[Swimsonny]

MiuAudio MRB Review

 
Introduction:
 
Not too long ago I got a PM from MiuAudio and it was a very unexpected one as well. I was extremely surprised to read that they would like me to review their new DIY portable headphone amplifier, the MRB. Now I am 16 and have no past experience with any DIY stuff or soldering but the whole DIY scene has always intrigued me so I gave them my address and the sent the kit my way.
 
So what we have here is instead of a already made headphone amplifier that you may be used to buying, you get a housing for the amplifier, loads of compartments in there own little bags, a schematics sheet and a PCB.
 
There was a few bumps along the way but it all turned good in the end and this is what I thought of the process and the finished product.
 
Making the MRB:
 
So as I have mentioned before I am a 16 year old with zero experience in anything remotely related to this sort of thing. First I would need some tools to make this and I picked up some solder and a soldering iron so that I could actually make these products. I think that they were a good investment for the future and it is not going to get near to breaking anyone’s bank to buy. Now because we are soldering a small PCB board your going to need a small tipped iron and thin solder otherwise you will just destroy the board so that is just what I got!
 
For the process it is rather straightforward, you need to solder the components to their correct places on the PCB. For that we refer to the schematics sheet and that tell you simply where each part goes. Now to make this easier for myself I numbered up each part and but the corresponding number on the schematics sheet to make it easier.  However this is where my first problem occurred as the first schematic sheet that I got had two parts in the wrong place which led to that amp not working. However fear not they fixed this and now you will get a correct schematics sheet like I did the second time and that worked fine.
 
As for the soldering it is nothing too difficult if a little bit fiddly. I practiced on some metal before jumping in and I soldered everything well in place and I can confidently say you do not need any real experience in soldering to make this amp well as long as you take your time with it and I had no problems.
 
Once the soldering is done, I checked it to make sure it worked (with some cheapie IEMs in case something bad was to happen) and then it is time to but the finished PCB into the housing.
 
To do this you use the included screwdriver tool to screw the two faceplates on and after quickly putting the volume knob on, voila, you have a finished amp. It did take a fair bit of time as I made sure I did not make any huge errors and that everything was done well but it was really satisfying in the end. Was it easy? I would not say it was easy but then it was not to taxing on any part of your body either. You did have to think about things when you done as well but everything were far from impossible. If I was you do not concern about not being able to make this because I am sure you will manage. It was a worry of mine if I would be able to make it or not but I should not have as everything is okay.
 

 

Finished Product

 
Design and Features:
 
The finished product looks really nice. It is a simple silver design with the Miu logo on the surface as well as the product name. Overall though it does look like a professional product and not something you have made yourself.
 
As for feature this is really just a too the point amplifier and nothing on the fancy side. We quite simply have a volume control knob, a 3.5 mm input and output and an on/off switch. You also if you use a rechargeable battery with it have a cable to charge it with if your buy a 12-16v charger separately, the cable included just makes the charge compatible with the input in the back of the amp.
 
One other feature it does have though is extremely handy and that is that the op-amps in the amp are mounted and not soldered in. This means that you can upgrade the op-amps and purchase more and change them in and out of the amp at your own will to tamper with the sound.
 
 

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Build Quality:
 
Now your making this amp so if you don’t screw everything up tight enough etc. it is probably going to be weak but it is not difficult to build this tightly and well. Once you do that you have an amp made completely out of metal and feels really chunky and solid. Overall I do not see anything that could go wrong with the amp and it is built very well indeed.
 
Phone Compatibility:
 
Another problem that can happen with portable amplifiers is if they struggle from interference from smartphones. This EMI has caused some amplifiers like my hippo cricri to cut out when using them with my iPhone and in the day and age now where a lot of people want to incorporate their phone in their portable rig that can be a deal breaker. However although here traces of interference can be heard every now and again, it is far from continuous and never causes the amp any trouble. What I will say though is it is not dead silent either.
 
 

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Size and Portability:
 
Now as this is designed to be a portable amp I can guess that you want it to be small as much as I do so that it is completely portable and not transportable like my Objective 2. Now I will happily say that this fits in as a portable amp but it is not one of the tiny portable amps you may find like the Fiio E5/E6 and the GoVibe MBA but more like the large portable amps such as the cMoy BB. This means that although unlike some of the small amps, it is really quite noticeable that you’re lugging it around with you but it is not impossible either. The main niggle with its size if anything is actually the depth of it as it shorter than an iPhone 4 and the same width but then it is roughly two in depth.
 
 
As for actual measurements we have:
 
Height – 4 inches
Width – 2.1 inches
Depth – 1 inches
 
 

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Driving Power:
 
This thing is powerful and it managed unlike most portable amps I have tried with my most mighty headphones, the Sennheiser HD580 with their huge impedance of 300 ohms. Now I am not recommending this as a desktop amp or anything but I am just saying that it can driver powerful headphones, do loud volumes, efficiently without lack of dynamics or any distortion.
 
Hiss:
 
These are prone to hiss because of what I can only see as a lot of output power. Sensitive IEM and Headphones will be covered in hiss at low volumes and you can still hear it present as you turn the volume to more listenable volumes. SO if you plan to be using this amp with your new Fischer Audio DBA-02’s for example, that’s not going to be ideal, try something that has a fairly low sensitivity and you should be okay.
 
Sound:
 
Finally we have sound quality and I was using the Epiphany Acoustics EHP-02 (Objective 2) as a reference. The objective 2 is fast, transparent, neutral and has a wide soundstage. In comparison the first thing that is obvious is that the MRB is tainted with a warmth and slight coloration. Now this is not a bad thing and helps it pairs with headphones that are on the brighter side but it is not a clean transparent amp at the end of the day. Depending on what your looking for though this may be ideal or plain awful as I know some people go out looking for a warm amp and others are all about perfect transparency. Moving on there is the speed and the MRB is no slouch here. However you can tell it slightly lagging behind the O2 a little bit and everything was just not as easy. As for soundstage, there was not actually a whole lot of difference and the MRB sounded really open and had really nice imagery as well as great height to it.
 
Breaking down the spectrums, the bass had the slightest of emphasis while maintaining great speed and punch with very good texture. The mids have a slight coloration with a presence of dark space shrouding the mids slightly. Finally the treble is very nice and extended with good texture and presence.
 
Op-amps used:
 
[size=small]AD8620X1, LME49720X1, NE5532X1;[/size]
 
 

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Conclusion:
 
I loved making the amp and it has given me a taste in DIY and I just want to do more as it I great fun, I think next up is another amp or DAC or maybe some cables for me. I want to thank Miu for getting me involved with a bit of DIY.
 
As for the amp it is great physically and is a rather nice sounding warm amp for on the go use as long as your headphones are not too sensitive. It is not ‘easy; to make but far from ‘hard’ and it is so rewarding once you finish. I am not going to recommend it as the best amp in its price range but it is a contender and is great fun, you also have the ability to op-amp roll to make this sound like you want it for a bit of extra money. I think this something everyone should try doing!

 

[bowei006]

Nice review! Mine will be out this week as well.

 

[kiteki]

You need to write which DAC you were using, and which IEM's btw?
 
This is a special amplifier, not really intended for smartphones, just in my view.  I use it with my Xperia Ray from time to time though - in flightmode - so there is no interference.  Introducing a filter to remove computer or smartphone interference tends to lower sound quality a lot, IME.
 
 
You can easily remove the RFI and hiss, try exchanging NE5532 with LME49720 as simplest fix.
 
If you don't like the 'warmth' in the sound with your equipment or music, you should remove the NE5532, they put that there for the colour of NE5532, it's quite easy to change this into a raw and transparent amplifier.

 

[Swimsonny]

Quote:

You need to write which DAC you were using, and which IEM's btw?
 
This is a special amplifier, not really intended for smartphones, just in my view.  I use it with my Xperia Ray from time to time though - in flightmode - so there is no interference.  Introducing a filter to remove computer or smartphone interference tends to lower sound quality a lot, IME.
 
 
You can easily remove the RFI and hiss, try exchanging NE5532 with LME49720 as simplest fix.
 
If you don't like the 'warmth' in the sound with your equipment or music, you should remove the NE5532, they put that there for the colour of NE5532, it's quite easy to change this into a raw and transparent amplifier.

I used my iPod as a source with a line out as well as my Audioengine D1. As for IEMs everything and anything. As i said i used DBA-02 for hiss testing and i used my Heirs, EX1000 and any other IEMs i was using at the time for reviews etc. What do you think this has a best use as then and i am guessing you really like it, what OPamps are you using, i have LME49720s sitting around from my Otomatsu but thats all.

 

[kiteki]

If min volume is 7 o'clock and max volume is 5 o'clock, I can only detect hiss or RFI starting at 1 o'clock, the rest is dead silent using my very sensitive TWFK IEM's.
 
 
I think this has a best use as a portable amp for a higher-end DAP like Colorfly CK4 or Sony A series.  I just use mine for desktop though and actually it won't charge, so I need a seperate 9V charger for it.
 
I use AD797 at the line-out on my DAC, then AD797 on the line-in of the MRB (where AD8620 is), LME49720 on the HP-out (where NE5532 is) and the third one is a secret.
 
If you have a spare LME49720, you can try that on the line-in and HP-out, that'll improve the sound.  Then on the third socket (between the four capacitors next to the battery) you can try NE5532 if you have nothing else, not AD8620 since it will die there.
 
 
Edit:  Wait don't you have LME49710 for the Otomatsu?  Anyway, you can start by putting LME49720 where NE5532 is, and put NE5532 where LME49720 is, and leave the AD8620 where it is.
 
Let me know if that reduces the hiss for you, and what you think of the new sound.
 
Edit 2:  Ideallly you want to get NE5532 completely out of there, if you don't have any spare op-amps at all, just move around the three inside of it however you wish, except don't put AD8620 in the socket next to the battery between the four capacitors or there'll be smoke coming out lol.