[adydula]

I sold all my other amps, and have 2 O2's.
 
One I built and one from JDS Labs.
 
Went thru all the things being mentioned here and its a good discussion, but I am so glad that I discovered this little gem of an a amp and that it
performs so well.
 
I have gone back to the 'music' and playing around with different cans and recordings....
 
Its a really amazing thing to have such a great performer run off of two 9v batteries for hours...no AC issues or problems.....gone.
 
It works very, very well with 90+ percent of cans out there....
 
Now back to the music!
 
Alex

 

[Bojamijams]

JDS needs to do that Upside down ODAC+O2 with batteries... that would be the bomb AND allow it to be used as a mobile rig with Android devices feeding the ODAC
 

 

[Cla55clown]

Interesting read through the thread. One question albeit a little off topic: What happened to the OP; the turtle guy? I feel like I'm missing something.
 
So the consensus is that this is a good amp/dac combo and well worth the money? Currently using a FiiO E10 with my PC and looking to upgrade to a full size desktop.  

 

[stv014]

Quote:

What happened to the OP; the turtle guy?

 
Changed name to "Lord Voldemort". More importantly, though, no one knows what happened to the designer of the O2 and ODAC.

 

[purrin]

Quote:

On another note, looks like the O2 measure quite well against more expensive amps: http://www.innerfidelity.com/images/121105_blog_update_FirstAmpTests.pdf
 

 
I've taken a few measurements of the O2 and ODAC myself. The O2 does not simply measure "quite well". The O2 destroys everything in terms measurements (distortion, noise, etc. as long as its not being pushed past its power capabilities). And will especially destroy anything of discrete design in terms of measurements.
 
The only thing that might come close is a META42 or well built CMOY (the CMOY will have much less power obviously.)

 

[BleaK]

Quote:

 
I've taken a few measurements of the O2 and ODAC myself. The O2 does not simply measure "quite well". The O2 destroys everything in terms measurements (distortion, noise, etc. as long as its not being pushed past its power capabilities). And will especially destroy anything of discrete design in terms of measurements.

That's really great to hear! Did you post or publish those measurements somewhere, I would love to see more amp measurement!
 
Also, how did the ODAC measure compared to other DACs? If you did a comparison there as well?

 

[purrin]

I think I may have published a few on my site. Not sure. I know I did publish a few ODAC jitter and distortion measurements (probably buried in a thread somewhere). I do not have instrumentation quality gear (higher noise floor), bit the measurements did corroborate those on nwavguy's site.

 

[imackler]

Quote:

 
I've taken a few measurements of the O2 and ODAC myself. The O2 does not simply measure "quite well". The O2 destroys everything in terms measurements (distortion, noise, etc. as long as its not being pushed past its power capabilities). And will especially destroy anything of discrete design in terms of measurements.
 

 
This makes me want another one! 
 
Can anyone confirm that with a higher power wall wart the O2 can operate on high gain without distortion with the HD650/HD600? I didn't experience it on every song but it was quite bad on a few and I don't listen at high volumes... 

 

[purrin]

Quote:

 
This makes me want another one! 
 
Can anyone confirm that with a higher power wall wart the O2 can operate on high gain without distortion with the HD650/HD600? I didn't experience it on every song but it was quite bad on a few and I don't listen at high volumes... 

 
Honestly, I wish nwavguy didn't put the pot in between the gain and current buffer stages, just for the sake of lowering the noise floor a few db.
 
In theory, a higher voltage wall wart should help prevent clipping at the gain stage. What are you running as a DAC or source? Do you know how hot the outputs are? At what gain are you using the O2? Reducing the output of the source (if possible) and turning up the volume on the O2 should help. It definitely not a power issue. The O2 should have enough power to make you deaf or at least give you serious hearing damage with the HD600/HD650s.

 

[stv014]

Quote:

Can anyone confirm that with a higher power wall wart the O2 can operate on high gain without distortion with the HD650/HD600? I didn't experience it on every song but it was quite bad on a few and I don't listen at high volumes... 

 
The O2 has a regulated power supply, so even if you use a higher power wall wart, it will still be limited to about +/- 11.8 V. The gain stage can only handle peaks of about 10 V before it starts to clip (the op amp used does make a small difference here), and it is before the volume control. Since the ODAC can output ~2.8 V peaks (2 Vrms) at a full scale digital input, applying a gain of 6.5 would require the gain stage to be able to handle about 18 V peaks, and that is well above the limit. Since the volume control is after the gain stage, reducing the volume on the O2 does not fix the clipping. You have to either reduce the volume on the PC, or just use low gain.

 

[imackler]

Quote:

 
Honestly, I wish nwavguy didn't put the pot in between the gain and current buffer stages, just for the sake of lowering the noise floor a few db.
 
In theory, a higher voltage wall wart should help prevent clipping at the gain stage. What are you running as a DAC or source? Do you know how hot the outputs are? Reducing the output of the source (if possible) and turning up the volume on the O2 should help. It definitely not a power issue. The O2 should have enough power to make you deaf or at least give you serious hearing damage with the HD600/HD650s.

 
Thanks for the response! 
 
I was using the ODAC when I had the problems but never noticed when I used the line out from an ipod classic. Should the ipod classic be fine? When I used to use an ipod classic line out and O2 w/ HD600, I was happy with low gain and didn't have any distortion. I didn't have problems unless I put it into high gain. The dynamics with the HD650 seemed better on high gain but the distortion was pretty much a disaster. I guess I should have left it in low gain. 

 

[purrin]

The O2 has a regulated power supply, so even if you use a higher power wall wart, it will still be limited to about +/- 11.8 V. The gain stage can only handle peaks of about 10 V before it starts to clip (the op amp used does make a small difference here), and it is before the volume control. Since the ODAC can output ~2.8 V peaks (2 Vrms) at a full scale digital input, applying a gain of 6.5 would require the gain stage to be able to handle about 18 V peaks, and that is well above the limit. Since the volume control is after the gain stage, reducing the volume on the O2 does not fix the clipping. You have to either reduce the volume on the PC, or just use low gain.

 
Ah I forgot the regulation. Do you what the +/- PS rails are after the regulator? I forgot what the stock op-amp is in the O2. What do the spec-sheets say the op-amp can actually swing with the actual voltage on the rails?

 

[Porter1]

Quote:

 
This makes me want another one! 
 
Can anyone confirm that with a higher power wall wart the O2 can operate on high gain without distortion with the HD650/HD600? I didn't experience it on every song but it was quite bad on a few and I don't listen at high volumes... 

i see you've gotten several answers above (this forum moves fast!), but this post by hekeli seems to explain why you were seeing distortion: http://www.head-fi.org/t/616331/o2-amp-odac/15#post_8523470
 
i don't claim to fully understand the principles behind it, but seems like using the ODAC and the 6.5x gain on the O2 puts you over the limit for distortion.  also explains why you didn't see it with your ipod.

 

[stv014]

Quote:

Also, how did the ODAC measure compared to other DACs? If you did a comparison there as well?

 
stereophile.com has some measurements of various DACs (including currently popular ones like the AudioQuest DragonFly) made with an Audio Precision SYS2722 analyzer. They are not as detailed as those you can find at the ODAC designer's blog, but are worth having a look at.
I have a relatively detailed set of measurements of the Xonar D1 sound card, which is fairly cheap, and the results are comparable to the ODAC. I did not use a professional audio analyzer, though, so do not expect great accuracy, but I did make efforts to avoid/minimize the hardware and software limitations and flaws of the typical RMAA tests you can find.
goldenears.net has DAC reviews and measurements, too, but they only use RMAA. They do have a table of output impedances for the headphone outputs of various devices, though.

 

[sling5s]

Quote:

 
Thanks for the response! 
 
I was using the ODAC when I had the problems but never noticed when I used the line out from an ipod classic. Should the ipod classic be fine? When I used to use an ipod classic line out and O2 w/ HD600, I was happy with low gain and didn't have any distortion. I didn't have problems unless I put it into high gain. The dynamics with the HD650 seemed better on high gain but the distortion was pretty much a disaster. I guess I should have left it in low gain. 

To fix distortion, lower the pre-amp volume on your computer or source.  Just by a tad.  It works for me when I'm using high gain.  I don't know if it's just my imagination but I too think the LCD-2 sounds better with high gain.