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 wideband 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.
Tonality
The RX is a revelation for its price and an instant winner for me with just about every IEM I tried. Pot balance was nigh 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.
Dynamics
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.
Bass
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
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 were pitch-perfect, relatively grainless and sibilant free. CC Colletti’s bluegrass 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.
Treble
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.
Matchability
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.
Alpha Prime
The power and sensitivity handling are 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 were 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.
Pairing Synergy
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.
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 behavior 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.
UE900s
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 a 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 outmaneuvered 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.
Our Verdict
I long since though the era of the portable analog amp has seen its best years, to be frank, and that convergence devices such as the Oppo HA-2, Aurender Flow and even the Creative E5 strapped to mobile phones were going to be the way of the future.
Heck even high-end DAP’s pack unbelievable amps in them now to make the concept of stacking almost seem redundant. This is why I think ALO Audio has been quite clever with the RX amp in how it’s built, tuned and pitched.
Headphone guys have got the desktops and the quest for power, for a few years now portable amps chased after that money shot – powering the planar became the thing portable amps MUST do in the last few years.
Yet behind it all the IEM guy was saying hey noisy guys what about me? FiiO and Cypher Labs came out with their amps, so now have ALO and its full of win for me with a list of positives that far outweigh any negatives, minimal as they are.
You have zero noise, you have excellent channel balance, fantastic dynamics and a speedy neutral but musical sound signature that compliments rather than fights with a ton of IEM’s and competitor amps. It is not a me-too toy, it’s a great amp and one which I personally will be using for a lot of earphones and strapped to a high-end DAP I might add.
Do you Need It?
That’s is a harder question. Do you have a mobile phone? Then no you do not, buy a Oppo HA-2 and be done with it. Nothing can touch that at $299 right now for convergence.
Do you have planars and powerful headphones? No, you do not need the RX either – it’s got some power, it sounds ok actually with the Primes but that is pushing it a bit too much beyond its intended use. Got searing bright earphones and need to tone it down and warm them up? The RX won’t do that either with its neutral signature, those earphones are going to remain bright sorry.
However, if you are an IEM guy, got a midrange DAP and want a little more juice to really liven up those IEM’s without any unwanted noise or hum then the RX is probably going to get my vote for one of the IEM analog amps of the year.
Rx Technical Specifications
- Frequency Response (Measured at 1V RMS Output):
- 20Hz to 20Khz +/- 0.05 dB
- 20Hz to 50Khz +/- 0.6 dB
- THD+N, (Measured at 1 V RMS Output):
- Less than 0.002% from 100Hz to 50Khz
- Input Impedance
- 10K ohm
- Output Impedance
- Less than 0.5 Ohm
- IEM optimized variation
- Output power (With an input of 2V RMS the Undistorted output power Into the typical IEM (Which can have an impedance of 5 Ohms) is limited by design to a safe power level of 28 mW.
- Gain: Approximately -14.6 dB.
