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Portable Amps item created by mscott58, May 25, 2015
Pros - Seemingly transparent sound quality, light weight, free quality micro-USB cable.
Cons - No gain switch, not as small as some other alternatives.
If I was to rate products by how easy they are to review, I’d pick amplifiers as an easy first, and headphones and IEMs last. While both have their complexities, with amplifiers those lie with the engineers and manufacturers, and it is fairly easy to determine to what degree the products goals have been met, whereas the complexities of headphones related to the listener, such as music tastes, how loud one listens, comfort and whatnot.
In that regard, the new Rx from Ken Ball at ALO Audio is on the dead easy end of the scale: Do you need an amp that drives IEMs well, especially high-end models with multiple balanced armatures? Do you not mind that it is not the smallest in category, but is a bit bulky? Yes to both? Then the Rx will do the job, all the way up to JHAudio’s new Laylas. That was easy, wasn’t it?
Of course, that is not only what a review is for. You’re hopefully reading this for the fine details, of which there are a few; and to answer a few questions, like “Do I really need this if I have an iPhone?” which is more relevant. “No” is actually the answer to the last question, but because this hobby is not about “need”, because even if an iPhone nowadays is “good enough”, this is about better than good enough, especially if you’re the kind of person who’ll put down a four-figure sum for the best custom, or now universal in-ear monitors.
The Rx is not four figures though, it is $349 at the time of writing. It comes from a line of amps that were first sold in 2009, when a phone really wasn’t good enough for the wave of new multiple-balanced-armature IEMs coming out and required very low output impedances in an amp to avoid quirky results. The Rx line went rather crazy over the next few years, ending up with the monster Rx MKIIIB and its desktop amp-level power. The new Rx goes back to its origins.
It is still, in essence, an opamp-based design, like the original, but every other aspect of the design has been optimised for the lowest distortion possible with IEMs. I have no doubt it was this care and attention to the design that resulted in the experience I had below when I first listened using it with the Laylas. That is why it is easy to review, as the first experience I had told me all I needed to know about amp’s capabilities.
But we still need to cover the physical design, which is a reasonably small nickel-plated case containing a recharchable battery, a power/volume knob, input and output sockets and a USB charging socket on the back. Looking inside the unit, the deliberate choice of a high-quality analogue volume control over a digitally controlled one has pushed the size up above what one might call ideal. Alongside that the sockets and volume aren’t aligned, which ruins the attractiveness a bit too. The case does feel quite classy though.
Functionality-wise, aside from the obvious connections, an orange LED on the front indicates that the power is on, and likewise one on the back next to the USB socket glows orange when charging and green when done. That is as complex as it gets. Holes on the sides allow heat, if any, to vent. Very simple indeed.
An unexpected bonus with the Rx is the inclusion of ALO's Green Line micro-USB cable for charging. It is designed as a high-quality USB data cable, so if you own a DAP or the like which you're using via a regular cheap micro-USB, Ken told me that he put in some serious effort with the design to ensure good digital transmission.
Unlike the original Rx, the actual circuit is more complex. Like we are used to seeing in high-end full-size amps, much care has been taken in the design of the power supply to ensure low distortion and noise in the amplification circuit. Amplification itself is not simply via an opamp as before, but a 2-stage circuit consisting of an OPA49720 opamp feeding a Texas Instruments TPA6120a2 headphone amplifier chip. This chip is a high-bandwidth, low noise design with independent power supplies for low crosstalk, critical for maintaining the sense of soundstage. Designed to maintain a high dynamic range even with high-power output (it can potentially output up to half a Watt) its use in a dedicated IEM amp makes the Rx an interesting design.
I plugged the Rx into my Chord Hugo, which is very much excellent with IEMs, and tried the JHAudio Layla universals both direct and via the Rx. Now I must explain that the Laylas, with their 12 drivers and sophisticated crossover are the biggest pain to drive when it comes to in-ear monitors, possibly more so than any headphones I own. While, say, my FiiO X5 (original model) is pretty fine even with multiple-BA IEMs, it just fails dismally when trying to drive the Layla. Not just less resolution, but wooly bass and mushy sound overall. The Laylas are extremely picky when it comes to amplification, and capable of amazing things when paired well. It is not surprising that they teamed with Astell&Kern to sell them with the AK240. That is the kind of amplification they require.
So I sat down and plugged back and forth between the Hugo direct and Rx. And….no difference! A perfect result! That was most pleasing. The articulation all the way from the bass through to the treble was delivered perfectly, much to my satisfaction. That left me to compare it with other amps and other sources, where there were some interesting discoveries.
I have been using DITA Audio’s The Answer IEMs since their release. Possibly the epitome of single dynamic driver IEM design, they set a high standard, with a price to match. More recently they released a version compatible with the Astell&Kern balanced socket and Danny from DITA kindly conceded to my request for a pair to use for comparison purposes. This proved quite surprising, as the amp in the AK240 is highly capable of driving everything from IEMs up to full-sized headphones with surprising authority. However the Rx had the edge with the easy-to-drive DITAs, even comparing it to the balanced output of the AK240. It wasn’t a large difference, but a sense of slightly more precision and space from the bass through to the treble.
Comparing the Rx to the AK240 with the Laylas was a bigger surprise still. Out of the AK240 in balanced mode they sound quite dark, but the Rx seemed to bring out the treble to a much greater degree than I was suspecting. I rotated through a few amps to try and discover if it was just the AK240 and the Rx still held the result as the amp with the most spacious overall presentation. The Pico Power was a touch more mellow and less spacious-sounding than than the Rx, which can sound slightly brighter in the treble. The Sound Potion Monolith seemed to put a bit more emphasis in the bass and was tiniest bit smoother-sounding. Between them they were all hard to pick. The main difference is with the more expensive Pico Power you get full-sized headphone driving ability and gain settings, as well as a leather case, but an amp that weighs considerably more as a consequence.
That leaves the main disadvantage of the Rx being the size and lack of gain selection, though it is quite a light amp and still smaller than the amps I compared it to. While most portable devices do a good job of driving IEMs, if neither of the negatives are an issue, but getting the most out of a pair of high-end IEMs is the primary focus when one's existing source doesn't do the best job, then ALO's Rx could be just what is needed.
Pros - Great resolution, small(ish) size, smooth volume control, no wasted effort, dead-quiet, well constructed, light-weight, cool visuals
Cons - Might not get loud enough on all IEMs, only an amp (but that's what it is supposed to be)
As my wife will tell you, at just about every major audio show I attend I buy something (shocker right?). There’s something cool about looking at my pieces of gear and thinking about the show where I got them. For example my Noble K10’s make me think of Denver and RMAF/CanJam and working feverously with the Head-Fi crew to build all the banners before the show started (good times Joe, Jim, Jude, Warren, and Andres!). SoCal this year was about finding the best portable amp for my wonderful Kaisers, and I think I tried almost every one out there. When I worked it down to the two finalists I was wondering how to best do the final A/B comparison. I got Ken Ball’s attention at the ALO table and asked him if it would be okay if I wandered off with one of his new Rx amps for a while. He said no problem at all. Nice! (in full disclosure I did volunteer to leave my travel case containing my LCD-3’s with him as collateral, so it was very low risk to him!). However, I think that Ken might have even let me even without leaving him ~$2K in gear – he’s just a good guy. Off I went to the other amp manufacturer’s table, and many swaps of amps later I had a winner. I wandered back to the ALO table and told Ken his Rx had won the portable IEM-amp cage-match against the also very good Oppo HA-2. “Great” he told me, “and thanks for supporting Portland!”. So what won me over and what do I think of the ALO Rx? This is a review, so that’s what comes next. Geeze, why ask such a silly question…
So Ken’s ALO Rx is clearly not a Swiss-Army type of amp, this baby is purpose-built, and what it does it is awesome at. This amp is no decathlete, it’s a one-trick pony. “My name is ALO Rx and I’m an portable headphone amplifier for IEMs and that’s all I have to say about that.” Stand proud my friend, for you do your duty and you do it well.
In fact I realized that the portable amps I had been using before had bells and whistles I didn’t need and wasn’t using, and that was okay, but they made the amps bigger and meant I was paying for stuff I wasn’t using. Built in DAC? Nope, that’s part of my DAP’s duty. Ability to change gain ranges? Sorry, my K10’s are my CIEM’s for travel (and everything else currently) and when I’m home my LCD-3’s have their own dedicated amp and the Rx has just the right gain for my CIEMs. Adjustable treble/bass/etc.? Not needed – the combo of the K10’s and Rx is just the blend I need for the sound I like. Balanced output? Well, that would actually be cool, but hey, that’s outside the remit for this value-packed, option-light amp. Ability to make me an extra-hot skim latte? Hey, that’s why by law we have Starbuck’s every two blocks!
Also the Rx is lightweight, but not in a cheap way. This is custom milled metal people. For those of us who have fallen in love with titanium (my bottle opener on my keychain is titanium – guess that isn’t what the material scientists were thinking about when they developed that alloy) know that Ti is super light, but not cheap. It’s light on purpose – same with the Rx, although it’s not made of titanium, but nickel-coated aluminum (and now is available in black anodized as well). Actually the ALO Rx is like a sports car that has ripped out all the excess weight to help it go faster. This is a stripped-down, purpose-built IEM amplification machine. Don’t ask it to make you a latte or shine your shoes (wait, didn’t I already use the latte line? That’s a lot of latte). It doesn’t slice or dice, it amplifies, and it does it wonderfully – the best of any portable amp I’ve heard to date. Size-wise it’s almost a perfect match to my Fiio X3. The Rx is about ¼” shorter (when you include the volume knob) and essentially the same width and depth. A few straps/rubber bands and a nice patch cord (ALO of course!) and you’re good to go. Since I just mentioned the volume knob it’s the right time to tell you that I find it to be one of the best implementations of volume control on a portable piece of gear I’ve ever used. It’s conductive plastic potentiometer has a great range of motion and is both smooth to turn, with no degradation of the music during adjustments, and is firm enough to not get turned inadvertently during normal use. Ever almost blown out your ear-drums when you bump against a volume knob? No worries on that with the Rx in my experience.
One very cool thing is that Ken picked an orange LED to show the amp is powered on. Why is that cool? It’s not Halloween after all. Well, with the drilled grills on the sides of the amp the LED gives off a nice warm orange light, making you think of the glow of a tube, which is a theme of Ken’s work and reminds you of his other new portable, the Continental Dual Mono (which is an awesome piece of gear in itself). Was this done on purpose? I’m not sure – but it looks really cool (warm actually). The ALO Rx is made in the USA and looks hand assembled (because it is!) - almost bespoke.
Okay, so what does it sound like? Well, like most reviews I waited until near the end to talk about that (why do we all do this? Are we afraid that people won’t keep reading our lame prose and stupid coffee jokes?). The Rx has a deeply engaging sound and offers amazing resolution and decay that goes places I didn’t know a portable setup could go. One of the great things about my current reference desktop amp (the Bakoon HPA-21) is its ability to pull apart the finest details, seemingly let you identify not only the type of guitar being played, but possibly even the manufacturer of the guitar! The Rx is similar, in letting you hear great levels of detail and in a way that doesn’t distract from your overall listening experience. One example of the ALO Rx’s ability to show the texture of the notes is in the bass line in the intro to Hotel California. The Rx shows a great level of detail and emotion in these low notes while not taking away anything from the detail of the plucking of the guitar strings being played at the same time. The more you zoom in the more details you can see as you focus on a specific part of the music. This reminds me of the Sydney Opera House, but not because of that venue’s great acoustics, but rather the fact that what looks like smooth white sails on the external surface of the incredibly designed building are in reality millions of small white tiles. Pay attention in life and it’s amazing the additional things you can see and hear.
The amp is also voiced in a way that I really like. What is that voicing? I would call it neutral, with maybe a slight tick towards warm. What does that mean? Well, describing this stuff is always the hardest part. Let’s say I love the K10’s, I love the Bakoon HPA-21 and I worship my LCD-3F’s – none of which are analytical, but are a bit warm and skewed a bit towards the lower end (IMHO). The Rx doesn’t add much, if anything on its own, but allows this sound signature to shine through. And speaking of not adding anything, this amp is like a black-hole in terms of background noise – it’s just black, which is one of the reasons it is able to resolve fine details so well.
As far as the other bits go, everything works as it should. The battery is great and I’ve never run it all the way down, although I am a stickler on charging it between trips. The plugs are solid and well built, the unit itself is very well constructed and has given me no issues at all. As a bonus you even get an ALO Green Line micro USB cable with the nickel version of the Rx, which is quite a deal seeing that this cable’s retail price is about half of the total cost of the Rx. No cheap after-thought cable here my friends.
So what’s the downside of Mr. Ball’s little Rx-reboot wonder? Well, as mentioned before it is only optimized for this one use, so don’t expect it to do more. Also be sure to ensure that the range of amplification fits your IEM’s well. It should most, but there is a chance it might not be quite powerful enough for some, depending on how loud you want to listen. For example on my K10’s the Rx powers them perfectly in the range I normally listen to, but if I really wanted to blow my eardrums out the Rx won’t go that high. Actually, this is a kind a safety mechanism for me, protecting me from hurting my hearing by playing at stupid-high levels of volume. That’s the only thing I can say about the Rx that isn’t totally positive, and it actually is not a downside for me. Ken’s done a great job on this unit.
Okay, I don’t usually go for the cheap humor (“that’s not true!” you’re likely shouting) and I’ve bit my tongue to not say it until this point, but the ALO Rx is just what the doctor ordered for this audiophile who has it bad for great sound while on the go. At the list price this is an awesome deal – at the show discount it was a no-brainer. Highly recommended and my current portable reference.