The Usual Suspects: 12 Portable Amps Compared



The tiny amplifiers are mostly designed for IEMs, with the exception of the Mustang, which has enough voltage swing to drive the typical full size such as the AKG K701 or Sennheiser HD650 to loud levels. If you happen to use a source that has a high line output level (I used the Hifiman HM-601/602, where the output level is noticeably higher than the Ipod), and your recording level is relatively high (most modern recordings are relatively high in output level), then I find that the Shadow and the Pico Slim can still drive a HD650 to good loudness levels indoors, though with very few headroom left in the volume level. In all fairness, if you plan to use the amp with the bigger full size cans, I would strongly recommend you to get the bigger amps as they do the job with more authority.

The usual suspects for tiny sized amps: (top to bottom) RSA Shadow, RSA P-51 Mustang, HeadAmp Pico Slim.


Front and back views.


RSA P-51 MUSTANG ($375)
The earliest entry into this category was the Mustang by Ray Samuels Audio. Ray Samuels had already built a very prestigious brand name in the industry, and when the Mustang was introduced, it was a ground-breaker as this tiny amp had enough power to drive the Sennheiser HD650 headphone to really loud levels. The Mustang practically made all the other portable amps in RSA’s line up almost obsolete with its tiny amps, and with enough power for anything from sensitive IEMs to big full size headphones. It is not quite as weighty as the bigger Hornet or SR71-A models, but given the size and versatility of the sound, I think a lot of people opted to go with the Mustang as opposed to the bigger RSA amps. Aside from the other, more specialized models like the Shadow, the Predator, or the SR-71a, the Mustang is probably the most versatile amplifier in Ray’s line up, and it happens to have a very likable sound as well. The sound generally follows the signature RSA house sound, though it was a little less dark than most of the other RSA sound. The treble remains soft and unagressive, which is signature of the RSA amps. The bass is not quite as weighty as the other RSA stuff, either the older Hornet/SR71A generation, or the newer Shadow/Protector/SR71-B. However, the midrange is probably the best deal with the Mustang, as it remains to be one of the sweetest midrange I’ve heard on portable amps, even besting the TTVJ slim, and just a tad less lush than the original HeadAmp Pico.

Among the three tiny amplifiers, the Mustang is the only one that comes with a three levels of gain, and with more power to drive big full size cans. This is of course a strong selling point, and despite not having the fancier digital volume control, I think some people would still be better off with the Mustang due to the higher power output. Although the Mustang has one of the most pleasant and most likable sound among the amps in this shootout, the introduction of newer amps that offer newer technology seem to have pushed down the popularity level of the Mustang. Quite a pity to see how this great amp loses its luster simply because there are newer, more technologically advanced products on the market. While the Shadow and the Pico Slim are just as great amps, I think the tonality of the Mustang makes it still the most likable amp of the group.

It’s ironic to see how the RSA Shadow happens to be one of the amplifiers that drowns the popularity of the Mustang. Never ending innovations from Ray Samuels brought us the first portable amplifier with digital volume control, and the Shadow was eagerly anticipated in the market due to the implementation of digital volume control in a portable amp. The dimension, even tinier than the Mustang, is a huge selling point with the Shadow, as it still remains the smallest, high fidelity, portable amp around in the market.

The sound of the Shadow very closely mimics the warm sound that you get from the Mustang. Both amps are well into the range of the RSA house sound, but with some differences. I had difficulty differentiating the sound of the Shadow to the Mustang at first. But now it’s very clear that the Shadow has quite an edge in separation and articulation. These are understandable, as the digital volume control provide higher level of accuracy and is less destructive to the input signal. Soundstage is slightly wider on the Shadow, but the Mustang has better depth, and the overall impression on the soundstage is more spacious on the Mustang. Busy passages are better articulated in the Shadow, especially in the bass, where the Shadow also  hits lower than the Mustang. Critical listening aside, the Mustang sounds sweeter and less dark, while the Shadow feels a little drier, mostly due to the difference in midrange.

Out of the abundance of portable amplifiers my friend Peter owns, the Mustang is still his favorite when it comes to vocal reproduction, and I really have to agree with him on this one. The Shadow, on the other hand is less engaging and relatively more sterile in the midrange compared to the Mustang. But where the Shadow does have a superior level of articulation, and so it becomes a choice between the two. With the Shadow you get better articulation and a more compact size, where with the Mustang you get a sweeter midrange and three levels of gain for better loudness level with full size headphones.

The HeadAmp Pico Slim is the latest entry to the tiny amplifiers market. Most of my friends who’ve heard the Pico Slim left feeling cold and unimpressed with the sound that they hear out of it. The original Pico had this sweet lush midrange that’s even better than the Mustang’s, and it still remains one of the most loved portable amplifiers today (Why did I miss including it for this article?). The Pico Slim, however, had a neutral vanilla colored sound to it, and to most who’ve heard it, it’s simply too plain. Actually, vanilla ice cream still have some sweetness to it. Instead, think low fat, low sugar vanilla ice cream, then you’re getting closer. In term of features, it’s quite similar to the RSA Shadow. Both are tiny, though the Shadow is tinier at almost half the size. Both comes with a high resolution digital volume control, and both are limited in gain levels and is optimized for IEMs. But if the RSA Shadow follows the similar sound signature as the bigger Mustang, and relatively to the other RSA models, the Pico Slim is a big departure from the sound of the original Pico. The vanilla color reminds me heavily of the desktop HeadAmp Gilmore Lite amplifier, relatively plain and “as it is”. Among all of the portables in this comparison, I find the Pico Slim to have the least amount of coloration, and closest to the popular adage “wire with gain”.

I realize that the previous paragraph may have sounded like a so-so impression of the Pico Slim. And yet, here is the twist, the Pico Slim happens to be my favorite amplifier of the bunch, and definitely my favorite pairing for my JH customs. I think the words to use for the Pico are articulation, resolution, bass, and soundstage. All impressive words, but I’m not just throwing them out there. When people ask me what the Pico Slim sounds like, those are the words I give them. In fact, people in my local forum probably knows me for being the biggest fan of the Pico Slim (good thing HeadAmp is not our sponsor, though they have good reasons to be one now).

When I was talking about the Mustang and the Shadow, one of the thing I mentioned was how the Shadow, benefiting from the digital volume control, brings up an even better level of articulation over the Mustang. The Pico is similar to that, but to an even greater degree. Simply put, I find the Pico Slim to have the best level of articulation among all the portable amplifiers in this comparison. This is definitely aided by the step less digital volume control on the Pico, though circuit and power supply design also contributes a big deal to the Pico’s overall level of articulation. Most of us today listens to fairly fast-paced, “busy”, and complex music, and articulation is really important when playing those kind of music. Even more, if you’re using a JH16 like me, where the task of controlling those quad-bass drivers becomes quite a challenge to the average quality amplifiers. This is where the Pico Slim really shines. Crisp, tight, articulate, well defined bass, even with the JH16 and the most complex passages. Added to the fact that the Pico Slim can punch quite hard on the bass, though it’s relatively not-dark signature tends to make people think it’s not good with bass. I actually love the bass punch on the Pico Slim. It’s powerful, tight, and articulate, leading to one of the best PRaT factor among the amps here.

Compared to the big portables such as the SR-71A and the i-Qube, I still think the level of articulation and resolution of the Pico Slim to be ahead those two highly touted amps, while closer to the articulation level of the Stepdance. While the SR-71A has one of the highest level of resolution, the Pico manages to match it, and even better it in the area of bass control and articulation.

Compared to the portable balanced amps, the Slim doesn’t sound as impressive, as it doesn’t boost up the lows and widens the soundstage as the balanced amps does. Nor does it have the kind of power output that you get with the portable balanced amps. But as with the case of the comparison with the SR-71A, the case with the Pico Slim is about quality and not quantity. The bass is punch is actually quite good, but it’s the bass definition and detail that beats the balanced amps handily. And though the soundstage is less wide, the overall imaging performance and coherence on the Slim is definitely superior. For IEMs, the Pico Slim is probably as good as an amplifier can get for now, and will remain to be my reference amp to judge the technicality of other portable amps.

I happen to love the Pico Slim very much, not only because it’s amazing articulation, but also the fact that it synergies beautifully with my JH16 IEM. However, I think the low coloration sound of the Pico is mostly what turns people off after they audition one at the meets. Although I find the Pico Slim to have better technicalities than the RSA Shadow, most people would prefer the warmer and darker sound of the Shadow, as a lot of people tend to be allergic to treble these days. The Pico Slim adds a little boost on the lower treble, and while it’s perfect on the JH5/10/16Pro IEMs, most other IEMs have plenty of treble to begin with, and for them I generally would recommend them to go with the RSA sound to give a better tonal balance. If you happen to be a JH user, you definitely need to find a way to audition the Pico Slim.

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  • MSKrishnan


    I currently use an iPod classic + Algorhythm Solo + FiiO E11 + Westone 4. All music is in Apple Lossless format.

    I seek suggestions on how I could improve upon the above setup.


  • MSKrishnan


    My current setup is iPod classic + algo solo + FiiO E11 + Westone 4 with regular cables.
    All music on iPod is in apple lossless format.

    I seek advice on how to improve the the above.

    • Improve the amp section. There are plenty of amps to choose from, Krishnan.

      • MSKrishnan

        Hi Mike,

        Wanted to put in an update. I bought a ALO RX MK2 to replace the FiiO E11.

        The sound now is a whole lot cleaner and crisper. 

        Thank you for your advice. 

        • Yes for sure the two amps shouldn’t even be compared, the Mk2 is a much better amp. 🙂

  • Hi I have se 535 iem and was thinking of getting the cypher algorhythm solo what amp would you recommend for portability

  • addsa sadasdas

    Hi I have the JH11 Pro and thinking of getting HP-P1/Algorhythm solo, which amps would you recommend to go with this set up? Preferably, also able to drive the HD 700s too because I have pre-ordered them..

  • will the RSA Shadow power a set of Swnnheiser HD800

    • Not sufficiently.

  • Hi Mike, my current setup is teclast t51>headstage 3g>westone4 and I’m not satisfied… how can I improve my music…sud i change amp…or dap? or wat is a better setup? thank you for your suggestion.

    • What do you feel is lacking?

  • saeed zolfaghari

    hi mike, I recieve my arrow 4G recently, but I found it some dark to my taste
    I want to upgrade my IEM.
    personally I think about westone 4, do you think that I will be satisfied ?
    (I think that I will be satisfied with a natural sound ,clarity and instrument seperations .)

    • If the amp is too dark, why not change the amp?

      What IEM are you using now?

      • saeed zolfaghari

        it’s dark to me, I think that ipod touch 3g is better.

        I’m using shure se315

        I put the amp in my pocket, so the size of amp is very important to me

        do you think that I need to change the amp?
        ttvj is not so big?


        • It’s probably easier to get a brighter sounding IEM. Say the Fischer DBA-02.

          • saeed zolfaghari

            yes I think about the bright IEMs

            do you think that DBA-02 is on of the best choice?
            what’s about grado gr10 or ath-ck100? ( I can afford about 400$)


            • The DBA-02 is more popular than the Grado GR10 and the CK100 so I think it’s a safer recommendation. The GR10 is good but somehow lacking any special aspect. the CK100 is quite polarizing, I wouldn’t recommend it unless you can get an audition.

  • Ryan Sim

    Hi Mike-

    First off- great article! Really apreciates such insights being available for reference for confused people like myself. 🙂

    Question: I have a Shure se535 + a Grado sr325is headphone and am recently taken interest in the RSA amp line-up to get a better music experience from them.

    With portability in mind- can you help advice if RSA Shadow or Mustang will be able to drive both output with high efficiency and result?

    Thanks and looking forward for your advice! 🙂

    • Ryan,
      The Mustang if you’re gonna use the Grado. The Shadow is quite limited, afraid you can’t get enough loudness.

  • Time to update since so many great amps have been released or updated.

    • Yes for sure, Steve… I will do that when the opportunity comes up.

  • Jordan Ingram

    I’m using the JH11s and I’d really like to audition the Pico Slim, but I have no idea how to make that happen. There aren’t any portable amp retailers in my area, so are there other way to audition things (i.e. a “test drive”)?

    • Nothing that I can think of. Find a head-fi meet?

      • Jordan Ingram

        Yeah ok, I figured as much. Guess I’ll have to take my chances on something!

        • Good luck, Jordan.

  • Hey Mike,

    I’m looking for a portable amp with DAC to power my westone 4’s. I’m looking to add a tubish quality (warmth) to my music as well as enhance instrument separation and soundstage. Tighter bass is always welcome. I’m quite happy with the mid-high range i get right out of my iPhone or macbook (although it just doesn’t feel analog enough for my taste, if that makes sense). I’d appreciate any recommendations.

  • james74

    HI Mike,

    Just to update you on some advice you gave me 6 months ago on amps to use with Sony X walkman – JH16’s & Sony MDR-Z1000’s. Been bit of a delay but have finally picked up the TTVJ Slim from someone I know and is is the non dac version but have to say it was worth the wait as I am currently still without a desktop rig this is the best I have heard my MDR-Z1000’s since I have had them and despite those cans meant to be efficient to drive @ 24ohms they sounded as if they was lacking sonically even with my new Z series Walkman and now the TTVJ Slim has defined to me the Z1000’s are a keeper. The Slim is just what I was looking for and is a tad more fun to listen to than my old PB1/DB1 set up.

    So thank you for the past advice/ direction in making an informed decision that has been worth the wait but now I have the Slim (non dac version) I just have to ask one final piece of advice; What external portable dac would suit the TTVJ Slim as a good partnership?

    I had the DB1 Boomslang originally and was impressed with that when it was in conjunction with the PB1 but am not sure what other alternatives there are other than the DB2 that have the ability also with both optical & Coax digital input as well as usb for use with my laptop. I am not on a budget as such so just want a dac that has the above digital inputs that can pair well with the TTVJ Slim.

    Thanks again Mike ; )

    • Hi James,
      I’m glad to hear that you are enjoying the TTVJ!

      On the topic of portable DACs, what player are you using? You know that the Sony X can’t be plugged in to a separate DAC.

      • james74

        HI Mike,

        I should of clarified a bit more clearer, the dac will be for use with my HP Envy laptop which has the el-crappo Beats audio installed and then I will use my Arcam FMJ cd player via Coax which could be a Meridian 24bit G08 player later on. Then you never in the future could go down a Hi-fi Man/ DX100 route….

        • James,
          A bit confusing there. If you are going to use a Meridian G08, why are you even considering these Ibasso DACs?

          • james74

            Sorry Mike, long day @ work yesterday!, was meant to say I will use it with my cd player (arcam FMJ) until I get a Meridian G08 (not sure when that could be though) but ideally need the dac to have coax/optical as well anyway for if I go for a premium dap later.

            But other than the Ibasso DB2 dac I was not sure what else there was to consider that was as good with the same input options in portable form which would go well with the TTVJ Slim as a pairing. Sorry for confusion there ; )

            • So this is for a desktop set up yes?

              If it’s so I would recommend you to look into something desktop-based like the Cambridge Audio Dacmagic.

              I’ve never tried the DB2 DAC, but from my previous experience with Ibasso portable DACs, I don’t think they are good enough to take on the $300 level desktop DACs.

              • james74

                Hi Mike,

                I ideally needed a portable dac for when I take my laptop on my travels but yes I was looking at also getting a nice desktop dac later on with a budget up to £1K. So portable dac wise there is not much to choose from then?. Desktop – Dac magic looks intriguing, have you had experience with the Audiolab M-dac which also has a built in headphone amp also?

                • Hi James,
                  Sorry I haven’t auditioned the M-DAC til now..

                  • james74

                    Ok, Thanks Mike, I will audition the Dacmagic in the near future anyway along side the M-Dac.

                    For portable dac I might just have to get a usb only dac to widen the choice that is currently out there. Just need to find one that pairs well with the TTVJ slim. Thanks again for your advice ; )

                    • You’re welcome James. 🙂

  • Hey Mike,

    Which one would you recommend for the Cowon J3 and the Sennheiser
    HD25-1 II?

    • There’s a lot to choose from, Stephen. I think something small like the RSA Mustang.

      • How about the Sennheiser HD25-1 II with an Ipod Classic? Would that change your opinion on ‘somthing small like the RSA Mustang’? Will the Alo Audio National be better than the Mustang?

        I listen to mostly: Pop, Rock & Alternative.

        Thanks Mike.

  • Hey Mike,

    Which of these would you recommend for the JH5 custom Pro In-ear monitors?


    • Stephen,
      I like the JHs best with the Pico Slim.

      • Hey Mike,

        How about Universal fit IEMs? Would you still recommend the Pico Slim?

        • It would depend on the IEM. Some people pair bright IEMs with dark amps and so on.

  • Hi Mike,

    Now I have the HRT Music Streamer II, which amp would you recommend for the Ultrasone Pro 900?


    • Budget? Desktop/Portable?

      • Under $500 would be ok. Since I will use it at home, either desktop or portable one would be accepted. From this article, I think SR-71A, P-51 and TTVJ slim are good for pro900 but I’m not sure. So I wanna ask for your recommendation.

        • Boonh,
          SR71A is best, but no rechargeable batteries if you can live with it. P51 I think doesn’t have enough impact power for the Pro900.
          The TTVJ Slim can be a good pairing.

          • Thanks Mike!
            I will have a chance to try both SR71a and P51 soon. Hope I can also try TTVJ slim in the future.

  • Hi Mike,

    Which one would you recommend for the Westone 4R? I listen to mostly: Pop, Rock & Alternative.

    • You need bass impact with the 4R right? I’ve only listened to the Westone 4 and I think the main problem is bass impact.
      Try the RSA Shadow. Small, precise volume control for IEM, good bass.

      • Hi,

        Thanks for reply. Just wondering, are there any other cheaper portable amplifiers that would help the Westone 4R for Pop, Rock & Alternative? Yes, the bass is lacking.

        • The Shadow should help, but I doubt it can add that much bass.

          What I am talking about here is the bass punch. I find the W4 to have very weak bass punch.

          • Hi,

            Are there any other cheaper portable amplifiers that can suit the Westone 4R?

  • thethirty3rd


    Which tiny amp would you recommend for the HD25s, the Shadow or the Slim?

    • I would use a bigger amp, I’m afraid the Shadow and the Slim won’t have enough gain for the HD25

  • Hi there Mike,
    I’m deciding between the ttvj slim and the pico slim to go with my JH16’s and the Iphone 4s.
    I miss the lush mids of the sm3 when i changed to the JH16’s
    Do you think the TTVJ slim amp is a better choice?

    • James,
      I think you should look into the RSA Mustang. It has a really smooth and lush mids.

  • Digging up an old article but …..I have a Denon D7000 that I’m happy w/ on my home rig, but I’ve been spending more time away and would like to go portable. Any suggestions on what portable amp that would match up nicely w/ them? I would like to stay under $200 unless there’s something that is just out of that range that would be a good match. They would also be used w/ FS Atrio M5’s if that matters. Music variety is electronic, hip hop and acoustic being paired to an (gasp) iPhone. Thanks 🙂

  • Hi Mike, Your website is truly amazing though my credit card would disagree. From a technical viewpoint, why can’t someone build a USD100 portable DAC that can take a signal from an iDevice’s LOD and feed it into a portable amp? Right now I use a HRT iStreamer with my headphone amps but I can’t venture too far from the wall wart!

    • L.

      Maybe Fiio one day will, but I think it’s mostly related to the costing price of the apple Certification

      • I’m sure you’re right and if HRT can build that into the cost of their iStreamer, I agree that Fiio can do it for less.

        • Go Android. USB Audio support with all Jelly Bean updated devices.

          And down goes the pricey CLAS and Fostex HP…

    • Thanks, George.

      I really don’t know if that can be done. One thing we don’t have an idea on is the amount of money Apple demands from manufacturers before they get access to tap the iDevices’ digital data. As time goes and manufacturers come out with more affordable solutions, I think we’ll be able to see how low you can build one for.

  • Mark Edmondson

    Hey mike, just wondering your preferences for portable amplifiers for the T70 250 ohm?

    • Mark,
      I didn’t spend too much time with the T70 250 ohm, but it would probably be something with a good bass weight like the ALO national.

      • Mark Edmondson

        Thanks 🙂 ill have to think about it

        • Alright, Mark. 🙂

  • still confusing which amp is the best for my HD6500? headstage arrow, RSA 71A, alo rx MKii, Ibasso PB2. can you recommend me with the exception of price and size of the amp.

  • Justin Q.

    How does the DACport feeding 2Stepdance (sonically similar to stepdance) compare against the DACport feeding Leckerton UHA6s MKII?

  • Kenneth Ong

    Which amp would you pair with the JH16 Pro?

  • Michael

    Hello Mike,
    Would you please be so kind to recommend anything for Sony MDR-MA900?

    • I would go with the RSA or the ALO amps. The portaphile is also good. If you’re on a budget try JDsLabs.

  • If I listen at a low to moderate volume, will the mustang be enough for the hd600 or the sr-71a is better on lower volumes as well


    • The SR71a will still be better.

  • Great article Mike! I have a pair of Shure SE535’s, not overly pleased by the fullness / warmth of the bass. What gear would you recommend?



  • Robert Madison

    Here is an extremely creditable review about the Creative Sound Blaster E3. Check it out!