I love the O2 I built.  It's a great little amp, and it does many things very well.  Effectively reference grade it is not unfortunately. Don't get me wrong, it measures great and I don't think it sounds bad just that there are other amps that sound better.  The Wire I built sounds better and measures better, but I still wouldn't call The Wire reference grade.  Let's be honest as well.  The Leckerton is the only portable option of the two.  The O2 is transportable at best since fanny packs went out of style.  It's just too big to be portable.

Well, obviously we differ on what's meant by 'reference'. By a full set of measurements the amp is perfectly reproducing the audio in so far as human ears are concerned, but with more power. So to say that other amps sound better would probably be because they have audio flaws that please you (and let's not forget that maybe your O2 is faulty).

Here are some examples of flaws positively changing reported audio experience:

• improved soundstage: phase issues faking 3D
• more clarity: phase issues, as 3D is sometimes experienced as greater clarity (thinking of recent review I read)
• In the band effect: strong 3D from phase issues
• compression due to lack of voltage, which can be useful for music that has inconveniently too much dynamic range
• more bass: boomy 100Hz bass boost from high output impedance, expense of less extension
• less bass: high output impedance attenuating lower bass on overly bassy phones
• in-the-audience effect, that some prefer, on tracks mastered with strong  spatialisation: poor channel separation

But all these are done best by quality DSP which is exactly how music is produced today. I boost my etymotics at 40Hz by 9 to 12 db and they sound awsome and well suited to it due to their ultra-low distortion.

Any 'reference' not specified in terms of measurements but subjective listening is really a moving target both because of the non-objectivity of the listener(s) and the issues I've listed above. In any case I've not heard of such a thing.

In the case of the Wire, you shouldn't be hearing any difference. It was designed the same way (by objective measurements) as the O2 and has similar specs (but more power). The improvement on specs is inaudible.

However, I do agree that the O2 can really only be considered semi-portable.

If I was looking for a portable I would go the the FIIO E7, which measures great and has enough power for most practical portable headphones, and has a perfectly decent DAC included in the price. The 16 bit DAC doesn't matter with Windows computers because Vista+ processes everything in 32bit any way.

The Magni/Modi combo is great. I personally favour the O2/ODAC because the professionalism of the EE who designed it means it is much less likely that a design flaw (a real one) will end up damaging my headphones or blasting out my ear drums.

Quote from: omegakitty on March 15, 2013, 08:07:50 PM

Quote from: lorriman on March 15, 2013, 06:32:02 PM

Quote from: purrin on March 15, 2013, 03:17:15 PM

The O2 has a serious design flaw with the pot between the stages. Many users have hit digital clipping well below the predicted max voltage from sources. I guess one could lower the gain to 1, but that usually results in running out of room with the volume knob with most headphones.

Get a Magni instead for desktop use.
Get a Leckerton for portable.

That's really not a design flaw; very hot sources are rare

They aren't. I've heard DACs/CDPs with outputs as hot as 5 vrms (single ended) and as little as 0.5 v. I measured mine to be a little over 2.3 v S/E

Sample size of 1 here. Seriously, hardly anyone even in HIFI, have very hot sources.

What is your definition of very hot?

Quote from: ocswing on December 20, 2012, 09:24:04 PM

Quote from: rhythmdevils on December 20, 2012, 09:04:14 PM

Is it thought that O2/Odac sounds as good as UHA6?

The general consensus is the amp in the UHA6s is better than the O2, but the Odac is better than the UHA6s dac (at least comparing USB).

I wouldn't pay any attention to consensus. It's too easy for 'interested partys' to manipulate the forums. It's very much in the interests of manufacturers to do this and I have little doubt they do. And some are strongly motivated to do down the O2/ODAC due to the history of it.

Another issue is that both devices should, in theory, sound the same unless they are faulty. So that 'consensus' means that 3rd party forum manipulation is therefore even more likely.

In the end, the O2/ODAC is effectively reference grade with very high power (there's almost nothing that they won't drive to dangerous levels) whereas the Leckerton is low power and will stuggle with many headphones and/or low voltage sources. If anything, certain heaphones will sound better with the O2/ODAC combo.

[Edit: all things being equal, the LEckerton is the better portable solution]

Funny you say Leckerton UHA-6S is low power. It can drive HE-500 (own) and HE-6 with gain switch on (+18 dB) and has some comfortable 50% headroom (reduced to 33% when equalized). Also Senn HD600, HD650 (both 300 Ohm), and Beyerdynamic DT880-250. I haven't tried it on any 600 Ohm headphone yet, but I suspect it will be able to drive those as well.

Try running some square waves with a real headphone load (both small and large signal) through O2 and Leckerton and you'll see it. O2's slightly overcompensated (by design, to be conservative) and thus a teensy bit slow, while Leckerton has some slight overshoot. (OPA209 version) The audibility of it exists, but differentiating is hard - and many people will use "fuzzy" terms to describe the sound.

Granted, the one I heard was not as perfect as the one measured by its creator, but it did exceed (80s) equpiment capabilities.

Overshoot might actually be beneficial - similar to how sharper normal bicubic scaling is perceived as better than perfect bicubic spline. And our ears are more sensitive to transients (edges) than to frequency - and more than Fourier limit.

--
I think O2 hate is more reactionist.

It's a good amp, but not the be-all end all in the default configuration - it's easy to improve though with minor modification.

This is all very disturbing, letters too big for my screen... 

The O2 has a serious design flaw with the pot between the stages. Many users have hit digital clipping well below the predicted max voltage from sources. I guess one could lower the gain to 1, but that usually results in running out of room with the volume knob with most headphones.

Get a Magni instead for desktop use.
Get a Leckerton for portable.

What about the Odac vs. the Modi?