Usually people think that IEMs (In Ear Monitors) or earphones do not need an amplifier because they are very easy to drive, unlike headphones. Amplifiers don’t just make your headphones or IEMs louder, but a good amplifier also drives your IEM or headphone to deliver its full potential with very minimal or no noise on the background. Today we are going to look at Alo Audio‘s new Rx portable amplifier (not to be confused with the old Rx) redesigned and optimized specifically for IEMs. If you are an earphone or IEM user you might want to stick around and read our Alo Audio Rx review because this is for you. Otherwise, you might want to check out the Alo Audio The International + Optical Edition instead. Before we proceed with the review, I’d like to thank ALO Audio for providing the sample for the purpose of this review.
Alo Audio Rx IEM Amplifier Review
You might be wondering why Alo Audio designed an amplifier for IEMs. You could use any headphone amplifier right? Well, basically it’s a yes. Yes in a sense that you can use your favorite DAC with headphone Amp, or Amp only with your IEM, and nobody will prevent you from doing otherwise. But the problem is most of these amplifiers were not designed for IEMs. They were designed to drive full sized headphones and some of them are designed to drive even the most demanding headphones. As a result, these amplifiers aren’t too friendly with IEMs, specially very sensitive IEMs. Background isn’t very black and worst case scenario, hissing sound (or unwanted noise) is noticeable even when music is playing.
When Audio Line Out LLC first introduced the Rx portable amplifier back in 2009, it was a very different amplifier back then. There are many factors that we need to consider to have a very enjoyable audio session, and one of them is that the amplifier should be dead quite or at least delivers a black background specially when using (very) IEMs. This is where the new Alo Audio Rx portable amplifier comes in. The new Rx has been redesigned and optimized for IEMs so that “you will hear the music and nothing else.”
The new Rx makes use of a wide band integrated amplifier with push pull power supply. It features improved power filtering that is all about ultra-low noise. It has a dynamic 15 volt Amp design that is enough to provide a good amount of loudness without any distortion or coloration. Alo Audio used the newest ESR Aluminum Organic Polymer Capacitors to give it extremely clean peak power performance. Meanwhile, its frequency response extends flat from below 10Hz to above 50Khz. It also features Super Low Output impedance allowing the new Rx to deliver superb audio performance to low impedance In Ear Monitors and earphones.
By the way, the Rx is not only available in Nickel, but also in Anodized Black as well.
Below is a table of the technical specifications of the new Rx. I’ll discuss more features after the table below.
Alo Audio Rx Amplifier 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 |
Packaging and Closer Look
The Alo Audio Rx comes in a plain and simple black box with Alo Audio’s logo in front. The packaging is layered with several smaller boxes inside. Just pull the green tab and it will immediately reveal the Rx. Accessories includes three rubber bands (Amp straps), a reading material, a small mesh-like carrying pouch and a 110-240V wall charger (not in the picture above).
Alo Audio included not just an ordinary USB cable in the package, but they also included the Green Line micro USB cable which retails for $149 separately. Yeah, it’s a really expensive USB cable, but at least you get it for free with the Rx. According to Alo Audio the Green Line is “designed from the ground up, featuring silver plated conductors and triple shielding for maximum resolution and signal isolation. Terminated with USB-A and USB micro B. Our digital USB cables deliver a sonic presentation that is noteworthy for its naturalness. Warm while retaining all of the detail of your highest resolution music, our Green Line USB cable is an excellent cable to maximize your digital audio experience.”
The front and back cover of the Alo Audio Rx has somewhat a grainy texture, but it doesn’t feel rough or coarse at all. The sides are a little bit shiny with a brushed finish. There are ventilation holes on both sides making sure that the Rx stays cool even at prolonged listening period. The Rx is small enough to fit inside your pocket. It measures 2.28″ x 3.64″ x 0.69″ and weighs just 4oz.
One important change that Alo Audio has implemented with the Rx is with the use of a plastic pot instead of the commonly used carbon pot. The new Rx features a “high quality conductive plastic element type potentiometer for extended life, high resolution and high reliability over carbon element type pots”.
There are basically several different pots available, the more common are the carbon potentiometers, cermet potentiometers and conductive plastic potentiometers. Carbon pots are the oldest and commonly used but Cermet pots (ceramic based) and conductive plastic pots proved to be better type of pots, not only in terms of longevity but also quality as well. Despite having a better pot, I find the volume knob to be somewhat small and very near to the input port.
Speaking of ports, aside from the volume control (that includes the on/off switch), right next to it is the 3.5mm input port, then an orange power LED, and a 3.5mm output port. The power LED will start to pulsate indicating that the battery is low.
At the rear portion of the Alo Audio Rx there is a microUSB port and an orange charging light indicator. You can charge the Rx via a computer’s USB port or by using the included wall charger. The rear light indicator turns orange when it is still actively charging, and turns green when the battery is fully charged. I haven’t recorded the charging time actually, but I think it was just a couple of hours or so. It’s faster to charge the Rx when using the included wall charger, and it takes longer to charge it via a standard USB port.
Check out how the new Rx sounds on the next page.
