So, the Objective2 headphone amp - designed entirely around the measurements? (PLEASE READ RULES BEFORE POSTING)

[Reticuli2]

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This is really wierd, how did this thread become O2 > mini3? From my reading, it appears that Ti threw the mini3 into the ring for purposes of illustrating the (small) noise differences related to the placement of the pot.
 
It seems the "friends" of nwavguy or nwavguy himself have some kind of axe to grind with Ti - using pseudo authoritative statements such as "So to paraphrase that, the maths is wrong, the argument is wrong and Ti appears slightly contradictory to the uneducated observer." Hmm, this sounds a little bit like nwavguy himself. This seems like a very aggressive method of discourse, keeping in mind that no one forced the topic of the O2 design in these forums.
 
I thought this thread was meant as sort of a public commentary on the design of the O2. Why can't the "friends" of nwavguy just politely acknowledge Ti's criticisms, i.e. "We've spoken with nwavguy, and he has taken Ti's design concerns into account and lowered the gain. (Thank You!) Nwavguy's real-world measurements of the opamps voltage swing exceed those of the spreadsheets. Therefore Nwavguy feels that this will adequately address the expected use and scenarios of the typical user." 

Case closed.
 
Geez!
 

 
 
[size=10pt][size=10pt]Little too ad homonym to go after a design's overall performance when they only want to talk about one teeny tiny aspect of it juxtaposed to the other design that trounced its measurements and didn't include any wanky crosstalk measurements that were kinda absurd even to laymen like me? Yeah, sorry. You're probably right. It is kinda like going after low-hanging fruit or the proverbial fish in the barrel. But how do you expect people to naturally respond? The 02 was designed to test better than many others and most people who build one or buy one will easily be able to use it properly even without this latest alteration. It’s kind of insulting us potential users. It's not like we said the guy or his amp was ugly, or anything. That would just be great fun...err... I mean out of line.[/size][/size]
[size=10pt][size=10pt]That said, I was told in 2009 to never put a volume pot (like, say, an in-line volume control) between the headphone jack and the headphone. Essentially isn't that what NwAvGuy is doing, but with it having no other pot anywhere else? Or is there more to it? I seem to remember something about being told the impedance load is changed as the pot is reduced with an in-line volume.[/size][/size]
 

 

[Head Injury]

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This amp will even drive (not that it was designed to) a Stax SR-009 to ~78 dB.

You hear that deadlylover? Get working on an adapter 

 

[SpaceTimeMorph]

Just to show, here are some graphs taken by NwAvGuy that show performance while overloaded on battery and again on AC power:
 
INPUT OVERLOAD ON BATTERY – Here’s the V1.1 O2 running on batteries at about 80% charge. The battery voltage was 9.2V. At 2.5X gain it can still handle a 2 volt RMS input signal, which is the Redbook standard for home digital audio equipment. On AC power it can handle 2.8 V RMS which is well in excess of the Fiio E9 which overloads at 2.1V input. So even on reasonably charged batteries the O2 is fine on battery power:

 
INPUT OVERLOAD ON BATTERY – Here’s the V1.1 O2 running on AC power with 2.9 V RMS in at 2.5X gain and half volume. No signs of overload:

 

[SpaceTimeMorph]

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You hear that deadlylover? Get working on an adapter 

hehe... yea, bored at work one day... what can I say.
 

 

[Reticuli2]

At what reduction of charge on the battery powered one would the 2V redbook standard voltage cause it to clip?  I don't need it to be portable, but I have to decide whether I want to wait for the desktop version or go with the portable now.

 

[mikeaj]

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Originally Posted by Reticuli2 /img/forum/go_quote.gif
 
[size=10pt][size=10pt]That said, I was told in 2009 to never put a volume pot (like, say, an in-line volume control) between the headphone jack and the headphone. Essentially isn't that what NwAvGuy is doing, but with it having no other pot anywhere else? Or is there more to it? I seem to remember something about being told the impedance load is changed as the pot is reduced with an in-line volume.[/size][/size]

 
Pardon me if I missed what you were saying, but in the O2 the volume pot is between the gain stage and the output stage.  Others are saying they'd prefer the pot to be before the gain stage, so clipping can be avoided with very high sources and high gains, by turning the position of the pot.  I'm not sure what this has to do with adding impedance between the headphone jack (or after the output stage, even if on the board) and the headphones.

 

[Reticuli2]

O.k.

 

[mikeaj]

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At what reduction of charge on the battery powered one would the 2V redbook standard voltage cause it to clip?  I don't need it to be portable, but I have to decide whether I want to wait for the desktop version or go with the portable now.

 
Change the low gain to 2X or lower (just pick a different resistor value) and it will never clip with a 2V source until about maybe 5-10 minutes before it cuts off.  On like 1X to 1.5X it certainly won't have an issue straight until shutdown.  Keep in mind that if you're using it on battery, will you be using portable sources or home sources?  Most portable sources will not output 2V rms.  If running on AC power there is no problem with 2V sources.  You need to be running on low batteries with high output sources and higher gain settings (that can be reduced), or potentially a very high output source with higher gain settings, for there to be clipping.

 

[SpaceTimeMorph]

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Originally Posted by Reticuli2 /img/forum/go_quote.gif
 
[size=10pt][size=10pt]That said, I was told in 2009 to never put a volume pot (like, say, an in-line volume control) between the headphone jack and the headphone. Essentially isn't that what NwAvGuy is doing, but with it having no other pot anywhere else? Or is there more to it? I seem to remember something about being told the impedance load is changed as the pot is reduced with an in-line volume.[/size][/size]
 

Actually the general rule is "don't amplify then attenuate", the best answer is to raise the signal level to the nominal preferred as soon as the signal enters the amp.  That way you aren't choosing between loss of headroom and noise as your two poisons.  However, given the space and price considerations, he choose to put it between the gain stage and the output stage.  You are always going to want something in front of your volume pot (a buffer at least) that way you aren't required to use a higher resistance to attenuate the signal (you would be forced to use roughly half the source impedance to drop a signal by 6 dB otherwise, which would greatly increase Johnson noise).  The O2 achieves this to a degree by using the 2068's for the gain stage, which allow a lower impedance into the volume pot => giving less noise while at the same time stepping up the voltage to what is needed for the output stage.  This is in addition to the lower noise due to not amplifying the Johnson noise from the pot.
 
All of that being said, I think we've beaten a dead horse into the pavement with the fact that there is plenty of headroom.
 
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At what reduction of charge on the battery powered one would the 2V redbook standard voltage cause it to clip?  I don't need it to be portable, but I have to decide whether I want to wait for the desktop version or go with the portable now.

 
He has revised his assessment of the low voltage situation with batteries and is claiming a 4.5V figure now.  Thusly his gain calculation is now 4.5/Vin on battery.  My reccomendation is if you want the desktop flavor, wait for that.
 
 

 

[Steve Eddy]

 
Just a quick comment.
 
Much criticism has been levied at the O2 for the designer's decision to place the volume control between the input/amplification stage and the output stage. The basis of this criticism has been that the O2 would tend to overload when fed from sources with full scale outputs greater than a couple of volts RMS.
 
I ask, why isn't the criticism being levied at the designers of source components which have full scale outputs greater than a couple of volts RMS?
 
For many years there have been standards for line level outputs. In the consumer world, it is -10dBu, or about 0.316 volts RMS. In the pro audio world, it is +4 dBu, or about 1.23 volts RMS. When the Compact Disc came on the scene, Sony and Philips set the "Red Book" standard 0dBFS level at 2 volts RMS, or about +8.24dBu.
 
I really don't see why any source component's fulls scale line level outputs should be any greater than this. To do so is just plain stupid in my opinion. And when you accommodate stupidity, all you do is just encourage more of it in the future.
 
So I think the criticism of the placement of the O2's volume control is entirely misplaced.
 
se

 

[amb]

 
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Originally Posted by Steve Eddy /img/forum/go_quote.gif
 
I ask, why isn't the criticism being levied at the designers of source components which have full scale outputs greater than a couple of volts RMS?

 
Sources that could output more than a couple of volts RMS is not a recent phenomenon.  In the analog days, "0dB" is only a reference but signal peaks routinesly exceed that by large margins.  For example, almost all Nakamichi cassette decks output 1Vrms at "0dB" as displayed on its level meters, but cassettes can be recorded at levels much higher than that, with peaks reaching as high as +10dB.  At that level, the deck would be putting out 3.2Vrms.  Same goes for phono stages -- depending on the recorded level on the LP, the output voltage of the cartridge, and the gain of the phono stage, it too could produce high output voltage swings.
 
At any rate, placing the blame on the source components is not fruitful -- they already exist in the market and the choice is to design an amp that could work with them, or not.

 

[Anaxilus]

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You mean it's absolute when not considering a confined space, right?  So in his little corner heat will not build up, but in the entire room it will.  Unless I misunderstand something about heat so that "heat is absolute and not additive" is completely correct.  I thought the opposite was true.

Should have worded it a bit differently.  Regardless, it's not rocket science in the context here so I thought it would be self explanatory.  Unless he lives outdoors in the desert at high noon, placing it in the corner has no effect to the absolute maximum but it has a minor impact to the rest of the room assuming the ambient temp is lower than the O2.       
 

 

[wakibaki]

I've seen a lot of people here trying to tear down what RocketScientist has done. Your efforts would be better spent trying to match or exceed what he has done. People have reacted very defensively when the flaws in certain designs have been pointed out. They have switched to the attack now that the opportunity presents itself. This is far from admirable. 
 
Having designed a lot of circuits myself, I appreciate the difficulties involved, particularly where objective test is involved. Test equipment, particularly calibrated test equipment, is not cheap. If, however, some of the designers who now find themselves at a disadvantage had had the foresight to reinvest some of their profits in creating designs which were a true improvement on the foregoing, instead of adopting dubious topologies on a speculative basis more for their advertising benefits and novelty (as it turns out) than any demonstrated technical advantage they would have been less vulnerable to soundly-based criticism.
 
The answer is to change. Not to try to run down the O2, not to try to step up the advertising, but simply to try to produce better-performing designs, either in terms of cost (unlikely), performance (possible), features (entirely possible), useability (entirely possible), cosmetics (?) or DIY-appeal. What is certainly necessary is to stop pretending that there is some ineffable quality (sound) that that some amplifiers might possess in contrast to the O2, despite its superior measurements.
 
As technology and circuit design progresses I anticipate that some of the designers of excellent full-power amps in the past will continue to publish new designs. Douglas Self was not discouraged from publishing his recent parallel NE5532 design by the fact that there are many excellent designs with flaws probably below the threshold of audibility already extant. I, for one, while not counting myself in that company, have not given up generating new designs simply because the O2 has appeared.
 
Come on guys, put your shoulders to the wheel and do something creative instead of being destructive. It's in your own interests, because if you don't you will undoubtedly find your sales being eroded in the future, as they probably are being already.
 
Perhaps it will be possible to persuade the nwavguy to review your future products, I can think of few things more beneficial than a favourable review from him.
 
w

 

[Anaxilus]

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Therefore, with a 1000ohm headphone you would need a sensitivity of <93 dB/mW to find a set of headphones this couldn't drive off of AC power.  This amp will even drive (not that it was designed to) a Stax SR-009 to ~78 dB.

 
Pardon my ignorance and apologies for detracting from the specific commentaries here.  I'm the first to admit to being out of my depth here wrt EE but is this a statement for the sake of Hyperbole?  Stax and Koss run their stats w/ a bias of 580v/600v respectively.  I'm not getting how the O2 is now an Energizer or did something just pass right over my head.  Sorry for the aside.
 
 

 

[Steve Eddy]

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Originally Posted by amb /img/forum/go_quote.gif
 
Sources that could output more than a couple of volts RMS is not a recent phenomenon.  In the analog days, "0dB" is only a reference but signal peaks routinesly exceed that by large margins.  For example, almost all Nakamichi cassette decks output 1Vrms at "0dB" as displayed on its level meters, but cassettes can be recorded at levels much higher than that, with peaks reaching as high as +10dB.  At that level, the deck would be putting out 3.2Vrms.  Same goes for phono stages -- depending on the recorded level on the LP, the output voltage of the cartridge, and the gain of the phono stage, it too could produce high output voltage swings.

 
Never said they were. But it doesn't make them any less silly. Especially where digital audio is concerned.
 
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At any rate, placing the blame on the source components is not fruitful -- they already exist in the market and the choice is to design an amp that could work with them, or not.

 
So you admit it's a choice. Then why bust someone's chops just because they may make a choice that's different from the choice you may make?
 
And I didn't suggest placing the blame on the source components. I suggested placing it on the designers (and/or manufacturers) of the source components.
 
se