Hifiman EF400

Hifiman EF400 ís the second all-in-one in Hifiman's history. It's fully balanced, built around an R2R DAC and a headphone amplifier that is told to be capable of running the Susvara. The price is set at $599.


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.

So, 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.


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.

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