This thread is to discuss the Hifiman EF400, a DAC/Amp combo with R2R technology and NOS/OS modes.
Specifications (from Hifiman):
THD+N (Line out) : Between 0.002% and 0.004%
Channel Separation : 125+/-3dB
Signal to Noise Ratio : 118+/-3dB (A Weighted)
Maximum Power Output : 4.4 W per channel
Dimensions : 246.5mm(L)×228mm(W)×61mm(H)
Weight : 3.08kg
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.
Intro…
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.
Presentation…
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.
Functionality…
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…
Sound…
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.
Conclusion…
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 always, this review is also available in Spanish on www.achoreviews.com and on www.youtube.com/achoreviews)
As usual, a well-written and well-considered review, @SenyorC. Your review gives me a couple of nits to pick (how would I say that in Spanish? macanas? A bit Argentine). First, no analog input. I do have a use case for a desktop DAC/AMP, and there are times that I’d like to be able to plug in an analog input. Here, we don’t even have a Bluetooth option.
The second… the second is my sensitivity to the plague of UN and Non. Unleaded gas. Unsweetend tea. did they remove the lead? Take out the sugar? What’s wrong with 4 modes - Hi Gain, Lo Gain, Hi Gain OS and Lo Gain OS. Or Low and High if you prefer. But leaving off the NOS and keeping OS would be just as clear and save the global repository of N’s.
We would basically say you are being “tiquismiquis”.
I can understand this, although personally I would rather have an extra digital input (mainly because I already have desktop amps I like and pair really well with this DAC).
NOS is a fashionable term.
@SenyorC Thanks so much for the detailed review less than 15 hours after I asked the question on the EF400 
! I now have this loaded in my Amazon cart to stew on for a few hours before pulling the trigger. I’m just too anxious to try out some different DAC/amp options just to see what difference it makes in the sound of the Clear. @generic was right, you all are a bunch of enablers! Lol
Yaaaas. Too much so.
New Old Stock
Nitrous Oxide System
Never On Sunday
New Orleans Saints
Non Oversampling
Nosferatu
Non Organic Substance
Nuke On Sight
and many more.
Really enjoyed the review. I actually read every word without skipping to the end. Been using new to me EF400 with HE6SE v2 ( picked up from a nice headfier)for a couple of days now and been missing my bedtime. Don’t know how to describe what I hear but the combo works for me. Looking forward to listening with other headphones , as am always curious.
Thank for sharing your thoughts
My unit (and several others ) had a issue with static noise through the usb input. And I had some transformer humm.
Hifiman said they fixed that after the first batch.
But I returned mine and got something else.
Yes, read about static noise which was why I didn’t pull the plug both times I had it seating in my cart to purchase. Buying a used unit from a trusted seller can be an option or from “newer” stock. Its worth a try.
What other amp did you go with?
Smsl SP400 in the end. Because of the relay based volume control
okay, admitted I had to look up what you meant by relay based volume control:). Happy Listening!!!
I think that @Lothar_Wolf has used both. He’s been pushing the Topping when I asked a similar question.
The thread for this and other DACs considered starts at the link below. I’m leaning toward the Topping myself.
Does the preamp output on the EF400 shut off when you plug in headphones? Or is the preamp output always on no matter what?
It’s always on at a fixed output.
Thanks! Here’s a funny and unhelpful response I got from HiFiMan:
“Thanks for your reply. The output of the amplifier and the headphones cannot work at the same time. The preamp output cannot shut off automaticlly when you plug in headphones.”
@GoldenSound reviews the HIFiMan EF400!
GoldenSound in the headphone house! Things just got even better here.
I just finally got around to measuring the LEFT vs RIGHT phase at various frequencies and found no offset. I was going to comment on the original review on headphones.com but found that there was an update to the article about HiFiMan fixing the issue at some point.
Big fan of the EF400 as an amp/DAC combo with planar magnetic headphones + as a DAC <3
Wish there was an amplifier line-in!
I have been researching on options to control brightness of b & w 706 s2… I mainly listen to streaming music Amazon Music with iPad directly connected to my Harman kardon 3380 and paired with b & w 706 s2 speakers. Can this r2r DAc bring warmth into my stereo setup