SMSL PA40 is VERY powerful, versatile and easy to use power amp. Review vs Fosi, Aiyima

I have reviewed now many SMSL products, DACs, Amps, CD Players etc. And after some time you get acquired with company enough that you know what you will get even before first time power up your sonic machine.

Budget amps are getting better and better, so is competition really tough...

So I was offered to review PA40, a cheap Amp, and I love those. I love to see how much we can push that envelope how much sonic goodies we can get for less money.

PA40 is actually now entry level in their lineup, with middle brother of PA200 and eldest brother of PA-X. Which I think is superbly interesting device. I hope that at price of 140 euros it will be able to bring enough sonic joy that I can recommend this amp. AS the competition in this price level from Fosi, Ayama and similar is really tough.

Build Quality, features, inputs and outputs

But let`s start with build quality and aesthetics. I think in this department SMSL have used all the best and worst of traits of budget gear. If you have seen one, you have seen all SMSL devices. Design language is very streamlined, and may I say boring. Screen and one big rotatable button. Nothing much to write here.

But interestingly this device does seem sturdy, it is an aluminium chassis, it feel impeccably constructed. The button, the potentiometer does seem also very firm, and responsive. IT might lacks tactileness but lets not get ahead of our self with this budget product. It is also really light, and compact making easy to integrate anywhere.

Regarding the back of device, don’t expect much, it is very simple line in speakers out type of deal. This is by the way a power amp, so adding additional DAC or preamp is always very recommended.

But what is happening inside is super fun. We have inside At its core is the Infineon MA5332MS, a familiar presence in SMSL’s premium lineup. This chip delivers impressive output: 165W per channel into 4 ohms and 85W per channel into 8 ohms, making it one of the most powerful in its class.

In addition, the PA40 is equipped with the NJU7391A from Nisshinbo—a modern two-channel digital volume control chip capable of adjusting in precise 1dB steps down to -95dB. For this model, SMSL limits the range to -60dB, which is still more than adequate for everyday listening.

SMSL also brings its usual precision to circuit design. The PA40 features an optimized PCB layout, low-noise power handling, and a signal path engineered for minimal distortion. As a result, even under load, it maintains exceptional clarity—with total harmonic distortion kept as low as 0.00035% at 1kHz, 5W into 4 ohms.

Really powerful small amp and surprise

Complementing this are the same audiophile-grade components found in SMSL’s more expensive models, their signature black PCB aesthetic, and a comprehensive suite of safety protections—covering overcurrent, thermal issues, and undervoltage. All in all, the PA40 is a compact yet powerful amplifier that confidently holds its own against more expensive competition.

But one thing I kinda dislike is the UI. I think it is horrendous, and as on their more expensive models of DACs and Amps as it becomes more feature rich. It becomes almost unusable. It is hard to use, and hard to understand. Hopefully they will with new iterations work more to improve UI.

But feature wise there is a surprise inside this amp, an equalizer. Now I am a person who believes does not like to mess with equalizers unless it have deep integration in DAC, so that it truly make a difference I live it the way it is. I don’t treat my room, so I can adjust sound post processing.

But If you do not have a pre-amp to give this amp a bit of character, rather than typical class D sound. You might really enjoy adjusting sound with equaliser, or using presets that they have. I found bass and rock decent, as they expanded a sound a bit by creating a more v curve in bass or in mid section. But yeah there are quite few presets here.

Sonic Quality

And yet again I am shocked how much you get with this amp sonically. Did I say that this amp is 120 euros, and in that price range this just overachieves so much that this is so great. I could not fathom this like 10 years ago.

This is D class amp, very common in this price range. But with very nice 85W in 8ohms and 165w in 4ohms. The power supply is not external, it is inside the device, which makes me wonder what kind of magic did SMSL pull to put this all in such a small box.

Now this is blessing and a curse, as it becomes more compact device, and they say the internal power supply is going to make current more cleaner, But external power bricks for device like Fosi allowed them to bring to 300W in 4ohms with some expensive power supplies.

Does that makes Fosi a better amp than SMSL not necessarily but we will talk more about that later.

But with that power it does truly gives more opportunity to expand its rather neutral sound signature. As same like many devices in this price range SMSL spots that neutral sound, which is more characteristic of class D than nothing. But SMSL with synergy with its DAC always try to add a bit more zest in treble. It tries to make things a bit more interesting in top end.

Which is always so much welcomed, it makes listening to music much more dynamically interesting. But this is very much that neutral, clean sound.

Exceptional clarity

But it did kind of surprised me how much space and transparency did SMSL allow between instruments. First thing what I was surprised I was when listening is to hear that background behind every instrument, or rather not to hear. It works well for more acoustic music, and in generally music that does not require so much passion in music in order to work. I think it also works well with classical music etc.

Bass

But the bass was a bit of mystery to me, while it had a attack and presence it also I think it had hard time to produce weight and presence that I expect to bring that full encompassing soundstage. I think bass was rhythmic but never commanding, never encompassing never big enough. And it work best with cheaper speakers, than a bit bigger speakers with big bass reflexes.

Treble

And the treble where great, that clarity I spoke about earlier, that lean sound made details quite vivid in upper mids and treble. That allowed this sound to have more of a pulsing characteristic which to me is such a tremendous thing for such a cheap amp. IT brought detail extraction with ease making it a great thing truly. The details made instruments 3 dimensional and made soundstage more easy for me to observe what is happening.

Mids

Midsection was great and bad at same time. Let me explain, so I love that this amp was clear and transparent making diffusing complex compositions easy, but the voices the instruments were very flat and unengaging. Making them good to observe but not best to dance to. But they were easy to see, but just not enough magic to make them be at spotlight.

Things that it could do better

Things that I did not like so much is definitely lack of inputs and outputs. This is very modest selection of with just in and out. And that is. No XLR no 12V trigger. No sub out, pre out nothing. Very stripped down. IT could do maybe a bit more here.

Otherwise beside that as this is a lean sound, don’t expect big soundstage presence. It opens okay, but I honestly expected a bit more width from this amp, as everything is lean, bass have attack but not scope it will not give the biggest soundstage presence.

Comparing it with other competition like Aiyima and Fosi, and why I would choose PA40

To me I will try to compare this with my favourite devices from this price level the Fosi ZA3, and Aiyima a70.

And this is a tough competition. To me Fosi and Aiyima did have more presence and dynamics in sound, making soundstage a bigger. They have more presence and scope of sound, it is more weighty and present.

They also have more power output, making it possible to drive even more versatility of speakers, making them even more future proof.

They have a lot more inputs and outputs, making them versatility also better.

And all of that and I would still choose SMSL PA40, and do you know why? Maybe something not so much important to you, but on my side by side comparison, I noticed one thing that improved my listening experience so much and that is Remote and screen.

I listen to large variety of different music and genres, I constantly change volume. And to have to stand up go to my amp and dial down or up volume is just a mood killer always for me. And that I can EQ and see volume from comfort of my seat. Just that makes it so much more better on long run.

As sound is so close to each other, while I notice what Fosi and Aiyima do better, I think the details and clarity is on SMSL side. I think it does extract a bit better. And all is a bit better, will that be Fosi, Aiyima or SMSL. In my listening I would purely sound wise go with Fosi as best of 3, but this remote just made me appreciate and love SMSL that more. And see it as better choice.

Conclusion

I think this is everything you need from power amp in 2025 for just 120 euros. It has great sonics, it have remote and screen, it have interesting and upbeat presentation of music. It is small enough to integrate wherever, it works great with large selection of SMSL DACs, and have enough power to drive most speakers in entry level with ease.

To be honest what more do you want, I heavily recommend you try SMSL PA40 and start your HIFI journey.

You can buy this amp here:

AliExpress: https://s.click.aliexpress.com/e/_omZ6oUk

Shop: https://bit.ly/4584z3G

✅ Pros

Sound Quality

• Excellent clarity and detail retrieval: Especially in the mids and treble.

• Transparent and neutral sound signature: Very clean, with good separation between instruments.

• Low distortion: THD as low as 0.00035% at 1kHz, 5W into 4 ohms.

• Surprisingly good imaging and spatial separation: Especially for acoustic and classical music.

  
  

Performance

• High power output for the price: 85W into 8Ω, 165W into 4Ω.

• Built-in power supply: More compact and possibly cleaner power vs. external bricks.

• Equalizer presets: Adds flexibility to tailor sound (bass, rock, etc.).

Build Quality

• Sturdy aluminum chassis: Solid and well-constructed despite low price.

• Compact and lightweight: Easy to place anywhere in your setup.

Features

• Remote control and display screen: Rare in this price range, highly appreciated for ease of use.

• Precise digital volume control: Steps down to -60dB with 1dB increments.

• Integrated safety protections: Overcurrent, thermal, undervoltage, etc.

  
  

Value

• Outstanding price-to-performance ratio: At €120, considered a strong overachiever.

• Ideal entry-level audiophile amp: Recommended for beginners.

  
  

❌ Cons

User Interface

• Poor UI design: Confusing, hard to navigate, even compared to SMSL’s higher-end models.

  
  

Sound Limitations

• Bass lacks weight and fullness: Rhythmic but not commanding or impactful.

• Midrange clarity but lacks emotional engagement: Voices and instruments feel flat.

• Limited soundstage width and depth: Doesn’t deliver a “big” or immersive sound.

Connectivity

• Very limited inputs/outputs: Only line-in and speaker-out, no:

  • XLR

  • Sub-out

  • Pre-out

  • 12V trigger

• Requires external DAC or preamp: Being a power amp, it's not plug-and-play.

Comparative Performance

• Falls little behind Fosi and Aiyima in dynamics and power: Those amps offer more output and a fuller soundstage. But is better in clarity, transeprancy and handling

• Not future-proof for more demanding speaker setups.