[fishski13]

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You forced me to get some books out to disprove your claims, and I don't appreciate that at all. I've enough on my plate as it is without having to devout hours of my time to this forum thread. In the future I'd suggest people look at claims that seem backed by math and physics with suspicion - unless you can verify the numbers for yourself, don't trust them to be accurate.

i was referring to the AKG 240DF.  they're fairly popular. 
 
like i said more than once, you need to consider the source recording volume it was mastered at.  i have amps here that can swing more V and higher gain a 5x that can be maxxed on volume driving these recordings.  i also have some older ECM label stuff that are the same.  the power requirements only tell you part of the story.  and no, the mini3 couldn't do it either, but it is a portable amp.
 
defining the performance limits of a design is de rigeur here on the DIY forum as well as heeding the real world experience of people with experience.
 
 

 

[limpidglitch]

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To mirror and expand on what others have said about most sources lacking volume control on their line outs...... many of us use ASIO on our PC's that disables software volume control as well. So this strategy will not prevent the issue in many cases.
 
You are seriously suggesting that somebody would spend $119 as safety factor on a "$30" amp, by putting a second volume control in the signal chain, and putting pot noise back in front of the input stage anyway, rather than changing the design to be more traditional?
 
Yeah, that makes a LOT of sense.
 

So will you be carrying one around in your pocket?
 
Frankly, I cannot understand why it has batteries, other than an attempt to try and one-up other portables - despite being far larger than the competition, and certainly too large to actually carry around with you.

 
I really do not see the problem here. If you have a particularly hot source, then just select a lower gain. If you have an insanely hot 4Vrms source, f.ex a tube output CD player (disregarding the silliness of such contraptions) max gain running on batteries will be ~1X. This will give you enough output to drive, say the LCD-2, to 115dB (following Ananominals most excellent spreadsheet, thanks a lot for the effort, dude). So you choose 1X as the low gain setting, and maybe 8X as the high gain setting, so you can drive your LCD-2s to the same level using an iPod as source.
What more can you reasonably ask for?
 
There really are no problems here other than what you make yourself, so if you can refrain from doing so, all should be fine.

 

[Beefy]

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Have you seen some of the popular portable rigs right now?
 

Indeed! Lets do a Sizeasy comparison, just to see how the O2 compares to the 'competition'......
 
http://www.sizeasy.com/page/size_comparison/32684-O2-in-B2-080-vs-Mini3-in-1455C801-vs-Headamp-Pico
 
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There really are no problems here other than what you make yourself, so if you can refrain from doing so, all should be fine.

The problem is that it won't be the builders who deal with this, but clueless noob end users who don't understand the problem. You shouldn't have to use the gain knob like a volume control to avoid problems or account for quieter recordings. That is why we have a volume control.

 

[limpidglitch]

Quote:

 
defining the performance limits of a design is de rigeur here on the DIY forum as well as heeding the real world experience of people with experience.
 
 

And as Nw has done this repeatedly, all should be fine, right?

 

[The Monkey]

Wrong. 

It was always designed as a portable amp, you could argue that it wasn't successful, but it the aim was portability. It's about the same size as the RSA SR-71, the iQube and much smaller than the Lisa III.

Go back and read his site--carefully. He makes clear that this can be used as a portable or desktop. It is clear from the actual words he uses, despite the fact that his writing is far from the model of clarity.

What is also clear is that some people are changing the stated goals of the amp and thereby the universe of comparators and criticisms as an exercise in obfuscation. Why?

 

[Focal1]

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So now it is a portable? Kind of a moving target, this amp.

 


Quote:

 

To mirror and expand on what others have said about most sources lacking volume control on their line outs...... many of us use ASIO on our PC's that disables software volume control as well. So this strategy will not prevent the issue in many cases.
 
 
 

You are seriously suggesting that somebody would spend $119 as safety factor on a "$30" amp, by putting a second volume control in the signal chain, and putting pot noise back in front of the input stage anyway, rather than changing the design to be more traditional?
 
Yeah, that makes a LOT of sense.
 

So will you be carrying one around in your pocket?
 
Frankly, I cannot understand why it has batteries, other than an attempt to try and one-up other portables - despite being far larger than the competition, and certainly too large to actually carry around with you.

As far as the size, portable doesn't have to mean it's meant to be carried around in your pocket and used while walking or on a bus, I think to me portable is something I can throw in a bag to use at work, at home, or while out of town where I wouldn't be able to bring a full-sized amp.

 

[nikongod]

 
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Add a passive preamplifier like the NHT PVC or set the gain properly for the source you'll be using - problem solved.  This isn't hard or something that can't be worked around unlike certain (and IMO larger) issues with other designs.

It seems extremely counterproductive to put a piece of gear like the NHT PVC (I actually own one) before a measurements first amplifier. 
 
Another analog volume control adding its distortions and noise, and a transformer with inherent bandwidth limitations, phase shifts, and distortions. Next thing you know people will be designing their own amps, for themselves, that sound great despite not measuring so well. 
 
Also, my PVC has 0.5db channel matching at best. Despite all of that, I actually like it quite a lot. It makes a quick and dirty test-bed for figuring out how much too much gain you have, and is an adequate band-aid fix when you have no real control over the gain. 
 
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People seem to also forget that the O2 has the same distortion levels from 0 to max volume, meaning that as long as you've got a volume control on your source or DAC you can make sure to stay within the limits of the amp clipping very easily. The misconception that the O2 clips before getting loud enough is just that, a misconception.

 
Your full of it. 
 
Have you seen a graphs of output power (or voltage into resistance, may be better for headphones) VS THD+n for a variety of loads? I have NEVER seen a flat curve for Power VS THD+n. Ever. I think this curve actually has a lot to do with how an amp sounds. Amplifiers whose THD+n rises like whoa as power drops make me laugh. Lowest distortion at 20W, but we only use 2. Jokes on you!
 
I have often wondered if the characteristic V-shaped THD VS power curve is part of why so many "perfect amps" could suck a golf ball through a garden hose. Its probably a combination of that, and something else that the designer overlooked.
 
"everything I thought of is perfect" 
"umm, what about that turd you gave me"
"I didnt think of that"
 
Keep trying. 

 

[khaos974]

Wrong. 

It was always designed as a portable amp, you could argue that it wasn't successful, but it the aim was portability. It's about the same size as the RSA SR-71, the iQube and much smaller than the Lisa III.

Go back and read his site--carefully. He makes clear that this can be used as a portable or desktop. It is clear from the actual words he uses, despite the fact that his writing is far from the model of clarity.

What is also clear is that some people are changing the stated goals of the amp and thereby the universe of comparators and criticisms as an exercise in obfuscation. Why?

It's an amp that can be used as a portable, thus it was designed as a portable and desktop amp. The portable criterion is included in the portable and desktop criteria. It's designed to be a portable amp.

 

[limpidglitch]

Quote:

Go back and read his site--carefully. He makes clear that this can be used as a portable or desktop. It is clear from the actual words he uses, despite the fact that his writing is far from the model of clarity.

What is also clear is that some people are changing the stated goals of the amp and thereby the universe of comparators and criticisms as an exercise in obfuscation. Why?

You're not exactly the epitome of clarity yourself. He says it can be used as a portable, and so it can. Yet somehow it can't?
 
It can be used without a tether and fits in the palm of your hand, thats portable enough for me.

 

[The Monkey]

lol, you people continue to surprise and delight.  Let's try this another way.  Based on the designer's initial treatise, the only difference between the amp in portable form and desktop form is the size of the enclosure.  However, when amps are discussed on this site, there is a distinction drawn between portable and desktop amps that loosely can be described as portables are not as "good" as desktops, and they should not be expected to have such performance.  Right or wrong, that is the general perception.  My understanding of the designer's goal is that there should be no such distinction except for the size of the enclosure.  However, several people in this very thread already are trying to define it as a portable and either explicitly or implicitly state that it should be used as such (e.g., someone mentioning that it will be used with portable sources only).
 
I'm curious why people want to categorize this as a portable amp.  Is it merely to emphasize the convenience of it, or is a preemptive attempt to invalidate comparisons to desktop amps?

 

[The Monkey]

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It's an amp that can be used as a portable, thus it was designed as a portable and desktop amp. The portable criterion is included in the portable and desktop criteria. It's designed to be a portable amp.

I have no idea what any of that means.

 

[khaos974]

I have no idea what any of that means.

Sorry, I was doing multiple things at the same time, the website claims it's designed as both portable and desktop. Since portable is included in the "portable and desktop", saying that the designer claimed from the beginning that it was designed as a portable amp is accurate.

 

[The Monkey]

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Sorry, I was doing multiple things at the same time, the website claims it's designed as both portable and desktop. Since portable is included in the "portable and desktop", saying that the designer claimed from the beginning that it was designed as a portable amp is accurate.

Accurate (arguably), but potentially misleading.  And I don't think you're doing it on purpose.  But as I explained above, there are many here who expect different performance from a portable than from a desktop.  It seems to me that is one of the "myths" the designer is interested in debunking; a laudable goal in my opinion.  So for the purposes of the O2, unless someone corrects me, I believe the difference in the size of the enclosure is the only meaningful distinction between a desktop O2 and a portable O2.  The real problem, as I see it, is that people are already trying to excuse potential performance issues by leaning on the old crutch of "but it's only a portable!" (And therefore any performance limitations compared to desktops should be excused.)  My sole purpose in going on like this is that I would hope, when discussing performance, people would discuss the O2 as just an amp, the portable/desktop distinction is meaningless.  Unless the designer is changing his tune, which his recent comment indicates might be the case.

 

[limpidglitch]

Quote:

lol, you people continue to surprise and delight.  Let's try this another way.  Based on the designer's initial treatise, the only difference between the amp in portable form and desktop form is the size of the enclosure.  However, when amps are discussed on this site, there is a distinction drawn between portable and desktop amps that loosely can be described as portables are not as "good" as desktops, and they should not be expected to have such performance.  Right or wrong, that is the general perception.  My understanding of the designer's goal is that there should be no such distinction except for the size of the enclosure.  However, several people in this very thread already are trying to define it as a portable and either explicitly or implicitly state that it should be used as such (e.g., someone mentioning that it will be used with portable sources only).
 
I'm curious why people want to categorize this as a portable amp.  Is it merely to emphasize the convenience of it, or is a preemptive attempt to invalidate comparisons to desktop amps?

 
Only happy to be a source of surprice and delight

 
I'm a bit out of the loop when it comes to audiophile logic, but I'm doing my best.
Is the problem here that Head-Fi consensus does not allow an amplifier to be both 'portable' and 'desktop' at the same time, since a 'portable' amplifier must be inherently iferior to a 'desktop' amplifier, and the impossibility of an amplifier being simultaneously both inferior and superior to a given reference?
If this is the case the remedy is very simple, as the dissonance is only imagined: The 'portable' and 'desktop' O2 aren't equal in performance.

 

[nikongod]

Beyond the higher voltage rails from wall power, it does not look like the O2 amp has any features that are intended for home use but not portable. 
 
Pimeta springs to mind as an example where there are things that one would do for a home amp (Class-A bias op amp, higher idle current for output buffers) that one would not do in a portable, in the name of battery life.