Disclaimer: the Rx in this article was supplied directly by ALO AUDIO. Thank you. The Rx goes for 299$ USD. You can find all about it here: ALO Audio Rx.
My history with the Rx is long. I leaked an original design piccie at TouchMyApps (ALO’s Prescription for good sound: the Rx for portable music). That was 6 years ago. And while I’ve not reviewed every iteration, I’m more than familiar with the lineup. By and large it is excellent.
The current Rx is the smallest Rx. It’s a bit thicker than the original, but takes up way less desk space. (It is the first Rx that makes a smaller footprint than an iPhone 4.)And it’s got grills now, likely because it gets a bit warm. It also looks like a tiny CDM. But that goes without saying. ALO Audio’s emphasis on cohesive branding is exemplary.
But the Rx series’s accolades begin with their performance. The first Rx was one of the stablest contemporary headphone amps on the market. Today’s is stabler, smaller, and an even better performer. But, it’s taken a hit. The Rx MKIII+ had a balanced output. Today’s is single-ended only. And while I’ve yet to publish my thoughts on balanced output, I am ready to say this: who cares.
2015’s Rx is the stablest Rx to date. It is the 2nd most stable portable headphone amplifier I’ve tested; the most stable being the Cypher Labs Trio. But unlike the Trio, Rx’s output surges past the confines of 16-bit audio in almost every metric, all while suffering very little load effect. it is s superb amp in all but two areas:
- base gain level
- low-level channel balance
- it doesn’t get that loud when playing headphones
The second is an artefact of the first. But it is real. With super sensitive earphones, there is little to no wiggle room from the amp’s off position to absolute balance between channels at comfortable listening levels. And this from an amp designed for IEMs. Through the Ultrasone IQ, I am uncomfortable listening to volume levels beyond that where L/R channels balance. Fortunately, channels balance almost immediately. Still, for my sensitive ears, it is too high.
And, while it’s not excessive, the Rx has a small amount of background noise that is audible through sensitive earphones. It is higher than competitors from Portaphile, Vorzüge, and select models from Cypher Labs. But, that noise low enough that many people may not notice it.
Apart from that, the Rx is superb. I’ve yet to find a load that stymies the strength of its signal. It doesn’t drop voltage in any frequency, maintains incredible stereo separation, and high dynamic range. Its ability to maintain strong stereo images in all frequencies is nearly unheard of. It’s an output that’s worth its weight in gold- that is, unless you primarily listen to insensitive headphones, in which case, its maximum output is meagre.
Anyway, onto measurements.
The following Rightmark Audio Analyzer tests were conducted through this equipment.
Amp: ALO Audio Rx
Source: Mezzo Hifi MS-AK100 (RMAA measurements); Astell&Kern AK Jr (RMAA measurements)
ADC: Lynx Studio HILO LT-TB
Computer: 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$)
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600
MS-AK100 -> ALO Rx (2015) 24-bit results @+0dBV (HILO input sensitivity)
MS-AK100 -> ALO Rx (2015) 24-bit results summary
AK Jr -> ALO Rx (2015) 24-bit results @+0dBV (HILO input sensitivity)
AK Jr -> ALO Rx (2015) 24-bit results summary
There are very few points against the current Rx. It is a superb performer. It is the smallest Rx yet. It fits the current ALO branding to a T. If only its base gain level was lower, it would be perfect for IEMs. As it is, I recommend it for all medium-sensitive IEMs as hands-down the best performance-for-value portable amp on the market.