UPDATE - 05/06/08 11:50PM: 7 USB DAC AMPS - ADDED HR Micro Stack Portable
(1) The Headroom Micro DAC and Micro AMP, 2006 version, AKA HR Micro Stack portable:
The HR Micro Stack came into my possession the first week of March, and I initially considered including it in this review, but I wanted to focus on the newer smaller combination portable USB DAC/amps first. Headroom now has a 2007 Micro portable DAC/Amp for $598; but the DAC chip is different, and they admit that the new Analog Devices DAC is a slight downgrade from the 2006 portable with Cirrus Logic CS4398 chip (they claim the 2007 desktop Micros with the CS4398 are still as good or better, but without 9v battery power).
This is a fairly large (for portable) two-piece set, with a separate DAC and matching Amp section. When strapped together with the optional Micro-Strap they act as one large unit and take up a 3W"x4D"x3H" piece of desktop. That is bigger than the iBasso D1, so it certainly wont fit in your pocket (not even a coat pocket), and is really what I would call transportable. Even worse, this means you get two medium-to-large sized power bricks, with proprietary connectors on the amp and DAC side, and no internal charging circuit. You have to buy a separate battery charger, and the one I have can only do two 9v at a time. Yikes. I haven't tested battery life, but I have read tales of the amp chewing through a pair of 9v re-chargables in 8 hours, and the DAC lasting maybe twice that. I will try to test out the 9.6v re-chargables that HeadRoom sells soon. See a recent previous post for battery life of the other amps reviewed.
I now have about 400 hours on the Micro Stack, about half from just regular use of music and not running it 24/7 after the first 180 hours. And I just feel that I need to add this to my review, and to let people know what to expect if they buy a used one down the line. There are a fair number of these out there, and they don't go up for sale used very often, and there is a good reason for that - they sound good.
I did my comparison against the Pico, and planned to pull out one of the other amps should the Headroom fall above or below the Pico, but I made a lucky guess and found them to be fairly equivalent. I used all the same program material, and listened with my RS-1 and D2000 (my HFI-780 were with mrarroyo at the time).
The HR Micro Stack via USB reproduces vocals and real acoustic instruments well, with no colorations and drop outs. Diana Krall was smooth, without sibilance, but female vocals and saxophones were just ever-so-slightly cooler than I like. Pianos were sharp with quick attack and smooth decay, and were not piercing. The sound does not seem boosted or sucked out in any areas.
There is a nice sense of ambience and space around the instruments, without making the venue sound cavernous (or microscopic). Rather, it is just right. With classical music I dare say it can recreate the large hall ambience slightly better than the Predator, and it reproduced the Cathedral-sized venue for Handel's Messiah as well as the Pico did. With smaller nightclub venues, and studio recordings, the ambience and dynamic range was good as well. I did not hear the sound of the instruments or the echos disappear too fast like with the Lyrix USB DAC (or Travagans Green).
Switching to optical digital, I can hear slightly better air and ambience with Headroom's optical input and my Macbook. I should note that while optical is a little more transparent, the USB performance is still pretty darn close to optical. Even when playing native 24/96 program material from Linnrecords.com Hi-res downloads, and setting the Macbook optical output to 24/96, the differences in sound between the HR optical input and the USB input of both the HR and Pico were fairly small (maybe a 5% improvement).
So, what about all my previous postings about the Micro Stack being a warmer and more musical setup, if it really sounds like a Pico? Well, I use the Micro Stack with crossfeed switched on 90% of the time. And the HR Micro Amp's sound warms up when you hit the crossfeed, even more than the Lyrix does with crossfeed. Whether it is better that way depends on the listener, the source, the program material and the headphones. With crossfeed off, there is very little difference in sound between the Headroom Micro Stack via USB and the Pico via USB. However, the HR Micro Stack is just a bit richer in the mids than the Pico when crossfeed is on, but also sounds slightly rolled off in the highs with crossfeed (more rolled off than the Predator). To my ears, the Lyrix and HeadFive tend to lose a little of their air and ambience when crossfeed is on; but the HR with crossfeed still seems to retain decent space and ambience, despite the slight rolled off highs.
Basically, via USB the $598 HR Micro Stack's performance and sound signature were similar enough to the $499 Pico to call it a draw. But, the optical S/PDIF digital input adds a small additional layer of ambience and transparency to the sound. The trade-offs for the gains with optical are bigger size, inconvenience of recharging batteries externally, out of production and higher cost. This is great for my iRiver and Sony portable CD Player with optical at the bedside. But if you are putting together a computer only rig and just wont use the S/PDIF inputs, then there are better choices reviewed here that will give you great sound in a smaller and more convenient package. If you need the crossfeed on a computer-only rig, get the 2MOVE - although it's affect was more subtle than Headroom or Headfive, it did not seem to affect the sound signature much, or cause a roll-off in the highs.
(2) Some notes about the Lyrix Pro USB Total, Lyrix Pro (and it's little brother the Caffeine Pro):
I've had several inquiries about the Lyrix, whether it is the DAC or the Amp that holds it back. I believe it is the DAC that holds it back, even though the DAC sounds better than headphone out of a 5.5G iPod or Macbook (which not surprisingly sound similar to each other and could use improving). It also confirmed for me how important burn-in is with these small amps, as I got to compare a new vs 500 hours side-by-side.
Let me preface by saying the Lyrix Total Pro needed about 70 hours burn-in to open up and smooth out, then about 200 hours burn-in to get to 95% of it's potential, and after 300 hours there were few if any changes to the refined smooth accurate sound they produce. Interestingly, I couldn't hear much change when flipping on the crossfeed when new out of the box, or even in the first 70 hours. By the time I had 200 hours on it, the effect was more audible. Other people have reported the same findings with the Lyrix crossfeed vs burn-in.
When I got an extra Lyrix Pro for my son a couple of weeks ago, my Caffeine Pro (basically the same amp) and Lyrix Pro USB Total had over 500 hours each. In comparing the new one I could hear the constriction in soundstage, less warmth in the lower mids, and a slight coarseness in the highs. Now, at 150+ hours it is pretty hard to tell the differences between Lyrix Pro and the Caffeine Pro, while there is still a slightly more refined quality to the sound of the Lyrix Total. The warmth in the lower mids doesn't seem to develop in the Lyrix till after 150+ hours of burn-in, and while it is still a little behind that of the Predator, Pico, 2MOVE or Headroom, the amp section by itself is close to the HeadSix and still ahead of the stock iBasso D1 or D2.
(3) Because of all the questions about whether the main differences in my review are from the DAC or the Amp section, after I got my D1 back from iBasso I briefly listened to most of them with analog input from an iMod, instead of via USB DAC. (except the 2MOVE which I don't have)
People keep forgetting how close they are already, as I've said many times, and I love them all. There isn't a big difference between an amp rated 9.4/10 and a 10/10 (which is where most of them sit). So, as expected the sound quality of most of the amps via analog input is just as close as when using their internal DAC (the exception is the Lyrix amp-only is now better than a stock D1 or D2).
Although their basic sound signatures remain mostly unchanged, using the same source (the iMod's DAC) slightly lessens the differences into just their own essence or flavor, what we call sound signature. The differences in sound quality would still be in the single digit percentage points, and subject to personal preferences (except the stock D1 with analog input is not terribly impressive - it really needs the DAC or new opamps to wow you).
Nice one.
