SMSL DO400 is a competent DAC and a Headphone Amp

SMSL DO400 front

SMSL DO400 (tested at $499)

Buy Now
Sound (Line Out) 9
Sound (Headphone Out) 9
Build 9
Features 10
Compatibility 10
Value 10
  • Well balanced sound signature
  • Capable across the board
  • Nothing of note

SMSL DO400 is a versatile unit that combines DAC and headphone amplifier capabilities in one device. Over time I came to expect great sound and great value from the SMSL, and this time is not an exception. So let’s see if SMSL can continue with its reputation.

Build and Features

SMSL DO400 is modestly sized, sitting somewhere between desktop palm-sized devices and full-size room components. The unit is very decently made of metal sheets and a plastic front plate. Its profile is slim and wide, and you can judge styling yourself. The front panel hosts a small LCD, a volume knob, and three different headphone outputs.

SMSL DO400 front

In the back, you’ll find a plethora of digital inputs: USB, Coaxial, Optical, AES/EBU, and even an I2S. Bluetooth is also onboard if you care for convenience more and you’re not such a critical listener (Bluetooth connection is lossy and not on pair with wired options). Once the D/A conversion is done, you have a choice between the single-ended RCA or balanced XLR outputs.

Finally, the whole power supply is located inside the unit so there’s an IEC mains socket on the back, and no power bricks that you have to worry about.

SMSL DO400 back

A small remote control is included in the box, and you can use it to select inputs or control the volume given that all the outputs are variable in level.

Looking at the list of features, you’ll see that a flagship Sabre DAC chip ES9039SPRO is used in unison with a very modern XMOS XU-316 signal processing unit. So this DAC supports any format you can think of, and if it doesn’t support something then you don’t truly need it. Even the amplifier power rating is very, and I mean very high at 6 Watts at 16 Ohm and 3 Watts at 32 Ohm, which is a true powerhouse. But let’s put all of these paper wins to the real test to see if they hold.  

Sound (Line Out)

DO400 is a modern SMSL DAC, meaning it rocks clean but never too analytical sound. The bassline is deep, clean, and well-controlled. There’s a slight warmth in the midbass and the midrange part of the spectrum. It’s the kind of warmth that doesn’t conceal fine details or dull the sound but gives them a hint of pleasant fullness. This is noticeable in all tones and vocals equally, which sound present and full-bodied. It’s something that I appreciate in the sound of a DAC, something that was not always given but that SMSL excels in lately. The highest frequencies are informative but not too prominent. DO400 will never prioritize the edges of notes and their perceived sharpness. Instead, everything sounds unforced and natural at all times.

Soundstaging is as good as it gets around this price. Instruments and vocals are given plenty of room to breathe and not cause clutter. It will not match the scale of some R2R DACs closer to one thousand, or even SMSL’s more expansive SU-10, but no DAC can at this price so it’s not to be held against DO400. If anything, the soundstage is noticeably roomier than what you would get a few years ago for the same price, with SU-9 for example.

Finally, dynamics and microdynamics are very decent, but if you’re after the most explosive, punchy, forward, and fast-sounding DAC – you should probably look for that elsewhere. DO400 is more of a laid-back, mild, and natural kind of performer. The one that will never grind against your ears and your brain in any uncomfortable way. That quality might not be as flashy and as impressive on the first listen, but tends to grow on you with time.

Sound (Headphone Out)

I love it when a combo unit, a DAC and a headphone amplifier in this case, is equally well done across the board. Headphone outputs have all of the same qualities just described in the previous section so I will not waste both mine and your time repeating them. The power rating is very strong with 6 Watts at 16 Ohm and 3 Watts at 32 Ohm. Sure enough, I never felt that the amplifier lacked power no matter what kind of headphones I attached to it. That said, while dynamics are more than decent – you don’t get some kind of exciting kick and slam here. Instead, headphone output once again follows that mild and natural approach to the sound that is comparable to line outputs.


Topping DX5 was my previous DAC/amp champion below five hundred. DO400 takes that title quite easily. First of all, DO400 offers noticeably better line output that can stand head-to-head with the best standalone DACs at this same price. DX5 could never do that when it comes to its line output that sounds flatter and more tonally grey. Moving to the headphone outputs, DX5 stands its ground much better. This time, we’re talking about the same-tier sound with only a slight advantage going to SMSL with its better-controlled bassline, which results in a tidier and cleaner sound overall. But this gap is much much smaller than the one observed on the line outputs. So if you’re only going to be using headphone output, DX5 and especially DX5 lite (same thing just no MQA) might still be a better value with their current pricing. If you’re planning to use the line output too, DO400 takes that win easily.

Chord Mojo 2 recently had a permanent price cut bringing it down to $650, which is still pricier than DO400. They’re very different in form and connectivity options too, but I’ll leave weighing those differences and their importance to you. Here I’m going to focus on the sonic abilities only. Chord Mojo 2 sounds better when used as a DAC. It offers a similarly natural and mild approach to the sound, with a hint of pleasant warmth. What lifts it above DO400 is even better detail retrieval and a richer tone timbre that’s almost seductive.

Moving to using both to drive headphones, you can notice that Mojo 2 can’t match the sheer power of DO400. If power-hungry headphones are going to be on the menu, DO400 might do a better job bringing decent dynamics and making them sound alive. On the other hand, if we stay in the Mojo 2’s comfort zone – it will sound more revealing and offer a richer tone timbre just as it did when we used them as line-out devices only.


SMSL DO400 is not some kind of giant killer or overachiever (both words have been thrown around too easily by many reviewers) but it’s a very respectable device for the amount of money SMSL asks from you. It managed to top my previous favorites in this category and take the place of the one that has to be beaten for around five hundred dollars. Fantastic value and an easy recommendation.


ES9039MSPRO Decoding Chip
Output Power: 6W(16Ω)/3W(32Ω)
Bluetooth 5.1
4-XLR/4.4mm/6.35mm Headphone Output
PLFC Ultra-Low Distortion Circuit
PCM 32bit/768kHz
Built-In Power Supply
DSD Direct Stream Digital DSD512
Full-Featured Remote Control

Official product page

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top