Headphone Amplifiers

Notwithstanding the fact that the constant upgrading, development and introduction of new components is the absolute lifeblood of HFC, how these upgrades are often named can quite frankly be a copy editor’s nightmare.

In this issue alone you’ll find KEF up-naming its LS50 to the LS50 Wireless II, Primare’s NP5 Prisma being promoted to the NP5 Prisma II, Klipsch relaunching its Forte in the guise of the Klipsch Forte IV, HiFi Rose running out a freshened-up version of its RS150 as the RS201E, Sennheiser adding to its dizzying array of headphones with a new model called the IE 300, not to mention iFi which as a company is seemingly prone to releasing DACs with new names like there’s really no tomorrow.

Quite the headache, then, for fact-checkers, meaning that any prospective buyer looking to enjoy the advantages and innovations offered by these upgrades would be advised to pay forensic attention to the fine details lest a number or letter slip means that they end up with some predecessor of their desired just-on-the-market model.

Which brings us rather neatly to Naim Audio’s Uniti Atom. In the 12 years since the company launched its network audio all-in-one, to which the buyer need only add speakers, its title has grown from the simple NaimUniti of the initial model, all the way to this, the £2,400 Naim Audio Uniti Atom Headphone Edition. And yet amazingly, less is more.

This new arrival, despite being the same price as the existing Atom, (which continues in the range), has shed the power amplification of what is the company’s most compact streaming system, slotting in below the full-width Nova and Star (HFC 433) models. Here the unit is re-purposed as a dedicated device for followers of the ‘head-fi’ trend, complete with a choice of conventional and balanced headphone outputs. Well, that’s almost the whole story…

This is the latest evolution of Naim’s in-house streaming platform first unveiled with the arrival of the current Uniti models, and which has gone on to underpin not only the Uniti range, but also both the Mu-so lineup and its latest-gen ND series of network players. The intention of futureproofing has been borne out, not least with the inclusion of Chromecast built-in, along with both Bluetooth and Apple AirPlay 2.

Just about anything you want to stream from your computer, phone or tablet is accommodated here, along with a hi-res UPnP/DLNA interface able to handle files up to 32-bit/384kHz and DSD128. There’s also Roon ready capability for those who are taken with it.

But back to the Uniti Atom Headphone Edition. It’s actually not the company’s first foray into headphone listening – that was the Headline headphone amp. Also, the DAC-V1 was designed in part as a bridge between PCs and ’phones. Similarly, much play was made of the quality of the Supernait 3’s (HFC 456)integral headphone amp a couple of years back – but the Atom HE is definitely Naim’s most complete offering for fans of personal listening.

Not only can it stream music from the user’s own collection, be it located on network storage or USB devices, it can also deliver online services including Spotify Connect, Qobuz and Tidal, not to mention the ‘hi-res’ 320kbps AAC BBC radio streams as part of its internet radio capability.

All these services are best accessed via the Naim app, although the unit also comes with an RF remote handset. In addition there are both optical and coaxial digital inputs, as well as a single set of analogue ins, the latter digitised at 48kHz.

It would be remiss not to note that none of the gains made in the development of the current Naim platform include greatly improved wi-fi capability. Despite the absence of any external antennae for this or its other wireless modes, the Atom HE is fully capable of handling hi-res PCM or even DSD given a reasonable home network signal strength, although many will want the reassurance of the wired Ethernet connection located on the rear of the unit.

Regardless of the input selected, all signals pass through Naim’s long-refined SHARC-based digital signal processing, and the company’s favoured TI PCM1791 DAC, and thence to the output stage – which is something Technical Director Steve Sells and his team have reportedly spent much time fettling.

Yes, this is a headphone amplifier, with both 6.35mm unbalanced and 4.3mm Pentaconn balanced sockets on the front panel, plus a four-pin XLR balanced headphone output to the rear, but it can also be used as a preamp – thanks to both RCAs and XLRs round the back.

This is actually rather interesting, as there’s no sign of Naim’s usual DIN connectivity here, although the company is at pains to emphasise that the current Uniti models have never offered such provision. However, balanced XLR preouts – and matching power amp inputs – are only currently found on the company’s flagship Statement pre/power, alongside the familiar DINs used for unbalanced working. So it will be interesting to see whether Naim launches more mainstream power amps (and indeed preamps) equipped with balanced XLRs going forward.

Sound quality
Most of the session listening is carried out using a variety of headphones, but it is also tested running as a preamp into a main system. As it turns out, the Atom HE acquits itself well in both roles, though a fixed output option on the preamp sockets – enabling it to be used as a source as well as a streaming pre – would have been welcome. It’s also worth noting that Naim says all three headphone outputs can be connected simultaneously, which could be handy given that rear-panel XLR output, but for optimum performance it proves best to use just the one output at a time. Incidentally, the front headphone outputs will mute the preouts when ’phones are connected, while a button located above them switches the rear output on and off.

It’s worth sticking to that ‘one headphone at a time’ suggestion because, while the Atom HE doesn’t sound laboured even if you do use all the outputs simultaneously, there’s a useful gain in impact and clarity to be had, whether or not balanced cans are being used. And that ‘useful gain’ in quality is sufficient to take the Atom HE from excellent to superb.

In fact whichever kind of headphone output you use, this is a device able to bring out the very best in a wide range of accompanying models, from easy-going moving-coil types to demanding planar magnetic designs such as the balanced and much-lamented Oppo PM-1.

But whichever you opt for, the essence of the Atom Headphone Edition is that it manages to drive headphones with both ease and conviction, while at the same time maintaining those Naim-esque qualities of detail and rhythmic acuity.

Even relatively lush headphones such as the B&W P9 Signature (HFC 421) are kept under strict control and made to work for their living, while more obvious ‘monitor’ designs including the original Focal Spirit Pro sound fast, wide open and thrilling, never straying into harshness.

Without resorting to the complexities and ‘fiddle factor’ of designs such as SPL’s Phonitor xe, Naim has managed to design a headphone amp all about the most important sonic trait – the direct communication of music. And that means just about every style of music you choose to throw at this streaming headphone amp, including really raw recordings like Motörhead’s No Sleep ’Til Hammersmith sound suitably driving and thrilling, for all its abrasive edge. Similarly, a characterful vocal such as Sonja Kristina’s cover of Emerson Lake & Palmer’s Still… You Turn Me On is beautifully resolved and has superb character throughout.

The sound here is never less than entirely focused on the performance, as is clear with American Quilt, the rootsy Paula Cole set of standards across a variety of genres. The singer’s voice is revealed with all its textures intact to glowing effect, while the accompanying musicians are exceptionally placed, for example on the stomping Black Mountain Blues.

Conclusion
Without recourse to any obvious signal-manipulation, the Naim Atom HE seems to do a fine job of dispelling that ‘shut-in’ effect that sometimes afflicts headphone listening, even when powering closed-back designs such as the Focal Stellia (HFC 452).

And the Uniti Atom HE puts in a good showing with the scale and drama of classical music, too. The gentle, small-scale scoring of Michala Petri, Marilyn Mazur and Daniel Murray's Brazilian Landscapes album is lucid and beautifully measured. It doesn’t shy away from the majestic weight of the Budapest Festival Orchestra/Iván Fischer recording of Brahms’ Third Symphony either. The Atom HE, driving Oppo’s PM-1 in this case, delivers a performance of real drama and impact, with a delicious sense of the orchestra ranged before the listener. In short, the wide-ranging ability of this compact but substantial streaming headphone amplifier is never really in any doubt. HFC    

DETAILS
Product: Naim Audio Uniti Atom Headphone Edition
Type: Headphone amp

FEATURES
● Rated headphone output: 1,500mW (16ohm)
● Chromecast built-in; Apple Airplay 2; Tidal; Spotify Connect; Bluetooth aptX HD; internet radio; Roon ready