Flyin’ High: JDSLabs C421


Back in 2011, John told me that he was working on a new portable amp with a slim form factor. I was so impressed with the JDSLabs Cmoy’s sound quality that I told John that I would be very happy if I can get the Cmoy’s sound quality unchanged but in a slimmer package and with USB recharging. I think the sound quality of the Cmoy is high enough for most people (me included), and the only thing missing from it are general convenience features such as USB recharging and a slimmer form factor. John assured me that the C421 was going to be better than the Cmoy in every aspect. Honestly I had my finger crossed then, as I’ve witnessed the Cmoy beat many amps costing more than it.

Prior to the C421, there were already several slim portable amps in the market. The TTVJ Slim and the ALO Rx (currently at Mark II) were among the first slim portable amps, and though they are both great sounding amps, I wanted something lower priced that I can recommend to a wider group of people. The Headstage Arrow was a pretty good amp with great features and price (when it first came out), but since then have seen a price increase to the current $299.00 price tag, and I’ve always thought that it fell short on the soundstage performance. Aside from these models, I know that Leckerton’s UHA-4 amp has been getting good reviews but I’ve yet to listen to it. You can also get amps like the RSA Shadow and the Pico Slim that are both slim and tiny, but their limited power output and relatively premium price means that they are quite niche. Perhaps the most phenomenal entry to the slim amp category is Ibasso’s D-Zero, released last year with an aggressive pricing of $109, complete with a built in USB DAC. It was a solid entry from Ibasso and I do recommend it once in a while, but the sound wasn’t quite as nice as I want it to be.

I’ve evaluated a lot of portable amps on the market and I think the sweet spot is on a slim form-factor amp, priced within the $100-$200 range (of course the cheaper, the better), have a relatively nice sound (even on par with the Cmoy would’ve been enough), and comes with all the convenient features such as USB recharging and gain settings. The C421 seems to hit all the checkpoints, except for the sound part, which at that time I’ve yet to listen to. And to be honest, I wasn’t that enthusiastic about it, as I only see it as another amp builder’s attempt to move up from a basic Cmoy assembly to something more advanced, but hardly ground breaking.

Initial Impressions on the C421

I don’t remember when I first received the C421 amp prototype, but I was definitely not too excited about the sound. It was the AD8620 version, and the only thing I can attribute to it is that it has a pretty good, punchy bass. Soundstage was quite flat, high and mids are quite dry. I gave it to some friends for them to audition, and they were also quite lukewarm about it. At that point I thought that the C421 would be just a slim amp with no other special qualities and I was quite disappointed. I wrote John an email explaining my impressions, and to my surprise he replied by sending me another C421. (I don’t intend to bash the AD8620 version, rather I just want to tell the story as it happens. I also am aware that JDSLabs recommends the AD8620 version so it’s up to you which version to get)

The second C421 was different. It had the OPA2227 op-amp, the same op-amp that John installed on his JDSLabs Cmoy. The treble/midrange/balance was among the best I’ve heard on any amps. The soundstage were extremely good, possessing all the right width and depth and with good ambiance. Midrange is among the sweetest and clearest I’ve heard from a portable. I immediately fell in love with this version of the C421, and I knew then that the Cmoy is not going to get much use from that moment on.

I noticed that the bass was a little loose and not as punchy as I’d like it to be (bass boost OFF), but overall this is among the best sounding amps I’ve listened to. It wasn’t as powerful, as dynamic or as impactful as the TTVJ Slim or the ALO Rx, but to my ears the C421 has the best tonality among all the slim portable amps I’ve listened to. In fact, I find the tonality to be so good that I very rarely use the bass boost feature as that adds bass quantity significantly, and to my ears the bass quantity is just right on the flat setting (I just want it to be a little more punchy).

(from now on any references, both mine and Lieven’s to the C421 will be based on the OPA2227 version).
Continue to the next page…

Flyin’ High: JDSLabs C421
4.67 (93.33%) 3 votes

  • Haja Randrianarison

    Seems really

  • Haja Randrianarison

    Seems really nice, it’s been a long time since we saw an amp which was as thin as the Alo amp 😀

    • L.

       and we really like it a lot!

      • And the C421 is actually a bit slimmer than the ALO Rx Mk2. 

        • Haja Randrianarison

           Omg !

  • Chong Yuxuan

    JDS Labs seems to recommend the AD8620 over the OPA2227 which you guys seem to like alot….

    • L.

      Well now you know how both sound, and we clearly prefer the OPA2227 🙂

      • Jeff Kong

        just to side track a bit. Did you guys have the chance to try the AD8066?
        just curious :3

        • Nope, not the AD8066. 

          • Jeffrey Kong

            figured, otherwise you guys wouldve written something on it : D

        • Well I just remembered I should have one or two AD8066 laying around somewhere… all I need to do is desolder the OPA2227 and install the 8066.. 

        • Talked to John over email earlier and he mentioned that the AD8066 version may be phased out. He told me he preferred the AD8620 and OPA2227 versions better. 

          • Jeff Kong

            Thanks for the info!

          • To clarify, we’ll probably remove the AD8066 from the item page within our store. Opamps are manually placed on c421, so anyone is welcome to request a custom opamp, even if it’s not listed (assuming it’s stocked).

            Regarding the AD8620 vs. OPA2227 debate, I enjoy both. This is a hugely conflicting decision for many. If you can’t decide, follow Mike’s advise. A small portion of customers have my ears, but more of the population seems to agree with Mike’s interpretation.

  • Jeff Kong

    Thanks for this review!! Been looking forward to this.

    Mike, what do you find lacking in its appearance? :3
    I have to say it looks great for the most part…it could use a massive logo of some sort like the other amps

    • L.

       I like it too 🙂

      • Jeff Kong

        dont know if I should love or hate you guys…these reviews…tempted to buy this… 

        How does the case feel in terms of touch? very smooth or slightly rough?

        • The black colored part are quite smooth. The silver are less smooth, but nothing sharp.

        • L.

           You know you love us 😉

  • Fabio_Rocks

    Mike is my Wallet’s biggest enemy…

    • L.

       So I’m not? Good 😀

  • hamid inomhodjayev

    Thanks for the both reviews. How C421 compares to ALO Continental? Is ALO much superior? I wanted to use either cmoy or ALO Con. with HM601. 

    • The ALO is the better amp.

  • Great review, Mike!  What’s the size of this thing?  Is it roughly about the same size as the Fiio E17?

    • L.

       It’s on the second page 😉

      “Measuring only 97,5mm x 14mm x 62,5mm “

      • Oh, somehow missed that; thanks!  That must make it no larger than an iPhone.  A super plus!! 🙂

  • 2xdaaim pp

    mike is this the one i tried before?

    • Yes though I don’t remember if you’ve tried the newer OPA2227 version.

  • Why no Fiio comparisons?  Does this best the E11 or even the E17?

    • David Ulrich

      I think I can deduce this answer for you.  Mike found the e11 to be a better amp than the e17.  He also said the JDSlabs Cmoy bested the e11 (at least in terms of sound quality).  In this review, Mike says the C421 trounces the Cmoy.  Using this train of logic, the C421 annihilates both the Fiios.

      • Thanks, David.. yes I missed the Fiio comparisons — I was mainly focusing on the slim amps.

    • L.

       I’ll try to get an E11 comparison up this weekend

  • You know it’s coming…how about vs PA2v2 (I’m in the market for a new portable amp)

    ….and any news about the v200, L? 😉

    • Of course different sound signatures and all, but I would compare the PA2V2 with the Cmoy.

      • John123John


        • I wish… i usually dont like plastic but with the PA2v2 i LOVE it.

        • Are they coming out with a PA2V3?

    • L.

       Sorry man, no news yet 🙁

  • I like Lieven am cursed with the high low gain.  (an oxymoron no?)

    • You got the early version? 

  • Hi Mike and L.
    Love your reviews and am after some advice , was planning on buying the Fiio E17 when becomes available for use with my iphone 3gs  and hd598 and my vaio laptop with hd598 . Having read the C421 review which would you recommend to me , I listen to a broad range of music but mainly indie , acoustic , rock , soul .

    • David,
      I would go with the C421 in that case, since you don’t need the E17’s USB DAC function.

  • Mike, reading the review I was unclear if this amp powers all headphone impedances well. Can you perhaps try comparing the c421 to the jdslabs cmoy using the hd580/600 and push it to around an average 100db level or something just a little below rock concert levels.

    I know for instance that the cmoy is practically garbage with my low impedance cans. The JDSLabs CMOY runs out of steam faster than an ipod with low impedance cans but is truly outstanding with my 300 ohm senns or 250 ohm Beyers.

    • Good point, and we did miss talking about headphone pairings. Probably should edit in those information since more people are going to ask. 

      I think these days it’s almost a given that any decent amp can drive high impedance cans quite easily. The Cmoy is not that great with low-impedance and I’ve made a not of that many times, but I don’t think the Ipod is better than the Cmoy.

      •  Well as far as high impedance cans and amps, the FiiO E10 for instance which is supposedly a powerful portable is pretty weak and lack dynamics with 300 ohm senns while the jdslabs cmoy slams like an E9 while having a better tonality at the same time with those cans.

      •  So in this specific case of comparing a jdslabs cmoy with the c421 for the hd580/600, which one wins in sounding good at relatively loud volumes?

  • justin biliran

    Hi sir! Would this amp be good when paired with the iPod/iPhone plus HD25/Marshal Major/any of the ATH SJ series? Thanks!

    • Justin,
      I haven’t tried it with the Marshall or ATH SJ, but it works great with the likes of the HD25-1 and the Philips Fidelio L1.

      • justin biliran

        All right sir thanks! Would you say I should update my amp from the PA2V2 to this?

        • Perhaps not urgently.. the PA2V2 is a very nice amp already.

          • justin biliran

            All right. More savings for me. 😀

  • ocswing

    So what’s the actual price?

    • L.

      Again, that was addressed on page 2: price point ($184);)

      • ocswing

        Kind of buried there. I did a cursory search with ctrl+F and saw references to price points of other amps rather than the amp in question itself. Just a suggestion to have that information be more prominent in the future.

        • L.

           Yes Sir!
          Normally the price info is at the bottom of the article, uess we didn’t this time 😉

        • Yes, that’s a good point. Next time I’ll make a note to make the price info more obvious.

  • Nice review! I’ve already ordered an O2. Perhaps I will get a c421 in the future. 

    • L.

      Thanks Chris!

  • Hi Mike, love the site man. very clean, concise, and reliable. I have been in the market for my first amp since the I heard about the E17, which I thought I’d get until I read this review…. I listen to just about everything, Zepplin, Floyd, Ratatat, White Stripes, Queens of the Stone Age, Eagles of Death Metal the Black Keys and just about everything else there is.

    For playback I use either a laptop(m-15x), J3, or a sansa clip. I have a pair of ATH M-50 cans, but down the road I’m thinking about investing in some Grados SR325i’s or the new Phillips Fidelio.

    That being said, is the c421 your amp of choice in the sub $200 category?  or should I keep waiting for the E17?

    • Aric,
      Amp section wise, the C421 is better. If you want to listen from a laptop, I think the E17 is the one I would get because it comes with a DAC.

      • Well a few months down the road and I have the E17. its a great product I LOVE THE BUILD QUALITY. However, when I bought the E17 I didn’t realize the DAC was the most prominent feature. and Id’ say 75% of my listening experience uses a sansa clip as a source which I believe has a decent DAC to it, not very grainy like my laptop or droid razer.

        So how does the E17 compare to the C421 just as an amp?

        and scaling up in the amp world to such products as the contenental Vs. the SR-71 how does the cost Vs. audio improvement compare to the later comparison of amps? or is the “WOW” factor there in the top of the line portable amps to justify paying triple the price of the C421?

        Obviously you wouldn’t get 3 times the amp performance, but I’m curious what you have to say of the diminishing returns curve and how hard its at work in this comparison.

        Sorry for the long winded questions by the way. I need to go to a meet or something… lol, but you do a great job of answering my long winded questions!

        • Aric,
          As I’ve said earlier, the C421 is a better amp compared to the Fiio E17 🙂
          I think it’s always hard to judge amp improvements by the dollar. I know we all want easy answers, but the same thing applies in just about anything. You buy a golf club, clothes, shoes, bikes, smartphones, the extra price can be justified by people who can discern the quality improvements. Not everybody can discern the quality improvements, but for those who do, I think that jump from the C421 to the SR-71 can be justified. But again you need to take into account that people’s financial situations are different. Some people make $60K a year, some make $100K.

  • Nice review! for now I am content with my Continental and E11 🙂 But reading these reviews will tempt me into trying something sooner or later. Saving for the JHs for now… Alok

  • EraserXIV

    I think a very interesting comparison would be with the iBasso T5. The D-zero really isn’t supposed to be in the same class as the C421. Have you heard the T5 and could you make any comparisons?

    • L.

       I have only heard the T3, and the C421 blows it to oblivion

    • I haven’t heard the T5, but the T3D was so overrated IMO I was really underwhelmed with it. Unless the T5 is a BIG step up from the T3D..

  • Had my c421 a few months now. I wish the low battery indicator was on the front. I usually don’t notice it’s on and then it just dies.

    • L.

       That’s a good remark. Personally it hasn’t bothered me as I charge it during the day so I never am without battery in the morning or evening

      • I guess I should get into the habit of daily charging, like my phone and I wouldn’t have to worry. You’re right. Now I feel silly for not doing that, but I still think the light should be in front. Also, I didn’t realize how tiny the actual LEDs are!

  • I’ve finally decided on the HD650. 🙂

    Now, I’ve been reading a lot about amps and the JDS labs c421 looks promising. At its price range, it seems to have lots of positive feedback. Have you tried your c421 with the Senn 6×0?

    • L.

      I have been using it daily for hours at work. It’s a nice sounding combination, but you better like the Senn darkness cause this amp will make it more pronounced. Soundstage and detail wise this combination is limited, but it is fun. With a better amp the HD650 would do much better of course, but as I said, I’ve been using it like that ever since I got the C421, so it must be good 🙂

      • That’s good to hear. 🙂

        You’re still using opamp 2227 right? May I ask what DAP do you use with your office rig? DAP>c412>HD650

        • L.

           Laptop – Fiio E10 – C421/2227 – HD650 . Great little “budget” rig 🙂

  • Jeff Kong

    quick question, by RX are you referring to the first gen or mk2?

    • Jeff,
      Mk2 or Mk1, the sound signature is the same. The Mk2 is slightly better, that’s all. 

  • thx1000

    I have read this review several times and came so close to ordering a c421/opa2227.  However, I am also interested in your opinion of the ALO National before I buy.

    • Sure, I have yet to receive the National though.

  • Fredo

    will the c421 put out more power than my first gen RX? I wanna be able to drive all sorts of cans…

    • I haven’t done an absolute A-B, but the Rx is extremely powerful and I’d put my money on the Rx.

  • jean xavier Henriel

    Hello and many thanks for this review.
    I have a i basso d-zero and i want somme help to find a better amp for an ipod ( better soundstage, better mid, better details …) to drive a grado SR325
    between this c421 or amp HP audinst  per ups another one (? )what will be the better choice to have an amelioration for a price between 100 and 200 dollars ?

    • Jean,
      Better soundstage and mids, go with the C421.

      • Mutnat

        Have to agreement, I own both and the. C421 buries the D-Zero in all those categories. It is also a bit less forward, slightly darker but not overly dark (just enough to avoid fatigue on my HD25’s), just all around better. It does lack a DAC though, but for iPod listening the dad on your D0 is useless anyway.

  • Anson5

    What DAC will you recommend to pair with C421 and Audio Technica ATH-ES7 for desktop use?  Is Audinst  HUD-MX1 a good pair-up?

  • I’ve had my c421 (2227) for a few weeks now. It’s very impressive for a portable.

    If you like the sound of the JDS BBcMoy, then you’ll love the c421. It takes all the best attributes of his cMoy (great smoothness and mids as well as large soundstage) and adds detail and even more depth and layering. It’s a cMoy on steroids!

    • Thanks for sharing your impression, Scott. Glad you like it.

  • zaynel

    After reading your review, I can’t stand not to get it.
    I got my C421(2227) for about a month now. simply just loving it!
    Looking out for a portable DAC now, but have no idea which to get?
    I am using Iphone4s playing FLACs.
    Do I really still need a DAC? will it give me a big improvement?
    Which are those that are more recommended to pair with C421?
    budget around $150 +/- may be stretchable slightly if It’s a really good choice.

    • Zaynel,
      Unfortunately the portable DACs are a lot more expensive than $150. Both the CLAS and the Fostex HP-P1 are around $500 and more I believe.

      • zaynel

        Oh wow that’s way over my budget! but will it make a big improvement or just a slight? is it worth too save-up and getting them?

        can those cheaper DAC/AMP work too? like the Fiio E17?

        • If you feel it’s way over your budget, I’d just not worry about it and enjoy the music as it is.
          No they don’t work with computers.

          • zaynel

            True. Thanks for all the advises.

  • Firstly, I really like your website. Reviews and comments are always very valuable, it’s a pleasure to follow your work.

    Well, I’m considering buying a C421 or a CmoyBB (I previously considered the D-Zero), but yet can’t decide which. I need your experience 🙂

    Here are 4 parameters that might help set the scene of my research:
    1 – I’m a large music enthousiast, from classic to hardrock with a slight inclination for electronic,
    2 – I tend to prefer well definite sound signature. Something that can be described as favorising separation of instruments, details. Where everything has to feel lively and “at its place”. A full but tight bass, meaning punchy not boomy. To me, the bass needs to be controlled.
    3 – For reference my full size hi-fi set is built around a ROTEL RA-05 amplifier, exploiting an ESI Juli@ soundcard and feeding JMLab Chorus 726S column speakers,
    4 – I plan to use my portable AMP with mainly 2 sets: Grado SR80i and Yuin PK3,

    With those information, which amplifiers between the CmoyBB and the C421 would you recommend me? Is one a difficult combination with one of my current headphones?

    • Just gonna jump in here as I own both amps.

      No contest, get the c421. It has far superior clarity without bloating the bass.

    • L.

      What Scott Says, If you don’t need a usb dac and don’t have a budget limit and only look at the amp part, then the C421 is the best amp, no doubt.

    •  Thanks for your answers.

      I’m a bit and a bit more on the go, so far my music source for trip have relied on HiMD or smartphones. But as it goes one day I might also rely on a portable laptop. That’s why I considered the D-Zero with its DAC. But now I tend to think that I should look for an EMU 0404 USB to do the trick.

      About the C421, between the AD8620 and OPA2227 versions:
      – will one be a better pair for one of my current headphones (SR80i or PK3) ?
      – or on the opposite is one of those amp known to be pointing out some defaults or exagerate one of the characteristics of those phones ?

      • Fneuf,
        I would still get the OPA2227 for the SR80 or the PK3.

        • Thanks for your reply.

          I just figure out that my current smartphone, a Nokia N8 has the ability to deliver digital audio stream via its USB On-The-Go feature. Then its DAC is pypassable. The first condition is that the external DAC should be driverless. So I ordered a Fiio E7 as a nobrainer to try this out.

          Which external DAC (as tiny as possible) would you recommend as a great buddy to pair with the C421 ? Gathering from your reviews I’m notably thinking about an “HeadStage USB DAC Cable”+”JDSLabs C421” combo.

  • lcamtai

     Hi Mike I just did what you recommend me. I bought a Fiio E10 and now
    waiting for my JDSLabs C421. Thanks for your helpful, intelligent,
    useful advice.

    I am using Fiio E10 on my HD598 and the sound is clearer, more clarity
    and mid is awesome but I do not really like the bass boost on Fiio E10.
    Of course it can add more quality bass and but sometimes it breaks out
    the total balance or tonal of the songs so I just enjoy using Fiio E10
    without bass boost setting.

    However I still have a question for you. I am a kind of guys who always
    think economically (or at least I could) so it is still true in
    audiophile. I only choose headphones that can play many genres as many
    as possible and that is why I chose HD598. After reading many your
    reviews and recommendations I planned out my paths of headphones such 
    as HD598 -> Hifiman HE-500 -> Stax SR-009. The question is JDSLabs
    C421 can pair well with HE-500? Of course at an acceptable quality
    (like 70-80% of HE-500) before I have more money to invest in better

    Thanks Mike again. Long live Heafonia, long live everyone and long live audiophile.