The HiFiMan EF400 is a balanced R2R-type DAC with integrated headphone amplifier, designed to optimally drive even the most demanding headphones. It is a well-known device among headphone listening enthusiasts, sitting (dangerously for competitors) in the ~500 euro price range.
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Introduction
HiFiMan Electronics is a Chinese company founded in 2007 by Dr. Fang Bian. HiFiMan gained great popularity with its line of advanced planar magnetic headphones, which have won numerous awards in recent years and are considered among the best in their respective price ranges.
In addition to headphones, HiFiMan produces other high-end audio electronics: DACs, headphone amplifiers, and portable music players. However, for many years, its production of relatively affordable desktop headphone amplifiers was limited to the EF6 model, specifically designed for the HE-6 headphone and costing around 1600 dollars, certainly not a small amount.
Things changed completely at the end of 2022, when HiFiMan released the EF400, a powerful and high-performance headphone amplifier with integrated R2R DAC, launched at a price of around 600 euros and currently also available for less, slightly above 500 euros.
The EF400 has achieved great success, so much so that HiFiMan later expanded its amplifier range by introducing a larger sibling, the EF600 (which we will cover soon), and more recently the EF500 and EF499 models, more affordable and equipped with network connectivity.
Build, features, technologies
The EF400 implements digital-to-analog conversion through an R2R-based DAC. This technology uses a carefully designed resistor network, generally controlled by FPGA units, to perform digital-to-analog conversion.
It is a solution that, when well implemented according to enthusiasts, delivers a richer, more natural, and more spatially defined sound compared to converters using other technologies. However, the need for extremely precise electronic components often makes this type of DAC quite expensive.
Using an R2R DAC together with a powerful headphone amplifier, all in a device sold for just over 500 euros, is something extremely rare, and is at the core of the EF400’s success. Thanks to HiFiMan, we were able to extensively test this popular headphone amplifier.
The EF400 comes in a rather plain cardboard box that contains only the amplifier and a standard power cable. To read the manual, which is very simple, you need to download it online.
Once taken out of the box, the EF400 immediately impresses with its size and weight, well above the average modern 500-euro DAC/headphone amplifier. Thinking of carrying it around easily is unrealistic: this is a device meant to sit on a desk near a computer and stay there.
The EF400 is not designed for mobility and performs best with large and heavy headphones used in a fixed listening environment, to fully enjoy a high-quality musical experience.
On the rear of the unit we find the power socket and power switch, two balanced XLR outputs and two RCA outputs. The position of the power switch is rather inconvenient.
The only available inputs are USB-B and USB-C, which cannot be used simultaneously and are not selectable via any switch. The RCA outputs are fixed level: there is no preamplifier function.
There are no optical or coaxial digital inputs, which in practice limits its use to a single purpose: what the EF400 was specifically designed for, namely as a digital-to-analog converter for computers or other devices with hard drives.
Those who need to connect a CD player, TV, or other devices with S/PDIF digital outputs will need to look at other products.
Small technical summary:
- THD+N (Line out): between 0.002% and 0.004%
- Channel separation: 125±3dB
- Signal to Noise Ratio: 118±3dB (A Weighted)
- Maximum power: 4.4W per channel
- Dimensions: 246.5mm × 228mm × 61mm
- Weight: 3.08kg
Functions and outputs
The front panel is simple and solid, featuring two large knobs on each side. The left one changes gain and digital/analog conversion mode between High Gain NOS / High Gain OS / Low Gain NOS / Low Gain OS.
NOS stands for “No Oversampling”: in this mode the signal is converted in a very direct way, without changing its frequency and with reduced use of complex digital filtering.
Whether oversampling is better or not in D/A conversion is a complex and long-debated topic in high-fidelity audio. In the EF400, NOS mode sounds more defined and less “veiled”, while OS mode is characterized by a warmer low end. The choice depends on the headphones used and personal preference.
At the center of the front panel there are four headphone outputs: 6.35mm and 3.5mm single-ended, 4.4mm Pentaconn, and balanced XLR.
There also seem to be small sonic differences between outputs of the same type: for example, a headphone connected to the 3.5mm jack sounds slightly different when connected via adapter to the 6.35mm output.
Output management is also unusual: if multiple headphones are connected, they all play simultaneously. In addition, the rear RCA outputs are not automatically disabled when headphones are connected.
Technically, the EF400 is fully balanced in design: two Himalaya R2R modules handle digital-to-analog conversion for the left and right channels.
The amplification stage is also fully balanced and rated at a maximum output power of 4.4W into 32 ohms. Power is supplied by a large and heavy toroidal transformer with OFC copper wire.
Decoding supports up to 24-bit / 768kHz PCM. However, DSD and MQA are not supported.
How the EF400 sounds
We had the opportunity to test the EF400 with a wide variety of headphones, including some of HiFiMan’s most famous planar magnetic models: Sundara, Edition XS, Arya, HE6v2 SE.
To test its behavior with high-sensitivity and low-impedance headphones, we also tried it with Grado SR80E and closed-back HiFiMan HE-R9.
The EF400 clearly needs some burn-in: straight out of the box it sounds too dry and thin, and only after several dozen hours does its true character emerge. It should not be judged immediately.
As expected, the EF400 shines particularly when used with HiFiMan planar magnetic headphones, which it drives with great dynamics and impact without becoming fatiguing.
The pairing with the Sundara is especially successful, adding a touch of extra warmth and musicality. The Edition XS with Stealth Magnets also perform excellently, with a beautiful stereo image and great balance across highs, mids, and lows.
The only slightly problematic pairing is with the HE6v2: the EF400 can actually drive these headphones (no small feat at this price), but at very high volumes the volume knob reaches near its limit, and it feels like the headphones could perform even better—especially in bass impact—with more power.
The EF400 also delivered very positive results with Grado headphones and HE-9, producing a warm, pleasant sound with excellent rhythm. However, when using low-impedance high-sensitivity headphones, be careful with volume levels: even in low gain mode, output can become very loud and potentially unsafe for hearing.
Conclusions
In summary, the EF400 does not excel in flexibility or convenience. It is a device that focuses all its effort in one direction and, in our opinion, excels in its price range in what ultimately matters most: sound quality.
The EF400 is a powerful headphone amplifier with an excellent integrated DAC, capable of driving even difficult headphones, designed to be connected to a PC and deliver outstanding music playback.
At its price point, very few competitors can match its sound quality.
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