100+ Head-Fier
Pros: Sound, build, features, price...
Cons: USB input only...

I have been lucky enough to receive a few exciting things recently and one of them is the Hifiman EF400, a DAC/Amp combo, that I will be talking about today.

The EF400 has been sent to me on extended loan by Hifiman for me to test and publish my thoughts and opinions on it, therefore I will be as honest and unbiased as possible (like always). However, as I always mention, it is good to keep in mind that it has not cost me anything to spend time with this unit.



My first experience with the Hifiman EF400 was back in May, when I attended the High End Munich show. Hifiman had the EF400, along with it’s bigger brother, the EF1000, in their listening room and I got to spend a bit of time listening to some headphones.

Of course, show conditions are not the best for getting in depth impressions of anything really, they give you a quick taste but, especially in my case, a lot of the time I was listening to music I am not too familiar with, through sources that I do not know, using headphones that I hadn’t tried before. Yes, Hifiman did have a few headphones that I know and love (such as the Ananda, Edition XS, Arya, etc.) but to be honest, I was more interested in trying out things I had not had a chance to try previously (yes, the Susvara was the main candidate!).

Therefore, when Hifiman sent me the EF400 to try with my own music, my own headphones, and in my own home, of course I was extremely happy to do so! Add this to the fact that I also have another very nice amplifier that I am putting through its paces at the moment (the Felkis Audio Echo Mk2, with a review coming soon), which I have been feeding from the R2R DAC of the EF400, I have to say that I have been struggling to actually turn off the music to do other things. It was especially difficult to stop listening and start putting together this review!

Anyway, this review is already going to turn into a long one (as my Hifiman, and my DAC/Amp reviews, usually do), so enough with the chit chat and lets get into the interesting part.



There is nothing exciting about the presentation of the EF400. If you are wanting beautiful packaging, tons of accessories and an incredible unboxing experience, well… I'm afraid you’re going to be a bit let down.

The unit is packaged inside a regular cardboard box, with a black stripe that shows a small image of the product, along with some details and specs.

Inside the box, surrounded by black foam inserts to protect it, we find the unit itself, an IEC cable inside another smaller black box with some QR Codes on it to register the warranty and… well… that's it. As far as I remember you don’t even get a user manual, not that it is needed as the basics are printed on the black stripe of the box.

So, a regular cardboard box which gets sent to the storage room to join many other boxes or random sizes and colours. As I said, nothing exciting but there is no need for anything more.


Build and aesthetics…

The build quality seems to be very good. Completely made of metal, with a lovely metal face plate, I really can’t find anything to complain about. It weighs a fair bit but I can’t see why anyone would want to be moving this around anyway.

As far as aesthetics, we all know they are personal but in my case I really like it. It is a simple no frills look, but at the same time, it is far more interesting than many of the black boxes we see over and over again. The brushed metal look of the face plate, with the dual matching knobs and a black center section, make it look very symmetrical and quite elegant, all in my personal opinion of course.

I can see this being something that will age well and not look out of place due to some trendy look that goes out of fashion.



Ok, so, getting into the more exciting bits, first up is how the EF400 works and how things are laid out.

I already mentioned that there isn’t an instruction manual included but really there isn’t much that isn’t very self explanatory.

On the front of the unit we have two knobs (possibly the most complex part of the unit), with the left one allowing selection of 4x modes. The modes are clearly marked at the side of the knob and they are High Gain NOS, High Gain OS, Low Gain OS and Low Gain NOS. If anyone is wondering what OS and NOS are, they stand for “Oversampling” and “Non Oversampling”, more on that later in the review.

The knob located on the right hand side is even simpler, you turn it clockwise to increase volume and counterclockwise to decrease it. I’m sure that is more than enough of an explanation 😉

In the center of the front panel we have 4x outputs. From left to right these are TRS 6.35mm (unbalanced), 3.5mm (unbalanced), 4.4mm (balanced) and 4pin XLR (balanced). This should meet the needs of almost everyone, especially on a desktop unit.

Moving around to the back of the unit, we have a balanced XLR output, an unbalanced RCA output, a type C USB input, a type B USB input, and IEC power input and the power switch (I’ll complain about that in a moment).

Finally, on the bottom of the unit, there is a sliding switch to choose between 110v an 230v, depending on where you are located.

So, in general, this is a very complete unit and well laid out unit, except for a couple of small things that are maybe more of an issue for me than for other people, but I will mention them anyway.

The first, of course, is the power switch on the back. This is something that I complain about with Schiit products and I am obviously not going to overlook it on this device either. For people who are using this as a desktop all-in-one, it may not be much of an issue, however, as my equipment is mounted in a rack, the switch on the back is a pain. It means that I have to leave enough space to the left of the unit to be able to reach around and access the switch. As my rack is a full 19” wide, it is fortunately not a problem for me to do so, but I would still much rather have the switch accessible from the front.

My other little complaint is the lack of digital inputs. It is nice that they have chosen to include both USB-C and USB-B but only one is usable at a time and I really don’t see the need for both. However, I do miss having an optical and/or a coaxial input. I know my set up is a little more complex than most but I have multiple sources and a small optical network that allows me to feed many things to different set ups, I would really like to be able to join the same optical network with the EF400 but as it only has a single digital input, I am limited to it being fed by only one source, in my case a Pi4 running RopieeeXL.

As far as power is concerned, I can finally say there is no lack here. I say “finally” because I did have a very strange experience with certain USB cables that were causing a noticeable reduction in power. I am not going to go into detail as it was not something that I feel was actually related to the EF400, although I really don’t know what caused the issue. Whatever the case, it is now solved and the EF400 is performing as expected as far as power. That is to say that with a max output of 4.4w, there shouldn’t be many headphones that it can’t push without breaking into a sweat.


My use case…

As with all my DAC and Amp reviews, I like to mention a little about how I use the device as your use may be completely different. This will allow you to get a better grasp on why I like (or dislike) something and what positives (or negatives) may apply to your own scenario.

Usually I will spend time with a device on my desk at work and then move it to home, where I will come up with my final opinions. In the case of the EF400, I did use it for a couple of days in the office but, as I was planning on this being a bit of a longer term review, I moved it to home and installed it into my main system, where I have been using it constantly.

I have been connecting it directly to a laptop on occasions but the majority of the time I have been having it connected to a Pi4, running RopieeeXL, via a powered hub and sending my music via network from any of my other devices (PC, laptop, tablet, phone, etc.).

I have used both the unbalanced and balanced outputs with many headphones and IEMs, and have also been using it’s analog outputs to feed other amplifiers. I have been using it both in OS and NOS mode. I am not going to go into too much detail about technical differences between the two, as there are people with much more expertise out there that can do so, but in short, a NOS DAC takes the digital data and converts it using an analogue filter, whereas an OS DAC uses a digital reconstruction filter to convert to analog, resampling it along the way. As with anything in audio, there are many opinions as to which is best and why, but as the EF400 has both as an option, I will get to my preferences on this particular unit in the sound section.

While touching briefly (with emphasis on “briefly”, as I am not an engineer and don’t pretend to be one), I guess I should mention what is special about this also being an R2R DAC. As a very brief explanation, the difference between an R2R DAC and a Delta Sigma DAC (the most common), is that an R2R DAC uses a ladder of resistors to do the Digital to Analog conversion, whereas DS DACs use a different technology. This is another subject that has many preferences and opinions in the audiophile world, which I am, again, going to skip.

That's enough tech talk for this review, so let's get on to my completely subjective opinions on how this sounds…



I am going to start this section of by reminding readers that my opinions on the sound of the EF400 (or any DAC/Amp that I review) are completely subjective and based only on my experiences, not on any kind of scientific measurements or single/double/triple/infinite blind tests.

I feel that expectation biases and personal preferences can play a large role in what sound we hear (or think we hear) from a source, the brain is a very powerful tool (sometimes, other times no so much 😉 ). I have read and heard many conversations where R2R and NOS are described as “more musical”, “less detailed”, etc. etc. This means that it is quite possible that these expectations play a part in my opinions on what I hear, no matter how much I try to avoid them doing so. At the end of the day, how I think I hear something is basically the end product for me, whether or not what I hear is actually there or is just being added by my brain.

Anyway, let’s get on with it!

I am not going to get into details on each and every headphone (and IEM) that I have used with the EF400 as this review would go on forever and I am sure it is already going to be one of my usual “too much rambling” entries, but to give you an idea, over the past few weeks I have used the HE1000se, Arya Stealth, Arya v2, Edition XS, Ananda, HE400se, Deva Pro (via cable obviously), HD6XX, DT1990 Pro, Beyer’ Custom Studio and a couple more that I am probably forgetting. As far as IEMs, I have used a bunch but as far as actual detailed listening, I have mostly used the Dunu Vulkan, Letshuoer S12, Moondrop Blessing 2 Dusk and the Yuan Li.

I really can’t say that I have anything negative to say about the pairing of any of the above mentioned headphones/IEMs. I found that each time I connected something new to the EF400, I just enjoyed the result. I didn’t find any lack of dynamics and detail with the Hifiman pairings, but honestly, if a Hifiman amp doesn’t sound good with Hifiman headphones, then they are doing something wrong!

In general, my opinion was that, in comparison to my usual test chains, the EF400 has a more smooth and relaxed sound. This could just be expectation bias on my behalf, my brain telling me that I am hearing what I want to hear, but at the end of the day, as long as I enjoy the outcome, I am not bothered where it comes from (even if it does come from my mind).

When trying out the Ananda, I did get the impression that it wasn’t quite as “in your face” as it is on other combinations, but at the same time, I didn’t notice any lack of details. The HD6XX sounded very alive, and while it is not the best I have heard from the HD6XX, it certainly wasn’t a negative experience.

It is difficult to actually pinpoint what the amp is doing on the EF400 (as there is no analog input) however, after testing the DAC section, which I am coming to next, I feel that the amplification is just a no frills clean sound and that a lot of the smoothness is actually coming from the DAC itself. Again, I can’t do any specific A/B comparisons of the amp vs other amps I know well, but when comparing the EF400 directly vs the EF400 feeding the THX789 (volume matched but still sighted), I didn’t feel that the outcome was hugely different. I did feel that the EF400 was maybe slightly smoother, especially in higher mids/lower treble in the comparison, but that could just be me believing it, I am not sure I would easily differentiate between the EF400 direct and the EF400+789 in a blind test.

So that brings me to the DAC section of the EF400, which I feel is the real star of the unit. I have no idea how this measures, to be honest I am not really bothered either, but I do feel that it has a large impact on the sound when paired with other amplifiers in my chain, in comparison to other DACs that I usually use, such as the SU-8, multiple Toppings, Modi 3+, Gryphon and a couple of mixing consoles.

Now, it is difficult to be able to do an exact A/B comparison with other DACs, due to the EF400 only having USB input (I usually use SPDIF for comparisons as I can run the same signal to all my DACs simultaneously) but I did use a set up that was as close as possible while still being fairly simple. Basically I used two laptops, both playing FLAC files from Foobar, feeding a DAC each and then using an input switcher to switch between DACs.

But enough rambling about non-scientific tests that pretend to try to be scientific and on to my subjective opinion of the EF400 DAC stage… I really like it.

With all the amplifiers I tested it with, there was a sensation of things being smoother and not as harsh, without any loss in detail. I couldn’t really say exactly what was causing the sensation, as there are no differences in FR (yes, I did some measurements to check) but there is just a sensation of things working better together.

My favourite pairings have been with the Asgard 3 and the Feliks Audio Echo Mk2 (I'll go into more detail on this combination in the upcoming Echo review). No matter what I connected to these setups, I found it enjoyable. I said there was no loss in detail and there isn’t, however, I find that it takes the focus away from actually pushing detail at you and makes it all click together a little better. Rather than there being images placed everywhere, there is just one overall image that contains everything in the right places. I feel it is a little like the difference between a recording before and after masterization, the info contained is the same, yet everything is just mounted better.

I know of many that roll their eyes at things like “musicality” to describe the sound of a DAC, and to be honest I do try to avoid similar terms when possible, but sometimes the description just fits.

Finally, before getting to the end of my rambling, I just wanted to mention quickly the OS and NOS options, as I really haven’t commented on them at all and I said I would.

I don’t really have any experience with upsampling etc. as I don’t use HQPlayer and I also don’t have any DACs with this option. I tried the various modes, with various sources, and to be totally blunt, I can’t hear a difference. I mean, I like to think I can, but honestly I really don’t think I am hearing it, just wanting to hear it. If someone was to set the mode without me looking, there is no way I would know which it is, at least not yet, maybe I need to keep listening and also give HQPlayer a try, but that is for another day.



I have no doubt that the Hifiman EF400 gives you a lot for what it costs, with a great build quality, good performance and a very reasonable price.

Is it the best system I have ever heard? No.

Is there something I have heard for this price that I feel is better? No.

My only complaint would be the lack of a digital input other than USB. I would usually mention the lack of an analog input to use just the amplifier section of the unit but in this case, I feel that the star of the show is the DAC.

I find the DAC to be a great pairing with my system, making everything a little more enjoyable than the more analytical options I have, and if I could add it into my usual optical network, then I think I would use the EF400 for 100% of my listening time. Even with something as “cold and straight to the point” as the THX789, the EF400 gives it a little flavour that is very enjoyable.

As it is, it has now got it’s own dedicated RopieeeXL source, and has become its own little independent system feeding the Echo and Asgard (well, maybe not little 😀), which I am always looking forwards to connecting to and sitting back with my favourite headphones to just enjoy music.

(As alwyas, this review is also available in Spanish on and on


Hifiman EF400
Pros: Lush, natural sound
Powers planar headphones with authority, even the notoriously hard-to-drive ones
Nice design with plenty of outputs
Works with anything from a computer to a smartphone. Even works with some DAWs
Cons: Lack of analog input
I can’t remember when I first saw the announcement of the EF400, but it was the reason I went out and bought myself a pair of HE6se. Somehow in the back of my mind, I was counting on those two being a good pairing.

Of course, the EF400 kept me waiting a few months, during which I lost my patience and got a Monopiece THX 887 to drive my Arya, HE6se, and numerous other less capable headphones. During this time, I also upgraded my audio interface to an RME UFX II, which had surprisingly powerful and clean headphone outputs, so I started using my Arya directly out of the RME because my THX was largely redundant at that point. The HE6se was collecting dust for a while because I thought it sounded too strident out of the THX amp.

Enter the EF400. I have had this unit for over a month at this point, much of which was spent out of town on an opera performance. During the past few days, I finally had time to give it a proper listen.

In short, I am going to be repeating what everyone else has said- the R2R DAC sounds great and very flattering/forgiving, the amp is plenty powerful, definitely powerful enough to drive my HE6se. For the first time, I am able to say I quite like my HE6se’s. Out of all the Hifiman cans I’ve heard, I have to say they are the brightest of them all, although part of that brightness comes from being under-driven.

VS Monoprice THX 887


I was using the internal R2R DAC of the EF400 for this test, as there is no other choice. It would have been nice if there was a set of analog inputs, but I guess I can’t have everything. The rear XLR outputs were handy when I want to stack my THX amp right on top of the EF400 for a quick A-B comparison.

With the EF400, the main difference is that now there IS bass. I’m not saying the pairing with the THX didn’t have ANY bass, however, switching back and forth between the two amps can reveal how much of the low-end information is missing from the THX.

The other major difference is the warmth and body of the sound. I would say the THX has a slight edge in the definition of the highs as well as the outline of instruments/voices. I listen mostly to classical music, more specifically early music, a genre in which bass instruments form the core of the ensemble, but don’t necessarily take center stage in terms of presence and volume. In this case, more treble definition is not what I need at all, since Hifiman headphones are already very sparkly up top, and I have mostly Hifiman cans. The warmth and extra body from the EF400 are very welcome. To make an analogy, if EF400 sounds like a nice stew of beef and potatoes, THX 887 sounds kind of like the same stew but with the broth dumped out and replaced with distilled water. It is in no way offensive to listen to on its own, but after switching back and forth with an EF400, I find it just not as interesting or pleasant to listen to in general. With the HE6se, it makes more of a “yes” or “no” difference. Now, I am happy to say that I can properly enjoy my HE6se’s and appreciate them as the capable cans they are.



Besides the massive price gap, I use those two devices for very different purposes. The RME is my work unit, I do all of my recording and mixing on this device, and have no doubt I am getting a high quality, faithful sound out of it. The biggest surprise is that the Arya pairs incredibly well with its headphone jack and delivers a very transparent yet 3D and lively sound. The EF400 presents music very differently, in a more laid-back, lush way. For longer listening sessions, it’s definitely less fatigueing. In terms of driving power, while the RME is quite powerful for an audio interface, it doesn’t have nearly as much power as the EF400. I did try plugging in my HE6se just for the heck of it- and surprisingly, I didn’t hate this combination, although they don’t sound nearly as full and “alive” as they do on the EF400. Despite the RME being nearly 3x the price, I find the EF400 holding its own very well.

Who’s it for?

I would say look no further if you have some low-sensitivity planars on your hands, or if you have decided to go the planar way. I guess if you can afford a pair of Susvara’s, you’d have big bucks to spend on a big amp as well. For those of us who don’t want to invest that much in a headphone system, the EF400 offers an incredible value with its very capable built-in dac.

Since I have my RME UFX II+ Arya in my studio, I am using this EF400-HE6se combination in the bedroom, sometimes just before bed. Being a professional musician as well as an audio engineer sometimes means you don’t have a lot of time listening to music for leisure; personally, I haven’t had a proper sit-down with headphones for months before my EF400 arrived. The EF400-HE6se combo is so good that I actually look forward to my late-night listening sessions now. It’s a rare thing for me to just enjoy the music without thinking about microphone placements, mixing, or getting competitive and start analyzing other engineers’ sound. This combo makes me forget about the technicalities and just immerse in the music. A nice treat indeed.

Gear used:

Hifiman Arya

Hifiman HE6se

Beyerdynamic DT990 pro

Beyerdynamic DT770 pro

RME Fireface UFX II

Monoprice THX 887

Reference recordings:

Cavalli: L'amore Innamorato — L'Arpeggiata - Christina Pluhar

Bach: Matthaus-Passion - Pygmalion, Raphael Pichon

Rameau: Les Indes Galantes- Les Arts Florissants, William Christie

Italian Virtuosi Of The Chitarrone, Jakob Lindberg
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Excellent review and comparisons.
It definitely has very good AMP too, would have been great if it had analog input.
This is the first time I am listening to my HD6XX without any EQ😀
Thanks for that Beethoven's 5th, Carlos!:wink:
Great review, and great reference recordings!


Reviewer at Ear Fidelity
Hifiman Ef400
Pros: Spectacular tone
Very powerful
Well-built, great design
Balanced outputs
NOS and OS modes
Can actually drive the Susvara pretty good
Just a joy to listen to
Cons: Only USB in


Every single time I write a review of Hifiman’s product, the introduction paragraph is getting harder and harder to write. How many times can I point out that this is the nr.1 manufacturer in the world when it comes to headphones.
They do offer arguably the best value models in every price segment when it comes to open-back, planar-magnetic headphones. Lately, they’ve released the dynamic closed-back model called HE-R9 (review here), and it’s just shockingly good, becoming one of my favorite headphones in my collection immediately after a first listen.
The new and exciting stuff doesn’t stop there for Hifiman though, as they also released an even more interesting product, the EF400 all-in-one.
Hifiman has some history with DACs and amplifiers, but none of them was truly spectacular, which we all grew to expect from every single product they launch. This is told to change now, as the EF400 is hugely impressive on paper, so much that I actually couldn’t believe the price when I first saw it and I thought it was just an error and they’re going to fix it soon. Well…I was wrong.
Seeing press pictures of the EF400 it’s easy to spot that this device is a successor not to their EF100, but rather the EF6, a behemoth of an amp that was originally dedicated to run their old flagship, the legendary HE-6. While it did the job with the hyper power-hungry HE-6, it was a bit mediocre with the rest of the high-end headphones from back then.
So, ten (!) years have passed, and Hifiman released the EF400. A device that looks laughably tiny when compared to the EF6, but tiny definitely doesn’t mean weak in audio, especially in the past few years.
While announcing the EF400, Hifiman stated that it has the power to run the Susvara, something that is widely regarded to be the hardest thing for any headphone amplifier ever since Susvara’s debut in 2017. There’s a lot of misconception of what the fully-driven Susvara can do, but I was fortunate enough to have heard the Hifiman flagship out of many $20k+ stereo amplifiers via speaker outputs, so I know what this godlike headphone can do. Also, lately in Munich, I tried the first headphone amplifier that gets the Susvara to sing in the same league as many high-end stereo amplifiers, so things are slowly changing, finally. Oh, that amplifier is called Feliks Audio Envy, a beast of an amp, but it’s a dedicated headphone amplifier at the end of the day, the first I’ve heard to drive the Susvara in 100% without any problems. Can we get the same result out of a $599 DAC/Amp from Hifiman? Let’s see.



First things first, the unboxing experience. This is going to be very straightforward. The EF400 comes in an aesthetically pleasing box that is secure, so don’t worry about the long journey this device is going to take to land on your doorstep.
Inside, apart from the EF400, you’re getting a power chord, and…that’s it. Simple, isn’t it? Listen up, you’re already getting such an impressive device for that change money, don’t expect any bonuses.

Design and Build Quality​


So, the first thing that will draw your attention is the design and build of the EF400. This, again, does not look like a $599 Hifiman device, especially if you know what’s inside.
I’ll start by saying that the EF400 is bigger than I expected when I saw the first promo photos. It’s not huge, but it’s not super tiny as well, sitting in the middle of what I’d call a good size for desk usage. Luckily, the top of the Ef400 is flat and doesn’t have any venting openings (those are on the back), so you can stack it. The question is though…would you need to? This is logically marketed as the one and only device you’ll ever need on your desk, and I tend to forget that not everyone has so many DACs and Amps as I do.
S0, how’s the actual build quality? Very, very good. The EF400 is rock-solid, quite heavy and dense feeling, with a great finish. There are no imperfections to be found anywhere on this little champ, and I gotta be honest, it does look good in my opinion. The front panel has this “polished” look to it, and while not everyone will appreciate a contrasty silver front, I definitely do.
The volume knob feels good to the hand and it sits very securely, so you won’t have any accidents while listening to music, but please, don’t try to prove me wrong on this one. The only downside to the entire physical aspect of the EF400 is the power switch for me. I criticize every device that has this feature, and unfortunately, the EF400 also went down this shameful path. Well, it’s on the back. Audio manufacturers, please, I know power switches are ugly so you’re trying to hide them, but having it on the back makes our lives so much harder that I can’t stress it enough. Imagine that you WILL stack the EF400 after all…if you’ll put it on the bottom of an audio tower of glory, then I wish you good luck with not losing your temper trying to power it on. Yes, you can never power it off actually, but you can also burn money to make yourself warm in winter…do you?
Yay, I’m probably making too much of a deal out of it, I hope you saw that slight sarcasm at the end. It’s just a power switch after all, not the end of the world. Let’s move on.

Tech and I/O​


Now onto some really cool stuff. In 2021 Hifiman launched the Deva Pro, our “Product of the year 2021”. Why do I brag about it? Let me explain. The Deva Pro has a Bluemini R2R module, which makes them into Bluetooth headphones. Nothing to write a book about you’d say, right? Well, what if I told you that this module had an R2R DAC inside? Now, this is a lot more impressive isn’t it.
So, Hifiman is run by really wise people, so they thought to themselves – we do R2R stuff now, maybe we should make it bigger, balanced, and put it in a stationary device for full-on peak audiophiles? Well, this is exactly what they’ve done.
Why am I making such a big deal of R2R? You see, for many, the best DACs in the world are R2R DACs, for years this technology has been limited for the TOTL, crazy expensive devices. This technology generally gives you a very natural, smooth, and extremely pleasant tone that is very, very hard to achieve for Delta Sigma models. And now, Hifiman made R2R affordable, they have no chill.
Okay, apart from the R2R stuff, what else are we getting? Well, the EF400 is also a very powerful amplifier that Hifiman says is capable of driving their ultimate monster, the Susvara. It is rated at 4.4W, but Hifiman doesn’t specify the impedance in which they’ve measured it. However, power ratings are one thing, and real power is usually the other. Is the EF400 really that powerful? I’m going to answer that question in a moment.
The EF400 has both RCA and XLR outputs, so you can use it as a standalone DAC and plug it into any amplifier you’d like. Maybe you want some R2R magic in your speaker setup and you want just a DAC? Go ahead, you’ve got that option. Speaking of the DAC section, you can plug it into your PC or MAC by USB-B or USB-C, which is awesome. We’ve waited for years for the audio market to realize it’s finally time to start using USB-C, and the EF400 is another device I laid my hands on lately that has it.


The last thing to mention is that magical second knob on the front. It lets you change between 4 different modes: high gain NOS, high gain OS, low gain NOS, and low gain OS. While the high and low gain is pretty self-explanatory, the NOS and OS situation might raise some eyebrows, so let me explain.
NOS stands for Non-Oversampling, and OS stands for…you guessed it, Oversampling. NOS R2R DACs used to be reserved as the most expensive DACs on the planet, as it’s believed to be the “purest” way to handle digital audio. The discussion lasts for many years now, and I’m definitely not going to take part in it. However, I will definitely tell you the difference in sound between the NOS and OS modes in the EF400.



Okay, so far this looks too good to be true, right? A NOS, fully-balanced R2R DAC + a very powerful amplifier with preamp for $599, what kind of sorcery this is you’d ask? Well, I don’t know the answer to that question, but if any manufacturer in the audio world is capable of doing some really crazy stuff, then we’re definitely talking about Hifiman.
Up until now, this review is literally screaming at your face saying “BUY THE EF400 NOW”, but we haven’t covered the sound yet, so don’t be in such a rush. The sound quality is all that matters at the end of the day, so let’s see if this is really as good as it seems. Can’t wait any longer? Fine, I’ll give you my answer…yes, it is.

This is an R2R device, so I’m going to continue this review the way it’s supposed to be continued. This technology is known to deliver an incredibly coherent and musical type of sound, so I’m definitely not going to split the sound impressions into different frequencies as I usually do. We need to focus on the sound as a whole.


Let’s answer the two most important questions about the EF400. First, does it really sound like a proper R2R DAC? Yes, it does. It offers that incredibly smooth, rich, magical tonality that every hardcore audiophile loves. Think of it as tubes of digital audio, that’s the closest I can get to explaining what’s so special about it.
You probably tried a good tube amplifier in your life, even once. It’s not that its sound is warm, fake. Tubes give you that euphonic, colorful, and amazingly natural tone that is loved by millions, so much to the point where I know a lot of people who just won’t buy a solid-state amplifier ever again, under no circumstances. So, basically, an R2R DAC is the same, but regarding DACs instead of amplifiers. It all sounds really tempting, doesn’t it?
However, I’m a reviewer after all, so I have to explain it to you somehow. Imagine a DAC that sounds incredibly neutral, smooth, and very detailed. And now, imagine that the sound gets a little wet, making all the textures and shapes a bit more rounded, but in a weirdly natural way. This is the sound of R2R for me. It’s not fake, it’s not altering anything in the recording, and it doesn’t “add” anything, it’s just ethereal, lifelike, naturally warm, and engaging sounding. I’ll try to elaborate more in the comparison section vs Yulong Aurora.
The second question is that output power: Is it really powerful enough for the Susvara? This is a hard one. Yes, you can get better results with a 100W integrated amplifier, but who would want to do that? Yes, you can get some crazy high-end amplifiers like Woo Audio WA33, or Nimbus US5 Pro. Actually, if you spent $6000 on the Susvara, then you can probably afford one of these. Should you do it? Don’t think so, if you really want the best of the best, try the latest amplifier from Feliks Audio, the Envy. I never heard the Susvara sounding that way, including the times I’ve tried it with some crazy power amplifiers like Accuphase A-75 or P-7300.


Back to the topic though. No, the EF400 is not the ultimate amplifier for the Susvara, but it really shouldn’t be at 1/10 of the price. But I believe this is the ultimate amplifier for the Susvara in this price category. Even more, considering that it has a DAC inside, we can easily assume the price of just the amplifier section at around $300, and for that money, you will never get an amplifier that drives the Susvara better than the EF400, no way. First of all, the EF400 has plenty of volume, I’m not even able to max this thing out without making my ears explode, so we’ve got one box checked. Secondly, high volume doesn’t mean that the Susvara is fully driven. How should you know then? It’s actually pretty simple, if its bass starts to hit hard, midrange gets otherworldly smooth and unforced, and the treble is just crazy detailed but never even so slightly sharp, then you’re definitely getting there. This is the definition of what the Susvara sounds like with the EF400. It’s not Envy level, hell, not even close, but for $599 this is absolutely spectacular.
To be honest, you probably won’t ever buy the EF400 as a daily driver for the Susvara, unless you went bankrupt after spending $6k for a pair of headphones and now you’re just trying to make it work. If you own these headphones then you’re only interested in the best of the best. So, the question is, how does the EF400 work with different headphones? Let’s try it out.


Meze Elite


Let’s start with Meze’s flagship, the Elite. Some time ago, my author Kamil visited me in Warsaw to hang out and to try different stuff I have here. The guy literally spent 80% of the time listening to the Elite + EF400 combo. I was asking him to try the Elite with different gear that I have to hear his impressions and comparisons, but every time I tried, he was looking at me with these shameless eyes saying NO, I DON’T WANT TO, I LIKE THIS. Well, who can blame the poor guy, when I tried this combo myself I immediately understood what he meant.
The Elite is a rich and analog-sounding flagship headphone, so it shouldn’t really benefit from the EF400 on paper, but in reality, this combination is just heavenly. Incredibly natural-sounding, rich, engaging, and romantic to the point where you’re just sitting with your eyes closed enjoying the good time you’re having.
The EF400 has full control over the Elite, it drives it with authority, which results in marvelous dynamics and power of the sound. At the same time, it never sounds forced or too extreme, which tends to be a problem with very powerful amplifiers paired with efficient headphones. Luckily, this is not a problem whatsoever with the EF400 and the Elite, as this combo is just putting you so close to the music that it’s hard to stop listening to it.

Hifiman Edition XS


A $599 AIO paired with a $499 Hifiman Open-Back headphone, this definitely seems like a very reasonable pairing. The Edition XS is wonderfully neutral and reference-like tuned, and when paired with the EF400 it gets that midrange goodness that further improves what’s already a hugely impressive headphone in its price range.
Of course, the EF400 has more than enough power to make the XS fly, hence you’ll be getting fantastic dynamics and grip in the bass department. However, this AIO makes the XS a little bit more forgiving and smoother sounding, which could be desired by some of you. Not everyone is into a hyper-neutral type of sound, but there are simply no better headphones for $499 when it comes to technical performance. If you feel that the Edition XS is slightly too neutral for your taste, the EF400 is a perfect choice to pair it with to achieve a more romantic, rich, and lush tonality.
If you seek the ultimate level of performance and don’t really care about functionality or other options, this is probably the best way you can spend $1099 on this hobby for new stuff.

Hifiman Susvara


I’ve already covered this pairing in the sound paragraph, but will also point out my impressions here.
The EF400 has enough juice to drive the Susvara. It doesn’t drive it to its fullest potential of course, as the Feliks Envy offered a much, much better sound quality when paired with Hifiman’s flagship. However, for $599, the EF400 gets the Sus unreasonably loud and it offers good dynamics and energy to the sound.

Additionally, paired with the EF400, the Susvara starts to sound like it really should – the detail retrieval is just simply the best, and it does maintain it while having that smooth and rich tone, sounding marvelously unforced and natural. This is definitely NOT the end-game for the Susvara, but for $599, you won’t get any closer, not a chance.

Hifiman HE-R9


I already covered this pairing in the review of the R9, so let me do some copy and paste action.

I got both devices in the same package, so I plugged both in immediately and paired them together. First seconds after an hour or two of warm-up and I was sold. This setup sounds incredibly mellow, rich, and bold while offering incredible dynamics and authority of the sound.

The R9 is not a power-hungry headphone, but the EF400 definitely has more than enough juice to power like 20 of those, so it handles that driver like a champ. I already gave you a spoiler that the EF400 is a “Product of the year” contender for me, and when paired with the R9 it made me very happy that I get to listen to such incredible audio stuff on a daily basis. I’ve got the Susvara, Elite, D8000 Pro, TOTL IEMs, Dacs, and Amps, and I still enjoy this sub $1500 system A LOT.

Sometimes technicalities are not the most important, and for these moments, the EF400 + R9 is my nr.1 setup for the past few weeks. Ever since getting them, the R9 is my most-used pair of headphones, the EF400 my most used DAC/Amp, and together they’re the most used system that I’ve been using throughout this time. Intoxicating.

Fir Audio XE6


What does the EF400 sound like with the best IEMs I’ve heard in my life? First of all, make sure to put it in the low gain option, to achieve cleaner audio and less background noise.
So, this pairing also does sound incredible. The XE6 is a rich-sounding, hyper-detailed IEM with a godlike bass response, and I’m happy to report that the EF400 handles it like a champ (with its power output it’s not a surprise though). The romantic soul of the EF400 makes the XE6 into an even more engaging IEM than it already is, so this is definitely a thing to have in mind if you’re about to pull the trigger. This is definitely not a neutral, analytical type of sound. Question is, should you get the EF400 if you already own the XE6? Well, I don’t think so, it would be better to go with something more neutral and suited more towards IEMs, as the EF400 has a lot of power that you won’t really need.
However, if you’re going to buy the EF400 to pair with your over-ears, then you can also use it with your IEMs for that incredibly engaging type of experience.


Yulong Aurora


If you’ve read my Aurora review (here), then you’ll probably be going to assume that these two are quite similar. This is partially true, but there’s a catch.
The Aurora has a more controlled and firmer sounding bass, and it’s overall a touch crisper throughout the entire frequency range. Also, when it comes to functionality, the Aurora offers much more, so if you like to have many options and sources, the Aurora is probably your guy.
However, the EF400 sounds even more mature and it has that R2R tone that is just different, more organic sounding than the Aurora. Truth is, both devices are just spectacular when it comes to the value and it’ll be up to you to decide. Take note that if you would like something that really sounds different than most of the devices in this price bracket, then the EF400 is a better choice.
Overall, while the Aurora has better functionality, I’d rate the sound of the EF400 higher, mainly due to that lovely timbre.

NOS vs OS​

Lastly, the EF400 actually lets you choose between two slightly different approaches to the sound with its NOS and OS options.

So, what’s the difference? It’s not huge, more of a fine-tuning of the sound characteristics, but no matter which option you’ll choose, the R2R magic is still going to be there. NOS sounds a bit more even and slightly more neutral (still not really neutral-sounding) than the OS. High-end R2R DACs are usually used with the NOS option, and I can see why. This is a perfect blend of that wonderful, incredibly natural sound with great technical performance and it’ll surely pair well with most headphones you’ll throw at it.

OS, on the other hand, is more rounded, relaxed, and smooth sounding, but it’s not a night and day difference. This option is great if you have some pretty extreme-sounding headphones and you want that extra richness to counter the analytical character of the headphones. A great example is the Hifiman Arya SE, which for me personally is a bit too much sounding. It has those hyper-fast transients and quite a forward-sounding treble, and the EF400 makes the Arya SE a little bit more enjoyable and calm-sounding for me.
While the option to toggle between NOS and OS shouldn’t be considered a deal-maker, it’s very cool to have it, especially considering (again) the asking price of the EF400. At the end of the day, you can fine-tune the sound a bit to your liking, which is always a good thing.



It’s not a secret that I absolutely adore Hifiman, and for a good reason. They do deliver incredible audio products at prices that are more and more affordable, and the entire audio market benefits from their approach.

However, they were playing safe for the past couple of years, focusing more on improving, rather than entering new market segments and coming up with new technologies. This changed with their Deva Pro, and now they just made the next step. The Hifiman EF400 is such an incredibly mature and rich-sounding AIO that I actually think that Hifiman could have easily sold it for $2000. Considering that it’s priced at $599, I’m going to recommend the EF400 to everybody looking for an all-in-one device with tons of power and a beautiful, rich, and incredibly natural sound.
This product is going to change the audio market in the upcoming years, as Hifiman just did something that they’re best at – raised the bar. Chapeau bas.

Wildly Recommended.

Gear used during this review for the sake of comparison and as an accompanying equipment:
  • Headphones – Hifiman Susvara, Final D8000 Pro, Audeze LCD-X 2021, Hifiman HE1000se, Drop + Sennheiser HD8XX, HEDDphone, Hifiman Edition XS, Meze Elite, Hifiman HE-R9, Fir Audio XE6, Hifiman Arya SE
  • Sources– MacBook Pro 2021, Yulong Aurora, Burson Playmate 2, LittleDot MK III SE, SMSL DO100 + HO100
Big thanks to Hifiman for providing the EF400 for this review. I wasn’t paid or asked to say anything good or bad about this product, all of the above is just my personal, unbiased opinion. Hifiman hasn’t seen this review before publishing it.
That thing has a line-out. It's not a preamp at all
Has anyone tried this amp with Focal Clears or Sennheiser HD600's?