I finished this to the point that I can turn it on. It worked with the 9v and hasn't caught on fire yet so I assume it's safe for use with the wall-wart. Right off the bat it sounds better than the uDac 2 in terms of overall sound balance. The music seems to come from a darker background compared to the uDac 2 headphone out, even via the uDac 2's line outs. 
 
Treble seemed more zingy at first, but on closer inspection is not just more zingy, but more clear, the two amps have similar tone in the treble region. Using the O2 I think the decay is better on cymbal crashes and overall there seems to be a bit more clarity to the treble.
 
Bass is where I'm hearing the biggest differences, not only quantity but quality. The bass is more pronounced and better defined with the O2. Bass is truly thunderous when called upon to be so and seems to come from outside your head.
 
Midrange is more full and more *real* sounding than the uDac 2. The uDac 2 can seem distorted or colored relative to the O2, although the uDac 2 can have a very musical tone that is appealing on certain tracks.
 
Dynamics seem improved with the O2, the uDac seems to be clipping during particularly loud passages, this is very evident when the digital volume is set to 0, knocking it down -2db alleviates that issue but clarity and that little extra oomph seem to be missing from the uDac 2 compared to the O2.
 
The O2 is very clean sounding, the uDac 2 is more musical sounding, the cello seems to have more music in it with the uDac 2, even as it sounds a little flat at times. The uDac 2 can sound flat in complex passages, and while it's musical tone is definitely appealing, it does not have nearly the clarity the O2 has, nor does it have nearly the power to drive a headphone like the HD650.
 
The above impressions are all at higher volumes, at lower volumes the clarity of the O2 is just too far beyond the uDac 2 to even warrant comparison. One is powered by AC and the other by a measly USB output, this is obvious to hear when listening at lower volumes... The uDac 2 is relegated to class F, for FAIL status at low volumes. 
 
Based on my initial impressions I hereby declare, officially, without reservation or psychic influences beyond my control or understanding, the O2 headphone amplifier superior in all respects to the uDac 2 headphone amplifier. It is a great sounding amplifier!
 
O2 >>> uDac 2
 
Objective > Subjective, most of the time
 
Thanks to the unnamed for providing this cheap and easy to build kit to the DIY community!
 
 
I'll post a more complete review of the amp in the appropriate forum at a later time. For now, enjoy these photos of the build process:
 
 
 
Resistors on:

 
Further along:

 
Almost done:

 
It worked...WOOT!

 

Glad to see the O2 completed, so when are you going to build a Beta 22   ?

Incredible! Thanks for the impressions. Any gotchyas you encountered that the rest of us builders might like to know?

Now you need to compare it to an amp that doesn't suck 

Wow awesome. Thanks for the impressions and comparison. I guess He Who Shall Not Be Named's main goal was accomplished - to listen to the music and not the amp.
I don't know if you're an experienced DIYer, but how would you rate the complexity of this build on 1 to 10 (10 being barely achievable, 1 being plugging the soldering iron on)?

Quote:

lizardking1 said:

Wow awesome. Thanks for the impressions and comparison. I guess He Who Shall Not Be Named's main goal was accomplished - to listen to the music and not the amp.
I don't know if you're an experienced DIYer, but how would you rate the complexity of this build on 1 to 10 (10 being barely achievable, 1 being plugging the soldering iron on)?

Click to expand...

I would rate it around 4-5, firstly its not even wiring anymore, its PCB based afterall. Its a matter of soldering parts only. But the only thing to be careful on is that you do not solder wrongly( can be a mess taking it out) and handling the MOSFETs. 

 
Quote:

firev1 said:

I would rate it around 4-5, firstly its not even wiring anymore, its PCB based afterall. Its a matter of soldering parts only. But the only thing to be careful on is that you do not solder wrongly( can be a mess taking it out) and handling the MOSFETs. 

Click to expand...

I will be doing some wiring to install a 1/4" jack and RCA inputs, but 4/5 is probably right.


Quote:

micmacmo said:

Incredible! Thanks for the impressions. Any gotchyas you encountered that the rest of us builders might like to know?

Click to expand...

Nope, it's straightforward, you only have to look at the circuit diagram when installing RCA inputs and 1/4" phone jack. I will be installing those as soon as I drill out my case, or have someone else drill it.
 
 
Oh, the knob from the uDac 1 fits on there, so, to add insult to injury I've started to strip the uDac 1 for parts...
 

Interesting, even a cable believer can appreciate the O2.

Congrat's on getting it up and running... just a reminder when using P1 for off-board inputs, if you have the 3.5mm jack plug inplace you need to cut the ground trace between pins 3 & 4 on J2. The off-board inputs won't work otherwise...
 
How long did it take to assemble?

 
Quote:

satellite_6 said:

Interesting, even a cable believer can appreciate the O2.

Click to expand...

I'm going to be measuring that soon, so be careful, you may eat your words!  
 
Seriously though, I can't even listen to the stock cable any more, it sounds bloated and muddy. Some might say it's "fuller" and more "musical", but all at the expense of clarity and most importantly rhythm. Having the mids bloated doesn't suit symphonic music, there's already enough mids there... 
 
Don't worry, I'll measure this, boy WILL I EVER!

 
Quote:

paul blythe said:

Congrat's on getting it up and running... just a reminder when using P1 for off-board inputs, if you have the 3.5mm jack plug inplace you need to cut the ground trace between pins 3 & 4 on J2. The off-board inputs won't work otherwise...
 
How long did it take to assemble?

Click to expand...

Took about 2 hours to assemble, and thanks for the tip!


Quote:

parall3l said:

Glad to see the O2 completed, so when are you going to build a Beta 22 

 ?

Click to expand...

When I forget about all the money I've spent in the past 2 months! Why are you people doing this to me, can't you let me live in blissful ignorance for one moment?

Quote:

cheapskateaudio said:

 


I'm going to be measuring that soon, so be careful, you may eat your words!  
 
Seriously though, I can't even listen to the stock cable any more, it sounds bloated and muddy. Some might say it's "fuller" and more "musical", but all at the expense of clarity and most importantly rhythm. Having the mids bloated doesn't suit symphonic music, there's already enough mids there... 
 
Don't worry, I'll measure this, boy WILL I EVER!

Click to expand...

 
The mids are not bloated, you are probably just used to V-shaped sound. 
 
I look forward to it. 
 
 

Quote:

lizardking1 said:

Wow awesome. Thanks for the impressions and comparison. I guess He Who Shall Not Be Named's main goal was accomplished - to listen to the music and not the amp.
I don't know if you're an experienced DIYer, but how would you rate the complexity of this build on 1 to 10 (10 being barely achievable, 1 being plugging the soldering iron on)?

Click to expand...

 
I'd rate it at 1.
 
All you need to know to complete this build is to know how to solder, and soldering isn't even difficult. Practice for 20 minutes (for someone who has never soldered in their life) with some cheapo resistors on a perfboard and you're good to go.
 
There are no pots to adjust, no parts to match, nothing to wire, and absolutely nothing to do at all except stuffing the boards. If you can follow a cookbook, you can build this amp.
 
You don't need to be able to understand circuit diagrams either, the silkscreen tells you what parts go where, and the orientation of said parts. Hell, the mouser baggies even tell you exactly what parts are inside the little bags, so you don't even have to know how to identify parts (although it's as easy as pulling up the datasheet and reading the letters on the parts).
 
I just don't understand why people are so afraid of DIY, there's nothing to it, especially on an amp like this.

deadlylover said:

I'd rate it at 1.

All you need to know to complete this build is to know how to solder, and soldering isn't even difficult. Practice for 20 minutes (for someone who has never soldered in their life) with some cheapo resistors on a perfboard and you're good to go.

There are no pots to adjust, no parts to match, nothing to wire, and absolutely nothing to do at all except stuffing the boards. If you can follow a cookbook, you can build this amp.

You don't need to be able to understand circuit diagrams either, the silkscreen tells you what parts go where, and the orientation of said parts. Hell, the mouser baggies even tell you exactly what parts are inside the little bags, so you don't even have to know how to identify parts (although it's as easy as pulling up the datasheet and reading the letters on the parts).

I just don't understand why people are so afraid of DIY, there's nothing to it, especially on an amp like this.

Click to expand...

Really. This amp is super easy to get together. It's essentially beginner level.

 
Quote:

deadlylover said:

 
I'd rate it at 1.
 
All you need to know to complete this build is to know how to solder, and soldering isn't even difficult. Practice for 20 minutes (for someone who has never soldered in their life) with some cheapo resistors on a perfboard and you're good to go.
 
There are no pots to adjust, no parts to match, nothing to wire, and absolutely nothing to do at all except stuffing the boards. If you can follow a cookbook, you can build this amp.
 
You don't need to be able to understand circuit diagrams either, the silkscreen tells you what parts go where, and the orientation of said parts. Hell, the mouser baggies even tell you exactly what parts are inside the little bags, so you don't even have to know how to identify parts (although it's as easy as pulling up the datasheet and reading the letters on the parts).
 
I just don't understand why people are so afraid of DIY, there's nothing to it, especially on an amp like this.

Click to expand...

 


Quote:

magedark said:

Really. This amp is super easy to get together. It's essentially beginner level.

Click to expand...

Yeah, the project's creator believes you should have a MM before beginning this, I don't have one and yet it worked without a hitch... but had something been wrong, like a mosfet or opamp busted, I would have had a hell of a time figuring it out with no MM. So I would rate it a 3 to a 5 especially if you want to go all the way with 1/4" jack, RCA inputs, and custom drilled panels for front and back, 5 for sure if you drill your own panel, (unless you own a CNC machine ). If I call something a 1, it would be soldering a wire or two here or there, I'd say making custom cables is a 2 or 3 because not a lot of precision is required but care is required. The key is to understand what can go WRONG, ie, you can blow up your headphones or maybe even kill yourself with anything that plugs into the wall...
 
When you get overconfident is when you get bit in the butt!
 
So yeah, 3 to 5 on the difficulty scale.