Compact USB DAC with built in headphone amp [Based upon the manufacturer's specification page:...

Audinst HUD-mx2

Average User Rating:
  • Compact USB DAC with built in headphone amp

    [Based upon the manufacturer's specification page:]

    * USB 1.1 and USB 2.0 Full Speed compliant (VIA Vinyl EnvyUSB 2.0 Audio
    * S/PDIF Optical on TOS-LINK

    Resolution/Sampling rate
    * 16/24bit
    * 44.1/48.0/88.2/96.0/176.4/192.0kHz

    D/A Converter
    * 24bit / 192kHz, 123dB SNR (Burr-Brown/TI PCM1796)

    * National Semiconductor LME49860
    * TI OPA2227 and OPA2134

    Headphone Amplifier
    * TI TPA6120A2

    Headphone Impedance
    * 16~600Ω

    Line Out / Headphone Connectors
    * RCA / Stereo phone & Stereo mini (all controlled by front-facing volume control)

    Digital Out(S/PDIF)
    * Optical/TOSLINK out (controlled by front-facing volume control)

    OS Support
    * Windows XP / Vista / Windows 7 / 8, Mac OS X, Linux

    Dimensions/ Weight
    * Dimension : 100mm(W) x 120mm(D) x 29mm(H)
    * Weight : 260g

    Product Content
    * HUD-mx2 main body
    * USB cable (USB A to B type USB cable, 1.5M)
    * RCA cable (1.5M)
    * User Manual (including a warranty card)
    * Bumpon (plastic stabilizing feet)
    * Hexagon wrench (for attaching and detaching the volume knob)
    * Power adaptor (DC 12V~15V)

Recent User Reviews

  1. crabdog
    "Audinst HUD-MX2 - Still hangin' tough"
    Pros - Input options, Build quality, Smooth sound
    Cons - Lacks energy, Gain switching inconvenient

    Audinst is a name that will be familiar with many audiophiles but perhaps not so much with fledgling enthusiasts. They're a Korean company, launched in 2009 who found great success with the HUD-MX1 which at the time impressed many with its great sound and affordable price. Today I'll be looking at the HUD-MX2 which according to Audinst is "a product that realizes the best hi-fi sound quality, enhances user convenience, has diversified connectivity, and has most functionality relative to the price while not emphasizing on a fancy exterior and demanding specifications".
    This product was sent to me for the purpose of this review. All opinions here are my own based on my experience with the product. I'm not affiliated with the company in any way. I'd like to thank Audinst for the opportunity to test the HUD-MX2.
    Audinst website:
    HUD-MX2 product page:

    Packaging and accessories:
    The HUD-MX2 comes in a clean looking, white box with an image of the DAC on the front and on the back are listed some of the features

    Upon opening you'll find the Amp/DAC and included accessories:
    1. Power Adapter
    2. USB Cable
    3. RCA Cable
    4. Rubber Feet
    5. Allen wrench
    6. Spare jumpers x2
    7. User Manual
    The supplied cables are pretty good quality and should be enough to get you up and running fairly quickly. Overall the unboxing feels satisfactory and gives an impression of a good quality product that's designed more for function over form. This DAC means business.

    Build and functionality:
    Boasting the TPA6120A2 headphone amp the HUD-MX2 can be used with both low and high impedance headphones. The DAC is handled by the PCM1796 and OPA2227 op-amp. But enough of that. I'm all about testing with my fingers and ears so let's get to it.
    Now, onto the HUD-MX2 itself. It has a black aluminium case and silver front panel. The case feels well machined with smooth edges and a nice finish. On the front panel are the dual headphone outputs, 1x 6.35 mm and 1x 3.5 mm - very practical and adds versatility. Next to these is the output select switch that enables you to choose outputting to headphone jacks or the variable RCA line out which can connect to an amplifier or powered speakers. Then there is the source select switch which has 3 settings (from top to bottom) Optical, Off, USB.

    Next is a multicolored LED indicator which has three states:
    1. Red light: Unit is on but there is no source detected
    2. Amber light: Source detected but no incoming signal
    3. Green light: Incoming signal
    The LED stages are a small thing but in my opinion they go a long way towards a better user experience. Another thing I like about this is that the LED is not overly bright like on some units. The HUD-MX2's LED lets you know what's going on but most of the time you won't notice it's there unless you're looking right at it. Perfect.

    Finally on the far right of the front panel is the volume knob. It's clearly marked with position indicators, has a textured surface for extra grip and moves nice and smoothly. Overall the front panel is functional and attractive and thankfully the text on the silver face-plate is black. There are far too many manufacturers who continue to use white text on their silver models which makes it near useless so thumbs up to Audinst for getting this simple but important design aspect right.

    Moving around to the back of the unit we find from left to right:
    1. Optical IN
    2. Optical OUT
    3. USB IN
    4. DC 12-15V power IN
    5. RCA Variable Level OUT
    So before I go onto the sound I'll talk a little about my experience using the HUD-MX2. For the most part I think it's a great product but there are a couple of things that I would like to see changed in future revisions.
    First of all I'd prefer to have a Fixed Level RCA Output or a separate volume control for the line out. The reason for this is because if you're using line out to an amplifier you are likely to have the volume turned up pretty high. If that is the case and you have a low impedance headphone or earphone plugged in and flip the output switch without first adjusting the volume there's a good chance your headphones or your ears will explode. Well this could also work in the opposite if for instance you were driving some high impedance headphones with the volume up and then flipped the switch over to your powered speakers and BOOM! In my opinion it's a less than ideal implementation and that's why I loved the way it's done on the JDS Labs The Element. The second thing is not such a big deal for me personally but still frustrating - the fact that you need to open up the case and fiddle with jumpers to change the Low and High gain settings. I can't be all mad about that though because even though it's inconvenient, it is indeed an extra feature that many DACs don't have.
    The MX2 is not what I would consider aggressive or particularly energetic. It has a rather relaxed sound with plenty of musicality which isn't as detailed as some but adds some warmth. So for pairing these might work better with brighter or more neutral phones rather than something that's already warm. For instance this seems to have a better synergy with the Ultrasone Performance 860 than it does with MSUR's N650. Dr Dre's "It's All On Me" from the Compton album can be sibilant on a lot of setups but with the MX2 remains tame enough without causing discomfort.
    Soundstage is pretty good but not the best out there, probably due to the MX2 adding a bit of fullness to the sound. The treble is a little smoothed over too, taking away some of the airiness in its wake.

    When the HUD-MX2 first lifted its head, I think it was around 2013 there were a lot fewer options in the entry level range. Nowadays it has a lot more competition to deal with and might be starting to show its age a little. That's not to say it isn't a good DAC because it definitely is still good. It has some conflicting points for me personally though. On one hand is the sensible layout of the front panel (bravo for the black text on silver). Little things like the black circles around the headphone jacks that at once make it easier to see exactly where they are and also add a sense of symmetrical balance with the black volume knob on the right side. There's also the 3 stage LED indicator which is brilliant. It seems like someone put a lot of thought into this front panel. But then there's the volume knob that handles the output of the RCA out and headphone out which is far from ideal and the hassle of changing the Low/Hi gain.
    Regardless there's a certain charm to the MX2 both physically and sonically. It's smooth presentation is perfect for brighter headphones giving them that little extra body. The addition of an optical output is also something I haven't seen a lot but I think it's great, making it super easy to connect to my AV receiver. Currently retailing for $200 on Amazon UK the HUD-MX2 is still holding its own and for those looking for a DAC with a smooth, mature presentation this is still a good option.

    CivilianForever likes this.
  2. YoYo JoKeR
    "Audinst HUD MX2: The Versatile Little Champ"
    Pros - Design, Build, Features
    Cons - Value

    Me: I am a 21 year old Engineering student living in a small town in India. I would like to call myself a music enthusiast, rather than an audiophile. I was inspired by music since childhood, and as the time passed, the passion of music grew in me, and that subsequently led me to join Head-Fi. Eventually, I found the pleasure of listening to music mainly by the HD600 and recently, by the seductive LCD2 headphones, and realized the true components of recorded music. I usually like to listen to Indian Classical Music along with Bollywood songs. My main listening genres include classical, vocal, instrumental, jazz and sometimes pop.

    Intro:  Audinst, is a renowned Korean amp/dac manufacturer. They are based in Incheon, South Korea. The brand was established in 2009. The MX2 is the successor for MX1, and hence is the flagship amp/dac offering from Audinst. All their products are made in Korea.
    Specifications of MX2 as per Audinst:
    DAC Sampling Support: 16/24 Bit
    44.1/48.0/88.2/96.0/176.4/192 KHZ 123dB SNR
    Input: USB 1.1/2.0, S/PDIF Optical
    Output: headphone Jack, Line out, Optical out.
    Maximum power output: 1.5W @ 32 Ohms
    Headphone Impedance: 16-600 Ohms

    Let us see what the MX2 has got for us,
    Packaging and Accessories: The MX2 arrives packed inside a large colourful cardboard box, on which features and other information have been mentioned upon. Once the box is opened, the main unit and all accessories are put in a typical-amplifier’ packaging.  Accessories are found beneath a pseudo-bottom compartment. No complaints here. Nothing special to mention about; all accessories have a good quality, build and feel to them. The accessories are made in Korea too.


    List of accessories in the box, which include the following: 

    Power Adapter: Standard 15V 1A DC power supply for MX2.
    USB Cable: Standard black coloured USB A-B cable, about 1.5m length.
    RCA Cable:  RCA Male to RCA Male cable of 1.5m length
    Rubber Feet: For attaching to bottom surface of MX2, thus making it scratch and skid resistant.
    Allen wrench: To remove the volume knob (and hence disassemble the MX2)
    User Manual: Detailed and informative Instructions about operating the MX2, also contains warranty information.

    Design and Build: The MX2 has an excellent overall build quality.
    The outer case is made up of aluminium, and is painted black. Front panel is silver coloured, volume knob is fully metallic, and has a solid feel to it. In pictures MX2 looks larger, but in real, it is very nimble.
    On the front side,We have Volume control knob, input and output select switch, and headphone jack in both 6.5mm and 3.5mm formats. An LED indicator shows the status of operation. 

    On the rear side, We have USB input jack and a optical input jack, along with DC power input jack. As for outputs, RCA line out jack and optical output are present.

    Speaking of Internals, MX2 has a double sided PCB with no wirings. All components used are of good brands; including all dale resistors, Alps pot, premium caps. There are only two user replaceable parts on board the MX2: OPA2134 for Line Out.  OPA2227 for Differential.


    There is also a gain jumper, which if removed, sets the MX2 to a higher gain for 300-600 ohm dynamic headphones.  For planar magnetic headphones, IEM’s, low gain 16-300 ohms (closed jumpers by default) suits much better.
    Audinst provides two years warranty for the MX2; which again reassures us of the build quality of the MX2.

    Function and Features:  Important features of MX2, which distinguishes it from others:

    1) It can churn out 1.5W @ 32 ohms power output at headphone jack.
    2) MX2 amp/dac can run solely on 5V USB cable, and also on 12VDC power.
    3) It has both ¼” and 1/’8” headphone jacks.
    4) Intelligent LED indicator and interface.
    5) Optical interface support.
    This is an intelligent little box that does it all; it automatically cuts off USB power, once adapter pin is plugged in. We are able to connect all terminals, at once and later select the desired input and outputs without disconnecting anything. The provided dual headphones out jacks are very convenient, I don’t need to buy an additional adapter. Both the headphone outputs can work simultaneously.
    MX2 works wonderfully even on just a USB cable. This feature has really impressed me. There are a very few devices who can do actually do this. This feature makes it semi-portable, and a dedicated power supply not necessary. MX2 DAC supports 24/96 on USB connectivity, and 24/192 on optical connection.
    When LED is red, it indicates input line has been selected but not connected.
    When LED is orange, it indicates input line is selected and connected.
    When LED is green, it indicates, input is connected and active.
    MX2 gets slightly warm in temperature during continuous operation on 15V adapter. But when it is fed off solely on USB power, MX2 remains completely cool.

    Sound: As for the most important part, I feel the MX2 is slightly warm and dark in presentation. Sound-stage width is moderate. Depth is pretty good. The overall presentation is intimate.
    With 5V USB cable, Soundstage is little closed in and intimate. But surprisingly, the output power is still very good. With 15V Adapter, Soundstage opens out by about 20% and lows get tighter and accurate, along with more driving power due to sufficient power supply. Rest of the qualities remain almost the same. On IEM’s I could not make out any difference in sound by using the adapter, so we are good with the USB power. For headphones, best performance is extracted by using the given adapter.
    But with any combinations, there is slight audible hiss in IEM’s when MX2 is idle. There is a presence of audible background noise. I could also hear a channel imbalance at the beginning of volume control with sensitive IEM’s. Left channel starts up first, followed by right channel. I could hear clearly music from left channel, even when I had completely turned down the volume knob.
    Lows are strong and accurate but does not go deep enough. 
    Mids feel far-off and blown away, definitely a deal breaker for those who love vocals.
    Highs are a touch laid back and smooth, giving the final impressions about darkness in sound output.
    Soundstage on MX2 is modest and for some, lacking in width. Depth is fair. MX2 does not give a circular imaging, instead gives out an elliptical stage (with comparatively more depth and lesser width) Detail retrieval, and dynamics are decent enough.
    Also, the sound of MX2 can be manipulated by using different op-amps.  I have changed the Op-Amps and I could observe instant improvement in sound output quality.

    But even after this upgrade, MX2’s sonic output will remain titled on darker side. After trying out more than twenty op-amps on MX2, I rested upon OPA2111KP in Line out socket and LME49860 in differential socket, and I was better satisfied with the sound output. I also used MX2’s Lineout function, to connect a powered speaker system by RCA cable. It performed up to my expectations. Volume control is functional. Infact, I liked the sound at line-out more than its headphone taps. I like the Line-Out of the MX2 better than its headphone outs.
    Comparing the MX2 with O2/ODAC, I feel the latter audibly outperforms the MX2. The O2/ODAC is also more pleasant, relaxing to listen to; MX2 is slightly darker and feels congested sounding, whereas O2/ODAC is greatly transparent and neutral, with relaxed and natural soundstage.  Although the MX2 clearly wins in design, build quality, utility and features; But O2/ODAC wins, in what matters the most: The sound. O2/ODAC & LCD2 are a great combo, but I feel O2 lacks power to comfortably drive them. Though MX2 drives the LCD2’s better, but the pair has less synergry (owing to darker sonic output of MX2)

    Conclusion:  MX2 is an all-in-one device; this device is actually pretty great on features and practical aspects. I can recommend MX2 for enthusiasts who travel often. This little box will be very handy amp/dac as it won’t need any dedicated power supply at all, and is nimble and powerful. 
    I expected much better sonic qualities from this champ; I have to admit MX2 has left me disappointed and longing for more in this regard. But In 250$ range this device is pretty decent, and stands next to O2/ODAC.
    The Pros: 
    1) Design and Build: MX2 was very well designed and implemented. It has a very practical and versatile design and build.
    2) Functions and Features: This is the area where no other amp/dac outrun the MX2. The MX2 particularly excels in this category.
    The Cons: 
    1) Sound: Since the MX2 did not quite live up to my expectations on the sonic part, I will list it as a con. But it is not necessary that others too should not like it.
    2) Value: According to me, there are much better performing devices available around the same price tag as of MX2 (example: Aune T1, O2/ODAC, M/M) But the competition is really stiff, and ultimately the choice solely depends on requirements.


    2Dutch likes this.
  3. sopon
    "Audinst HUD-mx2 with Galaxy Note 3"
    Pros - The sound was quite solid and with good resolution.
    Cons - It is a pity that I should have a restraint in the place of use.
    Meet HUD-mx2

    As years go by, the smart phone became a vital part of our everyday lives and it is not much to say that the smart phone is a part of our lives. Although the smart phone causes many problems such as addiction to the smart phone, lack of conversation, etc., we cannot deny that it is an indispensable device. My life style is also changing little by little due to the smart phone. For example, about PC at home, I had turned on the PC every day before smart phones came into use. Now, however, I turn on the PC fewer times and solve almost all of the matters on the smart phone.


    I can read internet articles, watch dramas, movies and play games without turning on the PC. I enjoyed upgrading PC peripheral devices such as mouse, keyboard, PC speaker and sound card. But now, I naturally turn my eyes to smart phone peripheral devices.


    While I was watching dramas and movies on this smart phone, the thing that I have not been satisfied with was the sound. I recognized that the sound from smart phones reduced sensation of immersion. Of course, the simplest way is to put on the earphone. But I feel that it is also not satisfying. So I have looked for some audio devices to connect with smart phones, and most of the search results were portable speakers.


    In particular, blue tooth speakers attracted my attention, but they cannot but reduce sensation of immersion, comparing with earphones or headphones. Of course, I could be satisfied with speakers. But as the one who enjoys listening through a headphone, I wanted to look for a device to connect with a headphone.


    While I was making the search, I found DAC, which is compatible with Galaxy Note 3, i.e., a smart phone sound card, HUD-mx2 of Audinst. 





    It is with a small size of 100mm X 120mm X 29mm, which can be held by a hand. The body is made of aluminum case and the finish is relatively good.

    I feel that the exterior is in modern design, which is faithful to the basics. 








    Headphone output supports 6.3mm and 3.5mm, and they both have the same impedance. Perhaps they made two sizes to prevent the sound from being decreased in case a conversion gender is used. They both support 600 ohm. When gain jumper setting is not made, they basically support 300 ohm. If you have a high impedance headphone of 600 ohm, you can open the case and change the jumper. Anyone can easily change the jumper, reading the user manual. As my headphone is 3.5mm, it seems that I would mostly use the right one.


    Output Selection Switch

    As you may know when you see the selector, you can select one between headphone and line output.

    Line output is located in the back.


    Input selection Switch

    You can select one between optic input and USB input. They are also located in the back. And also you can select OFF in the middle. If you select OFF, sound output stops and it is converted to power saving mode. In the previous model, HUD-mx1, there is no OFF function. So this OFF function is a new one added to the subsequent model, HUD-mx2. You may think that the OFF selector is not an important one, but it is very useful to make you feel much more convenient. Just next to it, indicator is located. It is an operation lamp that shows current status by each color. 




    There are optic input and output ports, and next to them, USB port where PC/notebook/smart devices can be connected. The smart phone can be connected to this USB port through OTG cable.

    All devices generate heat when used for a long time, but the heat is not a level to be concerned about. I actually operated it continuously for 2 hours, and the device was warm rather than hot.

    There were holes in the both sides and in the center of the back. It seems they cared about heat generation. 





    Inside Composition

    Relatively strong internal composition

    I decided to undress the device. To undress the device, I need to take out the volume knob by using a contained hex wrench. I did not recognize the use of this hex wrench when I first saw the components. First remove the volume knob on the front side, and then, loosen the 5 screws on the back to see inside.  


    Push in the volume control knob, and then, PCB pops out to the back side. 


    VT1728A of VIA is used for the main chipset. By using EnvyUSB 2.0 Audio Controller, it supports USB input 24bit/96khz and samplerate of 44.1/48/88.2/96/176.4/192kHz. This VIA chipset may use exclusive driver, and can use Qsound and AC3 pass through function, and supports 24bit/88.2kHz, etc. This driver must be useful for the users who do not use it for pure DAC. Driver CD is not contained in the standard package. But an exclusive driver and user manual are in the official homepage of Audinst. 


    It realizes dynamic range of 123db and deals with 24bit/192kHz by mounting PCM1796 of Brown company. As the IC is widely used and it is not much to say that the IC is generalized, the IC is quite stable. 


    TPA6120A2 of Ti is inserted into headphone part for headphone amplifier chip. The chip is known to be excellent in driving force and ability.


    In low-pass filter part, film condenser of WIMA, exclusive regulator, low-ESR and tantalum condenser are adopted for stable power supply. In DAC power part, low-ESR and high performance solid condenser are adopted. And also, high purity TCXO, which minimizes signal instability due to temperature and voltage change, is adopted.


    It realizes the best balance, being mounted with LME49860 of National Semiconductor, the fixed SMD type OPAMP, and OPAMP OPA2227 and OPA2134 of Ti, the replaceable DIP type OPAMP, as basic. LME49860, which is in charge of the right and left side, is a SMD type part, so it cannot be replaced easily. But OPA2227 and OPA2134 of DIP type, which are in charge of final output, can be replaced by anyone. So you can easily tune the tone as you like. AS the OPAMP in the final output stage is designed to be easily replaced, you can feel the tone change by easily tuning the tone. Recently, most of the middle class DAC or sound cards are designed with replaceable OPAMP. 



    Connection with Galaxy Note 3

    To connect with Galaxy Note 3, OTG cable is a must-have item. The way of connection is shown well in the figure in the user manual. Seeing the way of the connection to the smart phones in the user manual, I feel that that they want to stress the relevance between HUD-mx2 and smart devices.

    The important thing here is that you must connect an adapter. You may use it through USB, without an adapter, on PCs or notebooks. But when the device is connected to smart phones, it seems that the device works only when power is supplied separately. 







    Headphone: ATH-A700 (Impedance 38ohm)

    Smartphone: Samsung Galaxy note3


    I feel certain that the sound becomes solid and clear when I listen to through HUD-mx2. I feel that the sound is crushed down when I listen to only through smart phones, not through DAC. But I feel clear difference in the sound with DAC.

    In particular, I feel that the high-pitched sound is clear and well-arranged without bouncing. High-pitched sound may easily become sharp, but the sound through the device is felt well-arranged. When I listened to jazz and violin music, I could recognize the fact better. While I was watching the movie, I might say that the dialogues hit the ears better as the voice was clearer.

    While I was playing the games, effect sound, i.e. feeling of hitting, was not bad.


    The sound may be felt differently depending on headphone/speaker, sound source and the propensity of people. But in my humble opinion, people may get the above feeling in common with HUD-mx2.


    In conclusion, I am satisfied with DAC in the aspect of doubling the sensation of immersion as I intended in purchasing it. But an adapter must be connected to use it with the smart phone. So I felt inconvenient as I should be around the socket to get supplied with the power. I wish it would be a portable product that can be connected to smart phones without an adapter. Of course, I could understand the point as the device is mainly for the use with PC/notebook, and the use with smart devices is a subsidiary application.

    I want to compare it with other OPAMP later, if any. But as I am somewhat satisfied now, I will try later.




    HUD-mx2 DAC is mainly for the use with PCs or notebooks. But I use the smart phone most of the time, and so, it seems that I will use the device mainly for the smart phone. I listened to the sound through the device on PC, and I felt similarly as in the case of the smart phone.
    In my humble opinion, the sound was quite solid and with good resolution.
    As I said above, the sound is evaluated very differently and subjectively depending on the output device and propensity of people. So other people may feel differently from what I felt.
    It was an inconvenient point that an adapter should be always connected to use it with the smart phone. In order to use it, I should be always next to the socket. There is no trouble during using it, but it is a pity that I should have a restraint in the place of use.
    Considering the use with smart devices, I hope that a portable DAC is made in the next time.

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