Pros: Small, has both headphone connection sizes, nice volume control, RCA line-output , switchable op-amps
Cons: ... not much... weird flashing light... not much else at this price.
I just finished writing about the HUD-Mini for my blog, I will paste it in here for easier viewing. Enjoy :)
The HUD-Mini is Audinst's second ever combined DAC & headphone amplifier. The relatively new Korean company may be unheard of in traditional hifi circles but for afordable USB audio their first ever DAC/amp (the HUD-MX1) has made quite an impression.
As the name suggests this new model is smaller than their first. Apart from the size the main external change is the lack of a mains power connection. Internally the DAC chip has been changed to the PCM1791a (the HUD-MX1 used the Wolfson WM8740). Compared to the HUD-MX1 the Mini's price is nearly 30% less (£82, compared to £115), but it retains both the small & large headphone connections as well as the RCA line-outputs. With a very low THD+N distortion value of 0.00003% the Mini seems like a refinement of the HUD-MX1's specification. So does it all square up to make the HUD-Mini better value for money, or is it just a cheaper alternative?
Like the HUD-MX1, the HUD-Mini sounds nicely neutral and transparent for their price. Compared to a PCs on-board sound every element of audio quality is improved with the HUD-Mini. The bass is more powerful without becoming boomy or flabby, the detail throughout the frequencies is tighter and more focused. The midrange / vocals get more clear and musical, without feeling overly forward (louder). Treble is well Controlled, but perhaps lacks a little sparkle compared to some of the competition. The soundstage gets wider and deeper making music feel more three dimensional. Volume wise there is not a lot available here, it obviously can't compete with a mains powered DAC/amp, but in the volume department this is by far the least capable, even of all the other USB powered options that I've tried. My laptop managed to get louder at 50% volume compared to the HUD-Mini @ 100%. Plugging in the 600 ohm Beyerdynamic DT880 produced modest volumes for most music (not Classical) with the HUD-Mini at maximum, as long as the surroundings are quiet.
After reading Mike's review of the HUD-Mini, on Headfonia.com, I decided to try a couple of different op-amps in the Audinst HUD-Mini*. The above sound impression is with the default LME49860 op-amp installed (out-of-the-box). Here are my impressions of the Audinst HUD-Mini with two different op-amps installed...
SOUND: (OPA2227p op-amp) - £5.90
I noticed a small change here, the sound seemed to open up a touch (better soundstage). The bass got a little nicer too but this was slight and the problem with comparing here is that you can't do it too quickly. After unplugging the USB, switching the chips, restarting your software and then listening to the same track again you tend to forget the little details. I also liked to put the chassis back together again before listening too, but maybe I'm crazy.
Unlike others, who have commented on this op-amp switch, I didn't notice any change in volume between this and the default one.
NOTE: You can now buy the HUD-Mini directly from Audinst (eBay) with the OPA2227p already installed here and only for a couple of £ more, that's nice!
SOUND: (OPA2111KPG4 op-amp) - £10.60
This op-amp is described as a 'Dual Low-Noise DIFET**' whereas the OPA2227p was a 'High Precision Low Noise'. Make of that what you will, but I noticed a bigger change here than with the OPA2227p. As well as the soundstage opening up a bit more I found the midrange to get a bit brighter / more forward. The bass got more plump and the treble gained a healthy sparkle. Generally this was my favourite presentation of the three. It seemed to give the biggest improvement to Electronic, Metal and anything with strong vocals. The volume also improved with this op-amp, enough so that even the 600 ohm Beyerdynamic DT880 became usable. Classical music was also capable of acceptable volume, as long as background noise was fairly minimal and the HUD-Mini's volume is near, or at, maximum. These are open back headphones after all (OK so technically they're semi-open but really they sound more open than closed). I still advise caution with tough to drive headphones though, I would not describe the maximum volume as 'loud' here, even with this op-amp, and there are people who prefer higher volume levels than I do.
** DIFET = Dielectrically-Isolated Field Effect Transistor (just in case you're curious, I was :P)
Previously I've avoided talking about specific music tracks in the DAC and amplifier reviews. I was worried that it would get confusing, but I'm going back on this as I feel it will help better describe certain sound characteristics.
- Tony Bennett: "I Left My Heart in San Francisco" - This has an enjoyable vibrancy to the mix of vocals and piano. Tony's vocals come through clean, crisp and well rendered. The soundstage is a bit flat. With the OPA2111KPG4 op-amp the mid-tones feel more forward but also a little sharp / lack a little smoothness.
- The Crystal Method: "Born Too Slow" - Feels lively from the get-go. Like before the vocals feel clean and well defined, but with more going on here it's even more impressive that they still hold up through all the punchy electronic elements.
- Deftones: "My Own Summer" - I quite like how the guitar sounds grainy and quite forward here. Again this is mostly true of the OPA2111KPG4 op-amp, it also feels like it's making the presentation faster. There isn't an abundance of authority here, but clarity, detail and midtones are all quite impressive.
- Mozart: "Clarinet Concerto in A, K.622 - 2. Adagio" - This performance felt very engaging. The delicate notes from the clarinet feel solid and smoothly presented. When the strings come in there is a nice feeling of space between the instruments.
- Ramin Djawadi: Medal of Honor "Watch Your Corners" - This track starts with some nicely presented soundstage elements. There is a nice slam and texture from the low frequencies throughout the track that does well to immerse you into the action. The HUD-Mini also does well not to get too congested and overwhelmed towards the end of the track when the full orchestra comes in hard.
- Black Sun Empire, SPL: "Wasteland" - I was a little disappointed by a slightly flat feeling from the few opening instruments, but when the everything kicks off thing gets a bit more exciting. It impresses with punchy bass and quite a dynamic sense of depth.
I own most of these songs on CD, they are ripped as lossless files and played on a PC. The audio is output through a generic USB cable, using WASAPI - event style on JRiver's MC17 - buffering from the RAM. I also chose these songs because they're on Spotify, so if you have a premium subscription you should be able to find them easily and check them out for yourself in decent quality.
The Fiio E17 shares a similar footprint to the HUD-Mini. At £100 the Fiio is a little bit more expensive, but can be bought in Europe. Ordering the Audinst directly from Korea is highly likely to bring you a customs charge which will most likely bring it over the price of the Fiio so for now I will say the prices are roughly equal for arguments sake.
The feature sets for these two units are quite different. The Fiio E17 has a S/PDIF digital input that takes 24bit/192khz and a battery for using the amplifier only so makes more sense if you want to boost the sound from an iPod too. Lastly the Fiio E17 has bass, treble and gain control, changed via it's on-screen display. I don't put a lot of stock in the bass and treble manipulation but the three levels of gain make the Fiio E17 a better option if you have hard to drive headphones. The Audinst has a nice analogue volume control, a S/PDIF digital output (a bit niche perhaps) and RCA outputs. The latter of which make it easy for connecting the DAC up to an external amplifier and speakers.
Sound wise I found the Audinst to outperform the Fiio E17, this was reasonably noticeable even with the default op-amp, with either of the other two op-amps it gets better still so if it's purely sound quality you are after here is where my recommendation would be.
The HUD-MX1 has a bit more sparkle, a greater presence and a more impressive soundstage. If you are willing to change the op-amp in the HUD-Mini then the audio quality will improve but it won't do miracles. The OPA2111KPG4 gets the closest to the quality of the HUD-MX1. The HUD-Mini makes a great budget alternative to the HUD-MX1 whichever way you slice it.
Feature wise the two Audinst DACs are similar. The HUD-Mini cannot be mains powered. It also lacks the gain control from the original model so it's not a great option for demanding headphones (300-600 ohms are mostly out). Also note that the RCA line-outputs of the HUD-MX1 are controlled via the volume dial whereas the ones on the HUD-Mini's are fixed. If you have active speakers with no volume (or volume controls on the back) then the HUD-Mini is not so useful.
The chassis quality is not going to give Fiio anything to worry about but the strength and design are respectably solid, simple and clean (especially on the inside). I really appreciate the analogue volume control over buttons here. The dial is almost identical to the one found on the HUD-MX1, which is a precise feeling, rubber coated dial with an nice 'Alps' potentiometer at the core.
I really like not having to use adapters when I use headphones, especially with the larger (6.35mm / 1/4"), so I prefer it when amps use the larger connection. Admittedly most headphones use the smaller one, its much easier to convert up rather than down. No need to worry either way here as both sizes are included natively. If only more of the competition followed Audinst's example.
The S/PDIF digital output here seems a bit superfluous. I can't imagine many people buying the HUD-Mini, only to avoid using it's DAC and headphone amplifier just to pass-through the digital signal to another format. It's useful if you have an older DAC that doesn't have USB sure, but there are loads of cheaper & better options for this. An alternative digital input would have made more sense to me but then they would have to put the mains power option back in, or included batteries like the Fiio E17.
The RCA outputs are a very welcome addition for anyone with desktop speakers or an integrated amplifier and a desire to connect it to a computer. I plug these straight into my AE desktop speakers and it brings a nice boost to their sound quality too. Audinst even include a basic pair of interconnects in the box to get you started too, brilliant!
* Taking the chassis apart is very easy, which is great because of the op-amp switching (mentioned above). There is only one op-amp in the HUD-Mini to play with so it's not going to break the bank, or take long. If you want to experiment here are some instructions:
Remove all four screws (2 front & 2 back), the back panel will fall off but the front one will not. The easiest thing to do then is - grab the front panel and slide out the PCB (Printed Circuit Board). Once out a little way you'll be able to hold the PCB by it's sides and pull it right out.
You will probably want an IEC Extraction Tool for pulling out the op-amp, otherwise it's a bit tough to remove. The pressure needed to remove & install the op-amp barely flexes the PCB as it's pretty thick. This operation feels pretty low risk, this was my first attempt and it wasn't too scary.
OK one other thing I have to mention... The indicator light on the HUD-MX1 was 'orange' when plugged in and 'green' when playing something, this was fine. The HUD-Mini however flashes between both colours continuously when playing. Apart from being a bit distracting it doesn't interfere with the user experience, but what hell is this about?
The HUD-Mini is a great performer, giving a substantial audio quality boost to a computer's on-board sound. With great connectivity (both inputs & outputs) and a small & light chassis it makes a great companion for a laptop too. Both of the Audinst DAC/amps are a good buy for their respective prices but with a bit more to spend they soon work their way off the top of my recommended list. For around £150 things get a lot more interesting, but lets be more sensible for a second...
The HUD-Mini betters the already impressive Fiio E17 on sound quality. It might end up costing less too (depending on customs). If you can live without the Fiio E17's other features then the Audinst is a clear winner. Comparing the HUD-Mini to it's bigger (and older) brother is a bit harder. The sound quality doesn't quite better the HUD-MX1's, even if you change the op-amps, but then it is cheaper and smaller. If you can afford the HUD-MX1 then it makes sense to ignore the HUD-Mini. If however the HUD-Mini just fits into your budget then it makes a great choice. You can always spend a few extra notes later down the line to play with op-amps if you're that way inclined.
Here are some images comparing the Aundist HUD-MX1 to the HUD-Mini...
As you can see the size has changed a bit. Apart from the Mini having less writing it only loses the power adaptor socket. The chassis of the HUD-Mini hasn't come down to the realms of the Fiio units, but they they do still have the larger USB, both sized headphone connections and RCA line-out's which make it great for desktop use.
Here are a couple pictures of the internal circuitry to show the op-amps and tools...