I'll try to keep this concise, but I've had a number of thoughts about my Portable Micro Amp/DAC1 and feel the desire to share them with someone who may give a rip. There may be a number of threads that this is relevant to, but here's where this post landed.
Let me start this by indicating that my impression of this unit is overwhelmingly positive. Taking in to account what I paid for it, it is one of my most favorable audio acquisitions. I will carp a bit about it later on, so keep this in mind.
Associated equipment: Grado SR-60. Etymotic ER4P, & Sennheiser HD650 phones. IRiver IHP 120, DFI motherboard coax out, TOSHIBA Qosmio G35-AV660 laptop optical digital out, Music Hall RDR radio, Aragon 4004 MK II amp, B&W DM303 speakers, Headroom Total Bithead. I also used the Musical Fidelity XCan 3 for one comparison, but did not do a comprehensive head-to head.
I would first commend to you the SoundStage! review of this unit. With a couple exceptions I'll discuss later, it gets this unit right. Like most such reviews, it sounds like a shill job, but in this case, I don't think they are being overly effusive.
For me, I'll start with the prime directive of this unit - to be a headphone amp. If you have or are going to use the Grados, you're better off with the Total Bithead. First, they are a synergistic combination. If you know someone with a PC and a limited budget who is looking to get a taste of high-end audio on a budget, this is a pretty reasonalbly priced introduction. Frankly, if these are your headphones, moving up to a Portable Micro is not going to add that much to your experience. OTOH, if you can afford better cans, you will certainly be able to appreciate the advantages of the Portable Micro. The ER4Ps do a very good job, even with less-than-optimal sources. When portability is the priority, plugging them right in to the IRiver produces pretty reasonable results (Just don't use the IRiver remote. The design of the jack is an atrocity and it craps up the sound in ways I would not have thought possible). If you can stand just a slight bit of bulk, by all means insert the Micro Amp/DAC in to the chain. With these phones, it represents a major improvement. If, like me, you use this combo on a plane, it will be the most pleasant flight you ever had. The Etys are pretty sensitive, and don't need the extra juice of the Headroom that much, so I attribute much of the improvement to the superb DAC portion.
On to the headliner, the Senns. The combo of this and the original Total Bithead was a bit of a disappointment. Headroom must have understood the limitations too, as they issued an update with more gain. Never heard the new unit, but the old one didn't quite cut it. I'm not sure what cans Headroom used to develop the Portable Micro Pro/DAC, but if it turned out to be the Senn HD-650s, I wouldn't be surprised. This combination is dazzling. The Stereophile review of these cans describes the bass as being "indistinct" or something of that ilk. Obviously, they did not listen to them through this Headroom amp. Detail, top to bottom, is excellent. One downside of this is that I cannot listen to recordings of Glenn Gould or Keith Jarret through this combo, as their atrocious vocalization is too apparent to ignore. For everything else, this is a delight. I've always been a bit puzzled by the recurrent cliche of the audio press that a component is "ruthlessly revealing" of recordings that are less than optimal. Are those who use this phrase suggesting that they would sound better through inferior equipment? Rest assured that the Micro Amp/DAC contains plenty of Ruth as it reveals the details of the music to you. As a matter of fact, the Headroom/Senn combo made such a wide variety of music sound good, I wondered if it was contributing the infamous "euphonic colorations" to the source. Then I decided to stop worrying and enjoy.
This brings me to a point where I diverge from the SoundStage! review. On the issue of break-in, they state:
"I used the Portable Micro amp with DAC for a good month before I sat down to begin the review process. I wanted to make sure it had plenty of run-in time, whether it needed it or not. To be honest, I didn’t notice any great differences in the Portable Micro's sonics whether it came straight from the box or after a month's use. Maybe the sound was a smidgen warmer and smoother after some use, but I had to listen very closely to notice it."
When I first used the unit, I wondered if that exquisite detail was going to come at the expense of enduring an upper-midrange harshness that was often quite annoying. The helpful folks at Headroom suggested 50 hours of break-in. I found that it took about twice that much use for things to really smooth out. Don't know how many hours the SoundStage! folks actually used it during that month, but the change for me was unsubltle. I don't subscribe to all audiophile dogma (note the lack of discussion of cables) but this was a major change.
I don't use headphones much at home right now, and I haven't done a lot of traveling where I have had a chance to listen to music. This doesn't mean that I haven't had plenty of use from this unit lately. I have had to spend a great deal of time on my computer at home, and it has been an integral part of my desktop sound system. The SoundStage! review fails to mention this, but if you use the right adapter plug (which the ever-helpful Headroom staff helped me get) you can also use a coaxial digital source with the Amp/DAC. In this context, it becomes a DAC/Analog preamp. I take the output to a vintage-but-superb Aragon 4004 MK II. Isn't this overkill for the small, humble B&W bookshelf speakers? That's what I figured. I used the Aragon because I had it sitting around after an upgrade in my main system. I was unprepared for the superb depth and dynamics this system produced. If you don't believe me, try it sometimes. High quality, high current amps don't just benefit electrostatics and their ilk. I know the speakers are the weak link in this system and will upgrade someday, but it doesn't sound bad now.
Not to say that this system is all sweetness and light. I know that this isn't what this unit was primarily designed for, but as long as it has this functionality, a couple things need attention come time to do the first revision. Firstly, the volume control is a noisy POS. This is bad enough with headphones, but when your putting 200 to 400 WPC through bookshelf speakers, some mighty ugly sounds can ensue. If you do attempt using this apparatus as a DAC/preamp, keep one thing in mind. Don't do anything to the Headroom, including turning it on or off, plugging or unplugging anything, etc., with the power amp on. I am very fortunate that the Aragon has excellent protection circuitry built in to it. Also keep in mind that you cannot keep it plugged in to the AC indefinitely. Even if you do, it will abruptly and without warning go dead, resulting in awful sounds blasting through your speakers - regardless of where you have the volume set. It has no type of battery strength indicator, so unless you can employ your best precognizant skills, you will be hearing this noise. I wonder if this is where the White Stripes developed the inspiration for their album name "Icky Thump". None of this has, of course, deterred me in the least from using the Amp/DAC in this type of system. It sounds really good and, like I said, the Aragon has good protection circuitry.
Other thoughts:
S/PDIF inputs do sound better than USB, if you have a choice. You may have seen technical explanations for this. They know more about it than I do.
Up until I got this unit, I was never a big fan of Crossfeed. I thought the Absolute Sound reviewer who maintained that it was able to project a sonic image outside the head was smoking something better than I had access to. The sonic penalty it exacted wasn't huge, but it was enough to outweigh any other advantages. Clearly Headroom has been working on this. The negatives are now so negligible that the positive effects on some types of recordings are worth it. I still keep it turned off most of the time, but I definitely use it.
Even with high output sources, I usually keep the gain switch on high. It limits the useful range of the volume control, but I think it sounds a little better. It may just be that I'm not doing a real good job of volume matching during my A/B comparisons. I won't argue with anyone coming to a different conclusion.
I didn't compare it to the Musical Fidelity head-to-head as headphone amplifiers. However, since MF does sell a similar "tube buffer" which it purports to have a positive sonic impact when inserted in the chain, I did run the output of the Headroom through it and plugged the Senns in to the MF. The effect? Nada. My ears were unable to detect any sonic impact, positive or negative, from the MF. YMMV. Overall, I have a high opinion of both pieces, but they don't appear to augment one another.
Its battery life is excellent for a component of its type.
Most people who post on this site seem to have positive experiences with the sales/CS/tech staff at Headroom. Add my voice to the chorus.
Wish list for the next revision:
1) A volume control that doesn't sound like nails on a chalkboard when you turn it.
2) The ability to do something to the Headroom that doesn't cause awful noises when both it and a power amp are on.
3) A fixed volume line output for when you just need to use it as a portable DAC.
4) Some type of battery indicator, no matter how rudimentary, to warn you that all hell may be breaking loose soon.
These caveats aside, I am still very happy with this unit. With the possible exception of my IHP-120, it is the most versatile piece of kit I have ever owned. Most importantly, the sound is superb by any standards, and dazzling for a component of this flexibility at this price.
I guess this wasn't too concise. Hope you found it useful.
