HIFIMAN EF400 Review: Entry-Level R2R DAC + Class AB Amp Combo

The EF400 is an entry-level Class ABThe most common amplifier class, biasing the output stage into Class A for small signals and transitioning toward Class B at higher levels for better efficiency. headphone amp and DACDigital-to-Analog Converter - a device that translates binary audio data into an analog electrical signal that can be amplified and heard. combo offered by HIFIMAN. It has a few very cool unique traits and decent subjective performance. However, its objective performance falls short in measurements, and it appears to be slightly less powerful than it claims to be.

In my opinion, for the discounted price of $400, it can compete in terms of the sound quality it offers. However, if you’re someone who cares deeply about measurements, consider looking into some of the higher-end HIFIMAN amplifiers that have superior measurements.

Build Quality and Design

It’s a regular, rather compact desktop-sized black box, made fully out of black aluminum with a thick, silver, brushed aluminum front plate as a color accent. There’s a thinner outer sheet of black-painted aluminum going from the top to the left and right side, which screws in on the bottom. The bottom and back of the EF400 consist of a single piece of aluminum as well. The device feels quite heavy when held - because of the oxygen-free copper toroidal transformer inside and the all-metal chassis, it weighs a little over 3 kilograms (almost 7 pounds).

All of the inputs and outputs are on the back. For input, we’ve got USB - period. There’s just a USB, so this amplifier is made specifically for desktop use, which is okay for me. However, if you’re missing other types of inputs, you can look at the EF600 for example, which is a step up from this model and includes more of them. There are two types of a single input - the typical USB Type-B and a more modern solution which I appreciate a lot, USB Type-C.

It can also output a full line-level, non-volume-controlled, analog signal through the unbalancedSingle-ended signal transmission using one signal conductor and a shared ground, more susceptible to hum and interference over long cable runs. RCAs or balancedA signal transmission method using two opposite-polarity signal lines plus a ground; noise induced on both lines is cancelled at the differential input. XLRs on the back. There’s a standard 3-pin power plug with a ground connection and a power switch, alongside some small vents. On the bottom, a voltage selector lets you pick either 230V or 115V. It’s important to note that the voltage currently in use is displayed on the red switch itself - keep this in mind to avoid damaging your unit. The four feet are equipped with foam material to reduce vibrations and prevent scratches when adjusting its position on the desk. The feet can be removed by unscrewing the screws and replaced if desired.

The front of the EF400 is by far its best-looking part. I love the symmetry of the two knobs and the headphone outs. Going from the left, there’s a gainThe multiplication factor applied to a signal by an amplifier, expressed in dB; proper gain staging is critical for minimizing noise. selector / oversample mode knob with four options. It’s very tactile and feels great. For the headphone outs, there’s a single-endedAn amplifier configuration using one output device for the complete audio waveform; produces even-order harmonic distortion considered "euphonic" by many. quarter-inch jack, a single-ended 3.5mm jack, and two balanced headphone outputs in the form of 4.4mm and 4-pin XLRA professional locking audio connector with three pins: ground, positive signal, and negative signal; the standard for balanced studio connections.. On the very right, there’s a volume knob that, while being smooth, has some excess wobble to it. Some people seem to make it a bigger deal than it is - for me, it’s not a huge deal breaker, as it doesn’t make the volume control very difficult to use or anything like that. There’s maybe a millimeter of wobble in the rotation.

The DAC

The DAC part of this unit is pretty interesting, as it’s not a regular sigma-delta approach. It’s a Himalaya R2R DAC, HIFIMAN’s proprietary approach to resistor ladder array digital-to-analog converters on a chip. It can do PCMPulse-Code Modulation - the standard digital audio format, encoding amplitude as binary integers at fixed time intervals (e.g., 16-bit/44.1kHz for CD). up to 192kHz at 32 bits.

There’s a unique option of NOS - non-oversamplingProcessing audio at a multiple of the original sample rate before conversion, improving noise performance and relaxing the requirements on the analog output filter. - which is something that only R2R DACs can do. It often leads to even worse measurements (unless you’re using an external oversampling filter), but a warmer, or in some way more fun, listening experience. The difference between oversampling and non-oversampling is not huge, but it is audible. In my experience, oversampling led to a more busy, though detailed experience. On the other hand, non-oversampling sounded cleaner, yet warmer with an ever so slightly wider soundstageThe perceived three-dimensional acoustic space in a stereo recording - width beyond the speakers, depth front-to-back, and sometimes height information.. It’s fantastic to have the option to choose between two modes, depending on your gear, the track you’re listening to, or personal preferences.

This DAC has one more special feature - it operates in a 4-channel mode, allowing for fully balanced output and separation between each channel at once. The thing is, they either made a mistake or intentionally designed it so that one channel is delayed by one sample compared to the other. Although not noticeable in terms of one channel playing the sound later than the other, this delay creates a more euphoric soundstage for some people. However, others can get dizzy due to this effect.

Sound

The EF400 amplifier cannot be listened to without its built-in DAC, so my sound impressions are based on the entire DAC and AMP combo.

The first thing I noticed about it is that it sounded soft, very soft - even compared to the seemingly similar EF600. What often comes with the softness is some vocal sweetness added - that’s the case here as well, but it takes away from the punchy nature of some headphones, like the HE6se. I would not recommend this amplifier for the HE6se, SusvaraHiFiMAN's flagship planar magnetic headphone, famous for requiring enormous amplifier power (at least 1-2W) due to its extremely low sensitivity of ~60dBSPL/mW., or Modhouse Tungsten. If you possess any of them, you should be aware of their power requirements and probably step up the ladder to pick up higher-end source gear, as the EF400 won’t let them spread their wings in terms of dynamics, and probably lacks some power to get the most out of them.

The thing with the EF400’s power is odd. They advertise it to be 4.4 watts per channel, which sounds pretty impressive for this kind of device, but independent measurements were able to get roughly 3 watts into 32 ohms out of it. It is still plenty - unless you’re running a very high-end or power-demanding headphone.

The signal-to-noise ratio is 118dB, and THD+NTotal Harmonic Distortion plus Noise - a more complete distortion measurement that includes both harmonic products and broadband noise. is specified to be between 0.002 and 0.004%. The channel separationThe isolation between left and right channels, measured in dB; insufficient separation causes stereo crosstalk that narrows the soundstage. is 125dB. Everything that I just mentioned may sound unimpressive - as it is. The EF400 is clearly not supposed to be a measurement-chasing unit, even due to the choice of using an R2R DAC. They’re known not to measure as well as delta-sigmaThe dominant DAC architecture today, using high oversampling and noise shaping to push quantization noise above the audible range. units, but they offer superior subjective performance. I believe that subjective performance was this unit’s goal.

Regarding this, it offers a very full and rich sound, typical of Class AAn amplifier topology where the output transistors or tubes conduct current at all times, eliminating crossover distortion at the expense of significant heat and inefficiency. or in this case Class AB designs - though it can sound a little shouty with very raw vocals. You shouldn’t be expecting a lot of resolutionA system's ability to retrieve and reproduce fine detail in the recording; high resolution reveals micro-dynamics, spatial cues, and timbral nuance. out of it, but the details that it can resolve are presented in a very pleasant, not in-your-face way. The EF400 sounds very fun and musicalA subjective quality where a system seems to convey the emotional content of music effectively, often (though not always) involving some euphonic coloration., and it’s far from being overly analyticalA presentation that prioritizes detail retrieval and accuracy over harmonic richness; analytical systems reveal flaws clearly but may lack emotional engagement..

Headphone Matching

Almost every not-crazy-hard-to-power HIFIMAN that I’ve got sounded very, very pleasant. It takes a bit of the edgeA slightly forward, lean character in the treble that can read as either "detailed" (positive) or "etched/harsh" (negative) depending on the listener and recording. Distinct from sibilance, which is band-specific. off of the sometimes sharp or bright-leaning tuning. Anything from the HE-R9, open-backHeadphones with perforated or meshed ear cups allowing free air exchange; produces a more natural, spacious presentation with no isolation from ambient sound. Sundara, Deva Pro, or Edition XS sounded like it was a perfect fit. HIFIMAN knew what they were doing - making an amp that matched well with their headphones.

But there’s one exception - I didn’t particularly like the entry-level HE400se. That headphone doesn’t do particularly well with busy passages, and the added harmonics of this amp made it even worse. Maybe it was a power thing, as the HE400se requires quite a bit of it - but I doubt it. I also doubt that anyone would pick up a $400 DAC/amp for a $100 headphone.

Most of the IEMs I’ve tried with it were not the greatest experience, due to quite a bit of channel imbalance in the first 10% of the volume. However, turning down the source volume allowed me to get past the problematic volume level and enjoy a wide range of IEMs with the EF400.

Generally, all headphones - except for those that are extremely difficult to drive, mid-forwardA tonal character with elevated upper midrange or lower treble that pushes vocalists and lead instruments ahead of the mix; can sound exciting or fatiguing., or dark-sounding - sound excellent when connected to this amplifier.