Playback has covered two earlier ALO Audio portable headphone amplifiers—the original ALO Rx (click here to read our Rx blog) and the ALO Rx MK2 ($449, click to read our Rx MK2 review) with favorable comments on both. But now, we have on hand the Rx MK3-B fully balanced portable amplifier ($649), which is by far the firm’s most ambitious design to date. What, you might ask, would make a portable headphone amp not much bigger than a deck of playing card worth the princely sum of $649? We’re glad you asked.
ALO’s Rx MK3-B is a no-holds-barred attempt to build the most versatile and one of the most powerful portable headphone amplifiers ever brought to market. The target market for this amplifier consists, as you might expect, of very serious earphone/headphone enthusiasts (ones who might typically own multiple sets of top-tier earphones, custom-fit in-ear monitors, and full-size headphones), and ones who sometimes like to travel with more than one set of ‘phones. For these listeners, what’s plainly needed is a portable amplifier that offers performance comparable to a top-tier desktop amp, but in a pocket-sized format. The Rx MK3-B was created for just such listeners, and in fact Ken Ball, the founder and owner of ALO says the MK3-B is “arguably the most sophisticated portable amplifier design in the world,” one that includes a combination of features not found in any other portable amp.
Understand, then, that we are talking about a portable amp that must attempt to be all things to all listeners—an amp quiet and sonically refined enough to drive extremely sensitive custom-fit in-ear monitors, yet powerful and robust enough to drive the most power-hungry full-size ‘phones available today. In short, we are expecting the Rx MK3-B to cover not only the performance extremes but also all the performance bases in between. Does the ALO amp successfully pull off this daunting feat? That is one of the key questions we will attempt to answer in this review. We will also take a look at how the Rx MK3-B compares with the conceptually similar and comparably priced Ray Samuels Audio SR-71B portable amp as recently reviewed in Playback (click to read our SR-71B review).
• The Rx MK3-B is a full balanced portable amplifier that provides both unbalanced (single-ended) and balanced inputs and outputs.
• Switch selectable single-ended and balanced stereo inputs.
o The single-ended inputs are implemented via a 3.5mm input jack, while the balanced inputs are implemented via a miniature, square-shaped, four-pin connector. Users select between the two inputs via a rear panel-mounted mini-toggle switch
o A number of specialty cable makers (including ALO Audio, Moon Audio, and others) offer stereo XLR-to-miniature 4-pin adapter cables that make it easy to connect high-end home or pro-sound source components to the Rx Mk3-B.
• Single-ended and balanced stereo outputs (implemented, respectively, via a 3.5mm mini-jack and the aforementioned miniature 4-pin balanced connectors). Whenever the amplifier is powered up, both the single-ended and balanced outputs are live.
• Switch-selectable master gain switches, with settings for low, medium, and high gain.
o This feature lets users adjust the overall gain of the amp to match the sensitivity of their earphones and headphones. For instance, you might use the “Low” gain setting with high-sensitivity custom-fit in-ear monitors, the “High” gain setting with hard-to-drive full-size headphones, and the “Medium” setting for ‘phones falling somewhere in between.
o The gain switch also effectively serves as a means of controlling the amplifier’s noise floor (choosing the “Low” gain setting gives you a lower noise floor but also reduces maximum available gain, while choosing the “Medium” or “High” gains settings will give you more available gain, but with an attendant increase in noise).
• Four-color indicator light:
o Blue = play
o Green = charging
o Yellow = low battery
o Red = very low battery/charge now
• Bass boost control: The Rx MK3-B provides a distinctive, variable-level bass boost control that can be defeated by rotating the control knob fully counter-clockwise. By design, the effects of the boost control are subtle, for the most part applying low-frequency boost below 80Hz with maximum impact down below 40Hz. Used in moderation, the control helps provide a touch of low frequency foundation at the bottom end of the audio spectrum, while maximum boost setting also add audible mid-bass and upper-bass enhancement.
• 4400 mAh Lithium-Polymer battery pack that provides up to 10 hours of balanced mode playing time or up to 14 hours of unbalanced mode playing time. Charge time: 3 hours.
• Accessories include a wall-wart-type 9V battery charger and three ALO-labeled rubber straps for attaching portable DACs or music players to the Rx MK3B.
• Available in satin black and matte silver finishes.