• ALO Audio Rx Mk3-b Portable Headphone Amplifier Review

    ALO Audio along with a handful of other companies has been leading the charge on portable audio amplification. Their product lineup includes one of the largest and varied sections of both tube and solid-state portable headphone amplifiers. Sitting atop the mobile offerings is the ALO flagship Rx Mk3-b ($650). Offering both balanced and single-ended inputs and outputs, this battery-powered headphone amplifier is a reminder that head fi audio is slowly adapting the same principals as audiophile loudspeaker components. While close competitor Ray Samuels and budget brand Fiio provide even more illumination to the landscape, ALO pushes the performance (and price) of portable even further north with the Mk3 over previous amplifier-only incarnations. Even more recent than the Mk3, a new wave of amp+dac combinations is sweeping the countryside with the promise of everything you need for desktop listening in a compact package. This new arrangement however, doesn’t allow for the versatility that accompanies the Mk3. As I’m sure you know if you are reading this review, that DAC technologies and improvements are moving at a much faster clip than the rest of HiFi audio, especially in the portable realm. For the purpose of this endeavor, I paired the Mk3 with a wide variety of sources in an attempt to deliver the fullest viewpoint of applications. On both the giving and receiving ends the Mk3 is quite a flexible device.

    Rx Mk3-b Details

    The 2.42 x 4.03 x 0.32 inch casing of the Mk3 is durable and solid, much of what you might expect from something that makes its home around the term “portable”. The all-metal finish comes in both black and silver. The unit, which is roughly the size of a deck of cards, also ships with elastic bands. These bands can be used to strap the amp to your source of choice, or even just as protection from scratches in lieu of the more common attachable little rubber feet. ALO also sells the Cypherlabs AlgoRhythm series of portable DACs that match the footprint and finish of the Mk3. The two knobs that grace the front of the unit stick out fairly far (compared to many other portable audiophile products) which offers plenty of grip for people with larger hands. The unit turns on with the spin of the volume knob and rotary resistance is fair, if not a bit utilitarian to the touch. The bass control located to the left of the mandatory volume knob is somewhat unique as bass boosters go. In addition to the careful gradual blending a variable control allows (as opposed to stepped intervals) the augmentation’s influence seems to stretch beyond the bass domain and creep into other frequencies. The bass modification is listed on the ALO site as such: .5 dB @ 360 Hz, 1 dB @ 260 Hz, 2 dB @ 160 Hz, 3 dB @ 80 Hz, 3.5 dB @ < 40 Hz, and < .5 dB @ > 360 Hz.

    Overall the change is entertaining. To my ears it is successful in not only increasing bass presence, but also in adding a low-end richness that many may find appealing. It avoids the common frequency bloat of lesser boosts and also allows for the fine-tuning of its influence over the mix. With the knob tuned to its maximum, I could still see some bassheads walking away a little disappointed. The change is smooth and gradual, and the top delivery is still remarkably more balanced than many mainstream bass-forward headphones. I prefer a more flat response, so for most of my listening sessions I kept the bass knob turned off.

    One of the biggest contributions to the Mk3-b’s flexibility as an amp is the 3-way gain selector. The lowest setting provides a nice, smooth volume transition from low to high for in-ear monitors (like the Jerry Harvey JH13s), while the highest setting is able to tackle some of the more demanding, full-size headphones on the market. I did notice a faint line buzz with IEM usage, even on the lowest gain setting. The background was dead silent for the sensitive 18 ohm Sennheiser Momentums with loud listening at about 40% of the volume knob on the lowest of the three gain settings. The in-house battery includes 10-14 hours of playback time and should fully charge in 3 hours via the included wall wart. Balanced connectivity requires the implementation of a RSA custom connector for either output or input to the amplifier. The 4-pin socket usually requires a custom cable, but DIYers can find the connector online for relatively cheap. Volume output is comparable between the two variations.


    Using The Rx Mk3-b

    The iRiver Astell and Kern AK100 is a fantastic little DAP that excels at low to mid impedance headphone playback. Where it runs into a little bit of trouble is playing nice with the big, full-sized cans. Power output comes up a bit short driving high impedance headphones like the Sennheiser HD650s (300 ohms) and planar magnetic drivers like the Audeze LCD-3. Playback can get maxed out with softer recordings and it doesn’t leave much headroom to spare. I implemented the Mk3 into the chain via the AK100s headphone output set to maximum (75). Using the SE input on the Mk3 I was able to drive the LCD-3 to acceptable levels, even with softer, classical recordings. For most recordings the Mk3 did an excellent job maintaining the detail and articulation of the source and didn’t artificially color the signal. While listening to 24 bit/96 kHz version of Beck's Sea Change I found the Mk3 to tip slightly to smoothness over detail in the mids, while exuding just a bit more control over the low end than the headphone output of the AK100, although this was less noticeable depending on the track. It is noteworthy that I heard little to no sound degradation from the AK100 headphone output even when it was maxed, a fine testament to proper amplifier implementation. Overall I found the Mk3 to complement the AK100 quite nicely.

    Using Audirvana Plus on my Macbook Air, the AudioQuest Dragonfly output proved to have a bit more oomph to it than the AK100. Not limited by the same power restrictions as the AK100, loud volumes with the Audeze LCD3 are much easier to attain through the headphone output on the DF. But all things being equal, I found the ALO Rx Mk3-b’s ability to drive headphones with authority very pleasing via the Dragonfly. The AQ DF has a great treble energy that helps it stand out from the growing throngs of budget portable DACs available, and once again the Mk3 did a great job of relaying that information. My ears were again met with a more controlled sound, but to an even larger degree than the AK100. Comparing the equivalent volume output from the Dragonfly (direct to headphone) to the Mk3 (via the DF at 100% digital output) an improvement in bass accuracy and impact was much more noticeable. The David Chesky binaural track Pamafunk by the Brooklyn Funk Band places the bass guitar just to the right of center in the stereo mix and does a decent job of placing the instruments in positions that get them a little more “out of your head” with headphone listening. The bass guitar tone and texture was less murky and more fully-developed though the Rx Mk3-b compared to the AudioQuest Dragonfly headphone output. The staccato passages that pepper the song also hit with a more realistic sense of intensity and power. So in terms of headphone amplification the Dragonfly is a bit more gain and a little less grace. This also makes it a good candidate for the Rx Mk3-b, but for slightly different benefits. Even streaming services like Mog or Spotify showed improvement with the inclusion of Rx in the mix with the Dragonfly.

    Every product has its strengths and weakness, and limited internal real estate can unfortunately introduce design restrictions on portable products. So how does the Mk3 stand up to larger component head amps with much more room to spare? The Burson Conductor ($1,850) Headphone/DAC/Pre-Amp makes an excellent top tier partner for the Audeze LCD-3 headphone. To see how the two amps fared I connected the Dragonfly’s output to the Burson’s and Rx’s SE analog inputs. The 24/96 version of Jason Mraz’s I Won’t Give Up starts with a subtle, yet very textured bass guitar line which the Rx Mk3 has no trouble reproducing in its entirety. But as the song picks up the Burson was able to deliver a more “sitting in front row” sense of clarity and enthusiasm. While the Rx does a great job with low-end impact, in the end the Burson was able to edge it out with slightly better bass grunt and top end air around the vocals and acoustic guitar parts that drive the track. ALO founder and designer Ken Ball is also currently working on a new flagship piece called the Studio Six, which will be his solution for a high-end, full-size headphone amplifier.

    There are many factors that could influence your purchase decision for the Rx Mk3-b. Even ALO’s own line of portable amplifiers offers a fair gamut of options. The closest competitor feature for feature is the Ray Samuels SR-71b, and both companies have since produced products that include a built in DAC. If your needs meet at a crossroad of battery-powered portability, single ended and balanced connectivity with ample power for a wide variety of headphones then the ALO Rx Mk3-b should be something to set your sights on. Sonic benefits vary depending on both source and headphone pairings, but the Rx Mk3 does a great job with both transparency and flexibility. The total sum of the output is free from any major inconsistencies or sonic flaws that could get in the way of a proper listening session.



    The ALO Rx Mk3-b is a solid complement to any desktop space. Top tier portable audiophile performance lies just beneath its metallic exterior. Considering the battery power and relative size, the Rx is very much a product of convenience. The simple layout and compact design allow you to have HiFi coffee shop (or office) listening without putting in too much effort. The bass knob is a plus for those who like a little extra on the low end. The build quality leaves you with the notion that its not going to fall to pieces if you throw it in your laptop bag. It makes a great headphone all-arounder if you have upgrade tendencies, especially in the DAC department. The 12dB of variable gain via a three way switch allows you to rock out with control to your headphone of choice, connected to your DAC of choice. The Mk3 offers some of the best elements of the headphone hobby in a compact, portable package. Plug in your favorite source and you’ll have a slice of audio nirvana with you wherever you want to go.

    Product Information:

    • Product - ALO Audio Rx Mk3-b Portable Headphone Amplifier
    • Price - $649
    • Product Page - Link

    Associated Equipment:

    About The Author

    Brian Hunter
    I’m a recovering musician turned audio reviewer. I currently manage and write reviews for Audio-Head.com and freelance with several other publications. I love tech and the tools of music, especially the ones involved in reproduction. After I finished my undergrad degree in business I went to the local community college and got one in photography, which was way more fun. I like it when people have unbridled enthusiasm for something and I have the utmost respect for individuals who try to create, even more for those who are good at it.

    Comments 1 Comment
    1. mikemercer's Avatar
      mikemercer -
      I LOVE my RxMK3-B!! Gave it a Writers Choice Award last year in Positive Feedback.
      I couldn't agree with you more! I didn't think they could step it up from there, but The International
      is amazing!

      I do reach for my RxMK3-B often in the Sonic Satori Personal Audio Lab though!
      Great piece Brian