Interestingly, the Ray Samuels SR-71B might be just a smidgeon quitter than the Rx MK3-B, largely because the SR-71B offers slightly lower gain settings (and thus potentially lower perceived noise floors) than the ALO. Even so, I felt noise differences between the amps were so subtle that I doubt most listeners would even notice them.
Got Power? With its balanced outputs brought into play, the Rx MK3-B had sufficient power to drive even the brutally demanding HiFiMAN HE-6 headphones, although my sense was that the HE-6 pretty much used up every ounce of power output the ALO amp had to give. For all other headphones, though, I found the ALO amp had more than ample power, typically serving up expressive and, where appropriate, explosive dynamics.
Compared to the Ray Samuels SR-71B, the ALO Rx ML3-B seems at first to be the more powerful amp, although in theory the SR-71B offers somewhat more power output because it features higher voltage battery packs than the ALO does. What tips the balance in the ALO’s favor is the fact that its higher available gain settings help users tap the power at hand, whereas the SR-71B sometimes begs to be run with its volume control wide open.
Do balanced inputs and outputs make a difference? I found the ALO’s single-ended input sounded fine, but that sound quality took a subtle but audible step up when the balanced inputs were brought into play. I don’t know whether the improvement I heard was attributable to the Rx MK3-B’s balanced input circuitry, or to the fact that source components with balanced outputs often perform better in balanced mode. Either way, think of the ALO’s balanced inputs as a “turbocharged” version of the amp’s already very good single-ended inputs.
Balanced outputs give the ALO (and the Ray Samuels SR-71B) significantly higher power output than the single-ended outputs do, as the SPECIFICATIONS table, below, reveals. What is more, many headphone aficionados claim that balanced outputs afford superior control over headphone drivers, and thus yield a more nuanced and revealing sound over all—results that my listening tests solidly confirmed.
Rx MK3-B vs. full-size desktop amps? When push comes to shove, the Rx MK3-B is not quite as good as the best desktop headphone amps we have tried (e.g., the Apex Peak with Volcano power supply, the Burson Audio Soloist, the Cavalli Audio Liquid Fire, the HiFiMAN EF6, or the Woo Audio WA22), but it certainly is not embarrassed in their company. This is saying a lot given that these desktop competitors are much larger than the Rx MK3-B and cost anywhere from hundreds to thousands of dollars more.
I found the performance gap between the ALO and premium priced desktop amps was narrower than I expected, meaning that the tiny Rx MK3B gave me a generous taste of what top-tier sound is like, while also conferring the benefits of effortless portability.
To hear both the ALO’s power and refinement in action at the same time, I put on the track “O Vazio” from Jim Brock’s album Tropic Affair, which is represented in the Reference Recordings sampler, Jazz Kaleidoscope [HDCD]. I like to use this piece as a test track for several reasons, partly because it has some unbelievably loud, clear, low-percussion moment near the opening and close of the piece, and partly because all the other instruments in Brock’s jazz ensemble sound so rich, clear, and sumptuous—especially the delicate cymbal work heard throughout. The catch (or potential catch, in this case) was that I chose to listen through my terrific-sounding, but almost painfully difficult to drive, HiFiMAN HE-6 headphones, ‘phones that sponge up amplifier power the way camels in the desert soak up every drop of water they can find. Let’s be clear; asking most portable amps to drive the HiFiMAN HE-6 properly would be an exercise in frustration, if not a bad sonic joke. But not the ALO Rx MK3-B. It simply latched on to the HiFiMAN ‘phones and drove them with the kind of depth, punch, power, and articulacy typically associated with big, muscular desktop amps. As the low percussion notes arrived, I marveled at the way the little amp caused the headphones to unleash big bass pressure waves I could both hear and feel, and I noted with satisfaction that the amp caught the subtle modulation and gradual decay of those mammoth notes with terrific articulacy and precision.
But the ALO went much further on “O Vazio”, revealing the sonic craftsmanship with which Reference Recording’s “Prof.” Keith O. Johnson put this album together. In particular, I was struck by how beautiful percussion instruments sounded, so that I could hear the discrete parts of each individual note—attack, sustain, and decay—as they unfolded with remarkable realism. It’s one thing to talk about relatively costly desktop amps delivering this level of performance, but it was breathtaking to hear a $649 portable step up and sing at this level. Who knew? One further point I would draw from my experience with Brock’s “O Vazio” as heard through the ALO amp and the HiFiMAN HE-6 headphones is that the Rx MK3-B’s uncanny smoothness and refinement was everywhere in evidence. I my experience, many headphone amps tend to make the HE-6 ‘phones sound detailed, but also a bit “hot” and edgy. Through the ALO, however, I was able to enjoy gobs of inner detail in the music, without suffering any edginess or glassy-sounding distortions. I can’t speak for you, but I love it when audio components offer gain without pain, as the ALO happily does.