A portable amp can be a glorious device but something that is so commonly overlooked with them is what sort of headphone it is made for. This is so important because often they try to do to many things, it ends up doing a lot averagely or straight up flopping and while some do pull out the versatility card, too often I am reviewing a portable amp and not knowing the intended audience. ALO though have always been clear with their goals, the Rx MK3-B I own was about power, packing juice for harder to drive cans in a compact package. With the brand new Rx however the focus has been shifted for IEMs and if you know me, this is what I look for in a portable amp as they are the primary used listening device on the go. I also don’t feel that any of the top music players, including the AK240 (Josh always listens amped) and AK380, fully do justice even with IEMs without an amp and not simply through a lack of power, adding a well articulated amp technically really does go a long way. Going into an amp review knowing where to start and knowing what the goal is not only makes my life easier but excites me because an amp that wants to drive full sized headphones and IEMs, never pays enough attention to the finer details that an IEM needs.

We’re Going Through Changes

While keeping the Rx family name, the new version is nothing like my old MK3, not in size, not in look, not in function. It is even cheaper at only $299, fairly modest if you ask me. The main similarity is the volume pot where we have a shrunk down version of the two we used to have. Mentioning the pot and a lot of thought has gone into it. Volume control happens in the analog domain and therefore as we move past off/no volume, one channel gains sound first but as soon as we move into listenable volumes tracking is superb. It also leaves the tradition of using carbon potentiometers like what Alps use in exchange for a plastic one for improved lifespan. I love the knob feel as well, it is easy to use with a good grip yet enough pressure has to be applied for it to move, so no destroying your ears from a bump in your pocket. Not that this has the gain to do that either, another plus.

The Rx is what I would call a small amp, not a tiny amp such as the Fiio E10 but one that perfectly fits the dimensions of my modified AK120 for a compact and very much pocketable rig. Being someone who uses said AK120 as my go to player the form factor is perfect for me and even when I have used it with slightly bigger players such as the AK380 or Shanling M3, it hides nicely behind the bigger frame and using the included rubber bands, keeping them close is never a problem. One thing that is a big surprise for me is the weight of the Rx, it is quite mind boggling, it feels like it surely is made of plastic but the chilly touch is clearly metal. 113grams is the weigh in and thats is not much at all, in fact an obvious amount less than all my competitor amps from JDS Labs, Leckerton, Aune and Vorzuge. While on paper lighter gear should always be better as who wants to carry around something ten tonne, there is something satisfying about a heavy product and you feel like it must have a lot going on inside. Don’t let that put you off about the Rx though. That would be a mistake.

Even with its deceiving lightness, the build quality is stellar. Everything is metal, it is vented to prevent ever over heating and the anodised finish of my unit doesn’t want to scratch. Worth noting as well if you want to spend an extra $50 you can get an electroless Nickel version that looks stunning.

Also new for the Rx line is just how simple this device is. We are talking a 3.5mm input and output and a micro-usb port just like your mobile phone and Astell & Kern device has for great compatibility. In fact compatibility is that good it automatically adjust the current depending on what your charging it with and it gets to 100% really quick from my 5v USB distributor or the included power brick. I think while there is a place for more gimmicky amps, this a purist design with optimising sound quality of IEMs at best interest, and personally I couldn’t want anything more.


An IEMs Best Friend

There is one thing claiming its for IEMs and another actually doing everything necessary for it to perform with them. Hiss, channel imbalance, frequency skewing and lack of volume pot mobility (gain) are just some of the reasons IEMs don’t get justice. I think the misconception comes because if you plug a HiFiMAN HE-6 into your mobile phone, you don’t get good sound or enough volume and yeah, its obvious you need an amp. If you plug your brand new Campfire Audio Lyra into your phone you probably will not even be near max volume, but it is not taken into account how much better sound you can be getting (not that the Lyra sound bad from your phone). As of one of the biggest CIEM enthusiasts out there I do know how good they can sound and also how much of a pain some of the things I mentioned above can be, I refuse to listen with hiss and with the wrong output impedance… lets just not go there.

Thankfully ALO have taken all the necessary precautions. To make sure the noise floor will not be a problem they make sure the power supply is highly filtered. It works in a push pull arrangement and also utilises ESR Aluminum Organic Polymer Capacitors to keep things clean. Paired with the low distortion specs of this amp (.002%) and they have made sure everything is going to be quiet and controlled and you know what, it is. It bought out a little noise floor in my Vorzuge Pure than I never knew existed.

For output impedance (I have a look at some of the worries here) they keep it well under an ohm, in fact they say it is under 0.5, the lower the better. This is something that since the AK100 was released with its absurd 22 ohms most companies have had under control and I have not had a amp or DAP with much more than 2 since the Firestone Fireye HA and its 10 ohms of problems back in 2012. It still is a big tick off the checklist though.

For me gain is a much more common concern and they have just hit it on the head I think. At approximately -14.6dB its less than pretty much all portable amps low gain options and this comes without a high gain option. I can’t be certain but I think this is the lowest gain I have had in a portable amp. While you may scratch your head at why this is something I am so excited about then realise how frustrated I was with the Aune B1’s low gain of 5dB that even a tiny turn of the volume pot got me to a loud listening volume and I had no ability to fine tune it from there and that spoiled an amp that had ability and low noise floor. The Rx allows low level listening with IEMs if thats your things and great ability to tweak the volume from there up. I will be honest and say while I couldn’t listen there for too long, on some earphones I can get to full volume without the feeling of damaging my ears but for the levels I want to listen at it is just perfect and little adjustments really are little adjustments. It does also leave this truly as a IEM amp, the low gain and maximum of 28mw per channel means that any headphone with a slightly high impedance or low sensitivity, even portable models that are much easier to drive than say a HD800 wont be making moderate listening levels. But you know what, I don’t care, that is not this products purpose. On top of the easy tweaking of dB levels channel imbalance is on point as soon as you reach even the lowest of listening levels and stays that way.

Of all my portable amps, be it ones that have gain switches or are physically smaller, not one has been more tasked for sensitive earphones.

Listening Time

So far everything has been spot on, it has delivered everywhere I wanted it too and been the perfect match for all my earphones and CIEMs BUT does it deliver sonically. Too right it does. I find in terms of tonality it to sit on the warm and natural side of things. While not hugely you get a whiff of warmth down low and touching into the mids no doubt. That being said its superbly natural sounding with nothing coming across forced or aggressive. When listening to this amp it just seems like it manages to hit the right balance of everything, not too much of this, not too little of that. Its just spot on. By that saying, it of course is not super extreme at anything, it is not as crazy detailed or airy as the Leckerton UHA-760, nor is it as thin and border lining bright. Everything a competitor offers seems to have pros and cons, this is more of a jack of all trades.

The bass is not the hardest hitting, it has just the slightest bit of warmth and ease to hit that makes the previously mentioned Leckerton seemingly hit faster and harder. But in terms of body it is not close. Not in the vein that the Rx is bloated and wobbly, oh hell no. It still impacts with a certainty (more so than my Vorzuge) and also possesses that more natural timbre that is not achieved with things that feel to fast for reality. Worth noting as well is that I have found this amp to in no way limit extension, it gets low and lets the IEM do its thing.

Once again the midrange is again a perfect combination of two qualities, in my mind these are fluidity and dynamics. Comparing to my Vorzuge Pure, which puts dynamics first at the expense of it feeling a bit hard and to chiseled. The Rx is still very dynamic, it can explode off the hook, and can get all quiet with those small macro details (the dead quiet background makes these moments very special) but it doesn’t over step the mark, feeling refined and controlled and it flows a whole lot easier that way. The Vorzuge sometimes becomes a bit of a chore due to its excessive dynamics and boosted midrange, which accentuate heavily in the upper mids. The Rx probably has a slight favour to the lower mids, capturing a bit of the bass’s warmth and while the upper mids feel just a touch less present, it does not impact the tonal truth. Moving on and the other thing that hits me is how controlled it is. I think perhaps the upper midranges position most valued asset is just how composed this amp is at all times, not once will you find the music becoming too much for the amp, its hand is steady and it deals with everything as you would want, keeping things separated and spaced. Its when you starts to to notice these technical advancements you start thing how much sound your getting at the $299 price tag.

The warm signature is finished of with a syrupy and easy going treble. Both my Vorzuge and Leckerton are leaner and brighter, and while this may not have as much sparkle, the word control comes to mind again here. Clarity and air do take a small step back for something that is a little more forgiving but still its still a completely balanced frequency response, just once again we have the scales balanced out, everything is in its right place.

If I am honest its most mundane area is the soundstage. I feel both my Vorzuge and Leckerton feel airier and more spread out. Delving more into a comparison with these two, the overall most balanced seems to be the the Rx, it is super cohesive and just a full and friendly signature that just works with any IEM I have tried with it from cheapo Sony MH1c’s (£12) too my flagship CIEMs like the Heir Audio 10.A ($1299). It is something that will get on well with all sorts of sound signatures and in a rush it is always the amp I pick, because I know the pairing will sound good. My Vorzuge is the most dynamic of the three, but can lose its head a bit and just doesn’t have the composure of the Rx. Its hotness in the upper mids makes it very picky with IEMs, suiting darker products. The Leckerton also like thicker, darker products being very lean and detailed. It is more detailed than the Rx, more accurate in imaging too but doesn’t have the timbre in the bass or body in sound with some thinner IEMs. For that reason the Rx just seems like a winner. Its cheaper than the other two I have mentioned and while it no means whitewashes them and every one has their own highlights, this seems like the safest buy, especially if you have a range of earphones.

Alo Have it Going On

I really love the Rx, combining a great build, loveable sound and a clear purpose, it does exactly what it says on the tin, they don’t exaggerate anything on the product page and I have a lot of respect because of that. If you want an amp to truly bring forward the performance of your earphones, then why are you going to look further than this? For that reason we will give this our Great Value award!

Sonny Trigg