Head-Direct recently launched a new product line dubbed HiFiMAN which currently includes only two products, the (PMP) and the all new EF2 USB headphone amplifier. The EF2 is a headphone amplifier with an integrated DAC which means that you can hook it up to your PC. Besides the DAC functionality the amplifier can also be hooked up to another source via a set of RCA-jacks on the back of the amplifier. Like its bigger brother the EF2 is a hybrid design that uses both op-amps and tubes as amplification stages. Where the EF1 is equipped with one 12AU7 tube the new EF2 uses two 6J1 mini-tubes. At the moment the EF2 is priced at a very reasonable $189 as opposed to the EF1 at $300.
The EF2 looks brilliant. The new polished front plated with the simple HiFiMAN graphics makes it look quite classy. Unlike the EF1 which is just an amplifier the EF2 has an integrated DAC, the chip it uses is a Burr-Brown PC2702 which has a good reputation, and is used in a large variety of performance DACs and amplifiers.
One of the things that impressed me the most about the EF2 is its size. Only a little wider than a CD and very shallow. The fact that it is so small makes it the perfect desktop amplifier. The small circuit board is densely populated by quality components. Most of the caps are made by Rubycon. The 6J1 tubes supplied with the amplifier are from an unknown Chinese manufacturer, but they sound good in this combination. They are definitely better sounding in this combination than the stock Chinese 12AU7 tube sounds in the EF1.
With the amplifier you also get an AC Adapter and a USB cable that you can use to hook it up to your computer. You have to buy an adapter if you live in Europe because the 220V version of the PSU has the wrong type of connector on.
The Chinese tubes just pop out of the top of the amplifiers acrylic top. The only problem I had with the amplifier was that I had to reseat the tubes in order to get a good connection between them and the sockets. Another minute issue is that the precut holes in the acrylic top do not align perfectly with the tubes making it an odd fit. This is most likely due to the fact that the tube pins are slightly bent.
The power switch is a little flip switch on the left side of the device. Right next to the on / off switch is the 1/4" headphone jack. The jack is of a really good quality and is attached to the front panel of the amplifier so that it does not put excess strain on the PCB.
The EF2 is aimed at use with a PC, but can also be used with another analogue source at the same time. The input selector switch is located at the front and lets you choose input type easily. The volume control is really nice and smooth. The range is likewise very good. It powers Ultrasone PRO900s to high volume levels at around 8 O' clock on the volume dial.
Since the EF2 is a dual purpose device I decided to test it both by feeding it lossless files from my PC from Foobar2k with ASIO4ALL plugin and by my Marantz CD6002 CD player. As far as comparison goes I decided to compare it to my Octavart The ONE DAC & Amp since it costs about the same and is intended for use with a PC as source and can like the EF2 be used with a normal source. Besides the Octavart I also pitted it against my Head-Direct EF1 amplifier with a Sylvania 12AU7 tube installed. Before I began the listening tests I had the EF2 burning in for well over 100 hours. Headphones used to test the amplifier includes the following: Modded Grado SR-60, Modded Sennheiser HD 580, AKG K701, Ultrasone HFI-680, Ultrasone PRO900.
The EF2 surprised me quite a bit because it sounds similar to the EF1. It has a relatively warm midrange and a smooth sound without any muddiness at all and like its bigger brother the bass is nice and tidy. Actually the only major difference you notice straight away is that the EF2s gain is quite a bit lower than that of both the Octavart and the EF1, which is a nice thing. I find the EF2 to be the perfect match for the treble and bottom happy Grado SR-60s.
After my extensive testing I came to the conclusion that if you are not going to power extremely power demanding headphones the EF2 is a perfect solution, and its sound quality is well above that of the Octavart The ONE both in terms of definition throughout the spectrum plus the EF2 has a way more pleasing warm tonality whereas the Octavart amp tends to be a bit sharp and fatiguing to listen to.
With a set of headphones like the Sennheiser HD 580s which are high impedance headphones they sound a bit duller and veiled than on the EF1 which I suspect is due to the fact that the EF1 has a more powerful amplification stage than the EF2. The EF1 manages to power the HD 580s to a point where every minute detail is portrayed elegantly the EF2 with both soundstage and midrange details on some complex tracks. The Octavart is nowhere close to the two Head-Direct manufactured amps in this performance aspect. When it comes to soundstage width and depth the EF2 is quite a bit away from the EF1 although not bad. One pattern that followed throughout my testing with the Marantz as source was that the EF1 and EF2 were really close with a set of relatively efficient headphones and with the Octavart as distant third. With high impedance or a demanding set of headphones like the HD 580s or my old Phillips braded AKG K240s the EF1 managed to distance itself from the two other headphone amplifiers.
Just for kicks I decided to do a small listening test with my Ultrasone HFI-680 which is relatively easy to drive. To start up with I had them hooked up to my X-Fi XtremeMusic sound card and the result was not all that pleasing, the lows were muddy and the sound stage was completely absent. With the EF2 the sound reproduction becomes much livelier and for music listening it is miles ahead of the XtremeMusic card. Of course the XtremeMusic card is optimized for games and not surprisingly it does a better job here than the EF2.
The DAC in the unit is very well sounding perhaps not able to compete with the more expensive DAC only products, but generally very pleasing to listen to. Compared to the Cirrus Logic equipped Octavart the EF2 has way more potential.