[PTom]

I know what you mean. Settling on one amp possibly narrows down the list of suitable headphones for your tastes. However that might not necessarily result in the best sound quality or value for money just simplicity (or lack of choice depending on how you want to look at it).
 
I thought headphones were more important for SQ than amps? If that is the case it might be better to decide on a headphone and then find out from current owners which amps go well with it.
 
I used to be in awe of the O2 till I actually owned/heard it, now I'm a believer of systems and synergy. 

 

[Solrighal]

Even at the level I'm at this is pure indulgence but when I got my ODAC/O2 and plugged them in I was blown away. I've never heard music as beautifully as I'm hearing it now with the HD650's.

This will not be my last amp however. I intend to buy something with valves to emphasize the smoothness of the Sennheiser's, maybe a Schiit Lyr. I'd really like a Crack+SB but it's kinda out of my reach and I think the Lyr may prove useful to a wider range of headphones.

I would say headphones are more important for sound signature but "quality" to my mind is not exactly the same thing. Headphones are more about presentation whereas the amp only really has to provide a clean original signal.

 

[r010159]

  In the objective vs subjective debate I'm starting to think that both sides are right. The O2 might well be the 'perfect' amplifier if all you need is amplification, however you might not end up with a 'perfect' sounding system unless it complements your headphones. 

 
I agree with this.

 

[MrMateoHead]

***Delete

 

[SilverEars]

LOL.  O2 drives the HE-6 to loud volumes, just like the LCD-2.  There is no question O2 can drive HE-6 to listenable volume and louder.  
 
I don't know what it is in the Amp design would account for the better sound.  It is obvious that HE-6 sound better on the Beta 22.  Is it the THD, or flat FR, or the SPL or output impedance?  If you look at these numbers, they are well below the value that is audible compared to what is caused by the headphones.  Low quality amp can measure just as well as the best sounding amps.  Measurements are measurements.  

 

[MaciekN]

I remember a post from O2 thread at diyaudio where the deisgner of The Wire said he could easily tell his amp apart from O2 with HE-6. The reponse was that O2 was not designed to drive such inefficient and power hungry headphones - that these were simply the 1 or 2% that need a more capable amp.
 
By the way you may have noticed my General Headphone Amplifier Survey thread but just to be sure I am posting it here as well. I am doing a case study on what poeple expect a good amplifier to have and what are the qualities of amps that poeple here hold most important and I would really appreciate some feedback from those who have the O2.
 
Survey link: https://www.surveymonkey.com/s/773TTR3

 

[Solrighal]

Survey completed.

 

[MaciekN]

Thank you, much appreciated.

 

[gikigill]

Survey done.

 

[r010159]

Survey done.

 

[skeptic]

  Thanks for a well considered reply, it made for interesting reading.  Fwiw, I'm no electronics specialist by a long shot but I do agree with your observations about differently sounding OPA's and the complex -and mostly unpredictable- result of many small variances interacting.  Very interesting remarks about the slew rate, a couple of months ago I observed (don't recall if in this or another thread) that the slew rates the O2 could handle were imo marginal and almost got crucified for it 

.
 
My main point all along has been that perhaps there's more between heaven and earth than what's readily measurable.  I tend to shy away from both the absolute subjectivists -who tend to be good at burning other people's cash- as well as scope wielding objectivists for whom there's only 1 path to follow and where any deviation from the true religion is considered a capital offence.  Fanatics on both sides......
 
The booster board as well as agdr's overhauled and assembled product look very interesting, I'm sorely tempted to give one of them a try and compare with the ODAC/O2 sitting on my desk and feeding my HE-500 right now.  But don't want to be stuck soldering a bagful of tiny components and at the price of the finished product I'd be about halfway down a B22-build or 2/3 down a F5-clone.  But it sure takes up less desk space and (especially compared to the F5) one can run it without heating up the entire office.

 
Thanks for the thoughtful response Xenophon.  I love your humorous characterization of the hard core subjectivist vs. objectivist factional dispute!  Also, I tend to agree that the standard array of audio measurements just don't seem to paint a complete picture of everything that we seem able to perceive.  It should be fascinating to see what audio measurements look like 30 years from now.    
 
Per the thread on diyaudio, I think the earlier discussion of slew rate in this thread was what led agdr to suggest, test and ultimately recommend the substitution of dual LME49990's in the boosted O2 gain stage.  So thanks for your role in that!
 
As far as pricing goes though, I'm pretty sure I paid well under $100 total for the booster board, all its component parts (including the optional led's, extra zener, etc.) and the dual LME49990 adaptor (populated), from ebay.  That'll barely buy you a cheap imported chassis for a B22 or F5 build!  I'd encourage you to give it a go since it really does make for an excellent compact/bedside rig.  The booster was my first real smd project (aside from the op amps on my mini3), and as agdr commented to me, the 1206 sized smd components used on the booster really are a lot more humane than the ultra-tiny 0805's used on the Wire.  Just wipe a dab of solder onto one pad or the other.  Then pick up the component with your tweasers and set it on the board right up against the edge of the pre-tinned pad.  Then apply a little heat to the pretinned pad while sliding the component into position, effectively soldering that first side.  Then solder the other side just like you would with anything else.  Add a little more solder to the first side if need be.  It really is arguably faster and easier than through-hole once you've done a few.  Seeing the faint lines defining the orientation of the diodes was the hardest part!  I used a little chipquik paste flux for the op amps but found that I didn't really need it for the other components (was using rosincore cardas quad solder).

 

[Currawong]

I was talking to Tyll a while back and one measurement that isn't easily done without horrendously expensive equipment is Transient IMD. 

 

[miceblue]

I was talking to Tyll a while back and one measurement that isn't easily done without horrendously expensive equipment is Transient IMD. 

Speaking of Tyll, it was interesting to see that the O2 wasn't listed in his "Wall of Fame" for amplifiers even though it measures quite well and was comparable to the Pico Slim (I think?), which wasn't in the list either.

 

[Currawong]

 

I was talking to Tyll a while back and one measurement that isn't easily done without horrendously expensive equipment is Transient IMD. 

Speaking of Tyll, it was interesting to see that the O2 wasn't listed in his "Wall of Fame" for amplifiers even though it measures quite well and was comparable to the Pico Slim (I think?), which wasn't in the list either.

 
IIRC the Pico Power measured better (and is under $500, which was nwavguy's challenge, wasn't it?). The Pico Slim has some noise from the volume chip.

 

[skeptic]

I was talking to Tyll a while back and one measurement that isn't easily done without horrendously expensive equipment is Transient IMD. 

Interesting! Thanks for sharing this Currawong! I looked it up and found the following summary explanation:

"There is also transient intermodulation distortion (TIM) to which modern integrated circuits are susceptible. Such circuits depend upon feedback for their linearity, but time delays in the feedback can cause intermodulation distortion on fast transients in the signal."

So I wonder, if this arises based on time domain issues in feedback amps (all op amps require feedback to operate in a linear mode, for example) - does that mean this type of distortion isn't present at all in nonfeedback SET amps?

If so, here's hoping that the TIM measurement process and equipment become cheaper and more widespread over time.