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O2 AMP + ODAC - Page 183

post #2731 of 3214

As a general matter, I can't wrap my mind around why we are discussing the O2 and HE6 in the same sentence - maybe we should assess its performance with K1000's or maybe a pair of magnepans while we're at it?  The designer was totally candid about the fact that the O2 wasn't intended to drive outlier phones - which very few head-fiers own to begin with.  Fostex and, to a lesser extent, Audeze orthos are certainly fair game for discussion.  There is no question that the O2 drives the former very nicely, and we seem to have some divergent opinions as to the latter.  Fair enough.  The amp is also excellent with iem's at unity gain, and I like it with my dt880's but no so much my hd650's for whatever reason (although I should really try them again with the agdr booster in place).  

 

Quote:

Originally Posted by proid View Post

 

Don't take that post too seriously, O2 is very good indeed but it has its limit. I think the guy who posted that comparison just doesn't have really good hearing ability. I haven't heard the B22 with my own gear and setup but O2 is still 1 step down compare to my PPAV2 and 2 step down compare to my friend's Dynalo, with me i can hear the different very clearly and the O2 is definitely not up to level of these two so i don't even care to compare it to B22.

 

These are valid subjective impressions, but I think it is worth noting that other veteran head-fiers (e.g. as quoted below) have arrived at opposite conclusions on these points.  On the specs, the O2 trumps both of those amps in spite of the fact that the ppav2 measurements were made without a load.  So the interesting question in my mind becomes why many of us ultimately prefer other amps (at least with particular phones) that don't meet the same measurements.  I love my mainline, for example, and have often hypothesized that a certain amount of even order distortion is making up for the room effects we don't get with headphones, creating (for some of us at least) an illusion of music that sounds more like a live performance in an acoustically pleasing venue.   

 

I also chuckled a bit at the comparison to the dynalo since just the other day, USG, a head-fi veteran since 2004, posted the following about his GS-1 over in the hd650 thread:

 

Quote:
 Regarding the O2, the GS-1 can play louder than the O2 but I don't think I'd want to bet on my ability to distinguish between the O2 and the GS-1 at moderate listening levels with my T-1s (dac used was a North Star 192MKII with either a Blue Circle Thingee or a HiFace transport, ... the HiFace having more resolution and a hotter treble than the BCT and the Thingee having less resolution but a better tone ).  Unfortunately, once I discovered no apparent JND between the O2 and GS-1 with the T-1s, I never bothered to compare extensively or further with the 650s, '04/880s, or the 701s I almost never use. 
post #2732 of 3214
Quote:
Originally Posted by Zorrofox View Post

Would AGDR's Booster Board be of any use to my HD 650's?

 

I'm inclined to think there would be audible improvements, since I'm increasingly convinced that I like the amp with my AD's quite a bit better following the installation of the booster.  Admittedly, It has been a while since I listened to my 650's with my O2, since I didn't really love the combo stock, but I'll try to remember to bring the 650's home from the office to try them out with the booster.

 

If you implemented the further mod to raise the voltage on the power rails (which the booster makes possible - see the second asterisk on http://www.agdraudio.com/Page2.html), my guess is that that might further audibly improve performance with high impedance headphones.

post #2733 of 3214
I was getting excited at first but now I'm thinking (from what I've read thus far) that I might not be able to fit the booster board in my case as it has two sets of RCA's on the rear plate.
post #2734 of 3214
Quote:
Originally Posted by skeptic View Post
 

 

I'm inclined to think there would be audible improvements, since I'm increasingly convinced that I like the amp with my AD's quite a bit better following the installation of the booster.  Admittedly, It has been a while since I listened to my 650's with my O2, since I didn't really love the combo stock, but I'll try to remember to bring the 650's home from the office to try them out with the booster.

 

If you implemented the further mod to raise the voltage on the power rails (which the booster makes possible - see the second asterisk on http://www.agdraudio.com/Page2.html), my guess is that that might further audibly improve performance with high impedance headphones.

Sticking to the objective mantra and playing devils' advocate for a moment:  given the specs/measurements of the HD-650 and the pre booster-board O2, where do you expect to find objective improvements by adding this?  Going by the designer pages, power appears to be ample to drive it and I'll just refer to the qualities that have so vociferously been defended in this thread for the other aspects (neutrality etc).

 

So, let's have it, where are the auditive improvements?

post #2735 of 3214
Quote:
Originally Posted by Xenophon View Post
 

Sticking to the objective mantra and playing devils' advocate for a moment:  given the specs/measurements of the HD-650 and the pre booster-board O2, where do you expect to find objective improvements by adding this?  Going by the designer pages, power appears to be ample to drive it and I'll just refer to the qualities that have so vociferously been defended in this thread for the other aspects (neutrality etc).

 

So, let's have it, where are the auditive improvements?

 

A good question indeed.  Even though distortion measurements started off, and then were reduced further, below the what is often considered the threshold of audibility, my understanding is that different "measurement first" designs and topologies are still often (if not usually) perceived as sounding different [for reasons beyond my understanding and pay grade].  For example, I've read a lot of posts here and elsewhere regarding both the O2 and the Wire.  It could be the product of confirmation bias, but I have yet to see a single post here or on diyaudio where someone suggests these two ultra low noise/distortion amps sound indistinguishable.    

 

My sense is that perceived differences may have a few different sources:

 

(i) Different active devices (e.g. op amps, to say nothing of tubes) do seem impart subtle differences to sound quality, and I imagine this is further complicated by the fact some of these semi-conductors have fet vs. bipolar inputs.  Think about the fact that certain diy amps (e.g. the dynahi/dynafet and differing fet vs. bjt revisions of the ehh rev. A) were created based on this theory - that these transistor types have different flavors.  So by replacing my output chips with the booster board circuit, and also my gain stage chip with dual LME49990's, I think it is unsurprising that I would hear subtle but discernible differences - although I still do intend to build another stock o2 to compare back to back.  Making matters even more interesting, agdr's bom offers up several different chips that can be used in place of the OPA140's on the booster.  Some are fet inputs, and some are bjt's, and they all have differing impacts on noise, distortion and dc offset.  So there's also the potential to build and compare different versions of the booster circuit and see if we can hear any differences.

 

(ii) The serious reduction in dc offset on the headphone jack may also play in.  I used to think of dc offset simply in terms of not damaging the headphones, but as tangent and others explain it, minor dc on your jack also reduces dynamic range and possibly causes its own distortion.  The booster is a 150x reduction in dc offset from stock.

 

(iii) Some argue slew is inaudible above and beyond what the stock O2 can swing.  Others claim to love the 4 channel B22 because of its gargantuan ~170 something V/us slew rate, if memory serves.  Raising slew from the stock 3V/us to 20V/us with the LME49990's can't hurt.

 

(iv) Doubling current output on peaks compared to the stock O2 can only benefit transient response. 

 

All in all, to the best of my understanding, the booster is pretty awesome on paper, and my ears seem to like it a lot as well.  That said, if I'm off on any of the above - please jump in and correct me!

post #2736 of 3214

Just a noob question: :o

 

Will you be able to use the O2 without the batteries inside and just using the PS adaptor?

post #2737 of 3214

Yes the O2 can jut run on batteries...inside with the ac adapter unplugged...

 

Ptom...."Coldplay/Adele: Greatest Hits sound distractingly harsh with respect to the treble"

 

I humbly suggest that these sources are not even close to being the best in judging what the O2 is capable of doing...there are many other much higher quality choices to show what the O2 and other amps can do.

 

I really like Adele but the recordings that are out there IMO are not very well done...its sad but it is what it is.

 

I have many well recorded uncompressed and well mastered recordings that make me smile all the time with the O2 and other good amps....like the V800.

 

Good amps wont make ho-hum material sound better....and not so good amps or tube amps with distortion can help reduce certain frequency response making some material sound less harsh...but this is not the O2's fault.

 

Garbage in Garbage out..

 

When I listen to something that sounds like crap to me I always go back to my gold standards to make sure nothing else has changed.

 

A.


Edited by adydula - 4/21/14 at 5:37pm
post #2738 of 3214

How about the other way around? Using only the AC adapter without the batteries? I plan to use this on my PC and i don't want to worry about the batteries inside.

post #2739 of 3214

Yup that works too.... I run one that way with my PC.

 

A.

post #2740 of 3214

Thanks! ;) I appreciate it.

post #2741 of 3214
Quote:
Originally Posted by skeptic View Post
 

 

A good question indeed.  Even though distortion measurements started off, and then were reduced further, below the what is often considered the threshold of audibility, my understanding is that different "measurement first" designs and topologies are still often (if not usually) perceived as sounding different [for reasons beyond my understanding and pay grade].  For example, I've read a lot of posts here and elsewhere regarding both the O2 and the Wire.  It could be the product of confirmation bias, but I have yet to see a single post here or on diyaudio where someone suggests these two ultra low noise/distortion amps sound indistinguishable.    

 

My sense is that perceived differences may have a few different sources:

 

(i) Different active devices (e.g. op amps, to say nothing of tubes) do seem impart subtle differences to sound quality, and I imagine this is further complicated by the fact some of these semi-conductors have fet vs. bipolar inputs.  Think about the fact that certain diy amps (e.g. the dynahi/dynafet and differing fet vs. bjt revisions of the ehh rev. A) were created based on this theory - that these transistor types have different flavors.  So by replacing my output chips with the booster board circuit, and also my gain stage chip with dual LME49990's, I think it is unsurprising that I would hear subtle but discernible differences - although I still do intend to build another stock o2 to compare back to back.  Making matters even more interesting, agdr's bom offers up several different chips that can be used in place of the OPA140's on the booster.  Some are fet inputs, and some are bjt's, and they all have differing impacts on noise, distortion and dc offset.  So there's also the potential to build and compare different versions of the booster circuit and see if we can hear any differences.

 

(ii) The serious reduction in dc offset on the headphone jack may also play in.  I used to think of dc offset simply in terms of not damaging the headphones, but as tangent and others explain it, minor dc on your jack also reduces dynamic range and possibly causes its own distortion.  The booster is a 150x reduction in dc offset from stock.

 

(iii) Some argue slew is inaudible above and beyond what the stock O2 can swing.  Others claim to love the 4 channel B22 because of its gargantuan ~170 something V/us slew rate, if memory serves.  Raising slew from the stock 3V/us to 20V/us with the LME49990's can't hurt.

 

(iv) Doubling current output on peaks compared to the stock O2 can only benefit transient response. 

 

All in all, to the best of my understanding, the booster is pretty awesome on paper, and my ears seem to like it a lot as well.  That said, if I'm off on any of the above - please jump in and correct me!

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 :p.

 

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.

post #2742 of 3214
Quote:
Originally Posted by Xenophon View Post
 

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 :p.

 

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.


What does higher slew rate translate into sound? Faster... response?

post #2743 of 3214

Faster tracking and better response in (leading) transients, especially at higher frequencies.  That's what I could make of it at the time anyway.  But it's a complicated story and many factors (power supply, caps..) come into play, perhaps skeptic can provide a better answer as I'm pretty sure he's a lot more proficient in this stuff than I am..

 

Dug up a link for you:

 

http://www.onmyphd.com/?p=slew.rate

post #2744 of 3214
Quote:
Originally Posted by Xenophon View Post
 

Faster tracking and better response in (leading) transients, especially at higher frequencies.  That's what I could make of it at the time anyway.  But it's a complicated story and many factors (power supply, caps..) come into play, perhaps skeptic can provide a better answer as I'm pretty sure he's a lot more proficient in this stuff than I am..

 

Dug up a link for you:

 

http://www.onmyphd.com/?p=slew.rate


what i gathered from your link is that, if the SR is above a certain value, it doesn't do anything for the signal. Hence the question, what is enough?
O2 designer quote 0.2 uV/ Vrms, though I have no way of verifying it, nor the knowledge to:basshead:

post #2745 of 3214
Quote:
Originally Posted by anthk View Post
 


what i gathered from your link is that, if the SR is above a certain value, it doesn't do anything for the signal. Hence the question, what is enough?
O2 designer quote 0.2 uV/ Vrms, though I have no way of verifying it, nor the knowledge to:basshead:

 

Hi,

 

you might want to google "o2 op amp measurements slew rate", choose the first result and search for slew rate. This is the designers thoughts on this - his results are 0.9V/microsecond for 44kHz material, 1.8V/microsecond for 96kHz and 3.6V/microsecond for 192kHz. He comes to this result by assuming that the amp must be able to deliver +10V at point t0 for one sample and -10V at point t0+T for the next one. So you get Vpp/(1/fSample) or 20V/(1/44kHz)) or 20V/22microseconds = 0.9V/microsecond - rinse and repeat for the other sample rates.

 

O2 at 3V/microsecond meets all but the last and this is kinda irrelevant because this would mean you were "listening" to signal close to 100kHz at 0dB - not sure what this will do to the rest of your chain including your ears, though.

 

TLDR: The slew rate of O2 at 3V/microsecond is sufficient for audio at sample rates up to 192kHz.

 

Joachim

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