiers by reading our reviews for the Beam Echo tube amplifier and the EAR Paravicini M100A/312 amplifier.  You can also find more information on different products by visiting our Amplifier section.

First, you operate the rocker at the back. A light on the front panel above the source/monitor toggle glows orange for the valve pre-heating 'warm-up' period, then green for 'fully operational'. Another LED which glows green to indicate reception of the remote's signal, while LEDs to the extreme left and right indicate over-driving. A red flashing indicates overheating, and active protection shuts down the amp, which automatically restarts the SR1 when the temperature lowers sufficiently. Full-on red indicates that the mains input is too high or low, a fuse needs replacing, or the input signal is in overload. And if it comes on simply because you're working it too hard (when THD exceeds 1 percent), you simply reduce the volume and the light extinguishes.

I'm taking all of that on faith because I couldn't get this amp to misbehave, despite it being the first to leave the possession of Unison Research. Even with speakers which could take it, like the Wilson WATT Puppy 6, I couldn't get the LEDs to flicker because the output level was more than I could bear. Suffice to say that despite the review sample being 220V in a room typically graced with 245V from the mains, the amp never shut down, nor blow one of its fuses.

It should be pointed out that, confidence-inspiring safety trickery aside, there are no relays nor fuses in the signal path. And everything must be described as generous or 'overkill', including the Unison Research-designed and in-house-constructed power transformers and power supply capacitors, the robust and fully-gilded speaker terminals and phono sockets, massive heat-sinks and the rugged case. Aaah, the case!

Yes, gang, this amp is as gorgeous as you'd expect of anything Italian. The basic unit is black, with a pair of sculpted, solid hardwood accents (organic lacquering, natch) adding that touch of style and luxury. True, Unison Research could release the SR1 as a strictly utilitarian unit without the wood, or the curved stainless steel heat reflector, but then it wouldn't be a Unison Research amp. The wood flanks the ECC82s at the top, and the large, stainless steel volume and source select rotaries at the front, butting up to the heat sinks at the back. Mounted at the very rear are the on-off rocker and the IEC mains input, the speaker terminals, and sockets for tape in/out and four line-levels sources.

Along with an 80W/ch rating, the SR1's stated specification includes an output impedance of 8 ohms, a generous bandwidth of 2Hz-70kHz (-1dB), and an input impedance of 47kOhms/50pF. The damping factor is 50, the feedback a mere 8dB, and power consumption is 290W at full output power. Physically, the SR1 is a genuinely compact 270x450x150mm (WDH), the weight a substantial 15kg.

Oh, almost forget: the teensy remote. It's no larger than it needs to be (meaning: small enough to get lost) and it sports only two buttons, volume up and volume down. It drives a motorised volume control and triggers an LED so you can see as well as hear the operation. But the deft touch is that it's not an IR remote. Instead, it uses radio frequencies, with the added benefit of the user not having to aim it at the SR1; it even worked from the next room or outside the building. Whether or not it opens your garage door, I can't say. But no planes crashed into my back garden, my neighbour's radio-controlled model helicopter stayed in his shed, and my wife never complained about interference while listening to Radio 2. What it beg, though, is a nice wooden sleeve...

I should tell you that the SR1 will sell for only £1250. Yes, this is a crowded market sector, just above mid-fi and smack in the middle of what I would describe as 'first upgrade' level, and the market is bursting with all-tube amps at this price. Moreover, there are other Italian valve and transistor amplifiers in this sector, if you buy according to country of origin. But what the SR1 positively oozes are qualities which don't appear to be available in a single package (though the small Pathos comes close). In particular, it's the valve sound-plus-transistor reliability marriage which makes this so enticing, the price, size, security features, remote control volume and sexy styling being mere bonuses.

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HTR Product Rating for Unison Research SR1 Tube Amp

Criteria Rating

Performance

3

Value

3

Overall

3

Disagree with our product rating? Email us and tell us why you think this product should receive a higher rating.


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