A few short years ago dedicated headphone amplifiers were few and far between. With the explosion in popularity of high-end headphones all that has changed and we’re now seeing headphone amps from a wide variety of manufacturers, old and new.
When news got out that Unison Research were to release a headphone amp, we knew it was going to be something special. For those unfamiliar with the italian manufacturer, it was founded back in 1987 and spearheaded by the inimitable Giovanni Sacchetti, a veritable master of single-ended design. So to say we at The Music Room had high hopes would be an understatement.
We were certainly not let down. This is a Single-Ended Class A design which we’re told uses only two stages and a passive volume control. It’s typical Unison Research affair: simple, but not simplistic. Even before running in, a cursory test hinted at what was to come. After a few days, things were really starting to sing.
Valves at their best, a.k.a. having your cake and eating it...
Everyone’s different, but what I look for in valve amps is not so much “warmth” or “softness” or other such typical “valvey” traits, but rather something which good valve design seems to do better than anything else. Namely sparkling highs and robust mid-range focus, all without a hint of harshness. For headphone listening, the latter is particularly important. With a diaphragm sitting an inch away from our precious eardrums, harsh treble is very undesirable. And yet we don’t want a muffled sound. We want detail, but not ear-splittingly so. Like all true audiophiles we want to have our cake and eat it.
And this is the miracle of the SH: it smoothes edgy treble without diminishing the detail. But more than that, if a headphone has weak bass, it boosts it without overwhelming the rest of the music; if the mids need focus, it puts a magnifying glass on there without distorting the image; it glues the spectrum without making things gloopy; it boosts contrast without affecting tonality.
Case in point: take a headphone like Sennheiser’s love-it-or-hate-it HD-800. If I did a 9 word review of said headphone, it might go something like: “incredible soundstage, staggering detail, slightly sterile, a touch fatiguing”. Through the SH, the shortcomings are diminished and these cans take on a new life. That slightly sterile edge is softened, the gnawing treble becomes precise rather than piercing. That isn’t to say it attenuates the treble, no. It just seems to highlight the positives and diminish the weaknesses.
But the most intriguing aspect of all is that this same story of metamorphosis is repeated for any headphone I have tried through the SH. Like a beautifully made-to-measure Italian suit, it doesn’t fundamentally change what’s underneath, but simply flatters the wearer. Oppo’s magnificent and reasonably priced PM-3, for example, all but completely loses its slightly congested feel and through the SH sounds like a headphone double the price. Yes, this amp does for headphones what a well designed power amp does for loudspeakers… it grabs the drivers by the scruff of the neck and tightens everything up. A remarkable achievement.
What about build quality? Irreproachable. The volume control is weighty and smooth, the switches satisfyingly tactile, and the casework itself oozes class.
So where’s the rub?
If there’s one negative, it’s the lack of connectivity. And in some ways even that is a positive; keeping things simple on the reverse with only an IEC power socket, a USB, and a single pair of unbalanced inputs, we needn't fuss over balanced vs. unbalanced, USB vs. SPDIF, etc. However, it may have been nice to have at least a couple of analogue inputs. (A confession: I haven’t used the DAC, so I can’t comment on that. The specs tell us it’s the latest Sabre chip, but that tells us very little. After all, a DAC chip is only as good as its implementation. I’ll report back here when I’ve had a thorough listen to the digital side of this amp.)
On the other hand, I almost wish Unison Research were more minimal. Wouldn’t it be nice if there was simply a beautiful high quality set of RCA connectors, and no USB/DAC. But I didn’t notice any issues in real use, so that’s more of a superficial complaint.
And do we really need two headphone outputs? Seems a bit strange to have this as a standard feature. I’d love to see a distilled version of the SH. One headphone out. No DAC/USB. They could call it the SH Solo. Such a product at a slightly lower price point would be a really tempting proposition.
But let’s not end on a low note. In truth, any complaint about this amp is superficial. Where it counts, the Unison Research SH delivers. And delivers big.