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Audinst HUD-MX2 vs ODAC/O2 vs Graham Slee Bitzie. A few portable Dac/Amps.

post #1 of 13
Thread Starter 

Portable Dac/Amp Combo’s


1) Audinst HUD-MX2 (£150)

2) Epiphany Acoustics O2D (ODAC + O2 amp) (£190)

3) Graham Slee bitzie (£350)


Searching for an external soundcard for my laptop was the very fist thing that opened me up to the world of sound quality. Since then I've come across plenty of such devices, dac/amp combinations and here's a review of the three that I have been impressed with lately. Hopefully you'll find it useful...





1. Looks


2. Setup and Functionality


3. Sound I (dac+amp combo)


4. Sound II (elsewise)


5. Setup




1. Looks

1.1 O2D

The O2D is nice. It looks good though a bit ‘raw’ and aggressively matt black maybe. You know what I mean. Connections could be placed slightly better with more at the back, but for me that’s not a big disadvantage.


It’s solidly made with good dimensions and a volume knob allowing for proper control. A small turn of the volume doesn't result in a major jump in volume which is what I mean by ‘proper’ and this is true of all three units in this review. Of course at low volumes there is channel imbalance but that’s true of even amplifiers of £1k+ I’ve come across, so it’s fine.




1.2 Audinst

In looks the Audinst is the champion. The well designed, neat façade blends nicely with the black body and the connections are placed perfectly and most conveniently. In build it feels the best too, closely followed by the O2D.  I’ve got to say a quick word about the awesome packaging for this audinst. Wow. So much effort and professionalism went into this. Literally the opposite of the bitzie.




1.3 GS Bitzie

I’m really struggling to think of an item I’ve purchased to have shoddier packaging than this. It’s just like a pound toy. The amp’s volume knob actually pushes on the outer plastic making it loose it’s rectangular shape. This is held to the thin backing cardboard by two paper staples. Instructions are on a piece of paper. 


When you open it up and handle the amp it’s obviously better. There’s a sharp edge to the top, which if you run your finger along rapidly might hurt yourself (again resemblant of a cheap toy). So It feels like a toy too, especially because of it's very low weight. I have to say that the general build quality of the amp is absolutely fine which is I guess what really matters.


A massive positive now. The volume knob is genius. You have a lot of rotation and degrees to use for changing volume effectively allowing much better volume micro-movements than pretty much anything I’ve come across. Both my fostex mad dog’s and ultrasone sig pro’s benefit in the same way so it’s not down to gain. It’s down to good design. Great feature for me.






2. Setup + Functionality

For me there are three levels of portability:

a) Desktop  b) Transportable  c) Portable


The O2D is in category b) and the Audinst and Bitzie are in c). The last two run completely as a dac/amp combo off USB power, whereas the O2D needs AC power to do anything.


All of these units are small to be easily carried. Look how they compare to my phone:




2.1 O2D

You can use the amp separately. Connect a line output 3.5mm connection to the line input and you have the objective 2 amp. Of course the unit has to be plugged in via AC and the wall socket.

Funnily enough I tested other AC to AC adapters with the O2D and the one provided by epiphany acoustics was the audibly better. Not by much, but better.



2.2 Audinst

You can use the dac separately as it has RCA lineout built in (flick the switch on the front to speaker mode). It also has in built optical input, useful for Xbox/TV/DVD players. It is able to act as a USB to SPDIF converter offering both optical and coaxial outputs. It gets even better – it supports USB OTG from select android phones allowing the phone to act merely as a transport.


You may be wondering….so let me just state it as a fact.

Every feature works perfectly.


Round of applause.


I’m not even finished praising the features yet. It runs cleanly off USB power and can run off AC power.

Does AC make a difference? Yes. Not a massive difference and funnily enough, less pronounced with certain headphones (ultrasone signature pro for example). The VN10 Maplins psu (at 12v, 1.7a) which works well for stuff like the musical fidelity vdac and arcam rdac works similarly well for this. There’s better mid bass definition, slightly better instrument separation, a taller soundstage and more competency in its high range reproduction with the AC adapter, but the latter is audible mainly with harder to drive headphones (like the mad dogs). Note that I do use a power conditioner which helps with equipment displaying nuances such as these.



2.3 Bitzie

Actually this is quite similar to the audinst. You can use the dac separately though only by the 3.5mm output doubling up as a lineout. A nice connector is supplied and as for such a function no one will really desire the unit to be in view, no marks need to be deducted on looks/convenience. A save of space here was a good choice in my opinion.


It also acts as a USB to SPDIF converter and a USB OTG device for the android mobiles like the s3. It doesn’t have an optical input though so I can’t use it with my TV.


This is quite a big drawback: I could hear noise of my USB sockets through my headphones when plugged in to this bitzie. Neither the O2D or Audinst suffered the same problem or in fact have any among an entire stream of USB audio devices I’ve tried (probably 25 in total). My Ultrabook is customised to be audio friendly (ssd, battery powered, usb port power regulation….).

It’s a problem with the GS Bitzie where there should simply have been more of an emphasis on this in the design process. Graham slee mainly make amps so I guess it’s something they should look to fix for the future.


Before we move onto the sound, I should say that I used the bitzie with a standard belkin external usb hub which eliminated the problem.





3. Sound I (Dac+Amp Combo)

In any random situation with a random pair of headphones, any one of these can sound the best! There isn’t much in it to be fair and it is for this reason I’m not going to talk much on which is best. For harder to drive headphones I’d say the Bitzie. For other’s the O2D/Audinst. You Choose.



3.1 O2D vs Audinst (AC power)

The O2D has a slightly better soundstage which sounds more evolved and in place. This is especially true with the mad dog where the timbre is slightly better too. Moving onto other headphones we see differences take on other forms where sometimes both units are almost indistinguishable to my ears and in others I prefer the Audinst. The Audinst gives the highs a touch more of a softer and involving role to play where they stick out less especially when played at higher volumes. It just fits in a bit better favouring brighter headphones unlike dark ones such as the mad dog.


The O2D is clear in the midrange and so too is the Audinst. I guess the biggest difference between the two is in the bass presentation. The audinsts has a fuller bass with more weight and a touch more emphasis. For trance and electronic music I’ll pick the O2D and for orchestral pieces I’ll take the Audinst.



3.2 Audinst vs GS Bite (USB Power)

…Audinst advantages

This has a better faster tone. Lighter in notes and in bass, especially sub bass. It's highs hit more sharply, though that's nothing to do with being overly bright. The bitzie is very laid back and rounded, almost to a fault. This audinst therefore sounds more realistic and lifelike especially with instruments that rely on brilliance in the upper tier frequencies.


Vocals benefit from this especially when emotional tones of fragility and lightness should come through. The bitzie makes this too thick and thus sound unnatural. It's a very small difference in the grand scheme of things and often unnoticeable but it is, nevertheless, a difference.


…Bitzie advantages

It seems to give a more mature sound, laid back, warm and easy to turn up. It's less aggressive and less mid focused. Vocals present themselves rather than being presented. Actually, the soundstage is the most different. It's more 3d - not necessarily bigger but less left and right. If some sounds were to come from south east and south west in the bitzie, the audinst would project them more along the east and west.



In harder to drive headphones the bitzie asserts its dominance more convincingly. The T1 and mad dog, especially the mad dog, sound superior here in general to the Audinst. The midrange feels more enriched and the bass produced adds a lot to the soundstage which becomes even more bigger than the one on the Audinst.

With easy to drive headphones (D7k, Ultrasone sig pro…) I’d give it to the Audinst which gives a more convincing midrange portrayal and overall execution to the sound.





4. Sound II (Elsewise)

4.1 O2D - Objective 2 Amp

As an amp alone this thing is good for what it is. As an amp compared to bigger desktop amps, I’ve never rated the objective 2 highly. I hear the fiio e9 as being superior with a lot of headphones. The O2 is IMO a good portable amplifier that does nothing wrong at all but the fiio e9’s presentation is more wider, weighty, overall more mature and simply voiced more naturally.


4.2 Audinst and Bitzie – DAC & USB to SPDIF converters

Both DAC and USB to SPDIF converter functions were compared using the VDAC and VLINK mkII as benchmarks. Amps used were the Burson soloist sl and graham slee UL diamond.


In short the Bitzie performs very well here, close to the musical fidelity gear and overall definitively better than the Audinst.


- Dac only

The Audinst is good but not better than the vdac. It has a noticeably smaller soundstage, less sideways width, with lower resolution. There’s a more single tone where some female vocals have an artificial edge that the vdac rightly avoids synthesising. Graham Slee’s Bitzie does fall slightly short of the vdac too, but I do mean slight. Portrayal of micro details is better with the vdac and there’s a better high end extension too. Apart from that there’s not that much in it.


- USB to SPDIF (Coaxial Output)

The V link is much better than the Audinst. Much better definition all round and there’s a bigger more present sub bass. The crunch of violins shines through and nothing gets lost in the midrange as is the case with the audinst, which supports a more recessed, less detailed midrange response.

The difference is pretty clear all round and it took me only one song to differentiate the differences, though I did try around 5 more just for the sake of it.


Let’s move onto the Bitzie shall we. This and the Vlink are very close in performance and are virtually indistinguishable at times. Nothing more to say; very well done Bitzie!





5. Setup

5.1 Testing equipment

Power: Clearer audio copper line alpha power conditioner

Transport: acer s3 (128gb samsung 840 ssd, 4gb ram, i5, W7) & Dell Vostro 1500 (128gb kingston ssd, 4gb ram, core 2 duo, custom XP, usb hub)

USB cables: Belkin, Chord silver plus

SPDIF converter: Musical Fidelity v-linkII

Optical/Co-axial cable: wide range inc. QED profile/performance and others

RCA cables: wide range inc. Chord Chameleon vee3, QED profile, Belkin, Mark Grant g1500hd,


5.2 Conditions

Ambient noise levels: Home listening : <<30db (Absolutely dead quiet!). Demo listening <35db

Humidity and temperature: maintained 21-23c and 50-60% relative humidity

Volume matching: using test tracks of different noise levels calibrate amplifier volume and perceived loudness with headphones. Conducted at every test.

Listening Volume: Extremely important to note. Some headphones prosper/fail at high/low volumes. I listen at low to low-normal listening levels. 


5.3 Albums

All flac files (CD standard bit rates). Variety of genres, with a sample of artists being:

Riverside (prog rock), Within temptation (rock), Amethystium (New age), Secret Garden (Celtic), Lisa Gerrard (World), Armik (Spanish acoustic), Ah Ne Ma (Acoustic/world), ATB (chillout/trance), Tycho (Electro), Game (hip hop), MJ (pop), Yo Yo Ma (Classical), Hans Zimmer (OST), Diana Krall (Jazz) and the best out of them all... Einaudi (Neo Classical)

Edited by CantScareMe - 10/7/13 at 5:25pm
post #2 of 13
I really enjoyed the reading, pretty detailed. biggrin.gif I'm only missing a part when you conclude your review saying something like: "if I were to buy only one, this would be my choice because..." smily_headphones1.gif
Edited by Ashade - 10/8/13 at 7:05pm
post #3 of 13
Thread Starter 

Thanks - If I were to buy one I'll buy the second a month later and the third the next month. There's probably a few more here that do the same kind of thing

post #4 of 13
Hahaha. Well, I would definitely do the same if I could afford it, but at this moment my ratio would be more one this month, the next one the next year and maybe the last one in five years from now. That's why I was asking. wink.gif
post #5 of 13
Thread Starter 

Lol. True say.

post #6 of 13

nice review, but am i right to say that the difference is really quite minor between the o2d and audinst?

also a question on with and without AC power - how much difference does it make to the audinst?

and leaving it on all the time on AC power does it run hot?


i think the output selector (phones vs speakers) is a big plus for those primarily considering the audinst as an external sound card to a PC set up and want to switch listening modes without going through the on/off or plug-in-plug-out routine.

post #7 of 13

good info,There's probably a few more here that do the same kind of thing


post #8 of 13
Thread Starter 
Originally Posted by metalgear View Post

nice review, but am i right to say that the difference is really quite minor between the o2d and audinst?

also a question on with and without AC power - how much difference does it make to the audinst?

and leaving it on all the time on AC power does it run hot?


i think the output selector (phones vs speakers) is a big plus for those primarily considering the audinst as an external sound card to a PC set up and want to switch listening modes without going through the on/off or plug-in-plug-out routine.


Yep. The difference between the two is minor.


AC power makes a difference with headphones like the T1, mad dog and even (a tiny bit) on the d7k. For very easy to drive headphones like the ultrasone sig pro, then it makes a difference so small that it may not even be a difference! With the sig pro I use usb power


Yep. With the AC on all the time it does run pretty hot, though this may be because the power I give it is 12v * 1.5amp. It could function with less I believe.



The audinsts range of features is breathtaking and the fact that they all work is even more to the credit of this device. Love it to bits, I really do.

post #9 of 13

yeah i'd agree that the Audinst has the best feature range and the best looker of the lot.


you made a point of the better AC adaptor making a difference on one of the units - just wondering if this has been a neglected part of the chain.


lots of sensitive auidio devices have emphasized better power supply, especially up high in the chain, so I am thinking about the tweaking potential here.


as example is http://www.musicdirect.com/p-3667-graham-slee-psu1-power-supply.aspx .


I don't want to spark off some mad-audiophile power supply frenzy, but it often looks to me that the power supply adaptors are an afterthought, not part of the design of the audiochain.

post #10 of 13
Thread Starter 

Too often they are an afterthought. I fully agree. 

post #11 of 13

thanks for this review

post #12 of 13

Really on the fence between the O2 + ODAC combo and the Audinst MX2, specifically for my HD650s. Anyone have any recommendations on this pair up?

post #13 of 13
What settled it for me is that the mx2 has more than one input and output. So it makes the unit way more versetial.
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