Audinst, makers of the popular HUD-mx1 and AMP_HP units, released a new device recently called the HUD-mini. It's even smaller than the mx1, and sells for a lower price too ($129).
I've had this little guy in for review for a while but have not had a chance to write anything about it yet. I still haven't finalized my opinion about it, but I'm starting this thread for general info, and will eventually add my final thoughts.
The mini differs from the mx1 in several ways. First off is the size - the mini is about the size of a portable amp (in fact it is barely larger than their AMP-HP). The mini uses USB power only with no option to add an external PSU like the mx1. It also has fixed RCA outs rather than variable, which will actually be considered by some as an improvement. The mini has a different USB implementation, the VIA VT1728A, that can accept all sample rates up to 96kHz - the mx1 has a Tenor TE7022L which does not handle 88.2kHz data. They make a big deal of pointing out this fact which makes me think they had a lot of complaints about the mx1. Which is odd because 88.2kHz is a small subset of hi-res music, which is itself a growing but still relatively tiny selection of most music. In any case I'm glad it is supported now.
Aside from that, the mini shares a lot with the mx1. It has dual headphone jacks for 1/4" and 1/8" jacks. It has a switch to go from RCA out to headphone out. It uses the same volume knob and I believe the same potentiometer as well. Both have a Toslink output which means they could be used as a USB to SPDIF converter in addition to their DAC and amp duties.
The HUD-mini is based around a TI PCM1791A DAC chip clocked by a quality TCXO oscillator. It uses a National Semiconductor LME49860 for DAC output and an Analog Devices AD8397 for headphone output. I believe they are socketed just like the other Audinst gear but I need to open the case again to double check (it's been a few weeks since I looked).
I removed my Audiotrak DR.DAC2 DX Muses Edition from my desktop setup, and replaced it with the HUD-mini. RCA outputs connected to the Emotiva Airmotiv5 speakers, and headphone jack was used with a variety of headphones - VMODA M80, Heir Audio 4.A, HiFiMAN HE400, and others. I did try some of my higher-end headphones but I tended to stick with the lower priced stuff, since it makes better sense that the HUD-mini would end up being paired with more entry level (but still good!) headphones rather than flagship models.
The first thing I noticed was that I missed the preamp functionality of the Audiotrak unit or the HUD-mx1. The Airmotiv5 active monitors have individual volume control on each speaker and it becomes somewhat annoying to try matching them precisely. Aside from that, I didn't immediately feel underwhelmed by the sound. That's impressive because the Audiotrak unit is nearly three times the cost of the HUD-mini. I did feel a loss of soundstage definition, and a bit of a "smoothing over" of the sound compared to the more detailed and revealing Audiotrak unit. But overall I was not shocked by the change, and after some time for mental adjustment I was quite satisfied with the sound made by the little HUD-mini.
It seems quite capable of driving a wide range of headphones, from sensitive custom IEMs to the planar HE400s. The sound is clean and mostly clear, with just a small reduction in detail compared to more expensive units. I did notice that the mini doesn't play as loudly as the mx1 when it comes to higher impedance headphones. I tried the Sennheiser HD650 (300 ohms) as well as a 600 ohm AKG K240DF, and neither of them got very loud. Certainly not as loud as the mx1. But I would not hesitate to use the HUD-mini with any IEMs, Denons, Audio Technicas, Ultrasones, or anything else that we consider "lower impedance" headphones.
As with the HUD-mx1, the HUD-mini is capable of delivering the essential experience, and it falls short in areas that are not offensive. So while you do miss out on some things like top end airiness and soundstage expansiveness, you also miss out on the undesirables that some budget items have - top end glare, flat dynamics, loose bass, or clearly unrealistic timbre. The HUD-mini is a solid starting point for someone new to this hobby, or even a suitable "2nd system" for an experienced audiophile to use at work or in a bedroom rig.
I'll have more thoughts as time allows, including pictures. Any other early HUD-mini users feel free to post here as well. eBay shows that they have sold 30+ units already and probably more from their direct web store. I imagine that most early users would be HeadFi members as well, so maybe we can have them chime in.
UPDATED IMPRESSIONS - 9/17/12
So I've spent some more time with the HUD-mini and have come to some fairly solid conclusions. I still need to take more pictures and add them but for the most part this is my final review.
Essentially, I've listened for a good amount of time and come right back where I started - as stated in the above section, this is a good sounding unit if not quite reaching amazing/giant killer status. I compared it quite extensively to the original HUD-mx1, and I don't notice any major differences between the two. In fact I think that the HUD-mini is in some ways superior as a DAC - I hear a slight improvement in terms of inner detail. Background events, like the cough in the first few seconds of Stravinsky: The Firebird Suite - Infernal Dance (Eiji Oue and Minnesota Orchestra), come through a little more clearly, while the exceptional low frequency impact hits just as hard if not a bit harder.
Speaking of this track: I played the version from the Reference Recordings HRx format, which means high-resolution 24-bit/176.4kHz. Since the HUD-mini tops out at 96kHz sample rate, it can't play this file in the native format. But it can handle it when software downsampling is applied, resulting in an 88.2kHz sample rate (exactly half the native rate). This presents a much easier and cleaner conversion, and the loss of fidelity is negligible. In comparison, the Audinst HUD-mx1 can't handle the 88.2kHz sample rate due to its USB receiver. That means it has to A) convert to 96kHz which is not an integer and thus requires manipulating the data more than is optimal, or B) reduce all the way to 44.1kHz, which is a 4X reduction in sample rate. Does it still sound good when played these ways? Yes. I'd be lying if I said it sounded terrible. But the HUD-mini is superior.
So aside from that track, what is the sonic character of this device? For the most part I'd call it clean and neutral, while erring on the side of being a little forgiving. This is appreciated because at times I hear a hint of digital grain or grit on the top end. So I'm glad they didn't try to push this as a hyper-revealing device. That would not have worked as well for my tastes. Overall the sound is on par with what I'd expect from an entry level CD player: think NAD C515BEE, Cambridge Audio 350C, or maybe even the excellent Marantz CD5004. Obviously these all have their own unique sonic character, and I'm not saying the Audinst HUD-mini is exactly like any one of them, but it does play in the same league. And that's impressive. Audinst has the advantage in that they don't need to spend their budget on a large enclosure, LCD display, remote, or a disc transport mechanism - all things that CD players need but compact USB devices don't. This means they can pour a larger majority of the budget into the audio circuitry and still keep a lower price than those other units (which all go for $350 or so). So I consider that a good thing.
I do have to say that while I think the HUD-mini may be slightly better than the HUD-mx1 in terms of DAC performance, it ends up being not quite as good in the amplification section. The difference is small and not easily noticed unless using more difficult headphones such as the previously mentioned 300 and 600 ohm models. Even if we discount the maximum volume difference, the HUD-mini still sounds a little "soft" and indistinct with those headphones. Using IEMs or low impedance headphones returns the two devices return to equality, again with the mini possibly being superior due to the DAC section.
Overall the Audinst HUD-mini is a worthwhile device for the $130 asking price. It gives you a good amount of performance for a small amount of cash, and has a lot of convenience as well - the USB to SPDIF (Toslink) conversion is handy to have, and the integrated amp is respectable.
I'm still not quite sure who this is intended for; the mx-1 is similar enough to where they might be creating competition for themselves. Then again the mini is smaller so perhaps they intended that to be the defining characteristic. In any case, Audinst has another winner on their hands and I'm happy to recommend it for newcomers to the hobby or anyone needing a small 2nd setup.
Edited by project86 - 9/27/12 at 1:13am