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  • Josh Mound
    Josh Mound

    Flux Lab Acoustics FA-10 PRO Review



    A lot can change in a year and a half. When I bought my FA-10 PRO from Flux Lab Acoustics in the spring of 2021, the world was still adjusting to the trauma of the pandemic. Today, Ukrainian companies like Flux are not only faced with the continued challenges of COVID-19, but also with Vladimir Putin’s illegal invasion of their country. While the war has disrupted Flux’s operations at times, it’s still moving forward. That’s wonderful news, because Flux’s products deserve audiophiles’ attention.


    Something like headphone amplifiers might seem frivolous in the face of perhaps the most significant European conflict since WWII. In one sense, of course, that’s true. Physical safety is foundational to Maslow’s hierarchy, which includes nary a mention of “audio equipment.” But for most audiophiles, the gear is a gateway to the music, and both the search for beauty and the desire for transcendence are on that hierarchy. Those sound a lot like music to me. Social connection is on there, too, and one of the few unambiguously good things about living in the 21st century is that hobbyists in places like the U.S. can connect with companies in places like Ukraine almost instantly.


    FA-10 PRO REAR.jpgThe FA-10 PRO is solid-state, class A headphone amp. According to Flux’s website, “The FA-10 PRO amplifier circuits are employing Bipolar input stage and Toshiba Bipolar transistors at class-A mode with a supply voltage of 80 volts of output stage all that features are providing clean transmission for signal up to 16 Watt on 32 Ohm load of output power.” Its THD is spec’d at .002%, and it has an output impedance of .15 Ohms.


    The case of the FA-10 PRO is clean and utilitarian. It’s CNC-milled aluminum case measures approximate 12.5 inches wide, 13.5 inches deep, and 3.25 inches tall. I really love the FA-10 PRO’s build. It’s simple, but it doesn’t feel cheap. Instead, it reminds me of Yamaha and Technics gear from those brands’ classic made-in-Japan era.


    The FA-10 PRO includes both balanced XLR and single-ended RCA inputs on the rear of the unit, as well as balanced XLR and ¼-inch single-ended outputs on the front. A 64-step relay volume knob is the center of the front face plate — which can be customized with different colors — and to the left of the knob are switches for power and input source, as well as high (25.3 dB), medium (20 dB), and low (14 dB) gain.


    The FA-10 PRO retails for $849 USD and sits near the top of the Flux’s lineup, which includes several models priced below it and one — the $2,500 VOLOT — above it. Finally, Flux offers a 15-day, restocking fee-free return/exchange policy and a two-year warranty on all of its products.


    Reviews on other sites have shown that Flux’s products measure as well (or better) than the company’s reported specifications, so I’m not going to attempt to measure my FA-10 PRO with my modest E1DA Cosmos setup. Instead, I’m going to focus on subjective comparisons with two other well-regarded solid-state headphone amplifiers that I have on hand. The first is the Auralic Taurus MKII. When it debuted in 2014, it retailed for $1,899 USD. Its reported THD+N is .002%, and its power is 2W at 300 Ohms for balanced output (as compared to the FA-10 PRO’s 16W at 320 Ohms). The amp second is the first-generation Schiit Ragnarok. Before being replaced by the current model, the Ragnarok retailed for $1,699 USD. It’s reported THD is .006%, and it’s spec’d to put out 1.7W into 300 Ohms. Unlike the Flux and Auralic, the Ragnarok also functions as a speaker amplifier. Having owned and tried many solid-state headphone amps, I’ve kept the Taurus MKII and Ragnarok around because both are superb. Perhaps the only headphone amplifier that I’ve encountered that can top these two is the $3,299 USD Benchmark HP4. In other words, while the FA-10 PRO is going head-to-head against two slightly older headphone amps, they represent stiff competition retailed for more than twice FA-10 PRO’s asking price without even factoring in inflation.


    In order to see how each of the three amplifiers fared on a selection of material, I level-matched their balanced outputs and used my Mapletree XLR switch to toggle the output of my Crane Song Solaris DAC to the appropriate amp.


    For the first few tracks, I used Focal Utopia headphones to compare the amps. The Utopia is relatively easy to drive, incredibly revealing, and very sensitive to amplifier noise. Before level-matching, I turned up each amp to the point where I could detect audible hiss. I had to turn the volume on the FA-10 PRO to what would be ear-splitting levels — either about four o’clock on medium gain or about one o’clock on high gain — if music were playing in order to hear any hiss. These are approximately the same spots on the dial I had to reach on the Ragnarok for a similar level of hiss. In other words, the FA-10 PRO is a very quiet amplifier.


    It will come as no surprise for those who’ve read my previous reviews that my first audition track comes from Van Morrison’s collection of studio rarities, The Philosopher’s Stone. I love this collection because Morrison worked in some of the best studios in the world throughout the ‘70s, ‘80s, and ‘90s, and he always recorded live with minimal overdubs. As a result, his recordings from this era tend to have little after-the-fact equalization and feature instruments’ natural timbres. For this review, I selected the 24/96 version of “Wonderful Remark,” mastered by the great Tim Young.


    I initially spent a long time bouncing back and forth between the Flux and the Auralic, repeating sections of “Wonderful Remark” numerous times on each. Through the Flux, everything had beautiful texture and realism. Both the opening acoustic guitar in the left channel and the delicate, mandolin-like acoustic that enters in the right channel on the chorus have more body in through the FA-10 PRO than through the Taurus MKII. The annunciation in Van’s vocal was sharp and clear through the Flux without veering into sibilance. The decay of the reverb on Van’s voice seemed to last longer through the Flux, whereas it disappeared into the ether more quickly on the Auralic. Through the Taurus MKII, Van’s voice was drier with less reverb. Perhaps because of this, the Flux seemed to offer more front-to-back differentiation between the instruments, whereas everything sounded flatter through the Auralic. At the same time, the Taurus MKII felt somewhat harsher and more brittle. While I’d always considered the Auralic to be a smooth-sounding amp, putting it directly against the Flux level-matched made me notice the Auralic’s somewhat grainy treble for the first time. The most striking feature of the FA-10 PRO, however, was how it handled the two extremes of the sonic spectrum. It separated Bill Church’s bass from the mix better than the Auralic. It also rendered the details in Lee Charlton’s hi-hat clearly, whereas through the Auralic the hi-hat came closer to an amorphous metallic “shhh.”


    Switching to pit the Ragnarok against the FA-10 PRO, I found that the Rag did an equally good job — perhaps an even better one — on Church’s bass than the Flux. It also full close, but not quite, even with the FA-10 PRO when conveying Charlton’s hi-hat. The Schiit’s reverb decays, in contrast, fell between the Auralic’s and Flux’s — longer than the former, but not quite as long as the latter. Overall, the Rag’s resolution was on par with the FA-10 PRO’s. But the Flux offers superior three-dimensionality, as well as an overall smoothness and lifelike presentation that makes the Rag sound a bit unrelenting in comparison.


    FA-10 PRO INTERNAL.jpgThe next sample track is “Tangerine” from the 2014 24/96 remaster of Led Zeppelin III. The Flux displayed great ability to separate Jimmy Page’s banks of overdubbed acoustic guitars. It did the same to Robert Plant’s vocal overdubs. Meanwhile, his reverb-drenched, somewhat sibilant lead vocal wasn’t grating in the least through the Flux, even though the Focal Utopia can sometimes accentuate sibilance. When I switched to the Auralic, I had the desire to turn it up, even though the volume was matched. In part, that’s because some details that were readily apparent through the FA-10 PRO were less apparent —though not absent — through the Taurus MKII. The latter was less adept at separating both Page’s aforementioned acoustics overdubs, as well as the layered electric guitars during his solo at the 1:40 mark. At the same time, Plant’s vocals were more sibilant through the Auralic despite being drier. Bonham’s snare, meanwhile, had less snap through the Taurus MKII and sounded like it was buried deeper in the mix than through the FA-10 PRO. Finally, the Flux again showed its superior front-to-back layering.


    Turning to the Ragnarok, it again had a little better bass authority than the Flux. However, the overdub-heavy “Tangerine” demonstrated more than the live-in-the-studio “Wonderful Remark” did that the Schiit also produces more of a wall-of-sound effect than does the Flux, which excels at separating elements in a mix. I also noticed again that everything seemed a bit squarer through the Rag. The Flux sweetens Page’s acoustics a bit, or the Rag hardens them, deepening on one’s point of view. (I think the truth is probably closer to the latter.) Regardless, the Flux offers a more subjectively pleasing listen. Yet I didn’t feel like I was sacrificing detail in exchange for its pleasant rendering.


    For the final track, I selected “Gaslighting Abby” from the DVD version of Steely Dan’s Two Against Nature. I also switched headphones from the Focal Utopia to the superlative, but harder to drive, ZMF Atrium. While both the Flux and Auralic have enough power for the Atrium, the Flux’s ample reserves do seem to come into play. The FA-10 PRO has full control over the Atrium’s drivers, rendering the thump of Ricky Lawson’s kick and the crack of his snare more forcefully than does the Taurus MKII. As with the Utopia, the difference in ambiance is apparent through the darker-tilted Atrium. The reverberant guitar and keyboard that open “Abby” are much wetter sounding through the Flux. The FA-10 PRO again offers superior soundstage depth, too, creating an almost wraparound effect on this precise Roger Nichols-engineered track. The FA-10 PRO’s instrumental separation makes it easier to pick out small flourishes, like the thin, squawky, low-mixed electric in left channel that enters during the song’s chorus. Bringing the Ragnarok into the mix, it again seems to fall between the two amps, with the main exception being that the Schiit’s bass remains perhaps the best of the bunch (a surprising observation given that on paper the Rag has less power than the Auralic). Through the Schiit amp, “Abby” has more reverb than is apparent through the Auralic, but less than one can discern with the Flux. Likewise, the Rag provides better depth than the Taurus MKII, but lacks the FA-10 PRO’s wraparound stage. The Rag’s aforementioned wall-of-sound quality also makes it a little harder than through the Flux to pick out that squawky guitar, though the overall difference is modest.


    Taking everything into consideration, the Flux FA-10 PRO is an easy headphone amplifier to recommend. The FA-10 PRO handily beats the Taurus MKII. It sounds better, has much more power, and features a relay-based volume control, which ensures perfect channel matching. While the FA-10 PRO lacks the Rag’s ability to drive speakers, as a pure headphone amplifier the FA-10 PRO edges out the Rag, too. Even more remarkably, the FA-10 PRO is significantly more affordable than either the Taurus MKII or the Ragnarok, and it remains so even when looking at used prices for the Auralic and Schiit amps. Add in quality customer support and a two-year warranty, and the FA-10 PRO is a must-try amplifier for headphone enthusiasts who want the best solid state amplification available today.



    ProductFA-10 PRO Class-A Headphone Amplifier $849.00





    About the Author

    jm.pngJosh Mound has been an audiophile since age 14, when his father played Spirit's "Natures Way" through his Boston Acoustics floorstanders and told Josh to listen closely. Since then, Josh has listened to lots of music, owned lots of gear, and done lots of book learnin'. He's written about music for publications like Filter and Under the Radar and about politics for publications like New Republic, Jacobin, and Dissent. Josh is currently a postdoctoral fellow at the University of Virginia, where he teaches classes on modern U.S. politics and the history of popular music. He lives in Charlottesville, Virginia, with his wife and two cats.


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    Thanks for the review @JoshM. I'd never heard of Flux Lab Acoustics prior to reading the review. Also, love the use of Zeppelin in the review!

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    Very good review, and I really like that I can follow your step-by-step explanation while I listen to the test tracks. Just one comment on the last sentence, so that it is not just the positives. Flux Lab Acoustics' 15-Day Return policy is not yet in line with European legal values. When you buy it back, the cost of delivery is deducted, which is no longer possible in the EU. Restocking Fees are also a special regulation in this case, because they are only not charged if you ask for a replacement product.

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