Sources: Macbook Pro with Pico USB DAC-0nly, and with EF2 built-in USB DAC.
Music: Apple Lossless rips of Mark Isham + Kate Ceberano "Bittersweet", John H. Clark "Acoustik Guitar", Shelby Lynn "Just a Little Lovin", Jack Johnson "Sleep Through the Static" and "On and On", Arvo Part "Tabula Rasa", Eva Cassidy "Live at Blues Alley", Diana Krall "Live in Paris", Helge Lein Trio "Hello Troll", Infected Mushroom "B.P. Empire", Valerie Joyce "New York Blue", Eric Satie "Piano Miniatures" (mastered by John Willett), Glenn Gould "Bach: Goldberg Variations", Beck "Sea Change" Gold Master, Red Hot Chili Peppers "Stadium Arcadium", and Patricia Barber "Nightclub".
Headphones: Sennheiser HD800, Grado HF-2 and RS-1, Alessandro MS-1, Denon D2000 (woodied re-cabled), Ultimate Ears UE11Pro, Westone ES3X, and Nuforce UF-30.
Head-Direct has been developing their own "house-brand" headphone amps and IEM, with a soon to be released DAP with USB and coax DAC. Their new name for their own gear is HiFiMan. Prior to CanJam I made arrangements with Fang at Head-Direct to bring home a new model amp, the EF2, which would be unveiled at CanJam. The HiFiMan EF2 is a small $189 tube hybrid amp which I am estimating is about 2.5" tall by 3" deep by about 5" wide. It uses a pair of 6J1 tubes, and includes an integrated USB DAC with a Burr Brown Japan PCM2702E DAC chip. It has a switch on the front panel to change the input between the rear RCA to USB jack. The volume knob has tactile detents but is not a stepped attenuator, and it has very good low volume channel balance when using high sensitivity IEM at very low volume knob positions. It is powered by a small 16V AC wall wart, not DC, so it cannot be powered by a portable battery pack.
I first tried it out at CanJam at their demo table. I've previously reviewed and owned their EF1, which I enjoyed very much as a mid-range best-bang-for-the-buck tube hybrid amp. I preferred the EF1 over the Grahm Slee beta NOVO and my old Dark Voice 336i, for use with a variety of headphones but especially with my Grado RS-1 and Denon D2000. My first impression when listening to the EF2 with my HD600 was "wow this sounds like the EF1 but for $100 less money!" I tried it via RCA input with their source and via USB on their laptop, and I was sold on it as a nice small desktop PC amp. The only thing I heard at CanJam to distinguish the EF2 from the EF1 was when I listened to them with the prototype RE5 orthodynamic headphones which sit at something like 4-8 ohms, and the EF1 could clearly drive the RE5 better. But driving headphones at 4-8 ohms is not really a a fair test of how well the EF2 can perform.
I took the EF2 home with me after CanJam 09, and proceeded to burn it in with my HD800 and HF-2 that came home with me as well. It was fairly fresh with only a few hours on it at first, and seemed slightly bright at times with the HD800 and RS-1, but not bright at all with the HD600, D2000 and HF-2. Over the course of 300 hours the amp came into it's own, with a fuller bass and smoother treble, and so I began working on my review. At this time the amp has at least 400 hours on it, with 300 hours on the nice sounding stock tubes and 100 hours on the upgraded NOS Raytheon 6AK5 tubes that I bought from Skylab. I did much of my listening to the amp with the Pico USB DAC-only, to get a sense of it's best performance, and then towards the end I listened to the built-in DAC for comparisons. But, I'll go ahead and talk about the DAC first, and get that out of the way.
DAC: The DAC is nice but not mind blowing - it's a Burr Brown Japan PCM2702 and sounds about on par with the 3MOVE and XM5 DAC which use the same chip, and is also similar in quality to the USB DAC in my RSA Predator. It is a little less detailed and spacious than the Pico or iBasso D10 DAC via USB, but it still does a good job and sounds better than the USB DAC in the iBasso D1 or Headstage Lyrix did. The EF2 via built-in USB DAC is noticeably more detailed and transparent than using the Macbook headphone out with a mini-RCA to feed the EF2. I also preferred the built-in DAC over feeding a 4G Nano into the EF2 with an LOD>RCA cable.
The PCM2702 internal DAC as the source provides a slightly lower volume level than when feeding the Ef2 from the Pico DAC via RCA, but one or two clicks on the volume knob is enough to match the levels between the internal and external DACs. Both the EF2 DAC and the amp section are very quiet with my custom IEM and don't hiss or make noise - and the volume knob has very good control at very low volumes without any channel imbalance. When switching from the built-in DAC to the Pico DAC, the main change in sound is the expansion of the soundstage width and depth, and the extra micro-detail and ambience, but the sound signature and frequency balance don't seem to change much at all. It sounds the same in tone after the switch in DACs, but also sounds like a slight veil was removed from the sound with the upgraded DAC.
AMP: Moving on to the amplifier section, the rest of the review covers the sound when using the Pico USB DAC-only. The amp is good enough to scale up with an improved source and appreciate the extra detail. With the stock tubes the amp's sound signature became warmer after 200-300 hours of burn-in, but it still could be occasionally bright at times with HD800, APS V3 cabled RS-1 with bowls (better with flats) and Westone ES3X custom IEM. The stock tubes were a little better match with my new Grado HF-2, woodied re-cabled Denon D2000 and APS V3 cabled HD600. Speaking of HD600 - these are usually hard to drive but there was no problem driving the HD600 better than most of my portable USB DAC/Amps that I have reviewed in the past. Only the 3MOVE and Vivid Audio V1 portables could drive the HD600 close to the levels that the EF2 can, with the Pico coming in right behind them. The other portable DAC/amps could sound good with the HD600 at medium volume levels, but they just can't often be pushed without straining as you get close to "being there" volume levels. The HD800 seem a little harder to drive than the HD600, but I could still get more than enough volume with the little EF2.
After I changed the stock chinese tubes at 300 hours to the NOS Raytheon 6AK5 tubes that Skylab sold me, the EF2 ceased sounding bright with any headphone once I got about 24 hours on the Raytheon tubes, and improved over an 75-100 hour burn-in on the new tubes. It also sounded more refined, smoother, more musical and more involving. And, the sound signature almost seemed to change according to what headphones I was using. So with the HD800 I would get slightly more bass impact than with my ALO Amphora, yet with my low impedance Ultimate Ears UE11Pro and Denon D2000 the EF2 would actually tame the bass and bring it into line with the rest of the frequency curve. You would normally expect that if the bass is greater with one headphone that it will be greater with them all, but that was not always the case. Also, while it is only a slightly forward sounding amp, it did an excellent job of filling in the slightly recessed mids of my UE11Pro and D2000, making the mids more rich and inviting. It was basically a perfect match for my UE11Pro. Yet, the mids were not too much with my forward sounding Grados, and I absolutely love it with my Grado HF-2 headphones. The drum solo in Patricia Barber "Companion - Nardis" with the HF-2 and EF2 is simply stunning in it's dynamics, impact and extension (as well as timbre and tone).
In my comparison with the $995 ALO Amphora or $1250 maxed WA6 it was clear the Amphora/Woo had a deeper and wider soundstage, with more micro-detail and an extra degree of transparency and extension, but the EF2 was still very enjoyable even when you know what you are missing. The EF2 is a very musical and euphonic amp to my ears, which makes up for whatever else it lacks. As I said before, it sounds similar to the $399 EF1 (which is often priced at $299 now) - and like with the EF1 I would prefer to listen to the EF2 over the headphone out of my Apogee mini-DAC, or my Nuforce Icon desktop amp with USB DAC. I also enjoyed the EF1 more than the Grahm Slee NOVO, and that should extend over to the EF2 as well. While the mini-DAC headphone out has a wider soundstage and good power, it doesn't sound as dynamic and alive with my HD600 (Apogee line out as a DAC-only is fantastic though) - and with some headphones like D2000 the Apogee can become fatiguing after a while. The EF2 is not quite as detailed, neutral or extended as my Travagans Red with AD743 opamps, but it is more powerful, euphonic and "bigger" sounding. The EF2 has a similar "romantic" sound to it as my Meier Headfive, but still surpasses the Meier as well, especially with Grados at louder volumes where the Headfive begins to sound thin and strained.
SUMMARY: There is just something about the EF2 that, while I know it is not as detailed and spacious as some of my other headphone amps, keeps drawing me back for another listen when I want to use my Macbook as source. Will it replace my Woo WA6, ALO Amphora or balanced Square Wave XL, or even my iBasso D10 or Pico portable amps? No. But it has been getting more attention for the past month than many of my multitude of portable DAC/amps around the house. I traded a more expensive EF1 amp ($400 at the time I received it) for this review sample, and I have NO regrets about the supposed "downgrade" at all. The EF2 is a "big little amp", and even at $300-400 I would recommend it to others - yet at $189 it is a steal and will be a permanent fixture in my home. So, for those looking for an inexpensive DAC/amp, who don't want to worry about whether their headphones will work with it, this is an excellent starting point. Especially since it scales up with better tubes and a better external DAC later.