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ALO Audio Rx Mk2 Portable Headphone Amplifier (Playback 43)

Many portable audio enthusiasts invest in high-quality earphones that they plan to use with their iPods, iPhones, iPads or other personal digital audio players. But the further you go in this hobby, the more like you are to encounter serious, high-performance earphones or custom-fit in-ear monitors that cry out to be powered by high-quality portable amplifiers. To be perfectly clear, let’s acknowledge that you could drive most of these high-end ‘phones or monitors directly from an iPod or other portable device—if you really wanted to do so. It’s just that past experience has shown that high-end earphones can and do sound better—often a whole lot better—when driven by high-quality portable amps. Think of the step up to a separate portable amp, then, as a “graduation day”-like experience, where you can expect to take a big step up in quality from the sound of a box-stock iPod-powered system.

Which portable amplifier should you choose? Frankly, there are many good models on the market, a number of which Playback has reviewed or will explore in the future. But one of the nicest we’ve found, and a model that we have used as a reference in doing many of our high-end earphone and in-ear monitor review, is the ALO Audio Rx Mk2 ($449).

About ALO Audio

ALO Audio (the acronym stands for “Audio Line Out”) is an Oregon-based firm headed by Ken Ball that manufactures a very high quality portable headphone amplifier (the Rx Mk2 model under review here) plus a range of associated specialty audio cables and accessories geared for high-end headphone enthusiasts. In addition to building its own products, however, ALO Audio also serves as an online reseller that offers a broad array of home audio, portable audio, headphone, specialty cable, and iPod/iMod audio products.

In addition to ALO Audio, Ken Ball also operates a Portland, Oregon-based, high-end headphone-oriented specialty retail store called 32 Ohm Audio. To check out this gorgeous facility, which describes itself as “Portland’s only Headphone Boutique and Digital Audio Salon,” click here.

While ALO Audio quite reasonably asserts that it own amplifier and cable products are carefully designed and extremely well-made, it stops short of claiming that its products are “inherently superior to all others” or “the only valid choices for discerning listeners.” Instead, ALO Audio takes a welcome and thoroughly refreshing “live and let live” approach toward its respected competitors, whose hand picked components are offered for sale directly alongside ALO products through the eclectic and inviting ALO Audio web site.

About ALO Audio’s Rx Mk2 Portable Headphone Amplifier

ALO Audio’s first portable headphone amplifier was the lovely and great-sounding Rx (or “Prescription”) model—an amp that Playback first encountered in June of 2010 and that I began preparing to review in the fall of 2010. Click here to read my detailed “First Listen” blog on the original ALO Rx amp.

However, just before I was ready to finalize my Rx review, I met up with ALO Audio’s Ken Ball at the Head-Fi.org Can-Jam event held at the Rocky Mountain Audio Fest in October of 2010, and learned that a new and more highly-evolved version of the amp—called the Rx Mk2—had entered production and was ready for review.

As you might expect, the Rx Mk2 incorporates many of the signature features of the original Rx, along with several seemingly small but decidedly worthwhile changes. I’ve listed technical highlights of the Rx Mk2 below:

• A slightly larger brushed aluminum chassis with revised (and in my view, improved) cosmetics.
• A significantly larger, beefier, dual Li-ion onboard battery pack.
• A version of the “smart charging” circuit pioneered in the original Rx amp, which “constantly monitors the batteries’ voltage and current capability” and that also “determines the optimal current and voltage to feed the batteries that will best charge and preserve the life of the batteries.”
• A version of the special power supply used in the original Rx amp that features, says ALO, “a real bi-polar power supply not a rail splitter…” and that can deliver “a minimum of 5.25V peak to peak and over 200mA of output current.”
• A new “illuminated on/off ‘smart’ LED switch, indicating charging and battery status.” The color code for the switch works as follows:
     – Power switch off, no LED = amp is turned off.
     – Power switch off, LED is solid green = amp is plugged into charger and battery is actively charging.
     – Power switch off, LED is blinking green = amp is plugged into charger and battery is fully charged.
     – Power switch on, no LED = battery is exhausted.
     – Power switch on, LED is solid green = amp is turned on.
     – Power switch on, LED is bright green = amp is on, but also is plugged into charger and battery pack is charging.
     – Power switch is on, LED is blinking green = amp is one, plugged into charger, and battery pack is fully charged.
     – Power switch is on, LED is Red = amp is on but battery is low.
• Improved heavy-duty 3.5mm input and output jacks.
• A version of the very low distortion analog audio circuitry from the original Rx amp, with claimed frequency response of 10Hz – 20kHz ±0.1 dB @ 1 V output, with THD + Noise of 0.004% @ 1 V output into a 24 Ohm load.
• A version of the distinctive “digitally controlled dual stepped attenuator” volume control circuit from the original Rx amp, said to be accurate to within ±0.2 dB. The control features a tiny, spring-loaded volume up/volume down switch rather than a typical control knob. Upon initial power up, the volume is automatically set to a moderate middle level (so you can tell from the outset that everything is working properly), with users of course having the option to adjust levels upward or downward from there.
• A compact 100v-240v charger that comes fitted with a US-type plug.

Setting the Context: Why Go With a Portable Amp?

None of us wants to spend more than we have to in order to enjoy great sound, which begs the question: are portable headphone amplifiers really necessary? To answer this question, it is important to bear in mind that there is a big difference between driving high-performance earphones (as in “get them to make sounds at reasonably satisfying volume levels) vs. driving them well (as in “extracting the fullest measures of power, resolution, delicacy, and finesse of which your earphones or monitors are capable”).

Without knocking iPods (or there brethren) in any way, it is fair to point out that A) their analog audio circuitry is good but not great, and B) they do not offer the most powerful/capable amplifiers around. Therefore, the key to superior sound—at least for listeners with high-end tastes—is to A) find ways to bypass as much of the iPod’s analog audio electronics as possible, and B) to connect the iPod to amps that offer more power with less distortion. This, in a nutshell, is precisely what ALO Audio’s solution allows.

A Key Accessory You Won’t Want to Do Without

In the preceding paragraph, I mentioned that one of the keys to getting better sound quality from a portable, iPod-based system is to “bypass as much of the iPod’s analog audio electronics as possible.” To do this, you’ll need what many high-end portable audio enthusiasts call an “LOD” or “Line Out Dock” cable. Basically, an LOD cable pulls line-level analog audio signals from downstream of your iPod’s onboard DACs, almost completely bypassing the actual amplifier section of the iPod. When you use an LOD cable, for example, you’ll discover the iPod’s volume control has no effect on the outbound signal; that’s because the signal is bypassing the iPod amp, including the amp’s normal volume controls, etc. Then, the LOD cable routes this relatively clean, pure, unadulterated analog audio signal into your outboard portable amp, which in turn offers much, much higher performance than the iPod’s own amp section could ever hope to provide.

Note: As a general rule, LOD cables are configured with a multi-pin Apple-time connector on one end and a 3.5mm mini-plug on the other. Some manufacturers, ALO Audio among them, do build LOD cables for non-Apple devices, though for obvious reasons LOD cable for Apple products are much more commonly seen.

ALO Audio makes several different grades of LOD cables, and Ken Ball graciously loaned Playback a sample of his finest model—which is called (no, I am not making this up) the ALO Audio 18awg OCC Triple Pipe Cryo iPod/iPhone Cable ($195). Translation: this very special cable uses conductors made of 99.99998% pure Ohno Continuous Cast (OCC) copper wires, which have been cryogenically treated. The cable features three bunches (hence the name “Triple Pipe”) of 144 strands of finely drawn wire, each encased in a polyethylene (PE) jacket. The wires are connected, says ALO, to a modified “premium Switchcraft Gold mini plug,” through which the iPod makes connection with the ALO Audio Rx Mk2 amp.

Does this pricey little cable really make an important difference? You’d better believe it does—enough so that, once your hear that sonic difference through a really good set of earphones, you might never be willing to go back to listening the old way. Also note that, if the $195 price of this mega-cable is a little too rich for your blood, ALO offers many alternative LOD cables—some starting at about $55.

The Sound of the ALO Audio Rx MkII

Most portable headphone amplifiers improve upon the sound of the iPod’s own amplifier in some ways, but what sets the ALO Audio Rx Mk2 apart is that it improves upon what the iPod can do in virtually every way imaginable—often by quite dramatic margins. Let me provide some details to explain my point.

iPods can, when heard through high-quality earphones, have a somewhat brash, ragged or raw quality that can make music—especially music that hinges on sonic delicacy and finesse—sound clumsy, overwrought, or a bit “out of control.” With the ALO Audio Rx Mk2 in play, however, those problems largely go away. This amp sounds consistently smooth, yet at the same time very clear and detailed, which is one of those high-end audio feats that easier to talk about than it is to pull off in reality. To hear what I mean, here, try listening to “The Last Fallen Leaf” from the late Chris Jones’ album Roadhouses & Automobiles [Stockfisch]. The track features a beautifully recorded solo acoustic guitar performance that is richly detailed. Through an iPod, tiny performance details, such a finger squeaks, fretting noises, or high-pitched overtones, take on a glassy, exaggerated, “zingy” quality that, while initially exciting and dramatic, sounds more and more unnatural and just plain wrong as you listen further.

But play the same track, from the same iPod, but with the Rx Mk2 in play and literally everything about the sound immediately gets better. Suddenly, sonic details (which sound at least as clear through the ALO as they did through the iPod) become better balanced and properly portioned, so that overtones and harmonics become sweetly integrated with the fundamentals of the notes that produced them, rather than sticking out like sore thumbs as they do through the iPod. Moreover, the timbre of Jones’ guitar sounds much more natural and truthful (not to mention sweeter) through the ALO, losing the disjointed, edgy quality it sometimes exhibits through the iPod alone. Finally, reverberations within the recording space, which are beautifully captured on this track, become much easier to hear and more believable through the ALO. Taken individually, these sonic benefits might seem small on paper (er, pixels), but taken together they add up to the kind of truly substantial, night/day improvements that, once heard and appreciated, become addictive and oh-so-difficult to forego.

But the ALO’s benefits don’t end there, because one of its greatest strengths involves an uncanny ability to capture the power, depth, and natural warmth of well-recorded music—especially as pertains to mid- and low-bass performance. Significantly, this is also an are where some of the iPod’s inherent weaknesses are most apparently, meaning that the iPod’s bass can at times seem weak and ill defined, as if some of the life and potency of bass guitars, kick drums and the like has simply gotten lost in translation. As a result, iPods can make music that has (or at least should have) a solid bass foundation sound as if it has been “cut off at the knees,” so to speak—sometimes to the point of taking on an unnaturally midrange-forward character that simply isn’t right. But with the ALO Rx Mk2 in play, the low-frequency foundations or underpinnings of good recordings are wonderfully brought back to life, with appropriate (never overblown) power, clarity, and depth.

To appreciate my point, here, try listening to a later track form Jones’ Roadhouses & Automobiles, called “Don’t Need Your Religion”. The track opens with bassist Grischka Zepf laying down a simple but forceful and downright subterranean electric bass line—a line that becomes even more urgent and syncopated as the song unfolds, so that it becomes, in a very real sense, the locomotive-like pulse that drives the song forward. Or at least that is what is supposed to happen, and actually does happen with ALO amp in the system. But take the ALO out of the system, listen through the iPod alone, and notice what happens. In an instant, the depth, potency, and vigor of Zepf’s bass line drains away, leaving the song bereft of energy and drive. The same thing also happens with the song’s vigorous percussion lines. With the ALO amp in play, percussion instruments have drive, snap, and tremendous dynamic life. With the ALO removed, the drums suddenly sound listless, watered-down, and lifeless.

Multiply results like these across many different types of music as played through many different models of earphones and headphones, and you can begin to see just how valuable the sonic contributions of the ALO Rx Mk2 really are. No, this amplifier isn’t cheap, but yes, it is worth the money—or at least it is if you want hear your favorite music reproduced with the clarity, tonal richness, and dynamic life that it deserves to have.

Bottom Line

The ALO Audio Rx Mk2 portable headphone amplifier has been a wonderful, reference tool that has served Playback (and its readers) well in countless evaluations of high-performance earphones and custom-fit in-ear monitors. The Rx Mk2 is one of those rare components that can make all types of music and most if not all types of earphones/headphones sound their best. Though not inexpensive, the RX Mk2 does it all, offering clarity, detail, tonal purity and richness, and faithfully conveying the life and natural warmth of the music.

Associated Equipment

Sources: Various generations of iPod Classics and iPhone 3G loaded with lossless audio data files ripped from CDs (and hybrid SACD’s)
Cables: ALO Audio 18awg OCC Triple Pipe Cryo iPod/iPhone Cable, Moon Audio Silver Dragon LOD Cable
Universal-Fit Earphones: (not an exhaustive list) Klipsch Image X10i, Phonak Audeo PFE 122, HiFiMAN RE-262, Monster Cable Turbine Pro Copper Edition, Monster Miles Davis Tribute Model, Sennheiser IE8, Shure SE535, Westone TrueFit-Series 4
Custom-Fit In-Ear Monitors: JH Audio JH16 PRO, Sensaphonics 2MAX, Ultimate Ears In-Ear Reference Monitors, Westone Elite-Series ES5

Specs & Pricing

ALO Audio Rx MkII Portable Headphone Amplifier
Power output: Maximum output = 7.45V peak to peak
Frequency response: 10HZ – 20kHz, ± 0.1dB at 1V output
                                         THD + Noise: 0.004% @ 1V RMS output into 24 Ohms
Included accessories: three ALO Audio-labeled silicone straps (for attaching iPod or other personal digital music player to the amplifier), 100v-240V AC charger with cord.
Analog Inputs: 3.5mm stereo (3-pin) mini-jack socket
Input Impedance: 40 Ohms
Analog Outputs: 3.5mm stereo (3-pin) mini-jack socket
Controls: Hi/Lo gain toggle switch, On/Off switch (with LED illumination, color-coded to indicate battery status), charging jack
Dimensions (H x W x D): Not specified.
Weight: Not specified.
Warranty: Not specified.
Price: $449

ALO Audio
(503) 206-5931

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