This week we’re testing the HiFiMAN EF-100 headphone amplifier ? a hybrid model fitted with a tube power preamp section and two amp sections, one for running a wide range of headphones and the other to power speakers. This headphone amp features a 16 bit / 44.1-48 kHz DAC with USB input, to connect to any computer, be it Mac or PC without the need for drivers.
The benefits of tubes in hi-fi
In a headphone amplifier as in any other integrated amplifier for speakers, pre-amplification is an essential element. Its role is to adapt the voltage and impedance of the incoming signal to the sensitivity and impedance of the power stage as well as allowing the user to adjust the intensity of the signal sent to the amplifier, using the volume control. The pre-amplifier allows different sources/inputs to be selected. As regards the HiFiMAN EF-100 headphone amp, the pre-amplification of analog signals is performed by a 6N3J power tube. This original US design tube (5670) is frequently used by Chinese manufacturers in order to treat low-power audio signals. This is an example of a high quality version.
The advantage of using a tube for audio signal pre-amplification is based on the tone balance and smoothness of the sound produced. Only the pre-amplification sections in the really top-of-the-range models of amplifier can match up. The sound is very realistic and never cold and clinical.
Why can’t we see tubes anymore then’
For many reasons, rarely positive ones, the main one being stability of the tube whose service life is shorter than that of a transistor. Tube electronics require ?re-tubing? after a few years. This isn’t a delicate operation in the case of the HiFiMAN EF-100, which, with all the necessary precautions, can have a Chinese tube replaced with an American or Russian model (approximately fifteen euros). Another reason is that the installation of tubes in an amplifier imposes constraints in terms of design and space. Nevertheless, the tube is making a triumphant comeback and can be found in certain models of RIAA phono amps, CD players, integrated and power amplifiers from brands such as Pro-Ject, Magnat or McIntosh to name but a few.
Two amps in one
The specific feature of this EF-100 amp is that there are two stereo amps ? one for the headphones, operating with transistors in Class AB (standard design) and the other for Tripath type (Class T) high-sensitivity speakers. With headphones, HiFiMAN EF-100 delivers 2 Watts per channel under an impedance of 30 Ohms and approximately 300 mW at 300 Ohms. The headphone amp is very powerful. With speakers, power is established at 2×4.5 W at 4 Ohms. This output is minor and is mainly suited to close range listening (on a desk for example) with relatively sensitive speakers.
A 16 bit / 48 kHz USB DAC
A slight disappointment is the digital-analog converter in the HiFiMAN EF-100, which is limited to 16 bit and 44.1 or 48 kHz PCM stereo streaming. As the general trend is to integrate a 24 bit / 192 kHz DAC, which is in theory a pity, even if the presence of line inputs allow you to connect an external DAC. The 16 / 48 C-Media CM102 integrated DAC offers valuable benefits. It has an integrated N/A converter, USB controller, sync clock and Class AB amp with an ?extremely analog? signature sound. This choice has a certain logic to it, as regards the presence of the preamp tube which delivers a particularly well-rounded sound.
Test configuration and listening impressions
We connected the HiFiMAN EF-100 headphone amp to a computer using Windows, firstly with the supplied USB cable and then with an Audioquest Coffee USB cable. Two sets of headphones were used ? a HiFiMAN HE-500 and a Sennheiser PX-100, as well as a pair of Focal Aria 906 speakers, connected using Viard Audio Premium HP cables. The files we listened to were in FLAC and DSD format (under-sampled at 44.1 kHz via Foobar2000).
We may as well admit to it, the amplification section test didn’t last long. While the medium and treble ranges are remarkably smooth, bass is absent. The results aren’t unpleasant but this 2×4.5 W amplification should be reserved solely for occasional listening with small speakers placed near the listener. Even with high-sensitivity Klipsch Heresy III speakers and a large diameter bass driver, listening lacks presence despite the incredible softness.
Listening with headphones, however, is completely different, even using the supplied USB cable. The use of Audioquest Coffee brings even more details to the listening experience, which is surprisingly smooth. The HiFiMAN EF-100 headphone amplifier impresses with its power which seems unlimited: bass frequencies are powerful and very well articulated, medium is soft and detailed and treble is airy and open. Although the DAC only supports CD quality files, listening doesn’t lack character. Sound levels are well structured and you never have any difficulty in locating an instrument or voice. Simple recordings reveal an impressive array of details with the EF-100.
Take Stairway to Heaven by Led Zeppelin for example and you’ll rediscover this gem. The focus which is normally centred on the acoustic guitar and the high notes of the flute is, with the EF-100, concentrated on Robert Plant’s voice, whose tremolos are delivered right up to the note fades. The flute’s low notes are much clearer than with most DAC amplifiers in this price range (and beyond). Take Attractions Désastres by Etienne Daho and you’ll easily follow the artist’s phrasing (this is even more rare). You’ll find that, finally, the mixing is far from being poor quality. On Duel of Fates by John Williams, you’ll experience spine-tingling joy on hearing the choirs and the orchestra and the crash of cymbals is uncommonly powerful. This headphone amp is never aggressive, regardless of the music, USB cable or set of headphones.
We can criticise this HiFiMAN EF-100 headphone amp on several fronts, like for example, the absence of HD audio stream support, the speaker output lacking in energy in low frequencies or a slight lack of precision in the high treble range. The lively listening experience you get with headphones makes up for all that. The deep, full-bodied bass, the smooth medium, free-flowing treble, well structured sound levels and impressive power all make the EF-100 a high class headphone amplifier, venturing into areas reserved for more costly models.