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Glove Audio A1 headphone amplifier / DAC review

  • From a certain perspective it could appear that the development team behind the runaway success of iRiver’s Astell&Kern digital audio players are making it up as they go along. In early 2013 the AK100 arrived and despite selling in good numbers it was met with some fairly robust criticism: the exposed volume knob invited in-pocket damage and the output impedance was too high for some IEMs. A matter of months later the AK120 dropped into the marketplace with sub-1 Ohm output impedance and a modified extrusion to protect the volume rotary. Criticisms checked, the AK120 outsold junior five to one.

    May 2014. A mere eighteen months after the AK100’s inception Astell&Kern launched second-generation AK100 and AK120 players at the Munich High End show. These new models were taller, sleeker than their predecessors, clearly following the shinier aesthetic established by their top-flight AK240, itself announced five months earlier at CES. On the inside, the AK100 II and AK120 II each saw Cirrus Logic supplanting Wolfson D/A conversion. A Linux operating system made way for Android. There were double-barreled price hikes too: US$699 to US$899 for the AK100 and US$1299 to US$1699 for the AK120.

    Those who had forked out for the originals were already staring down at yesterday’s news. What to do? Live with what you have or sell the first generation unit for 50% of its purchase price and swallow the upgrade cost whole?


    Then there’s the issue of power. The Astell&Kern DAPs positively trounce the iPod on sound quality when paired with more portable-friendly headphones like the KEF M500, Sennheiser Momentum and Sony MDR-1R MK2. With more demanding loads it’s a different story: MrSpeakers’ Alpha Dogs sound a little bloodless with the AK120 running solo; ditto the Sennheiser HD800 which come on with too many needles and pins in the top end when under-powered.

    A similar issue presents with the Truth Edition of DITA Audio’s Answer universal IEMs – an oversupply of treble etch could only be smoothed away by strapping an ALO Audio International+ to the AK120 for amplification duties. The ALO brings forth a fuller, richer sound that’s smoother and notably weightier in the bottom-end. The improvement is far from subtle.

    I point this out not to bag the Astell&Kern DAPs but to point to their limitations. Limitations that can be mitigated by an outboard amplifier. The ALO unit has no optical digital input so it’s a relief that the AK120 plays nice and clean with nary a hint of distortion, even when feeding the International+ at full ’75.0’ volume.


    Whether or not Michael Goodman of CEntrance had the inside tip on these second generation Astell&Kern models is anyone’s guess. Still, his timing in debuting the Glove Audio A1 (US$599) in Tokyo a week prior to the Munich High End show was positively spooky. Goodman had the Glove Audio A1 casually sitting on Jaben’s table at the Fujiya Avic Spring headphone festival. What the hell was that thing? A five-minute demo from Goodman himself showed his new product was smart, ‘Best in Show’ smart.

    The A1 isn’t a portable DAC and headphone amplifier for pairing with ANY device; it’s aimed squarely at first generation Astell&Kern AK100 and AK120 units (used for this review). It is also more exoskeleton than it is strap-on addendum. After sliding the AK120 onto the A1’s fixed optical plug, two screws lock the Astell&Kern device in place. The A1 then leeches all digital audio from the AK120’s fixed-level optical output before exacting its own D/A conversion and amplification – the Astell&Kern DAP serving only as transport.

    The Glove’s circuit is fully balanced from input to output with 2.5mm and mini 4-pin socketry offering twice as much output power (320mW into 30 Ohms) as the 3.5mm unbalanced counterpart (150mW into 32 Ohms). Only the latter was tested during the review process here.


    In response to my requesting details on the output stage Goodman says, “This is new design with very low THD. For now we will keep the actual topology private, since we may want to reuse it in more designs.” He’s protecting his IP as much as a fellow can – fair enough.

    What we do know is that the DAC chip inside the A1 sees Goodman departing from his preference for AKM silicon found already in the CEntrance HiFi-M8 and Mini-M8. In the Glove A1 we find ESS Labs’ relatively new 9018-2M, a lower power draw chip designed for use in portables such as this. Due to bandwidth limitations of the TOSLINK protocol, 176.4kHz and 192kHZ PCM are down-sampled to 96kHz by the AK120 before being handed off to the A1. The same goes for DSD – it plays flawlessly after first being converted to 24bit/96kHz PCM.

    Next to the Glove’s power button atop the unit is a micro-USB port for re-charging the internal battery from a computer or wall-wart. Expect a maximum of 11 hours’ playback between charges – enough for long haul flights and long days at the office. Down the side, clickable volume up/down buttons. There’s no volume indicator so users are advised to proceed with caution when hooking in more sensitive IEMs.


    The Glove’s casework can best be described as robustly utilitarian, looking like it could withstand the most careless of treatment. Good news for those who throw it in a bag and run.

    How does the A1 + AK120 sound? First off, know that both generations of AK120 sound more similar to each other than the Glove-d 1st gen unit. The A1 really likes to flex its musical muscles, easily the most powerful of the three units here. This doesn’t just mean that the Glove A1 plays louder than its rivals but that it also takes better control of your headphones’ drivers, which in turn translates to superior rhythmic propulsion as well as more obvious separation. And whilst it’s impossible to know how close the Glove’s take is to the original performance, it connotes accuracy as a sensation: clean, crisp, and detailed.

    In comparing the Glove + original AK120 with the AK120 II, I noted more rambunctious, deeper bass on Leftfield’s “Inspection (Check One)” and – especially – Bjork’s “Hyperballad” where you can almost feel the song’s introductory low notes in the back of your throat. Cleaner, cymbal shimmer was more evident on Peter Gabriel’s “Red Rain”.

    With portable friendly cans the AK120 II vs Glove A1 + AK120 standoff resulted in a more even playing field. Your preference will largely depend on your headphones. Do you want more juice? Urgency? That’s the Glove. Or do you need a more mellifluous take on events? That’s the AK120 II.

    The Sennheiser Momentum benefits more from the latter and, at times, sounded over-driven by the Glove. Same same with the Xiamoi Piston IEMs. These ‘phones are both specifically tailored to sound good with less specialized players and can sometimes sound a little too strident at the hands of beefier amplification.


    With the Cardas EM5813 Ear Speakers it’s a different story. These IEMs enjoy a much-needed lift in the presence region when Gloved. And as per my experiences with International+, the DITA Audio IEMs also benefit from the Glove A1’s firmer hand. With the KEF M500 I could go either way depending on music choice. Goodman’s Glove is bang on the money for Rrose’s techy Little White Earbuds mix which plays through with clean lines and rhythmic urgency whereas the AK120 II turns in a gentler interpretation.

    Things get more interesting when switching up to Mr Speakers’ Alpha Dog. This is where the Glove A1 really comes into its own, properly nourishing Dan Clark’s overhauled Fostex. More grunt and cleaner incision being a CONSIDERABLY better complement to the Dogs’ dark chocolate vibe than the AK120 II’s more touchy-feely reproduction.

    A similar improvement over the AK120 II can be heard with the Glove feeding the Sennheiser HD800: you get the SPLs and acoustic mass. Music no longer presents as bare bones.

    In comparing the Glove A1 with the International+ we must first consider pocketability. The ALO + A&K won’t slip into a front jeans pocket whilst the Glove + A&K will…just. The ALO couples a more standoffish top end to heftier lower bass. In comparison, the Glove A1 is sounds more lit up from within making it easier to conceive of the mouth movements behind voices; there’s also more caffeination in the lower treble and kick-ass dynamics.

    Users of first release AK100 and AK120 should be advised that drag-and-drop file loading has been replaced by Android File Transfer (on OS X) – it’s faster but far less flexible. For this alone I can foresee some users wanting to stick to original models. What we have here is some very innovative thinking from the House of CEntrance; it paves the way for other devices to get Glove-d. The A1 provides a considerably cheaper upgrade path than a direct route to second generation Astell&Kern players whilst leapfrogging their sound quality, particularly with more demanding headphones. That it remains pocketable ices an already rich and tasty cake.


    Associated Equipment

    • MrSpeakers Alpha Dog
    • KEF M500
    • Sony MDR-1R MK2
    • Sennheiser Momentum
    • Cardas EM5813 Ear Speakers
    • DITA Audio The Answer / Truth
    • Xiaomi Piston 2
    • Sennheiser HD800
    • Astell&Kern AK120
    • Astell&Kern AK120 II


    Audition Music

    • Rrose – Little White Earbuds DJ Mix (2014)
    • Peter Gabriel – So (1985)
    • Leftfield – Leftism (1995)
    • Beck – Sea Change (2002)
    • David Byrne and Brian Eno – My Life In The Bush Of Ghosts (1981)
    • Bjork – Post (1995)


    Further information

    Written by John

    John currently lives in Berlin where he creates videos and podcasts for Darko.Audio. He has previously contributed to 6moons, TONEAudio, AudioStream and Stereophile.

    Darko.Audio is a member of EISA.

    Follow John on YouTube or Instagram

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