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This is the only Class D amp you should be looking at SMSL PA-X Review


Audiophile world is experiencing a change, we see many cheap devices coming that sound great, we see more and more different offers, with a lot of features and functionality below a 1000 euros. But also a drastically movement towards more efficiency of Class D.


Explaining classes in amplifiers


It used to be that Class D are nothing but good for cheap amps, but we see more and more new amps coming with Class D. Here new Bluesound Powernode is coming with Class D. And it makes me think about the future what is coming in next 5 to 10 years.


But let me first explain differences in classes for those who do not know. I will tackle the 3 most common classes even though they are not only that exist. There are class G and H that brands like Arcam, Naim and NAD use. So I will talk about Class A, A/B and D.


White shelf with audio equipment including a speaker, amplifier, and turntable. Gray wall background, wooden floor, cables visible.

Class A


Class A is usually the audiophile favourite class of amps. The most purest signal that is coming from single transistor, which conducts 100% of time avoiding crossover distortion.


It is an amazing sound quality it is pure, clean, with a lot of micro dynamics.


But it comes with a lot of problems.


As the power that transistor receives, creates 75% of heat and only 25% of power for speakers. Making the superbly ineffective. For any decent power to get out of them it requires a large heat sinks and power supplies. Making them very expensive, to get some decent power.


And it needs to run constantly. The amplifier always draws full current, even when no music is playing.



Class A/B


For developers, to make HIFI more accessible they decided to merge two classes together. Class A and Class B. Class B is very unusual to be seen in audiophile devices, as it has very poor resistance making the signal very distorted. But it has great efficiency, and it does retain some qualities from class A.


Now one transistor is Class A, and other is Class B. Making the current flow only 50% of time, not all the time. It at low levels use Class A, but as the power increases it switches to class B to gain more power.


It is far more effective than Class A, as it can transmute 50 to 70% of current into power for speakers.


It is the most common class in amplifiers, as it retains great quality, and great efficiency. Now depending on quality it can have some distortion especially when it switches the amps, and it does not sound as pure and smooth as class A. And the transistors are far smaller.


It is a compromise to get best of both worlds.


Class D


And here comes class D. Which was usually shunned in audiophile worlds. Its transistor can be completely turned on and off, the power goes through pulse-width modulation, transistors and filters before becoming a power for your speakers.


It is extremely efficient as most of the current that gets in it 90% gets out.


But it also was not that great into controlling the signal, making a lot of artifacts and distortions on the way. Especially with more power output.


Therefore it could mostly been seen on cheaper amps, as it was efficient, it always ran cool and the size of it is really small. It fits nicely in small boxes, and when executed correctly in architecture brought good results for cheap.


The boxes became small and easy to reproduce and easy to implement.



What is Gan FET?


And now in past few years we can see a lot of improvements in class D. Both in efficiency and quality. Topping is the leader in clean output, with B100 and B200 but there are Fosi, SMSL and bunch other trailing on that sonic race. With every new iteration it becomes better and better. Most common are Metal Oxide semiconductors. They are cheap easy to acquire, and when properly integrated sounds good.


There is also a Silicon carbide which is used to power powerful rigs. It is not as cheap or easy to get like metal oxide. They are a bit harder to implement, but they provide a lot of power. There is a great power voltage and temperature resistance. But also is much larger transistor.


But now the newest revolution in technology is Gallium nitride, And it is an amazing step forward. It is smaller, yet remains a lot of power. And it has a ultra fast switching creating less distortion.


A more cleaner signal. Better transients responses details and response. It creates a best choice in class D for transparency, speed and power.


And now in my hand I have culmination of all that in this device SMSL PA X. It is Gan Fet 250w in stereo and 500W in mono. And I don’t have to tell you how amazing that power is.


It is a full mature SMSL from the ones I used to listen. And there are a couple of surprises here. Its ability to dig deep into song you listen to extract details is just crazy good.


But let’s go first quick word on design, and features.


Sleek audio equipment on white shelf, silver amplifier with a blue display showing "20." Background has a black device and turntable.

Design/Features/Monoblocks


I am not huge fan of design of SMSL, but this silver color with black screen and sides is really nice. When I unpacked the device I thought the whole black stripe, is a screen. And I was amazed, but unfortunately only small part of this is screen, and rest is just decorative.


Behind you have very typical affair for stereo amp. You analog ins and out. There is RCA and XLR inputs which is great.


The ace under the sleeve of this device is that this can work as Mono Block, if you have two SMSL PA-X you can via XLR connect them and have them work together to produce 500W.


But the weirdest thing is the, UI is SMSL UI I also am not so happy with it. But the weirdest thing is you have to know the impedance of your speaker, and you have to manually select 4 or 8 ohms for it to send correct power to your speakers. Usually it is automatic, but here you have to manually choose.



One thing more that I hate is remote. It is basic remote, it is not that. But the SMSL remote for all their devices is the same. So if you have SMSL DAC and SMSL CD and SMSL AMP they all have same looking remotes, which cannot work interchangeably. Like some companies create a universal remote that can control more of their devices with single remote.


No, it is the same looking remote and so many times I grabbed the wrong remote trying to raise the volume. Just to be confused that nothing is happening. Please SMSL change this somehow. There is a lot of people under your ecosystem of devices, and this is not how you should be treating them.


It could also be nice to have auto-shutdown functionality, after prolonged time not not using the amp.


In conclusion it is nice looking device, and not that heavy or big. It fits everywhere and it is ready to rock your world. So let’s go to sonics.


Audio device with display sits on a shelf beside a large pot plant. A framed painting with blue and yellow tones is leaning against the shelf.

Sonic Signature


And this is a bit typical SMSL affair, if you like its sound you will love this amp. It is neutral amp, which is a class D standard, but attack and transients are very forward with highs open and extended.


This does not create a bright sound per se, as it is neutral sound, but it has certain leanness towards treble and can push speakers that are already bright into uncomfortable territory a little bit.


But this sound is just very clear, transparent and fast. I love that instruments are well defined on soundstage. They have a quick transient so don’t expect them to decay longer on soundstage, but it is a sound brimming with life and textures.


There is no lack of micro dynamics here, as it is sound that is able to fastly open and close and across the board do that will it in bass, in midsection or treble.



Sound Quality


Bass


Going bottom up in sound. The bass is as expected a bit of a minus here. Not that it does not have its own presence, it pushes a lot of air in the direction of listener. But that air is condensed and have this attack and forwardness. It is not scoping and big. It is not smooth, it is not prowling.


It might be a problem for some who are used that soundstage here is large, that bass grabs you in all directions. But it was nice. It was detailed which was super nice. On Blade Runner tracks you can definitely feel that it is not most smooth, most large, but the lower notes of synths have this vivid texture to it. It is not smooth, but it is almost raspy, like you can imagine in your head that sound.


It is just the nature of cleanness of class D, and without a proper preamp to add spiciness here, it is just the way it is, with it. Even in gallium nitride.


Mids


But things get much better the way you ascend up, there is certain joy even in balanced nature here. As the sound become more forward and clean. So if you listen to more acoustic music, more vocal driven. Like for example Court and Spark from Joni Mitchell, her vocal will be nicely rounded and separated and a bit forward. That makes it so nice.


There is not much clutter here as the amp organize properly things here. Transparency is on par with more expensive amps, it gives room to breathe. And that helps with organization on soundstage as well, give great breath to soundstage.


Soundstage is not the widest, or biggest, but it is not shy. It is proper, and with good pairing it can become great.


The complexity of instrumentation are being completely held together by this lean structure. Even listening to rock, or jazz, or some chamber music it holds itself to not fall apart and lost in the mud. A really big plus for SMSL.


Imaging was nice, nothing mind blowing but same with everything I said here it is very well controlled and it does not allow to fall off to any side. It represented vocals in the middle. And I can say it plays a bit better with female vocalist rather than male.



Treble


And then it comes the treble, the hot treble. We should speak about dynamics here a little bit. While the extraction and insight benefits a lot of Class D here, it is lack of dynamics that is a bit capping it to become this amp that rivals all other amps on market. It did remain fast and open at top. Providing details and insight. But it did never extends a lot and this can be said on all dynamics on entire frequency spectrum.


You can see that in bunch of details you find in percussions, in pianos, violins, and synth voices. It had their place on the stage, mostly helping the sound expand. It is fantastic for those who like a bit more punchy sound, as it brings a lot of energy to it.


Listen to some Love Supreme to understand what I mean here. But it is lovely how much SMSL is catering us with details. It is unprecedented for amps like this. Just amazing transparency, details and control.


Silver audio amplifier with various input ports and switches on a wooden stand. Blurred background with plants and shelves.

Pairing and Synergy Suggestions


For pairing, I loved Polks with them. I think R200 is an amazing choice with them. Another amazing choice with them is Wharfdale Linton, or special Denton. Its size and scope adds to lower end, and soundstage, allowing this amp to be more dynamically rich, while the amp is allowing speakers to be more clear in midsection.


Same like Q Acoustic 5020, and 3020i as a bit darker character to them is complementing the sound well. It is just that lean nature of SMSL is better complimented with this smooth warm sounding speakers. Dynaudio Special 40 as well, some Buchardt etc. It can go well with balanced, something like Elac 3.0 is nice, but aim with speakers that have bigger bass reflex.


Avoid bright speakers, here and I think you should be fine.


Regarding DACs, go with ESS Sabre if you can as they are a bit more neutral and will fit the character the best. You can also go with AKM if you like a bit more spicy treble rich sound.


Good and perfect companion is SMSL SU-X, or maybe if you can find Denafrips Enyo for that money. Or SMSL Raw DAC Pro 1, it works great.



The Future is hybrid (and who owns the next 5-10 years)


Now that intro where I explain classes was not accidentally, I really think it ties to the overall picture of future of HIFI. Currently most common class in amplifiers are Class A/B. But I think that is going to change soon.


With evolution of Class D, in ability to control distortion and to retain quality of sound. We can see that Class D which is more efficient to change Class B. And we can expect soon hybrids of Class A/D. To retain that beautiful sound of Class A, and to give weight to the sound, while using efficiency and clarity of Class D.


It is a bit difficult to engineer, because Class A and B are very similar, and while Class D uses a bit different architecture to power the speakers. But we also see the progress in that area. It is in expensive amps now Like Devialet amps, Marantz and NAD. The amps in question are Devialet Astra, Nad M23 and Marantz Model 10. But with time the technology is going to become more cheaper, and we will have new hybrid on market which will dominate.


And I am looking forward to it. And I am looking forward to continuous progression of class D, and I think the future is hybrid. The future is Class A/D.


Audio equipment on a shelf; left has blue display showing volume, right displays music info. Cords hang in background. Neutral tones.

vs VMV A1 Pro


To me the closest competitor is actually a sister brand to SMSL and that is VMV. With VMV A1 Pro.


It is a 500 dollars Gan amp, that uses almost the same architecture as PA-X. But in more prettier chassis, at least to me. But there are a few differences to think about here.


A1 Pro is cheaper, 200 dollars, which is a plus but is 2x the less powerful from SMSL PA-X. But it lacks one big thing unless you use it in stereo, you do not have XLR. There is only mono XLR, while PA-X allows full XLR integration.


Now together in stereo mode A1 Pro is more expensive, 300 more expensive. But unless all in one box with PA-X, the A1 have mono blocks separated which creates a bit cleaner sound with same power. So combined it is a better product. It is a product that is also a bit stronger power output wise, and could drive potentially more speakers.


So to you is all about fast route or slow route. The fast route is buying SMSL PA-X and you have all in one box right away. Or slow route buying one and eventually another one, and you get a better product than single SMSL PA-X.


But then again two SMSL PA-X are better than two A1 Pro, but that story for some other time.


vs. Advance Paris x-i75


The other alternative is equally priced Advance Paris x-i75. Now this is a completely different beast. It is a fully integrated amp, which means, it have DAC, it have preamp inside. So I think at some the value is more on Advance Paris side.


It is not as powerful as SMSL, as it does 110 to 250w of power. It does not have clarity and details, and precision of SMSL. But it have nice warm sound, a more deeper bass, a smooth sound and gorgeous silky vocals. But also everything else it does good, not at SMSL level, but very good. And it is great price too.


It is for those who want all in one box, they don’t want to buy extra cables, extra DACs, extra preamps. If you invest in SMSL you will get more, but if you want all in one for the price of SMSL PA-X you might want to look at Advance Paris.



vs. LAiV harmony GaNM


Other option is a strange one it is Laiv Harmony GaNM. Now I have to say I have not heard them. I don’t have experience with them. As I am a bit reserved into spending 4500 to buy this amp.


As it is such a steep value for amp, at that price you can get some amp monster. My favourite and end game amps. Like Hegel H190v, which is cheaper, a Primare i35 again a bit cheaper and they are all integrated amps with great DACs, great preamps and amplifications. And my end game flagships.


It is true Laiv Harmony does have 400W in 8 ohms. But if you buy two SMSL PA-X you will also have 400w in 8 ohms, and 500w in 5 ohms for 2800 dollars less.


Like that is so much more expensive, and I wonder is it worth it? Like imagine this scenario, You buy two SMSL PA-X and it costs you 1400 dollars. You add, a fantastic DAC of SMSL SU-X and that is a 1000 dollars more creating a 2400 dollars bill. You add Polk R200 and that is 700 dollars more and the bill now is 3100 dollars. You add streaming, you add Eversolo DMP-A6 and that is 850 dollars more. It is 3950 dollars. And you add some fantastic preamp like Schiit Kara F, which is 800 dollars to final total of 4750 dollars. And I could even out the price if for example instead of Eversolo you go with Wiim Ultra.


That is a bit more expensive than only Laiv Harmony power amps. But you get amazing full system. That is easily very high end. So I wonder how good it is.


Hopefully I will test it someday to see how it works, and compares, but I think about this every day. Every day I wonder how good it is.


Stereo receiver on a shelf surrounded by green plant stems. A colorful album cover is partially visible in the background.

Can this be my daily driver?/ Conclusion


This is a first time in my audiophile career that I can consider that a Class D amp can become my daily driver. Usually before I said that Class D are astonishing value from amps like Fosi, SMSL, Ayima etc. As they bring so much to the table for little money.


But they could never compete with the amps I owned, in Class A/B as I just preferred the character a bit more.


And also if you had a floorstanding speakers like Dali Oberon 5, Q Acoustics 5040, or Fyne Audio F302 which are not big floorstanders and not complicated to drive. The smaller Class D always struggled.


But not anymore this can comfortably drive even floorstandings. It have great transparency and details to reveal more expensive integrated amps. And I can see myself use this as daily driver. This is a point in my career as an audiophile reviewer that I am shocked and happy with the progress of amps.


This is a great amp that have plenty to offer, and if you don’t mind a bit more neutral sound signature that does not have that wow effect. And just purely enjoy this on terms of details extraction, precision and clarity you will be more than amazed with what you have.



Pros


Sound Quality


  • Excellent detail retrieval: Extracts micro-details and textures with great clarity.

  • Clean, transparent, and fast sound: Especially in mids and treble.

  • Good instrument separation and imaging: Instruments are well-placed, vocals well-centered.

  • Very low distortion for Class D: Thanks to GaN FET technology.

  • Dynamic and energetic: Sound has good punch and transient response.

  • Clear midrange: Vocals (especially female) are well-presented and lively.

  • Open treble extension: Highs are forward and detailed without being sibilant (though could become hot with bright speakers).

  • Great synergy with warm/dark speakers: Works well with Polks, Wharfedales, and Q Acoustics.


Technology & Efficiency


  • GaN FET implementation: Smaller, faster-switching transistors lead to better efficiency and reduced distortion.

  • High efficiency (90%): Runs cool and allows compact design.

  • High power output: 250W stereo / 500W mono—can drive demanding speakers comfortably.

  • Supports monoblock configuration: Enables upgrade path and higher performance if needed.


Build, Design, and Features


  • Compact and not heavy: Easy to place in setups with limited space.

  • XLR and RCA inputs: Flexible connectivity.

  • Clean visual design: Attractive silver/black color scheme.

  • Upgradeability: Pairs well with other SMSL gear for building a full, high-end system.


Value


  • Incredible performance for the price: Competes with amps many times its cost.

  • Flexible system building: Allows audiophiles to gradually assemble a high-end stack with preamps, DACs, and streamers.


Audio amplifier with text "S.M.S.L." is on a table beside a floral lamp and blurred plant, creating a calm and cozy atmosphere.

Cons


Sound Limitations


  • Bass lacks depth and smoothness: Has texture and punch but not scale or warmth.

  • Soundstage not very expansive: Accurate but not immersive; lacks "holographic" width.

  • Treble can get hot if wrongly paired: Especially with already bright speakers.

  • Lacks deep dynamics and decay: Fast transient response, but doesn’t bloom or fade like Class A/AB amps.


Comparisons & Trade-offs

  • Less musicality vs. warm amps: May not satisfy listeners preferring lush or colored sound.

  • Synergy is important: Needs warm DACs or speakers for optimal performance—can sound too lean otherwise.


Subjective Reservations


  • May lack "wow" effect: Sound is more about precision than emotional engagement.

  • Still not everyone’s taste: Class D tonality and “lean” signature won’t appeal to all audiophiles.



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