Review: Aune X7s – shooting the moon



Original article:

Disclaimer: Aune graciously provided the X7s sample for the purposes of this review. The X7s goes for about 250$ USD. You can find out all about it here: Aune X7s Class-A balanced output headphone amplifier.

Relevant links:

Review: MyST OrtoPhones – Uplifting
Aune B1 Review – Vincent
Vorzüge Pure ii Review
Vorzüge PURE II+ Review
Lynx Studio Technology HILO Review

Not sound

Aune’s X7s’s attenuator knob is mostly naff. Its sharp edges are of no utilitarian value. Neither does it pivot equally between MIN and MAX values, my unit favoring MAX by about thirty degrees. And, it sits off kilter, wobbling slowly with every nudge up or down. The good news is that it turns smoothly.

For 249$, just about everything else is groovy. Purists may decry its use of a phase splitter rather than an IN-OUT dedicated balanced circuit. They’d have a point. And yet, despite its few faults, the X7s is a powerful, sensible amp.

Another insensible thing is the X7s’s electronic manual. Aune have buried it in a plastic USB sliver. At least it’s not on a CD or DVD. It can’t have been done for environmental reasons. I mean, gee whiz: if you’re going to thrust it in a plastic blister inside another plastic blister alongside a business card, why not just first print out a simple manual and forgo the plastic? Why make it that much harder for users like me, like Thom, like Gracie, and Kuko, to find use?

Isn’t it time to away with electronic user manuals.

Let’s get back to the volume attenuator. I understand that Aune added a top plate to help suss its position when in a dark room. I get that, I really do. But nowhere else in the X7s is such stylistic flourish used. And, as I said above, it’s not properly aligned between stops. Shame that.

But let’s be done with design criticism.

Everything else about the X7s can be judged against its feature set and price- not a tack I like to take. Price is price. Branding, build, quality of after-sales support do fit into that. But it’s complicated. Things simplify a bit when a product offers so much for so little. Which almost perfectly describes the X7s.

Two pair of RCAs run the amp’s IN/OUT array, including the pre-amp output. The volume attenuator governs the voltage spat therefrom. It’s a dead-simple, tried and true method. It’s problem is cross-talk. Plugging an output line into the pre-out results in a minute portion of the music turning back into the headphone output section where it shouldn’t be fed back into the input at all. The other problem is that the last 15% of the attenuator’s travel is dead, with no perceptible rise in volume. Of course, that travel is beyond its MAX label.

At least for its ostensible targets, the latter issue is of little import. Crossfeed between the IN and OUT ports, however, could present problems and should be looked into.

Sound and more after the jump or the click below:


It’s a safe assumption that an amp whose only outputs are a 4-pin XLR and a 6,3mm stereo TRS isn’t designed for earphones. And the X7s isn’t. First, line noise is higher than average, reminiscent of the B1, but scaled up for the X7s’s power (which is considerable). Second, it isn’t perfectly stable when driving low-Ω earphones. Light frequency deviation is measuring low Ω multi-armature earphones. Since base THD is 0,0002% it’s hardly notable that THD numbers shoot up under load. Of course they do. But under the load of an Earsonics SM2, and at volume levels similar to what an iPhone 4s kicks out at maximum volume, that figure jumps by 5740x to 1,148%. Whether or not that amount of THD is audible to you, is moot. It is a lot of distortion at that volume. Similarly, IMD levels under the same load and volume level, are higher than average.

All of its kinks are ironed out by the time you plug in a pair of headphones. Even low-Ω classics like the Grado RS1, or portable ohm-image mainstays such as Audio Technica ES7 induce very little distortion, even at painful listening levels.

Under the load of headphones such as the RS1 and ES7, and against total harmonic distortion, (which I measure as low as 0,0027%) you’ll be able to suss the X7s’s clean, extended signature. I find a slight signature shift when driving high-ohm headphones, mainly, that midrange stereo depth and detail go up a notch against highs and lows. In general, however, this is an even-Stephen amp, with great detail throughout the range.

Its signature is contrasty, equalising pressure between lows and highs. It’s a speedy sounding amp with a decently-sized stereo image, the depth of which is best revealed when driving headphones in the 300Ω range. It is an excellent pair with MyST’s amazing OrtoPhone, whose speed and midrange warmth make a wonderful set. The X7s has loads of power, slightly edging out the Lynx HILO, but falling below the LinnenberG Maestro. The thing is that it doesn’t appear to take in high voltage signals well, returning high-distortion signals at any volume level when fed signals that the Vorzüge PURE II eats for breakfast. Again, this is a 249$ amplifier.

I can't imagine a situation where you’d need to raise the gain, but you can. I set the X7s to 0dB and stayed there. Because its input appears limited to low-to-medium voltages, gain serves only to boost initial signals before hitting IMD walls at extreme volumes. Whatever the case, the X7s’s output is more powerful than a number of 1000$+ amps.

It errs sharp rather than cool, and by dint of its flat-driven midrange, its firm center grounds its signature. No amp I’ve heard in a long time rides as fine a line between detail-oriented and cozy. As long as you take line noise out of the equation, the X7s is clearer sounding than the Lynx HILO. By small degrees, it is also less intimate.

It is my opinion that it will appeal to two groups:

those with middling warm headphones
HiFi enthusiasts looking to break into the headphone world
For both groups, its price point and feature set should be the biggest draws. Stabler amps exist. Amps at similar price points with lower noise floors exist. Typically, that competition doesn’t spit as powerful a signal. Rarer still will an amp in the X7s's price point boast balanced output, phase split or not.

There appears to be a small uptick in stereo separation when a headphone is used in balanced mode.

End words

It's almost unfair to demand noiseless signals, or design disunity in a 249$ amp whose most marketable feature is balanced output. But it's equally silly to let off the hook bad or incomplete design. Which leads me to the conclusion that the X7s is a powerful, capable amp for headphones of most designs and impedance ratings. That its design allows for balanced output is a boon, especially at its price.