The Power Pack: ALO RX MK3-B
Enclosure and User Interface
Looking at the photos of the Mk3-B, I guessed that it’ll be finished in the same hairline anodized finish as the Mk2 and CLAS portable DAC. Instead, the Mk3-B comes in a smooth semi-gloss paint finish similar to the National amp. I have no idea why ALO did that, and would rather they keep it uniform as the finish on the Mk2 and the CLAS. After all, I appreciate the fact that they stick to the same enclosure dimension (and even design), as it makes for a good looking stack with the CLAS portable DAC. Indeed I find it impressive that ALO was able to manage the same enclosure size, while doubling the amplification circuit for a balanced amp, and I suppose a higher capacity battery as well. One thing worth noting is the power indicator light that conveniently points out the state of the battery level through its color (Blue = Play, Green = Charging, Yellow = Low Battery, and Red = Very Low Battery/Charge Now).
One thing that you have to know about the front faceplate layout is that when you can’t plug in two headphones into both the single ended and balanced output port at the same time. This is due to the design of the 4-pin connector used, which physically blocks the 3.5mm single ended port.
I always prefer conventional shaped volume knobs to anything else, and the two knobs on the Mk3-B’s front faceplate is a big win for me.
The Rx Mk3-B comes with balanced and single ended ports both on its input and output sections. That means you can use either a balanced or single ended source, to drive either a balanced or single ended headphone at the output. I only used the CLAS throughout the time of this review, as I didn’t have any portable balanced DAC around. I did alternate between the single ended and balanced headphone out as I didn’t have a balanced cables for all of the headphones I use (the AKG K550 for instance).
One thing that surprised me is that there is no difference in loudness level between the single ended and balanced outputs. Usually, due to the balanced out having twice the effective voltage than the single-ended, you get higher loudness level on the balanced out. I asked ALO about this and they did intentionally raise the gain of the single ended port so that it matches the balanced out. Indeed the single ended out sounds great and there is no reason not to use it, but this is a balanced amplifier after all, and I figure that most people will want to use the balanced port most of the time.
Having such a powerful output, I find that the only problem I find is when using sensitive IEMs. The lowest of the three gain settings is not low enough to provide good volume control with my JH5Pro or Shure SE215 IEM (out of a CLAS portable DAC as the source). I can listen to it just fine on moderately loud volumes, but for low level listening I would get imprecise volume tracking.
Driving the Sennheiser HD650 headphones out of the balanced port, low gain setting is enough for most recordings except for classical. It doesn’t quite have the midrange quality of the hybrid tube Continental amp, or the full bodied mids of the National, but the Mk3-B was able to pick up the pace of the HD650 and make it a quicker headphone than when driven on single-ended amps.
The real magic happens with the Hifiman HE-6. Not only does I have no problem getting enough loudness on the medium gain level, but the amp also has a really good synergy with the HE-6. I’ve always been a bigger fan of the HE-500, but that’s probably due to the fact that most amps I review can’t drive the HE-6 right. The HE-500 is much easier to drive than the HE-6, but in this case, I can see why the HE-6 remains the flagship model, it’s just far more impressive on the Mk3-B.
I didn’t have an LCD-2 to test the Mk3-B with, but based on the results with the HE-6 and the HE-500, I think the LCD-2 should be an easy load to the Mk3-B.
I still can’t fathom how the slim Rx Mk3-B amplifier is able to drive the Hifiman HE-6 so brilliantly. I’m not saying it defies the law of physics, but I know how difficult it is to drive the HE-6 and I’ve seen the majority of desktop amplifiers, even BIG ones that fail to deliver the job. The Mk3-B not only drives it with sufficient authority, but it strikes such a beautiful synergy with the Hifiman as well. I’ve tried some speaker amps that have plenty of power to drive the HE-6, and while they still have more oomph than the Mk3-B, the sound synergy is not always very good. The Mk3-B is not like that. Good power with plenty of punch, and with a good synergy going on as well.
The race for the most powerful headphone amp in the market is still on, and currently I declare the ALO Rx Mk3-B as being the most powerful of them all as it convincingly drives the Hifiman HE-6.
Gear used for review
Ipod Classic, Cypher Labs AlgoRhythm Solo, Hifiman HE-6, HE-500, AKG K550, Sennheiser HD800, HD650, Philips Fidelio L1, Shure SE215, JHAudio JH5Pro
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