I am sitting in a serviced apartment with a laptop and a headset. My home is 1450km away. After a week of suffering came my goal: grab my old headphone, a portable HDD filled with music files and get a headphone amp. So let me state you the requirements here.

I have a Sennheiser HD600, a little old fashioned and not that portable. I remember having an awful experience using it directly from a laptop and had a wonderful experience using it directly from a Denon CD player. So I need a headphone amp that can handle the HD600 well. That means two things (thanks to the hi-fi forums): I need something with power. The 5V DC won’t be enough. I need something with external DC input. And I have to make sure that the amp does not get shy driving a headphone with impedance well above 300 Ohms. I need a target price as well. I stated that is 200USD. I also stated that I don’t want to use the mini jack plug on my computer. From this budget I won’t get a separated DAC as well so I also added my requirement of having a single unit of amp and DAC. Just like an external soundcard with USB connection.

I don’t listen to music at too high levels, so I won’t buy anything that has problems at low volume levels. Looks like many amps has balance issues at low levels. Another thing is the hiss. I don’t want it. And not just because the music is so loud that it is faded. About the DAC I don’t have any specific requirement. 24/96 support sounds great but since I don’t have source for that it cannot be a serious factor. Replaceable OPAMP? Not interested now, but sounds nice for the future.

So I want to spend 200USD maximum and I would like to be happy with the sound that should remember me what I’ve left at home for the patrolling dust bunnies to conquer without having to turn up the volume too much. No hiss, no channel imbalance, no lack of dynamics, no poor frequency response and minimum hearing fatigue if possible.

I’ve checked the forums, used google with keywords like the ‘best amp for HD600’. I’ve actually found Audinst name on ebay first. Then checked the official site (specs looking good) and the reviews (compared to the others under 200USD) and the user comments (also no shop stopper issue here).

In theory all the criteria seem to be met so I took a deep breath and ordered a unit in 3 minutes. Note that the price includes the worldwide shipping as well. The shipping was surprisingly fast, took only a few days from Seoul to London. The stuff is super safely packed, no chance that the unit gets hurt. The box suggests that the amp is much bigger than it really is. The doubled headphone outs are nice (no adapter required for the headphones), the line out and the optical SPDIF out might get handy as the unit can be used as an external soundcard if necessary. What was important on the back panel for me: USB type B connector (I have seen too many faulty USB mini/micro connectors recently) and the 15V DC input, suggested by so many people on different forums. Only one more thing to mention: no power button. I don’t like auto sleep features I like to control my unit and know that I can turn it off and don’t have to unplug it, but this one actually works well. I connect it, it powers up. If no DC input, it feeds on the USB. If no music, it sleeps. If no PC, it powers down. So forget the power button, not needed that is why it is missing.

From software point of view it is just an external soundcard, windows already has the driver for it nothing to do here. I use Foobar2000 with ASIO4ALLv2 as a source, lossless CD rips only. Please note that the correct impedance should be set by setting a jumper inside the unit. As there is some risk of damaging the unit and have not found serious volume or frequency response issues, I did not make this tweak. (A hint for the manufacturer: a nice addition would be to question this before shipping and setting it in the factory.)

Goal #1: Low level balance. It is excellent. Nothing else to state here.

Goal #2: Hiss and noise. It does not exist. No computer noise at all. I like this very much.

Goal #3: Amp gain. At 9 o’clock setting it reaches the point of loudness that I need in a quiet room. It also has the most potential in terms of dynamics. Below this point it quickly loses the small details. Above this point it is just too loud and drives my ears into an uncomforted state very quickly. It is easy detectable with rock music which is not that ear friendly. I am not talking about gain issues here, but the middle frequency range gets a little more punch than necessary. Otherwise the performance of the set is stunning; some tracks just rock me out of the seat.

Goal #4: Dynamics. Connected to the output level. On low levels it is easy to miss something from the music that is there just not getting enough attention to itself. Sometimes hard to identify until some gain is given.

Goal #5: Flat frequency response. It is very good in a certain volume level. In my preferred listening volume it is well balanced, not too much from anything, not lacking anything. Check for example R.E.M.: Drive from Automatic For The People, 1992. The bass guitar is beautiful here; no signs of the loudness war (the good old days…), everything is in its right place, the strings find their place in the music easily. Also worth mentioning James Horner’s Titanic soundtrack here (Never An Absolution from Titanic OST, 1997). The bass punch is impressive and very deep. I mean catastrophic deep, like with a REL sub in a room. No shaking in the chair, but that is not for a headphone to produce. Now I am impressed.

Goal #6: Listening fatigue. It is present. At 9 o’clock setting the smile from my face is fading away about 20 minutes. Giving up one tick from the volume delays this problem but then something else is lost from the music. Is it a fair trade or not? It depends on a few things. Writing this review with a moderate level volume setting is fine. Getting the punch of 80dBA from some harder metal music is fatiguing. I am not sure though that is the problem of the unit or a general problem of using headphones. With speakers I’ve only experienced this with cheap components especially with cheap power amps. Even if we are talking about a fresh albums in the era of the loudness war. Even moving back a little and trying older stuff, I cannot say that the fatigue is gone. The only option is to take breaks during the listening session.

Goal #7: Stereo imaging. It is very far from listening to real speakers or live music. As there is little space between the headphone and my ears I have not expected anything that will simulate the room. Don’t get me wrong, listening to Apocalyptica: Harmageddon from Inquisition Symphony, 1998 for example is something worth mentioning. It is just not real. It’s like I have two cellos right next to my right ear and another two next to my left ear. I don’t get used to this experience, I like the space around me, I like playing with the room acoustic, but this is just me. There are situations where that room with the big fat standing speakers is just not available.

CONCLUSION:

So only one more question to answer: does it actually worth it? 179USD is comparable to the price of the HD600. I can safely say that I like this little amp. Also tested the DAC with 24/96 input and it worked just fine, no issues here. The only disappointment is that I still cannot listen to music for long hours; my ears just get tired too quickly. But I can listen to music now with pleasure away from home. For 179USD it is a bargain. The spikes under my speakers cost more than this so I think I can live with what I have here now.

STRENGTHS:

Low level balance is excellent, no hiss at all, amp gain (used with external DC in) is more than enough for me, frequency response is quite flat.

WEAKNESSES:

Somewhat lack of dynamics when used on low volume levels, listening fatigue is present.