O2 Build Complete: Let the objective, subjective listening tests commence!

[mikeaj]

If I remember correctly, Voldemort claims to have designed speaker amps.  He also claims to no longer be involved with audio as a day job and thus has no direct commercial interest in the blog or amp.  The talk about consulting or getting help has to do with reading others' documentations and borrowing their ideas about audio amplifiers in general.  i.e. don't innovate for the sake of innovation.  The gain and output stages, or the "actual" part of the amp, is mostly boring and by the textbook.  And apparently that's indeed the way to go for high performance at low cost. 
 
A few minutes searching, and I think I found the relevant text regarding this:
 
"I HAD SOME HELP: Some really smart and well respected guys, like Douglas Self, Bob Cordell, Bruno Putzeys, Jan Didden, Walt Jung, Cyril Bateman, Samuel Groner, Siegfried Linkwitz, and others, have done extensive audio hardware research and published their findings. These guys have solid numbers, math, measurements and science on their side. Their published results often have an “Ap” for Audio Precision watermark in the corner indicating they use professional instrumentation. Many have published multiple books, papers, technical articles, etc. Their work has been extensively peer reviewed and has stood the test of time. They’ve found what works best from input circuits to capacitors to grounding schemes. They helped perfect the “wheels” of high quality audio. So, rather than go off and try to re-invent the wheel as many DIY and audiophile designers seem bent on doing, I liberally took advantage of their well proven research. Very few can match their expertise in their respected fields and I’m certainly not going to pretend I can do better. So to all of the guys above: Thank you!"
 
 
In my estimation, the typical EE graduate does not have enough background in analog electronics to do the design that was required and the documentations, at least without some significant practical experience or self study (though maybe not in the past, since cirricula has changed over the years to de-emphasize some relevant areas).  Maybe my interpretation of what's written is off, in any sense.  Anyway, people lie about credentials, so it's up to you about what you want to believe.
 
 
All that is irrelevant regarding the performance of the amp though, which I'm still waiting to be evaluated by a third party for comparison.

 

[skeptic]

To combat speculation with more speculation - based on the handle he uses on some other forums, I have been operating under the assumption that the designer may be an aerospace engineer.  That would be entirely consistent with his having (perhaps substantial) experience in analog amplifier design, albeit not in the audio industry.  

 

[snakeeater69]

So to those that don't like the amp. What sounds better than this for less than $200. Please name a few.

 

[fishski13]

Quote:

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.

 
you don't have a clue as to what DIY is about.
 
 

 

[cheapskateaudio]

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.

Is it stupid? Or am I simply the guy who isn't a dumb sucker for psuedo objective hyperbole?
 
Somebody actually change the coupling caps (YES IT HAS THEM, LOL), and tell me if you think it sounds *better* with the HD650's, I certainly don't hear any noise or distortion.
 
People like you are a danger to communities like this, communities where it is essential that we question everything we are presented with as part of our journey. And to avoid being taken for joy rides by lunatics with a rabid intolerant religious following.
 
Don't be surprised if "NwAvGuy" suddenly comes out with a new and improved amp, that is patented and *FOR SALE*. lol.
 

 

[cheapskateaudio]

 
Quote:

So to those that don't like the amp. What sounds better than this for less than $200. Please name a few.

Driving the HD650, the uDac 2 sounds better with most music types. The FIIO E7 is pretty good based on reviews, haven't heard it though.

 

[mikeaj]

Quote:

Originally Posted by cheapskateaudio /img/forum/go_quote.gif
 
People like you are a danger to communities like this, communities where it is essential that we question everything we are presented with as part of our journey. And to avoid being taken for joy rides by lunatics with a rabid intolerant religious following.

 
Yes, which is why people are questioning your approach and attitude (and most importantly, your results).
 
Anyway, here is a serious question:  do you believe that you are improving the fidelity of the amplifier, making it sound better, or both?

 

[cheapskateaudio]

 
Quote:

If I remember correctly, Voldemort claims to have designed speaker amps.  He also claims to no longer be involved with audio as a day job and thus has no direct commercial interest in the blog or amp.  The talk about consulting or getting help has to do with reading others' documentations and borrowing their ideas about audio amplifiers in general.  i.e. don't innovate for the sake of innovation.  The gain and output stages, or the "actual" part of the amp, is mostly boring and by the textbook.  And apparently that's indeed the way to go for high performance at low cost. 
 
A few minutes searching, and I think I found the relevant text regarding this:
 
"I HAD SOME HELP: Some really smart and well respected guys, like Douglas Self, Bob Cordell, Bruno Putzeys, Jan Didden, Walt Jung, Cyril Bateman, Samuel Groner, Siegfried Linkwitz, and others, have done extensive audio hardware research and published their findings. These guys have solid numbers, math, measurements and science on their side. Their published results often have an “Ap” for Audio Precision watermark in the corner indicating they use professional instrumentation. Many have published multiple books, papers, technical articles, etc. Their work has been extensively peer reviewed and has stood the test of time. They’ve found what works best from input circuits to capacitors to grounding schemes. They helped perfect the “wheels” of high quality audio. So, rather than go off and try to re-invent the wheel as many DIY and audiophile designers seem bent on doing, I liberally took advantage of their well proven research. Very few can match their expertise in their respected fields and I’m certainly not going to pretend I can do better. So to all of the guys above: Thank you!"
 
 
In my estimation, the typical EE graduate does not have enough background in analog electronics to do the design that was required and the documentations, at least without some significant practical experience or self study (though maybe not in the past, since cirricula has changed over the years to de-emphasize some relevant areas).  Maybe my interpretation of what's written is off, in any sense.  Anyway, people lie about credentials, so it's up to you about what you want to believe.
 
 
All that is irrelevant regarding the performance of the amp though, which I'm still waiting to be evaluated by a third party for comparison.

The gain stage is boring? It's not just boring it's almost literally the example circuit cited for various non-inverting feedback circuits all over the internet. I'm sure that with a couple hours of Googling I could design this gain stage, design the PCB layout, and have that part of the amp ready to roll. 
 
To the naysayers, I'm not saying it's bad, wrong, or flawed, I'm saying it needs improving for HD650's. Right now the amp sounds GREAT driving HD448's. The HD650's however, look, I prefer the uDac at this point, that is not subjective bias, it is the fact of my perception. Between HD448 and HD650 with the O2, I prefer HD448's. No joke they sound GREAT.
 
How and why does the amp sound like utter trash with the HD650's?  I'm trying to figure that out. Pardon me if I don't have the time to research the names of 9 different scientists and name drop to put the stamp of approval on all my ideas. 
 
Am I being a meanie or something? Am I not being "humble" enough? Gee I'm sorry if I offended anyone, but I'm simply offering my honest opinions and experiences, what else can I do? Factually I know nothing about NwAvGuy, who he is, where he comes from, what his background is... So pretty much I can only assume that if he can't make an amp sound good with the HD650's then he is just another DIY hack. Sorry. 
 
 
 
 

 

[Anaxilus]

Quote:

The FIIO E7 is pretty good based on reviews, haven't heard it though.

Ewww....I think you'd be lucky to get 25-30dB from that thing w/ the HD650 let alone maximize the potential of the driver.
 

 

[cheapskateaudio]

 
Quote:

 
Yes, which is why people are questioning your approach and attitude (and most importantly, your results).
 
Anyway, here is a serious question:  do you believe that you are improving the fidelity of the amplifier, making it sound better, or both?

There is a difference between me and NwAvGuy, I'm just a DIY hack saying "try this". I don't claim I built the worlds most perfectly objective amplifier and bestowed it free of charge on the unwashed masses in his infinite wisdom and kindness. 
 
If you have some caps lying around, try it, if not, don't or spend $5 bucks and buy a few, give it a shot. Are you telling me you can't take 5 min to solder in some new caps? I mean come on, do it or don't and get off my case! I'm not asking you to move mountains so don't act like I need to prove anything beyond the most basic point of simply listening to it.
 
Really, I'm just trying to understand why my HD650's sound like pure tripe with this amplifier. I honestly prefer the HD448's at this point, and that is beyond question! (With other amps I vastly prefer the HD650's)

 

[Anaxilus]

Well, there is a reason for the desktop amp and it's not to power Stax.  People seem to be claiming some of the hardest to drive phones out there can all be driven to optimal levels out of the portable version using their rudimentary math skills, even though a desktop is in the works.  Should tell you something.  Though this is just speculation as I haven't heard it yet.  I'll be sure to hook up my easy to drive HD800s w/ it and see how transparent and dynamic it is compared to my overkill desktop amps.

 

[cheapskateaudio]

 
Quote:

Well, there is a reason for the desktop amp and it's not to power Stax.  People seem to be claiming some of the hardest to drive phones out there can all be driven to optimal levels out of the portable version using their rudimentary math skills, even though a desktop is in the works.  Should tell you something.  Though this is just speculation as I haven't heard it yet.  I'll be sure to hook up my easy to drive HD800s w/ it and see how transparent and dynamic it is compared to my overkill desktop amps.

Maybe that is true, maybe this amp simply can't drive HD650's, that probably should have been mentioned at some point. It does have a gain switch, so... Maybe the gain switch is pointless and should be left off the board.

 

[mikeaj]

Quote:

Well, there is a reason for the desktop amp and it's not to power Stax.  People seem to be claiming some of the hardest to drive phones out there can all be driven to optimal levels out of the portable version using their rudimentary math skills, even though a desktop is in the works.  Should tell you something.  Though this is just speculation as I haven't heard it yet.  I'll be sure to hook up my easy to drive HD800s w/ it and see how transparent and dynamic it is compared to my overkill desktop amps.

Depends on what is being meant by being driven to "optimal levels."  If supplying a signal with very low distortion to levels that result in volumes in range of 110 dB SPL peaks counts, then yes, that should happen with most headphones (vintage AKG K240 models, K1000 of course, HiFiMan HE-6, etc. will not get quite that loud obviously, and most headphones will get much louder than 110 dB SPL...due to rudimentary math skills as you say).  Are you claiming that headphones will not be driven well if given a clean signal, or that something else will have better enough performance that you can tell the difference?  Maybe you need to go lower than 0.0005-0.002% THD typical (IMD SMPTE also under 0.002% at 15 ohms load) to get high fidelity......?
 
The desktop version is not about audible improvements in sound quality, mostly just usability tweaks like different jacks placement as well as space for some kind of (3rd party?) DAC module.  Maybe the input stage is getting reworked so there is no input clipping of hot sources on higher gain settings.  That would be nice I guess, if you own such sources.
 
It seems like the main reason for a desktop version being developed is that enough people asked for one.  Originally the response was more along the lines of suggesting that people use the current version minus batteries but with a larger enclosure, preferably with panel-mount jacks of desired type and location.

 

[Willakan]

@Anaxilus
Driving headphones is maths. How the hell do you think you work out how to drive a headphone to a given SPL? Wizardry? There is absolutely nothing more to driving headphones.Anything else is simply BS.
As it happens, the HD800s are a relatively easy drive for the O2. Yes, this observation is based on maths. It's not "rudimentary," it's right. It can also drive the crap out of the HD650s and the K701s. What exactly do you think sensitivity ratings are for?
 
cheapskate:
NwAvGuy has measured the currents across the capacitors when the amp is operating to ensure they don't wreck performance. Whatever you've done, you've either degraded the performance of the amplifier to sound different or you are a victim of involuntary bias.
You can lob around accusations of religious fervour all you want, but it doesn't change the facts.

 

[EddieE]

Quote:

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.  

I was actually speaking hypothetically with the precise example I gave. But whether people find headphones bass shy or bass heavy depends entirely on what they are used to and have adapted to. There are headphones that make me feel physically sick from the overdone quantities of bass that I've heard described as "bass shy" by people with Sony mega-bass-monster whatever they're called things in their signature. There's also thread here right now which complains about the LCD-2 being anemic and bass shy...
 
For a more relevant (still hypothetical) scenario - If the poster has been listening to a headphone amp that, for example, has been heavily attenuating the treble, and he's got used to that sound and that is what the HD650 "is" for him, then it is going to sound completely wrong when he hears it as it is supposed to be.
 
Maybe there is a problem with the O2, I'm not ruling it out, but whether a headphone has too little or too much treble or bass or mids or whatever, are not objective properties. They are based on the individuals preferences and what they are used to.