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.

Balanced Input/Output

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.

Headphone Pairing

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.


End Words

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

alo_rx_08 alo_rx_07 alo_rx_06 alo_rx_05 alo_rx_04 alo_rx_03 alo_rx_02 alo_rx_01

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  • If you happen to own the Hifiman HE-5 (the original). I have just tried it on the RX Mk3-B running balanced, and with the Hifiman leather pads, the sound is absolutely amazing. The best I’ve heard the original HE-5 with. Obviously the leather pads help in taming down the treble, but the amp strikes a brilliant synergy as well.

  • Hmm, for the HD800, how would you compare the Mk3 to the SR71b? I really like the hd800 because it has the pace, punch and attack of a grado (almost) so its good for metal, but also an incredible amount of detail etc. so it is good for classic and other genres too. I’m sorta wondering if I should try switching to Mk3 and maybe even switch to a HE6 as well… Any thoughts?
    Cheers 🙂

  • No mention of very sensitive IEMs and how they fair.

    • I did Steve, please check page two. 🙂

  • Is the HE-500 or HE-6 best with this amp? Or to put it differently, can the HE-6 compete with the HE-500 out of this amp? Because having a speaker amp at home, the HE-6 would definitely be the best there… But on the go? 🙂

    • The HE-6 is much better than the HE-500 on the Mk3-B.

      • Mike, so you would say with HE-500 is not the best synergy with Mk3-B? Because currently im funding for HE-500 and go with portable DAC and portable amp. Do you have any suggestion mike? Sorry I’ve been looking for the answer in the net but wasnt any.

  • Trent_D

    You say the clarity is also good with this amp. How were the mids with the K550?

    • I think the mids are okay. Nothing particularly special but not weak either. You need to go with the Continental if you’re looking for nice mids. 😉

  • Hi Mike. I have the National right now, and I’m using it primarily to drive Ultrasone’s Signature Pro (it has the stock single-ended cable). I was wondering if the Rx Mk3 in single-ended mode only
    would be significantly better than the National.

    • Peter,
      It would be an improvement, but sound quality wise it wouldn’t be a big jump. The Rx Mk3’s main strength is the power output, which your Signature Pro doesn’t really need.


  • Hi Mike. I’m looking for an amp that works well with my Hifiman re262 and a Cowon c2. My budget is around 200 usd. Could you please help me? I listen classical, electronic and rock music. Cheers.

  • Andre Sneed

    Hey Mike love what you do over there! I’m looking for a portable amp to power my DT990/250 with some umph!! I have a e11 and it doesn’t feel like I’m getting the most out of my cans. I’m familiar with the Headstage Arrow and TTVJ Slim being some of the only portable amps that can drive 250ohm headphones properly. Doesn’t look like the Rx-MK3 will do the trick either… HELP!! 🙂

  • stan zorin

    “Like all the other balanced portable amps I’ve reviewed, the Mk3-B does suffer from the same shortcomings compared to the best of single ended portable amps. It doesn’t quite have the composure of high quality single ended amps, the mid range, the soundstage depth, image, and coherence…”
    Does the single ended output of this amp have the same sound signature / shortcomings as the balanced output ? How does this single ended output compare to the Alo Continental sound ?

    • Stan,
      The Continental is superior to the Mk3B single ended.

    • Less problems in single ended but if you want to go single ended the Continental is better

  • CLAS is source
    RX Mk3 is amplifier.

    Different things. Having both is good.

    • disqus_0ADxuk4tWH

      Does a source alter what comes out of my digital player, iPod?…I see they sell the amp/CLAS as a package, so I’m curious…are the benefits dramatic?

      • google dac ( digital to analog converter) understand what it is first and you can find your answer.

  • disqus_0ADxuk4tWH

    Thank you for the quick response…I await delivery breathlessly…

  • disqus_0ADxuk4tWH

    Excuse my ignorance as, I’m a newbie, I don’t know diff betwixt source and amp

    • Ipod, CD Player, Laptop + Medial Player, Walkman, DVD Player, Sony Playstation = Source Amplifier amplifies the signal before it reaches the headphones / speakers.

  • disqus_0ADxuk4tWH

    Hello all….myRx Mk3 has arrived…..but, alas, a cable is missing or I’m unaware of something I should have had…..can someone guide me?….seems I need something to connect Mk to iPhone…

    • Can you take pictures so I can see what you got?

  • disqus_0ADxuk4tWH

    Mike…..I just got my Rx Mk3…all it has is a power cord…there’s nothing to go from amp to source(iPhone, iPad, etc)…I’m not sure how to attach fotos here…ur kind for the response, so thanks

    • Yes you gonna need a cable to hook up the iPhone to the Rx. Better call ALO

  • disqus_0ADxuk4tWH

    Got it….anything I can buy at radio shack or Frys?

  • disqus_0ADxuk4tWH

    Mike…Seems I’m missing a “triple pipe L.O.D”….I wish I would have known, and, it’s another 200…goodness…what have I gotten myself into….thanks for ur time

    • You don’t need to get a triple pipe LOD. The one from Amazon would do as well.

  • disqus_0ADxuk4tWH

    I’ll DEF be looking at that…can a cable that’s an inch long be worth 200 bucks?…I’ll drive around and see if I can find one….uve been very kind…

    • You’re welcome, not a problem.

  • Gauchomb

    Hey mike, this is me, the rx mk3 newbie…thanx again…I’ll prob have more questions in future, I hope I don’t impose

    • Yes, no problem.

  • Gauchomb

    Hey Mike, rx mk3 is just great….size,weight,sound, defintion,amplitude were as good as defined and described…I use beyerdynamics dt1350 for bumping around and ultrasone pro 900 at home…is there something I can improve on?

  • Gauchomb

    Also, I run alot and bought westone ie2s, billed as the ultimate running earplugs…the actual plugs get saturated with sweat and flat out fall of my ear…in my call to westone, I was told that sweat “compromised” the seal of the earbud…do u know any other high end running headphones?

  • Nishy Wijewardane

    Hello Mike, Nice review. I have the HE-6+SR71B as my ‘portable’ gear (and EF6 as my unportable). You clearly say the ALO does a better job and I’m interested though I have no complaints on the SR71B: does the ALO give a better bass (for jazz); is the soundstage wider, does it have more power output, does it have a longer battery charge, and can it run on the same Silver Dragon balanced cables to the HE-6? Also what amps better than EF-6 with HE-6 can you point to? Have you reviewed the HE-6+EF-6 combination?

  • Vincent

    Hey Mike,

    Can you please tell me how far off between the mk3 and the mk1?


    • The one advantage the MKI has is the digital volume control. Smaller size is up to the owner. The digital volume control allows 100% perfect balance at all volumes with every headphone out there. If you are using single ended headphone or earphone set, the performance differences between the two are slim, but slightly in favour of the MKIII.

      The MKI was such a great amp that bettering it is rather difficult. While the MKIII is, overall, a better-performing amp, the MKI is a phenomenal piece of kit that will hammer it to most amps out there.

      • Yeah the Mk1 is special. Maybe talk to ALO to re-release the Mk1. 🙂

  • George Lai

    Hello Mike, can the same 9V charger be used for both the CLAS and the RX3?

    • If it’s both 9V then yes

  • George Lai

    And the newer model, the B+, is out.

    • Yeah

    • Yeah, bigger battery and supposedly improved sound. I’m still waiting for the store stock to come in.

      • George Lai

        Though I’m already very pleased with my CLAS -R and ALO National and Continental v3 as my main portable, or rather transportable, rigs.

    • It is. Both are great amps. If you are going to choose the best now, the B+ model may be the best investment, but if you already have the MKIII, staying the course is a great idea.

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