Hifiman EF400 - R2R doesn't have to cost an arm and a leg! - Updated Review and Measurements

 

NOTE: We previously tested a unit of the EF400 which exhibited some issues with the left and right channels being out of phase, and some issues with low level signals. These measurements are available here. Hifiman has fixed this issue in new units and this post shows measurements of the fixed version.

Existing units may still have this issue. Information on affected serials has not been provided, please contact customerservice@hifiman.com with your unit’s serial number to find out if yours has the fix applied or not. A test method you can use to check yourself is also described in the last section of this post.

Introduction

The Hifiman EF400 is a $599 DAC and amp combo unit that offers quite a different design from many of the other products in its price range, most notably the fact that the EF400 uses an R2R DAC design instead of the typical delta-sigma DAC chips found in most other products. R2R DACs are an older technology that has the benefit of being able to convert PCM digital audio natively, unlike delta-sigma DACs which must oversample and modulate the 44.1khz 16 bit audio to a much higher sample rate, much lower bit depth format, often around 22Mhz and 3-6 bits. Whilst R2R DACs typically (though not always) perform objectively poorer than competing delta sigma designs, many listeners swear by the resulting sound they produce, as well as many enjoying the sound of ‘NOS’ or non-oversampling modes that R2R DACs are often capable of.

The EF400 uses Hifiman’s proprietary ‘Himalaya’ R2R design, with a linear power supply and an inbuilt amplifier.

Unfortunately the inputs for the EF400 are rather limited, with the only options being USB type B and type C. This means that you won’t be able to hook the EF400 up to a TV or any other SPDIF source, nor will you be able to use it with an alternative external DAC, though it is always nice to see USB type-C on products.

Measurements

Measurements Index

• THD+N / SINAD
• THD+N vs Frequency
• Power / THD+N vs Output Level
• Low Level Signal Output
• Nyquist Reconstruction Filter / Oversampling
• Noise When Idle
• IMD
• Linearity
• Crosstalk
• Jitter
• Multitone
• Wideband Noise & Distortion
• Volume Matching
• Power On/Off Behaviour (Safety Test)
• Interchannel Phase

Additional measurements and test information available in the full reports

Test Setup

• Audio Precision APx555 B-Series Analyzer
• Neurochrome HP-LOAD Dummy Load
• 100kΩ Input Impedance used unless otherwise stated
• USB Source: Intel PC via intona 7055-C isolator
• Measurement setup and device under test are running on regulated 230V power from a Furman SPR-16-Ei
• EF400 was warmed up for 24 hours prior to testing
• Measurements shown are from the balanced headphone output with a 32Ω load unless otherwise stated
• Measurements shown are using the ‘Low-Gain OS’ setting unless otherwise stated as this produced the best objective results
• Exact analyzer/filter configurations for each measurement are detailed in the full reports
• CH1 (Blue) = Left, CH2 (Red) = Right

Full Measurement Reports

Full Report (Balanced Headphone Out OS 32 Ohm)

Full Report (Balanced Headphone Out NOS 32 Ohm)

DAC XLR Out OS

Results

Dynamic Range (AES17): 105.0dB

SNR: 105.2dB

IMD SMPTE: -76.2dB

Noise Level RMS (20-20khz): 19.99uVrms

Noise Level RMS (20-90khz): 30.62uVrms

Noise Level RMS (20-1Mhz): 50.6uVrms

DC Offset: 1.14mV active, 1.46mV idle

Susceptible to intersample overs: Yes (in OS mode)

Output Impedance: 9.8Ω

THD+N / SINAD

1khz 0dBFS Sine, 4V output (32Ω):

1khz 0dBFS Sine, 700mV output (Headphone Level, 32Ω):

1khz 0dBFS Sine, 50mV output (IEM Level, 12Ω):

1khz 0dBFS Sine, (DAC XLR Outputs, OS):

1khz 0dBFS Sine, (DAC XLR Outputs, NOS):

THD+N vs Frequency

This test measures the THD+N at different frequencies, which can reveal information about how the device performs in areas other than just 1khz.

Note: a 96khz bandwidth is used on the analyzer to capture harmonics above 20khz. Do not directly compare figures here to standalone THD+N results taken with a standard 20khz filter

The THD+N vs frequency on the EF400 is quite U shaped, with a rise not only into the higher frequencies which is not too uncommon, but also a rise into the lower frequencies. This may result in a softer/sweeter subjective sound.

Power / THD+N vs Output Level

This test measures the THD+N at various output levels. This can be useful for DACs, but is also used for amplifiers, where maximum power is typically specified as the maximum output a device can supply before reaching 1% THD.

XLR Headphone Out, 32, 50 and 300Ω loads, Voltage in dBV on X-Axis

XLR Headphone Out, 32, 50 and 300Ω loads, Power in Watts on X-Axis

The EF400 does not meet the specified 4.4W power output. Best case I was able to get roughly 3W @ 32 Ohms.

XLR DAC output, 200kΩ analyzer input impedance

Low Level Signal Output

This test puts a very low level signal through the device to check for any unusual behaviour.

-90.31dBfs 24 bit dithered sine

The glitching behaviour seen on the old unit has been fixed!

-90.31dBfs 16 bit undithered sine

Thanks to this fix, the undithered sine is also much cleaner.

Nyquist Reconstruction Filter / Oversampling

White noise at 44.1khz sampling rate is played through device, the result shows us how effectively the oversampling/reconstruction filter removes unwanted content above 22.05khz.

The reconstruction filter is very similar to those seen in many DACs. However, thanks to the EF400’s NOS mode, you can also use external high performance upsampling and noise shaping with tools such as Remastero PGGB and Signalyst HQPlayer and ensure no further processing will be done on top.

Noise When Idle

This test simply shows an FFT of the output of the device when idle/not playing anything.

IMD

This test plays a 60hz and 7khz tone through the device. Intermodulation distortion is the unwanted content that shows up around the 7khz tone as a result. This type of distortion is not harmonic distortion, and is considerably more audible.

Linearity

This test plays a 1khz tone through the device, and steps down the level in small increments. Linearity measures how accurately the actual output of the device reflects the intended output. For example, if the level was stepped down by 20dB, but the output of the device was 19.7dB quieter, there is a 0.3dB nonlinearity, which would show as a 0.3dB rise on the graph.

Crosstalk

This test plays a signal through one channel of the device, and measures how much of it leaks through to the other channel.

Jitter

This test uses a ‘J-Test’ signal, which shows distortion caused by variation/errors in timing. Even if all data is correct and other distortions are very low, timing inconsistency can cause inaccurate output from a DAC. Please note: the J-Test is a workaround to show a time-domain error on a frequency domain FFT. Please do not directly compare levels of distortion here to other types of distortion.

The J-Test is significantly improved from the previous unit thanks to the glitching issue having been fixed.

Multitone

This test plays 32 tones through the device to test behaviour with a very complex waveform. It does not usually show anything that would not be shown on a THD+N vs frequency graph, but is a useful check to make sure there is no unexpected behaviour.

Wideband Noise & Distortion

Volume Matching

A signal is played through the device. The volume knob is then adjusted to different levels, and the difference in volume between the two channels is noted. The lower the result the closer the channels are matched. Some devices with lower quality potentiometers will show larger channel imbalance particularly at lower levels which can present a challenge for quieter listeners and/or IEM users.

0dBV (1Vrms) = 1.1dB

-10dBV (0.32Vrms) = 0.82dB

-20dBV (0.1Vrms) = 0.28dB

-30dBV (32mV, quiet IEM level) = 0.61dB

The volume matching seems to vary and can change depending on whether you reach that level by turning the knob up or down. It can have over 1dB channel difference even at higher levels. It would have been ideal to see a better potentiometer on the EF400.

Power On/Off Behaviour (Safety Test)

This shows the output of the device when switched on/off. A large transient, or a significant DC offset may pose a risk to headphones if they are left connected whilst the device is switched on or off.

Generally well handled, a slight transient upto 10mV when turning on but this is extremely unlikely to pose any risk to headphones. May not wish to turn it on with IEMs connected and in your ears though.

Turning off the device, it simply goes from the static 4mV DC offset to 0.

Regardless of what this test shows, we would always recommend you disconnect your headphones before turning a device on or off.

Interchannel Phase

A device should always be outputting the left and right channels at the same time, however in some instances, DACs may have a slight offset between the left and right channels due to a design flaw.

The interchannel phase issue has now been fixed. Hifiman has not said which serial ranges are affected by the issue. You can contact customerservice@hifiman.com to ask if your unit has the fix applied or not, but can also check yourself if you have an audio interface with two inputs, such as a Motu M2.

To do this, connect the XLR or RCA outputs of your EF400 to your interface inputs (ensure that 48V phantom power is turned off!). You may need to turn down sensitivity.

Then, download the 15khz test tone file below, and play it through the EF400.

-3dB 15khz test tone

Use a tool such as Audacity or Adobe Audition to record both the left and right channels simultaneously (if using Audacity, I would highly recommend recording at 192khz to more clearly see the waveform).

Now, check if the two 15khz sines are aligned, or misaligned. If they are aligned, your unit is fixed. If they are misaligned, your unit still has the interchannel phase issue.