Audinst HUD-mx2


Headphoneus Supremus
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
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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.

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YoYo JoKeR

100+ Head-Fier
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.
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List of accessories in the box, which include the following: 
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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. 
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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.
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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.
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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:
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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.
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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.
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New Head-Fier
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. 


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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. 


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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. 



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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. 


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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.  


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


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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. 


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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. 



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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. 



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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.


100+ Head-Fier
Pros: Neutral and almost nothing to complain really
Cons: Soundstage, No bass boost
Audinst HUD-MX2 reached Earmass!
Audinst HUD-MX1 must be the most recommended budget entry audiophile DAC/Amp combo, while they are still a good DAC/Amp combo, but after years they are better players and competitor keep popping out in the market.
This is a good time Audinst make their announcement that they released the long waited Audinst HUD-MX2 that Earmass will review today. Thanks Audinst for sending me this review sample first of all, congrats to makes us a replacement/successor to the HUD-MX1.
Outlook and Packaging
Pictures talk million words.
Included accessories are hefty
Packaging Box
MX2 is very versatile and easy to use.
Pairing headphone/Iem with HUD-MX2 is quite easy, it is neutral and give body to the sound, which in my opinion, is the best sound signature that I want.
Although it can powered Beyerdynamic DT770 Pro 250 Ohm  up for good and beyond listen sound level, but I have to turn the volume more than half (About 70%) of the maximum volume, which I don’t like. But power wise, it is indeed quite good and enough for most of the users.
I paired it with Creative Aurvana Live!, Sony MDR-1R, Hisound Wooduo 2, Koss KSC75, Yuin PK1, Thinksound TS01 and TS02, RHA MA350, NuForce NE-700M, all get fairly good to excellent sound. I love how MX2 cope with IEM and low impedance headphone.
From Left to right, 6.25 and 3.5mm headphone jacks, Headphone or speaker selection switch, Optical or USB input switch, Volume knob
Generally I have nothing to complain on sounding of HUD-MX2, why? Let me dig it up one by one.
From Left to right, Optical in/Out, USB input, DC power supply in, RCA output jack.
High : Treble is quite crisp even with headphone such as Creative Aurvana Live!, treble is crisp and extension is great and quite smooth. Some sibilant can be detected during the review session.
Mid: Midrange is good and expressive.
Low : Quite neutral but provide good quality of bass, punchy and deep.
Sound Signature : It is quite laid back I can say, not as lively as I like. To be said, it is quite neutral but not boring, it is just that MX2 will not bring the music as front as most of the amp do. However MX2 will give body to sound and quite enjoyable to listen to. I am not particularly surprised or whatsoever in the first time when I listened to MX2, but this is not a bad thing as MX2’s voicing allowed me to listen to music for a very long hours.
Neutral sound signature
Sound Stage : Sound stage is just normal. Not really big in size, anyway, it will not give you in the head feeling though.
I like how Audinst do for the sound so far. All seems right in place, price to performance ratio is great as well. MX2 is extremely versatile and will work in almost every way you connect it. You cannot use it as portable DAC/AMP though, it does not have an internal battery. But this is no big deal, it can powered directly by USB power and choose to use the included PSU, to be frank until now I have not plugged in the PSU yet, why? Because I am enjoying the convenience that with just a single USB output you can enjoy a good DAC with a headphone amp. I know this is quite common but I appreciated this convenience that Audinst provided.

Besides, Audinst had also features that more than I can use, such as a pre-amp for speaker and connect with ipad. An optical (Use Optical input can support bit rate to 24bit 192) input/output, also RCA output (so that you can just use the DAC section), MX2 has strike me with a lot of conveniency and flexibility.
Speaking of the matters of sound, it is good and performed solidly, For sure I can’t compare with something as big and as expensive like YuLong Audio D100 II. But if I did, the differences is clear, so no means for me to comparing them.

I compared it with iFi Audio iDAC (50USD more expensive than MX2) which can be powered up using  USB power as well, I still think that iDAC is a better choice although iDAC hiss and has more noise floor (For the amp section), but iDAC stunned me with lively and vivid sound (Also better sound staging) that I wished to have for MX2. If you are going to pair with IEM, I will say MX2 is a good choice already though.
I hooked up MX2 with Hisound Wooduo 2 and Thinksound TS02 at office, MX2 never stopped impressed me with hours of good music from my office computer. MX2 is easily transportable and light as well, so I have no problem at all to carry it everywhere, and I know that as long as I plugged in the USB power to MX2, I will not be disappointed by bad quality of music.
Nice little box
Sound is indeed neutral and clear, with good amount of detail. MX2 will add body to the sound which is always a good thing, also provide some reasonable sound stage. MX2 does not have some true shine point nor weak point, it just sounded good, simple enough.
I can tell you that Audinst HUD-MX2 just lets your headphone/IEM show their true colour, it will not boost them in any mean, just let them sounded better, but a bright headphone will remained bright, bassy headphone still a bassy headphone, just they are better through HUD-MX2. I do however, really hope MX2 can have a better midrange and add in a bass boost function.
Easy and straight forward front panel
Time goes by quickly and every player in audio equipment seems stronger and stronger, this is a ultimate good news for consumer like us. We have so little of reasons to spend more on audio equipment. Audinst HUD-MX2 is a solid performer, in fact HUD-MX1 is one of the best DAC/Amp combo that available in few years back, it is quite normal to see audio reviewer and headfiers recommended the MX1 all over the place.
It is a nice amp/Dac if you are not into forward sound signature
But things are different though after few years and now ae are in 2013, we can see a lot of good and talented manufacturer start to play in the audio market. Some of the older players keep improving their sound quality and launching better stuffs lately. So things are different now, can Audinst HUD-MX2 withstand the competitors in the market?
Neutral sound signature is a good thing, but I wish that MX2 can have better soundstage and a bass boost trigger.
I will say Audinst HUD-MX2 is a good entry level amp/Dac, it worth more than its price stated. MX2 is a solid performer and give a lot of good sound particularly my IEMs and headphones. Depends on your sound preference, if you would like to hear the most upfront sound MX2 is not for you, but if you are after a good and well performed DAC/Amp, give MX2 a serious thought.


Headphoneus Supremus
Pros: Improved DAC section and especially amp section, powerful and more refined overall, low noise, improved volume knob
Cons: Nothing major.... async USB would be nice I guess.
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[size=small]The Audinst HUD-mx1 compact DAC/headphone amp was a great little unit. It also happened to be one of the very first reviews that I did at HeadFi. In the subsequent years I've gone on to review dozens of other products from amps to DACs to headphones and more, and I also went on to become something of a "real" reviewer at InnerFidelity. Through all that, I've never stopped recommending the Audinst mx1 as a cheap, reliable unit that sounds good and doesn't take up much space.[/size]
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[size=small] Audinst later went on to release a portable amp (the AMP-HP) and another DAC/amp unit (the HUD-mini). Both of these were strong competitors in their respective categories and the HUD-mini came dangerously close to being superior to the mx1, despite being a bit cheaper. Now Audinst launches a refreshed version called the HUD-mx2. It looks nearly identical to the mx1 but adds several important features and upgrades a lot of other things too. With a price increase to $248, a roughly $70 increase over the original, is the mx2 a worthy successor?[/size]
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[size=small] DESIGN[/size]
[size=small] The mx2 looks almost exactly like the mx1. The case is slightly larger but for the most part they look very close. Both have the same silver faceplate with a slight curve to it. Both have the same black chassis. Both use the same dual headphone jacks (1/4" and 1/8"), the same RCA jacks, etc. Aside from added features, the only thing that is really changed is the volume knob. Gone is the rubbery, slightly tapered knob of the mx1, replaced with a larger aluminum knob that looks and feels superior. I never had issues with the original but I can see how this new design allows for more precise volume tracking due to the larger circumference.[/size]
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[size=small] Despite their similar looks, those familiar with the mx1 will notice a few new things. A Toslink input joins the Toslink output, meaning this is now a dual source DAC. A front panel switch allows the user to choose from Toslink or USB connections. The output still works the same as it did with the mx1, essentially making the unit act as a USB to SPDIF converter in addition to the DAC and headphone amp capabilities. It also keeps the same Dolby Digital pass through function for those using surround sound receivers.[/size]
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[size=small] The rest of the changes reside on the interior of the unit. And those changes are numerous. The DAC has been switched from a Wolfson WM8740 to a theoretically superior TI PCM1796. The USB receiver, formerly the Tenor TE7022L, is now a VIA Envy VT1728 which means the unit now supports all sample rates up to 96kHz, including 88.2kHz (which the mx1 did not). The mx2 uses dual LME49860 opamps for I/V conversion instead of just one like the original. Following the I/V stage is a differential amplifier based around an OPA2227. From there the signal passes to the line-out stage which appears very similar to the mx1 and uses the same OPA2134 opamp. The OPA2227 and OPA2134 are socketed and can be swapped. The LME49860 opamps can not. [/size]
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[size=small] The headphone amp section is changed as well - where the mx1 had an AD8397 opamp handling all amp duties, the mx2 uses a TPA6120A2 driver chip. This allows for significantly more powerful output. The specs on the mx2:[/size]
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[size=small] 1.5W at 32 ohm, 5Vrms[/size]
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[size=small] 300mW at 300 ohm, 7Vrms[/size]
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[size=small] 160mW at 600 ohm, 7Vrms[/size]
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[size=small] Those are some high numbers. The TPA6120 is certainly capable of that much output (and even more according to the datasheet) but the problem is heat: it gets very warm, and requires a thermal pad underneath to help with dissipation. That's why it can be difficult to implement in a DIY design. That probably also explains the venting holes on the rear of the mx2 which were not present on the mx1. I'm doubtful these are the actual measurements, especially on USB power, but are probably more of a "best case scenario" type of deal. Either way, there's no shortage of juice here.[/size]
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[size=small] Output impedance is a mere 2 ohms, down from 5 on the mx1. This means very little chance of impedance related interactions even with the crazy impedance swings of multi-driver balanced armature IEMs. It also means sufficient power for difficult planar headphones. The mx1 was released before planars became prominent, and could only deliver a few hundred mW into low impedance loads. That was plenty for most dynamic designs but headphones like the LCD-2 and HE-500 thrive on high current and the mx2 is far better suited in that area. I'm not sure how many people will be using expensive LCD-2s and HE-500s with this budget DAC/amp unit, but it's nice to know they can if they want to. [/size]
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[size=small] As some astute readers may already know, the TI TPA6120 datasheet specifies a 10 ohm output impedance for stability. And we normally see this followed, in designs ranging from the budget Fiio E9 to the high end Kao Audio UD2C. But there are ways around it. For example, NwAvGuy shows one method HERE  where he drops output impedance below 1 ohm by adding some SMD ferrites into the circuit, on top of the 10 ohm resistors. Looking at the mx2, I believe Audinst used a similar method - but it's difficult to tell for sure with these tiny SMD parts. NwAvGuy noted a penalty paid in terms of measurable distortion but it was arguably below the audible threshold and overall a worthwhile trade-off for the superior output impedance. [/size]
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[size=small] Like the original model, the mx2 has an internal jumper to adjust gain. In this case it has 2 jumpers but the function remains the same - output impedance doesn't change but the gain factor does. Audinst recommends the "normal" gain setting for loads up to and including 300 ohms, and the high gain setting for 300 ohm through 600 ohm loads. In practice, I ended up leaving my unit on low gain all the time. High gain may be useful for certain 600 ohm headphones like the AKG K240DF but I no longer own anything like that. 300 ohm Sennheisers work fine on normal gain so I see no reason to switch for most users.[/size]
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[size=small] The last feature has to do with functionality. The USB input is now able to interface with devices such as the iPad through the Camera Connection Kit, or Android phones such as the Samsung Galaxy S3 through an OTG cable. For some, this feature won't mean much, but I think it's a good thing based on the target market for a device like this. I can totally see a person using it at work, for example, where an increasing amount of companies lock down their computers for any external peripherals. That means adding the mx2 as a USB DAC is not an option, and likely neither is adding an external hard drive or SD card full of music. But the mx2 could still work by using a phone or iPad as the transport. Same situation in a college dorm, a bedside setup, or many other scenarios. Bottom line is that the added functionality is very welcome.[/size]
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There is slightly more free space here compared to the mx1, due to the widening of the board,
required to fit that extra front panel switch to select USB or Toslink:
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The new headphone section:
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The new differential amplifier for the DAC section:
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The actual DAC chip:
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The AKM receiver, TXCO clock, and VIA USB chip
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[size=small] LISTENING[/size]
[size=small] The HUD-mx2 builds on the Audinst "house sound" originally established by the HUD-mx1 and continued with the HUD-mini. It's a relatively neutral sound, not overly dry or boring, and it works with a variety of equipment. I started by using the unit as a USB DAC with my desktop PC, also acting as a preamp to feed my powered Serene Audio Talisman speakers. The mx2 does a good job of controlling volume - balance is essentially perfect across the range and there's no static or undesirable noise during adjustment. I normally use a more expensive Audiotrak DR DAC 2 DX Muses Edition in this setup, which is actually very similar to the HUD-mx2. But more on that later. I played some of my favorites tracks from Marta Gomez, Livingston Taylor, and Eric Clapton, and all sounded excellent. The detail level seems noticeably improved over the original mx1 model - it isn't a complete night and day difference, but enough to move the mx2 one step higher on the food chain. I also played my 24-bit/88.2kHz version of Classic Brubeck and appreciated the native 88.2 support which was not present on the original model.[/size]
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[size=small] Next I tried a dedicated headphone amp, using the mx2 as a DAC. I plugged in my Violectric V200, which is an amp I know very well, and listened to the Audeze LCD-2.2 with various hi-res test tracks. Again I noticed a neutral and fairly transparent sound, with very little character of its own. Bass had nice depth and realism, and timbre was accurate. Soundstage was nicely sized too, with believable imaging. This combo sounded pretty darn good. [/size]
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[size=small] I normally use the matching V800 DAC with my V200, which is far more expensive than the little mx2. The Audinst sounded more closed in, with less of a clear window into the performance. It had less extension on both ends but particularly in the lowest lows - which is exactly what I'd expect given the price discrepancy. Yet taken on its own, the mx2 was a capable performer and didn't represent a massive bottleneck. Sure, one could spend more and get more, but nothing about the mx2 is completely objectionable. [/size]
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[size=small] I tried the Toslink output from my motherboard and got a sound which was very similar to USB. I thought perhaps USB was more "crisp" and had more defined leading edges, while optical was ever so slightly more relaxed. But this could reflect the optical signal from my motherboard just as much as the Audinst itself. In a computer situation I'd choose USB just out of convenience anyway but Toslink is nice to have around since it opens up new possibilities. [/size]
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[size=small] Next, I got rid of the V200 amp and started using the headphone jacks on the mx2 directly. This is where I noticed the single largest difference as compared to the original model. The mx2 simply does soundstage, drive, clarity, and pretty much everything else, better than the mx1. The sonic signature shifts a little bit from slightly forgiving to bold and energetic. Vocals sound especially good - from sultry singers like Jacintha, to the powerful and soulful Beverly Knight, to Annetet Olzon (formerly) of symphonic metal band Nightwish, vocals seem more present and up front. More "believable" for lack of a better word. Not that the mx1 was bad in this area but the mx2 just goes farther. The only potential drawback is with brighter headphones with peaky highs. If someone found a set of Grados barely tolerable on the mx1, the mx2 might push them over the edge. That's not really the fault of the Audinst though - it's just giving you more of a true representation of what the headphone is all about. [/size]
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[size=small] I really like the LCD-2.2 straight from the headphone jack. Again, it isn't as good as the dedicated and far more expensive Violectric unit, but it does a very credible job. It also sounds great with my HE-500, HE-400, and Thunderpants planars. I don't care how efficient HiFiMAN makes them, planar magnetic headphones seem to love high current, so the redesigned amp is very welcome here. All of these models should be seeing 1W or more from the mx2 and it really works well, especially compared to the original model which wasn't very satisfying with those models. [/size]
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[size=small] I also tried some more affordable headphones which are far more likely to be paired with the mx2 by regular users. The NuForce HP-800 and the VMODA M80 both sounded very nice. Both have a somewhat darker presentation, the former more so than the latter, and both benefit from the slightly energetic Audinst. It's not enough to turn them into a K701, but it helps even things out a little compared to a completely neutral amp. I can't decide which one I like more - the HP-800 has thunderous bass that sounds very good for the price, but the M80 has sweeter and more engaging midrange. Either way, this would make a great starter system for someone just getting into the hobby and not wanting to spend a ton of cash. [/size]
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[size=small] Next I switched to IEMs which can be a good test as they can reveal issues with the noise floor in a lot of amps. The Audinst is thankfully very quiet, with no buzz or hiss or anything like that. It's a small thing, but I appreciate having a dedicated 1/8" jack on the front panel. Not that using an adapter is a big deal, but the dedicated jack just feels better. I really enjoyed it with the Heir Audio 8.A and particularly the 1964 Ears V3, which is a relatively affordable CIEM that is more likely to be used with the mx2 as compared to the more expensive 8.A. The V3/mx2 combo produced a detailed sound that remained smooth and grain free, with excellent dynamics and deep bass extension. I'm spoiled by my high-end gear but even I am impressed with this simple and reasonably priced combination. The only thing to watch for is with brighter IEMs - I'm not sure I love the mx2 with my Lear LCM-5 or even with my JH13 FreqPhase. It seems to accent the upper mids and highs just a little too much, making them seem overly aggressive. It's listenable but not ideal. This would probably apply similarly to other universal IEMs like the DBA-02. Interestingly, I didn't have a problem with the HiFiMAN RE-400 at all. It sounded clear and present but not overly so. So I guess it's worth trying everything to see what works best. [/size]
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[size=small] All of the above comparisons were done straight from USB power. In that case the device runs at 5V internally. Adding the bundled external power supply brings operating voltage up to 12V. The benefit in terms of DAC sound quality is limited - I sometimes thought it sounded slightly better, but it might be my imagination, and I really doubt I could reliably tell them apart in an A/B comparison. The downside is when running from the external PSU - the enclosure of the mx2 gets fairly warm, which doesn't happen with regular USB power. It's not a huge concern of mine but I figured I'd mention it. [/size]
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[size=small] It is worth mentioning that this higher operating voltage determines which opamps are suitable for use. So opamp rollers need to take note. Something like a Muses01 needs at least 9V which wouldn't be satisfied when running in USB mode, but would be fine with the external PSU. Not that Audinst users will likely be lining up to try that particular opamp which is around $50 a pop, but you get the idea.[/size]
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[size=small] For headphone use, I do notice a difference when using external power, depending on the headphones being used. It does seem to help with clarity and drive on the HE-500 and to a lesser extent the LCD-2. With most dynamic headphones I notice less of a difference if any difference at all. I'd say that 90% of the time or more the external power is not necessary, but it's sure nice to have the option. I do have a NuForce LPS-1 linear power supply which should theoretically work with the mx2 - I need to give that a try one of these days and see how it does.[/size]
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[size=small] Comparisons[/size]
[size=small] The main comparison that came up for me was with the Audiotrak DR DAC 2 DX Muses Edition. The Audiotrak sold for $329 (but was often available for less) and has many similarities to the Audinst in terms of features and appearance. Unfortunately it appears that Audiotrak has upgraded yet again to what they call the "Top Edition" which uses Muses 8920 opamps in place of the 8820 in my unit, as well as some upgraded capacitors and other parts. The new TE sells for $329 and I can't find it any cheaper. So the comparison I'm doing might not be all that relevant at this stage but here it is anyway.[/size]
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[size=small] The Audinst is nearly a match for the more expensive Audiotrak unit in almost every way. The key difference is the sound signature of the headphone output - while Audiotrak is slightly warm and smooth, the mx2 is more energetic. It has more sparkle, and thus creates a more lively feel. The result is dependent on headphone pairing - mx2 sounds better with LCD-2 and Audiotrak works better with bright headphones like K701.  [/size]
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[size=small] As a DAC both units are very similar. Audiotrak has a slightly more laid back, relaxed midrange, while Audinst is more forward and "snappy". But the differences are small. Overall the mx2 is impressive here - it competes with the $329 Audiotrak which is a nice unit in its own right. And subjectively I like the mx2 appearance much better.[/size]
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[size=small] The Grant Fidelity TubeDAC-11 ($350) is very stiff competition, and the Audinst doesn't quite beat it. The TubeDAC-11 is more resolving, and more natural, though the margin is not huge. Audinst has some functionality that the TubeDAC doesn't - Dolby Digital passthrough via optical out, USB to SPDIF conversion, support for 88.2kHz sample rates, a dedicated 1/8" headphone jack. In return, the TubeDAC has some unique options of its own - more inputs, a tube headphone output (by way of an adapter), and multiple options for DAC output (tube, SS variable, SS fixed). It has a more robust power supply and looks like a more "serious" audio component if that matters to you. Obviously the Audinst is far better suited to be used as a transportable solution, so each unit has its place. For ultimate fidelity the TubeDAC is king, but the Audinst is not completely blown away and has some advantages, including its low price.[/size]
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[size=small] In a surprise comeback, the Matrix Audio Cube DAC has dropped from $299 to $199. That's a great price for a quality unit, and it becomes serious competition to the Audinst HUD-mx2. Ultimately I believe the mx2 is the better sounding option, with more refined highs and superior transparency. The Cube is a compelling buy for the price though. Companies are competing heavily for this market segment, and there's no way the Audinst would walk away with the category without some tough competition. The current version of the Cube has swappable opamps (mine doesn't) and could possibly be tweaked to extract further performance. But the same applies for Audinst.[/size]
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[size=small] Conclusion[/size]
[size=small] Audinst has shown itself to be an established audio company by consistently releasing one good design after another. The HUD-mx2 is the best of the bunch so far - it takes the established Audinst "house sound" which first debuted in the original HUD-mx1, and turns it up a notch or two. In this rapidly progressing field, where many good options exist, and there's simply no way the mx2 could be a "giant killer" or anything of the sort. It lies squarely in an area where spending more can certainly get you more - unlike high end multi-thousand dollar DACs where spending more often nets a "change" but not necessarily an improvement. [/size]
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[size=small] But don't let this dissuade you - the HUD-mx2 is one of the best values currently available. For a lot of users it will surpass the "good enough" mark where more spending will simply not be necessary. With its powerful and refined headphone stage, it makes a good argument for throwing the bulk of your cash at the best headphone you can afford. The HiFiMAN HE-400 makes a particularly good combo, though others also work well. IEMs are also fair game thanks to the low noise, low output impedance, and improved volume control. All in all the Audinst HUD-mx2 just "works" and I can easily recommend it. [/size]
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I'd agree but with a few more criteria - features, price, form factor, and even looks. Like if you might use the device with active speakers, the Audinst has preamp functionality. That's very useful to me but might not matter to you.
That is exactly why I bought the MX-1, I had to use a passive preamp when I had the fiio e7-e9 which seemed to affect the SQ in a bad way.
for my pc setup as an external sound card the output switch itself is a godsend!