[cheapskateaudio]

TL; DR
 
Interesting responses there, I didn't read most of them, quite frankly I found them boring and predictable.
 
Here's the deal, the O2 just kind of sucks stock with HD650's.
 
Can you imagine a headphone amp that makes the HD650's sound thin and harsh? 
 
Yeah... maybe it's my source, a DAC known for being bass heavy and overly smooth, the uDac. And, I guess Sennheiser should have designed their headphones with the most objective amp ever created, the O2, clearly, Sennheiser has failed.
 
Do something smart and easy, swap out some caps and get an amp that is actually listenable with HD650's. 
 
------
 
BTW, I'm not saying this amp is bad, in fact, I really like the amp...modded.

 

[Willakan]

 Well, everybody else seems to be enjoying theirs*, so perhaps an equaliser would have been rather easier than claiming the amp is somehow flawed stock. There is nothing wrong with liking colouration - almost everyone does to some extent. What is wrong is positioning anything that deviates from that expectation as somehow broken. Trying to fix it by doing your utmost best to potentially seriously degrade the performance of the design is just insane. 
 
Besides, we have yet to establish your changes have actually made a significant difference. It's likely we'll never know, you lacking a test bench and suchlike and blind-testing modifications is invariably difficult.
 
*Although if they weren't I can't say it would affect my opinion of the amplifier.
 
EDIT: Just occurred to me: the uDAC clips from its line outputs on peaks. Could explain the harshness...
 

 

[LizardKing1]

Actually, I really hope they used something better than the O2 when designing a 600$ headphone! And by better I mean more of a wire-with-gain.
 
Just posting to inform you I have placed an order for 2x O2 boards. I'll work on ordering the components now. The only problems so far seem to be that the only 2 "good" headphones I have are the Shure SRH750 and Hifiman RE-Zeros (at least those are quite detailed and pick up hiss easily). I also know enough about electronics to be able to turn the soldering iron on and barely more. And finally, the components are a bit expensive, leaving little financial room to get 2x the components.

 

[SobbingWallet]

 
Quote:

You're assuming amps are perfect. The proof that they do make an unwanted (by neutral lovers) sound is the coloration they cause. An amp should be a silent device, but it isn't, the same way as an engine should 100% performance, but it doesn't. You can't say something like "amps don't have a sound because they do not make a sound" and then go "the amp is flawed". They contradict each other. I think that's what an amp should do, but unfortunately it's not the truth. But hey that's why we're in this thread =)

 
I think you misunderstood his meaning:  He was saying that amps do not actually make a sound, because they do not output sound.  They output electricity, and their performance revolves 100% around electrical measurements and 0% around audio, no matter how colored or uncolored their output signal is.  If they directly produce any sound (except for maybe a low-level whine), it probably means they're about to explode and burn your house down.

  In our particular case, we encode audio information in these electrical signals, but a signal is always a signal (whether distorted/accurate), and an amp doesn't need to know/care whether the signal is carrying audio information or newspaper text about the latest fads in Bangladesh.  You put headphones around your ears and listen to them, because they actually translate electricity into sound; you don't put an amp up to your ear and listen to it, because you'll either hear complete silence, a slight whine, or fiery death.
 
In this sense, no solid state amp makes a sound, but some have more accurate electrical output than others.  Hopefully his post makes more sense now.

 
Quote:

TL; DR
 
Interesting responses there, I didn't read most of them, quite frankly I found them boring and predictable.
 
Here's the deal, the O2 just kind of sucks stock with HD650's.
 
Can you imagine a headphone amp that makes the HD650's sound thin and harsh? 
 
Yeah... maybe it's my source, a DAC known for being bass heavy and overly smooth, the uDac. And, I guess Sennheiser should have designed their headphones with the most objective amp ever created, the O2, clearly, Sennheiser has failed.
 
Do something smart and easy, swap out some caps and get an amp that is actually listenable with HD650's. 
 
------
 
BTW, I'm not saying this amp is bad, in fact, I really like the amp...modded.

Heh.  It's interesting how you can dismiss responses as boring and predictable without reading them.

 
Nobody ever said the O2 is the best possible amp for the HD 650.  The point is that it's neutral, which makes it a whole lot better [unmodded] than any other sub-$1000 amp if you have (or wish to try or compare) multiple headphones.  If you think it sucks with the HD 650, that really just means you don't like how the HD 650 actually sound without doing additional processing to the signal before it gets to the headphones.
 
Since you already have the HD 650 and convey no desire to switch, then maybe swapping out op-amps and capacitors as a random trial-and-error process is an "easy" way for you to get a better sound from what you have.  However, if your individual subjective opinion of the O2 + HD 650 is in any way reliable, then perhaps the rest of us should "do something smart and easy" as you say...and not get an HD 650.

 
 

 

[Paul Blythe]

LizardKing1: I printed out a copy of the BOM and circuit board diagram for easy reference of part placement, it helped me through my first O2 build. I've no electronics experiance/knowledge and had only built 2 CMoy's before the O2 and it all went smoothly... I'm hoping to get a SE-SE version of the The Wire and the idea of doing SMD stuff has me scared.
 
At the moment the only thing I'm not liking about the O2 is the enclosure I put mine in... Quite happy with the way my HD650's sound, though I did reduce the gain down to x1 as it was way to loud for me.

 

[EddieE]

Quote:

You're assuming amps are perfect. The proof that they do make an unwanted (by neutral lovers) sound is the coloration they cause. An amp should be a silent device, but it isn't, the same way as an engine should 100% performance, but it doesn't. You can't say something like "amps don't have a sound because they do not make a sound" and then go "the amp is flawed". They contradict each other. I think that's what an amp should do, but unfortunately it's not the truth. But hey that's why we're in this thread =)

No I mean quite literally that amps do not make a sound. Transducers make sound.
 

 

[cheapskateaudio]

 
Quote:

 Well, everybody else seems to be enjoying theirs*, so perhaps an equaliser would have been rather easier than claiming the amp is somehow flawed stock. There is nothing wrong with liking colouration - almost everyone does to some extent. What is wrong is positioning anything that deviates from that expectation as somehow broken. Trying to fix it by doing your utmost best to potentially seriously degrade the performance of the design is just insane. 
 
Besides, we have yet to establish your changes have actually made a significant difference. It's likely we'll never know, you lacking a test bench and suchlike and blind-testing modifications is invariably difficult.
 
*Although if they weren't I can't say it would affect my opinion of the amplifier.
 
EDIT: Just occurred to me: the uDAC clips from its line outputs on peaks. Could explain the harshness...
 

I read NwAvGuy's posts on the uDac before I built the amp or even ordered the parts for it. So I already took that into account. 
 
Why is what I'm doing insane? I'm taking my destiny into my own hands, that is far from insane, and is in fact the real core of being a DIYer. If I can make it sound better without unduly increasing noise or distortion, then it's a win-win. 
 
I do thank and admire NwAvGuy for making an amp that was so easy to upgrade that even a total noob could do it. 

 

[EddieE]

Nobody has any problem at all with you doing anything at all to your own amp if you prefer the sound of it.
 
The issue is your saying things like you've "upgraded" the design and that it "sucked" to start with.
 
The thing is, we've all seen the measurements of the amp as it was to start with, and there's nothing wrong with it. 
 
The simple explanation is that you're used to hearing the HD650 with its sound messed up a bit by an inferior amp, you prefer it that way, and your "upgrades" make it sound more like the headphones you're used to.
 
There's actually no problem with that. Sound is subjective, and you're free to prefer whatever sound you like and enjoy it.
 
It's just stupid to keep going on that you've improved a flawed design against all available evidence.

 

[SobbingWallet]

Quote:

Nobody has any problem at all with you doing anything at all to your own amp if you prefer the sound of it.
 
The issue is your saying things like you've "upgraded" the design and that it "sucked" to start with.
 
The thing is, we've all seen the measurements of the amp as it was to start with, and there's nothing wrong with it. 
 
The simple explanation is that you're used to hearing the HD650 with its sound messed up a bit by an inferior amp, you prefer it that way, and your "upgrades" make it sound more like the headphones you're used to.
 
There's actually no problem with that. Sound is subjective, and you're free to prefer whatever sound you like and enjoy it.
 
It's just stupid to keep going on that you've improved a flawed design against all available evidence.

This times a million.  The "spirit of DIY" is usually to hack things together and see what works, because nobody usually knows quite what they're doing, everyone's flying blind, and throwing darts at an invisible target to feel out its shape (and getting a decent result from it) can be a lot more fun and rewarding than paying out the butt for a professionally built but hugely overpriced product.
 
In this particular case, someone who actually does know what he is doing decided to rigorously engineer an inexpensive amplifier that is objectively correct (at least under sane conditions).  The "spirit of DIY" can still be fun here, and it can still get better results with a particular set of headphones, but repeatedly calling modifications "upgrades" is just insulting and arrogant, especially considering that they surely degrade the objective performance.  (The end result is not just that the measurements will be worse:  The end result is that mods specific to one listener's HD 650 preferences will most likely degrade subjective audio quality on average, over the broad spectrum of available headphones on the market.)
 
It's cool to swap out op-amps and capacitors to suit your preferences with your headphones; it's galling to call them "upgrades" and thumb your nose at the audio quality of the original design, based exclusively on your individual subjective listening with a particular headphone set.  For instance, underlining the word "upgrade" is flat-out trolling.

 

[cheapskateaudio]

Quote:

 
Since you already have the HD 650 and convey no desire to switch, then maybe swapping out op-amps and capacitors as a random trial-and-error process is an "easy" way for you to get a better sound from what you have.  However, if your individual subjective opinion of the O2 + HD 650 is in any way reliable, then perhaps the rest of us should "do something smart and easy" as you say...and not get an HD 650.

 
 

RE the HD650's, I'm not putting that beyond the realm of possibility. But before I blame Sennheiser and their time tested award winning products, I'm going to point the finger at the O2.
 
Swapping caps was not random, it is a common modification (thats why I found it so easily), especially changing the coupling capacitors. What I have read is that coupling caps by their very nature and position in the circuit color the sound. The fact that the amp has them means that it is already less than neutral and that the sound of the amp will be affected by changing the cap, to either good or bad effect. 
 
 

 

[SobbingWallet]

Quote:

RE the HD650's, I'm not putting that beyond the realm of possibility. But before I blame Sennheiser and their time tested award winning products, I'm going to point the finger at the O2.
 
Swapping caps was not random, it is a common modification (thats why I found it so easily), especially changing the coupling capacitors. What I have read is that coupling caps by their very nature and position in the circuit color the sound. The fact that the amp has them means that it is already less than neutral [citation needed] and that the sound of the amp will be affected by changing the cap, to either good or bad effect. 
 
 

 
EDIT:  Whoa, wait.  The O2 doesn't have any electrolytic caps in the signal path anyway, let alone capacitor-coupled output, so aren't you barking up the wrong tree?  In any case, the O2's measurements clearly refute any claims that it's "less than neutral."  It definitely doesn't have bass rolloff for low-impedance headphones, which seems to be the hallmark of amps with capacitor-coupled output.
 
Just because Sennheiser's products are time-tested and award-winning, that doesn't mean you'll necessarily like them.  Apparently you don't like the HD 650's sound unless you color the signal before it reaches the headphones.

 

[Anaxilus]

 

Quote:

 
Nobody ever said the O2 is the best possible amp for the HD 650.  The point is that it's neutral, which makes it a whole lot better [unmodded] than any other sub-$1000 amp if you have (or wish to try or compare) multiple headphones.  

Unbelievably religious comment.  Ignored.
 
Quote:

No I mean quite literally that amps do not make a sound. Transducers make sound.

What is the point of this observation?   All amps have an effect on the source input to one degree or another, the point is to minimize it.  If you want to eliminate it then eliminate the amp.  I hear the iPhone and Clip+ should suffice.
_______
 
Is there some new evidence on Voldemort's site that he is a 'trained amp designer' as someone earlier put it?  Last I was on his blog I saw no mention of credentials or professional background.  In fact, he had to consult with actual amp designer(s) on this project if I recall despite his 'extensive' background.  Last I heard he was an EE that had enough time and interest to measure stuff and make an amp for the sake of making a point, hence the name 'Objective 2'.
 
Don't get me wrong, I appreciate all the actual objective work involved and the project itself, just not any of the other 'objective' nonsense that has and continues to rear up here.  That said, I look forward to hearing the amp.

 

[SobbingWallet]

 
Quote:

 

Unbelievably religious comment.  Ignored.

If you mean I'm on your ignore list, that's my loss; I really respect your posts, and you know a lot more about this hobby than I do.  At the same time, I think you took my comments the wrong way.  Instead of just criticizing my comment as "religious," can you please at least correct me and cite counterexamples?  I am honestly just not aware of any other objectively neutral, well-measuring amps short of Violectric amps and the Benchmark DAC1.  If I'm wrong, I'll retract my comment.  I may have overlooked the Burson amps too; I don't know much about them.
 
Then again, maybe you think it's "religious" to say that neutral amps are better for trying and comparing multiple headphones (with different signatures) than colored amps.  Rereading my comment, I can see why you might have taken it as a direct insult to amplifiers you like [with multiple headphones].  In all honesty I think I overstated my point, because amps that specifically introduce harmonic distortion or crossfeed can indeed sound subjectively good (or better) overall with a wide variety of headphones.  I was really referring to colored amps that exhibit slowness, ringing, intermodular distortion, bleeding, etc., or which impact the frequency response in a particular direction (whether directly or via high output impedance), which adds an additional source of hardwired error to the signal path.  Those kinds of error (except IM distortion) may match up well with some headphones, but pairing them with a random headphone is just rolling the dice with arbitrary added error.
 
In hindsight, I was improperly conflating all colored amps with amps that have the kinds of error that don't translate well to vastly different headphones.  In reality, there are probably a good number of sub-$1000 amps with neutral or mostly neutral frequency response (etc.), and they'll fit well with a wide variety of headphones even if some of their other metrics don't measure well.  I'd still be surprised if any were near the price range of the O2 though.
 
In short:  I suppose I did overstate my point, but would a "religious" person admit to that?

 

[EddieE]

Quote:

 

Unbelievably religious comment.  Ignored.
 

What is the point of this observation?   All amps have an effect on the source input to one degree or another, the point is to minimize it.  If you want to eliminate it then eliminate the amp.  I hear the iPhone and Clip+ should suffice.
_______
 

 
The point was made in the two posts I made before it.
 
Since you can only hear how an amp affects a transducer, and not an amp itself, the listeners preferences regarding the test transducer is going to render any subjective impressions useless.
 
If someone thought a headphone had too much bass, they might think an amp that rolled off the bass was "better" than one that measured flat across the frequency response.

 

[Anaxilus]

Quote:

 
If someone thought a headphone had too much bass, they might think an amp that rolled off the bass was "better" than one that measured flat across the frequency response.

That is the assumption being made about how the individual in question is hearing the HD650 and O2 combination.  Though considering the O2 is supposed to be the ultimate expression of neutrality and performance for the price/package, it seems odd the HD650 would be described as thin w/ harsh treble.  That is certainly not a common impression of the HD650 plugged into a neutral and powerful desktop amp.  Unless of course the O2 is the first truly neutral amp to be made and most everyone has been hearing the HD650 colored for all these years.  Seems unlikely.  Perhaps something else is at play as well.  I'm sure someone else w/ an HD650 will be able to chime in eventually.