Sound Impressions

What’s Inside?

This is where the important changes have come about in the revised RX unit. Previously it was all about power and load, now the switch is to sensitivity and low noise floors without sacrificing those all-important dynamics. To achieve that ALO have opted for 15v swing integrated wide band amp and a power filtering system designed to keep noise to an absolute minimum whilst at the same time ensuring nothing gets distorted either when you crank up that volume (THD+N at 0.002% is pretty darn good). ALO also wisely created the RX with a much lower output impedance than its previous line of amps with the RX rated at less than 0.5 ohms and should be ideal for IEM users with any type of armature or dynamic hybrid setup in keeping things detailed, with zero unwanted harmonics and of course noise free.


The RX is a revelation for its price and an instant winner for me with just about every IEM I tried. Pot balance was neigh on perfect with zero noise floors on sensitive BA such as the W4 and the dynamic IE800. Volume control was steady and never maxed out or felt too vague. The RX tonally is neutral with a hint of warmth and plenty of top end air, extension and sparkle without every sounding tizzy, bright or too hot.


The dynamics on the RX are superb and the sound stage is incredibly grand and arena like for such a small amp. I really did not expect such a small amp to sound well so big. I remember the Island from ALO eliciting that same response when I reviewed it but the difference between the Island and the RX for me is that despite both amps having cracking width and height the whole presentation of the RX sounds more coherent, linear and able to retrieve a better level of micro detail than the Island could muster, especially in the vocal presence and top end. The RX just sounds more balanced than the Island which tended to lack a bit of bite compared to the RX across the range despite its weightier bottom end.


Unlike the Island also the RX exhibits a much faster sound signature with a straighter, truer bass response that is pretty tight and with good snap also. It is not in your face bass, it won’t dominate and rumble in that manner. I do honestly find myself preferring this type of bass to the fatter elevated slower bass that can sound more impactful initially but gets in the way in the long run. Bass heads might find this more neutral bass response a little lean for their EDM but those hankering after some old time rock or arena rock will appreciate hearing their double kick drums loud and clear with plenty of space and definition. This is a versatile bass signature for a ton of genres that need accuracy over primacy.

Mids & Treble

The bass to mids transitions are pretty smooth with the mids continuing in the same relatively neutral, uncolored but free flowing manner. Nothing feels congested with the RX mid-section. Timber is accurate and there is a nice sense of space and above average instrument separation. This is where the RX shines for me over the Island. It has a superior level of detail in the mid-section with more bite, better clarity and much less veiled.

Vocal presence on the RX is clear, centered and without being too forward with only minute traces of sibilance. It can be a touch source dependent with it sounding a bit smoother and more natural on the AK120 than the DX90 but overall it still conveyed satisfying levels of detail and texture. Amber Rubarth vocals on “Storms are on the Ocean” using an IE800 and Ak120/Glove A1 was pitch perfect, relatively grainless and sibilant free. CC Colletti’s blue grass infused folk rock “In My time of Dying” was probably my highlight on this setup with a precise acoustics guitar string plucking in the left and a steady acoustics bass guitar beat in the right and a clean textured vocal detail shining through the middle. Intended space in music can be a good thing with the RX, a very good thing indeed.

The RX treble is never overly aggressive though it does have a bit of sparkle and zip to it. The extension is excellent and there is above average headroom giving a nice airy feel at times. The RX’s treble articulation is in keeping with the rest of the signature; quick natured and detailed personality with a delicate and precise presentation.



Lots of surprises

The neutral speedy tonal quality of the RX had a surprisingly high level of flexibility when it came to matching with plenty of earphones and surprisingly a few good headphone performances also. Naturally the focus is on earphones. The power and sensitivity handling is set up for this but a few honorable mentions can be had for its ability to handling some reasonably demanding headphones such as the Alpha Primes which surprisingly was just fine volume wise with the RX. Sound staging was still above average but the dynamics and imaging was a touch less convincing than my desktop setup (EF6 and HA-1) but that was not surprising since I prefer my EF6 with the Primes and feel a little spoilt as a result.

However tonally I was impressed by how the two of them gelled together using an AK120/Glove A1 combination. The Prime/RX pairing delivered a very neutral and clear presentation with decent dynamics and a vocal presentation that exuded plenty of texture and detail. Whetton’s vocals on Asia’s “Closer to you” off the 2014 “Gravitas” album sound suitably melodic and manly but you can actually pick out the hard touring years on those set of classic pipes with the Primes and the RX combo. Dash Berlin’s mighty Eastern influenced EDM “Like Spinning Plates” off the “Music Is Life” 2013 release still had that snap and speed with the Primes/RX combo though bass heads might want to consider both the Primes and the RX have a relatively linear and more neutral bass response. You get all the musicality and a smooth treble response with this pairing but the EQ might have to pop out somewhere to get a more satisfying or deeper slam.

The IEM’s

Before we get into the meat and bones of the matchups I have to honestly say I didn’t get a single iota of unacceptable noise on any IEM I tested with the RX and every single one of them had excellent channel balance from zero to acceptable listening levels. I normally expect to find one to buck the trend but after testing about 10 in total I came up empty handed for the dreaded hiss. The one common theme I did find in most of the testing with IEM’s was the impeccable behaviour and attention to detail that RX brought to most of the pairings as well as a nice sense of scale and of course those dynamics.


I was also initially thinking that little treble sparkle and clean presentation in the RX might not gel with some earphones and sources but as it transpired this was not the case at all. If anything the RX accented a lot of strengths of my existing earphones in a very engaging manner without adding any unwanted coloration. One such unexpected combination during testing was the UE900s/RX pairing. Normally the UE900s for me has this slightly laid back treble response that is quite clear but never its top selling point and the odd time some pairings with bright sources have caused me to ignore it a little as the match just came out all wrong. Luckily this time the RX injected a better sense of pace and dynamics into the UE900 but still managed to keep a lid on any lower treble monkey business with percussion. Bass performance with this pairing was pretty coherent and tight also making this quite a little musical pairing.

Westone W4

Paired with my usual reference mid-tier vanilla set, the W4 paired with the DX90 line out was actually a solid performer for EDM and heavy 80’s rock. Tracks from Deadmau5, Dash Berlin and Whitesnake provided excellent depth and width with an impressively clean and speedy signature. The W4 did tend to exhibit a bit more fizz and sparkle on some of EDM laced with high end synth work but not overly aggressive. Vocal presence remained clear and emotive throughout especially good old Dave Coverdale; bless his cotton socks he can still reach some of those high notes but man just like Whetton on the RX the long touring years are etched right into those vocals. Such a shame but thanks for the memories Dave.

Dita The Answer (The Truth Edition)

The Dita’s The Answer (The Truth edition) combined with an AK120, a Glove A1 and the RX and a touch of Diana Krall for about an hour or two is very enjoyable at this price point. That nice full mid-section the Dita’s are known to produce match really well with the neutral mids of the RX. The slight top end sizzle with the RX/W4/DX90 pairing was toned down with only a mild elevation in the lower treble, zero sibilance and a slightly weightier and more natural bass response from the excellent single dynamic driver of the Ditas. It was really pleasing actually the RX didn’t mess with the Dita’s more natural sounding tonality especially with the bass detail, slam and attack. Instead of coloring it unnecessarily the RX instead added a sense of scale to the presentation. It will never give you intimacy, especially on acoustics. For that I would go back to something like a BA setup but the Dita/RX pairing is something I think I would use a lot in my daily listening.

RHA T10i

Another dynamic driver with a filtering system but this time a whole lot cheaper at $199 and maybe a combination with the RX that might find some popularity for those not willing to empty the wallet in the pursuit of good sounds. As ever my only reference filter I used for the T10i is the treble filter and unlike The Bakoon HA-1M which turned the T10i into a complete juggernaut of bass menace the RX toned the bass delivery back quite nicely and added a little added touch of clarity and edge that I sometimes find lacking in other T10i matchups. It’s not the second coming of Jesus but I did notice myself picking up a little bit more treble clarity on the T10i than I am used to.

Final Audio Heaven VIII

A ridiculously good single BA setup that provided the perfect vehicle for the RX’s stellar dynamics and huge sound stage. Smit actually mentioned before in his review of the VIII that it was pretty darn hard to find a single BA setup that can compete with the VIII for a sense of space and instrument separation, all the assets indeed for a very engaging pairing with the RX which did much to highlight these strengths. Using the AK120/A1 pairing again the treble was lively but smooth with very little lower treble peakiness and a good body in the mids. The VIII could well live up there with the Ditas as a very credible pairing indeed with the RX for daily use.

Other portable amps of note

Of course there are a few other analog amps vying for your money at this price range. Some like the E12a and C5 from FiiO and Cayin are a little lower on the price scale and others like the Cypher Labs Piccolo amp and the Vorzamp Duo just a shade higher. Two, above all others I can see as being the primary competition, the FiiO E12a on the budget end at $160 and the Cypher Labs Piccolo analog amp at $399. I am tempted to throw in the Vorzamp Duo, Cypher Lab’s Duet and the Glove A1 but they are either too specific in the case of the Glove or just a touch too pricey and therefore the potential improvements would be expected.

Cayin C5

The Cayin C5 is all about power for me and the noise floor is not dead silent on zero for IEMs at ground zero for volume. It simply doesn’t have that same level of precise control in the first 1-2 notches with a slight imbalance favoring the right channel over the RX’s excellent channel control and dead zero noise floor. Given the superior power of the Cayin you may likely hit your comfortable levels of listening a lot quicker on your pot than the RX’s more gradual and smoother pot control. The Cayin in its favor might seem a bit smoother for longer listening and has a fattened bass response that is better suited to modern pop and rock but it feels a bit too smooth and soft compared to the clarity and detail retrieval of the RX which feels far more incise and involving. Both offer great sound stage and the imaging on the C5 is above average but the engagement and superior speed of the RX tips it for me.

Piccolo Amp

It is a much tougher call though between the Piccolo Amp from Cypher Labs and the RX. Both are tailor made for IEMs with only a $50 price difference between the both of them and both display excellent pedigree but there are differences. The Piccolo is a touch darker and more full bodied than the neutral speedy RX but the RX has more headroom, better dynamics and a super sound stage. I find the Picollo excellent for medium paced rock and EDM and hard rock vocal work where I want a smooth experience. The RX seems better adjusted to giving a more expansive presentation with a bit more sparkle and articulation in the top end. The Piccolo just feels a softer smoother slightly more gentile amp with good body whereas the RX has a more neutral speedy articulate signature that’s a bit leaner but more dynamic. Take your pick, both have excellent noise control, both have great channel balance and both work exceedingly well over the majority of IEM’s. The Piccolo though might be the amp of choice for the IE800’s in how it controls the lower treble fizz or for pumping a bit more low end body into lean sounding earphones. I preferred the RX for customs which either needed a small treble lift or something to fill out demanding sound stage presentations like the W300AR from AAW and the VE6X.

FiiO E12a

FiiO’s reworked E12 which we reviewed a few weeks ago really does a number on the original in terms of versatility and balance for use with IEM’s and at $160 it’s a tempting distraction from the RX for those on a budget. The E12a has very good channel balance also and a better than average low noise floor with very little or no hiss though the RX edges it slightly for me for its blacker background. The E12a tonally is much superior to the old E12 but its decay is bit slower than the snappier RX. Vocal presence on the RX was also more convincing with much better detail and texture than the E12a and a little less grain also. The E12a was also out manoeuvred by the RX on sound stage and separation with the better accuracy and imaging on the RX. The E12a does a decent job for the price to be honest and I have always been impressed with how FiiO reworked the E12 but the RX’s presentation it just a notch up in almost every way. In this case you get what you pay for.

Page 3: Final Thoughts

The RX Portable Amp from ALO Audio – It’s Back!
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37 Responses

      • Eddy

        Btw, I am always wondering how dita truth is compared to those a flagship CIEMs. Are they at the same level in terms of soundstage and tonality? I know it sounds like a stupid question, but I cannot help noticing u choose truth as the daily equipment instead of CIEMs. Your advice will be so valuable because I really want to know whether I should upgrade to ciem.

      • headfonics

        Oh i used the Truth for comparisons but in truth I use a wide range of iems and ciems for daily use chiefly the Campfire Audio Jupiter and the M-Fidelity SA-43 in the last few outings. I am always a firm believer of ciems.

  1. stas

    hey :) but have this amp also DAC?? i m looking for amp/dac betwen 180-200-250 $.. and i listen Korn and heavy stuff. i hope you will find a good amp/dac for me :) . cheers from Belgium

    • headfonics

      Just a portable amp but made specifically for efficient IEMs and cans. For that budget I suggest Ibasso D14.

    • headfonics

      Sadly I do not have any JH customs to test it wit h but most other high end customs I have sounded good, particularly if the custom exhibiting an already excellent soundstage and a natural response. (VE6X, Custom Art Harmony 8, UM Merlins etc)

  2. Goggs

    Can I just ask how you paired the AK120 + A1 with the RX? From what I know, there is no lineout option for the A1, so I would supposed you took the analog out from the A1 directly into the RX, essentially meaning double amplification?

      • Goggs

        Cheers. Does the RX really improve on A1 HO itself? I’d be somewhat doubtful considering the A1 is pretty good by itself, and double amping isn’t such a good idea for many people.

      • headfonics

        Its more of a difference thing and I was testing it for something else at the time so why the heck not. The RX is very transparent anyhow so you get all the goodness of the A1 with the control of the RX for more sensitive IEM’s.

  3. Boogie6301

    I would usually audition any headFi gear before purchasing. The Rx is a very rare exception and I relied a lot on the review here. The sound impressions from the review is spot on to what I’m looking for. The Rx looks great specially with my iMod.

    My excitement lasted just moments because when I powered this baby up the output was really low. I understand that it is optimized for IEMs but should have decent gain for small to medium cans like my HD25-1 II or even my LCD-3. It also says that in the review.

    With my 1964 V6-Stage my normal comfortable level is already around 3-4 o’clock. At full volume you can really hear distortion. It sounds great matched to the V6-Stage at mid volume but for all my other cans and iems it was a disappointment. I’m sure it has nothing to do with my cable or player because when I tried a stock iPod Video and LOD the volume level is the same. Interestingly, using the Fiio X1 as my DAP the volume was loud even at 12 o’clock with the HD25-1 II.

    I think I pulled the trigger on this one too early. It seems it doesn’t match well with the iPod ecosystem – I should have waited for more reviews. However If I got a dodgy Rx I really would like to know. I’ve been emailing the ALO helpdesk for 3 days already and all I got was the auto-reply acknowledgement.

    • headfonics

      It may have something to do more with your output on the iPod video than the RX as in all test I did use a DAP given this is an analog amp and will not decode anything so in effect you are double amping. Did you try the X1 into the RX?

      Try using the source volume as a pre amp so you can get the right setting which is what I basically did using the DX90 and the Ak120 and the Glove A1.

      It will power what you need to varying degrees beyond an IEM that I am 100% certain off but the volume pots on all my sources where set to different levels to compensate.

      • Boogie6301

        Thanks for the very quick reply.

        I tried your suggestion but (1) the gain was more at only the iMod max volume (I’m using Rockbox by the way), (2) it defeats the purpose of the iMod where the inferior analog output stage is bypassed and (3) yes, I used an X1 with the Rx and the volume is as expected via X1 line out setting and not headphone with variable volume.

        I haven’t made measurements but I’m assuming when you use the line out on a player, regardless if it’s an iPod, Fiio, AK or any other DAP the voltage should be at or near the standard 1Vrms. I also have the JH16/JH3A combo and my iMod works perfectly on that one – although the JH3A digitizes the analog input for its DSP before converting it back to an analog out to the JH16s.

        Oddly I’m hoping my Rx is just a case of a manufacturing defect (so I can just have it replaced) because I really like it’s sound signature similar to my Pure II. However, If this is the way it works – most likely I’ll return it.

      • headfonics

        Hmm.. my test setup was the DX90 on line out and the AK120 with the Glove A1 in line out also. In both cases I did some manual adjustment to get the right balance for using th RX.

        For the DX90 it was low gain line out, not so sure on the precise volume setting to the A1 since the A1 has not precise guide compared to the AK120.

        For the Prime match it was the AK120 and the Glove A1.

        I might give the RX a spin with my old iPod 7th gen this weekend and see what happens though to be fair I stopped rockboxing a while ago.

      • Boogie6301

        If you can test it on an iPod that’ll be great and I’d appreciate it. I had the same results on a iPod U2 5.5g as with the iMod. Testing it on a 7th gen should be close enough to validate or dismiss my observation. I’m looking forward to your tests. Thanks a lot.

      • headfonics

        I can throw on the Nad HP50, senn momentums and some of the original IEMs I had tested just to see how portable cans stack up using the iPod/RX.

      • Boogie6301


        I finally got a response from ALO support

        “…..The Rx is a IEM (In ear monitor) only amp, not meant for headphones so If your using the Rx with Sennheiser HD25 then yeah it will not have enough gain. The Rx page is pretty specific about that it is a IEM amp. I would use it with IEMs only”

        It still didn’t explain why when using other sources like the X1 the gain is more than enough. I asked for more specifications like input voltage and impedance because I believe this is a matching issue with the iPod rather than power.

      • headfonics

        The X1 is not that sensitive with IEM’s compared with the RX for me though, has a bit of hiss now and then and higher noise levels.

        Will be checking that iPod match up shortly after my nightly Vikings episode catch up :)

      • Boogie6301

        Thanks. Looking forward to your iPod+Rx impressions

      • ohm image

        It depends somewhat. If inputs and current-to-voltage outputs are designed properly, it really doesn’t matter.

      • ohm image

        It is all maths. There is no magic or synergy to it. ‘Synergy’ is all down to personal preferences. But actual performance of the output to the input of an amp, come down to simple mathematics.

      • headfonics

        What are those simple mathematics? Sources pls? Anyhow this is OTT since you misinterpreted my original statement when I did not state double amping was wrong. ;)

      • ohm image

        I think you’ll find electronics to be a purely mathematical thing. What you like in sound, however, is 100% personal. Properly driving signals is 100% maths.

      • 24bit

        I’d probably do the same thing, I’d keep it in the glove and output it to another amplifier, instead of taking the dap out of the amp. If the glove increases the sound quality or alters it from the player alone, then that is always the wiser choice if you need more power in a larger amp. Maybe I am not reading this right, was that the argument happening here? haha. Just curious :P

        Synergy is a hell of an important factor in your rig and is the direct result of great “maths” as you put it. Bad “math” probably won’t result in a specific desired tone, would only happen as a fluke.

      • ohm image

        Synergy comes down to personal preferences and there is no accounting for them but by me saying I like A and you saying you like B.

        That aside, driving ability, ability to resolve and sustain input signals and output signals is 100% down to maths: the current sustained at a specific voltage. it is all maths.

        But manufacturers can do what they want to affect those maths: add distortion through various means, lower or raise input or output impedances, use caps, or other in the signal path.

        SQ is hardly ever what we reviewers write about. We write about what we like. And there is no accounting for personal preference. I wish we’d be more honest about that as SQ is something for which no definition exists in the audiophile world.

        The audio world is as plagued by lack of measurebators as the photo world is plagued by them. I’d prefer a better balance.

        All that is to say that ‘desire’ is the product of a specific preference. And Preference is the object of a person, not a standard.

      • headfonics

        Just thought I would mention Nathan try to re-read my first statement – it says I am double amping my glove combo to the RX rather than stating his problem is double amping.

        My contention was maybe the amp of the ipod is not a good match for the RX amp – remember the second amp just adds gain to the flavor of the first amp unless the second amp has a poor design to begin with which the RX does not.

        Through testing the RX through my own double amping with the Glove A1 I found the results more than acceptable.

    • headfonics

      I have the Duo not the pure 2. Different sound signatures. The Duo is Warm almost tube like tonal quality with faster transients, a coherent bass and a very slight roll on the highs. The RX is neutral, thinner, speedier and more dynamic.


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