[Arkady Duntov]

  Its a "him"....send him a pm directly over at diyaudio.com.
I know he is a bit out of pocket due to some personal issues, but hopes to be back soon, dec? 

 
I decided to buy, after reading most of this thread and quite a bit of a few others, a DAC+amp now and perhaps get an ODA later. In doing so, I had to ignore innumerable posts with topics like "it's good for a small device" and "need to spend at least $3,000 to get a good amp." The one that looked the best in price and performance was JDS Labs' ODAC+O2 combo.
 
I had one problem. When I attached it to a USB2 hub, Windows7 recognized it and "installed" drivers. However, the ODAC never showed up under Sound>Playback devices. When I attached it directly to a USB2 port on the PC, everything worked as planned.
 
So far, with about 16 hours of listening time, I find the ODAC (rev B) and O2 provide great sound. I think I made the right choice for me.

 

[castleofargh]

not helping sorry, but for the anecdote, my main use is on an old laptop with usb2 and usb3 ports on one side, and 2 usb 2 on the other.
the usb2 on one side comes from a separate card(not the motherboard), and is the only port where I could use the crappy amazon powered hub I bought. I don't know why, I tried all kinds of drivers, old and new, flashed the bios tweaked all the settings I could find about usb(energy saving stuff and the likes). only one out of 4 usb ports let me use DACs and ADCs plugged in the hub.
 
with an older hub, it wouldn't plug&play with the scarlet 2i2, but if I were to boot with everything already plugged, then it would show as an output(and input in this case). windowzzz is magical, sometimes it's black magic. 

 

[raoultrifan]

   
[...]
 
I had one problem. When I attached it to a USB2 hub, Windows7 recognized it and "installed" drivers. However, the ODAC never showed up under Sound>Playback devices. When I attached it directly to a USB2 port on the PC, everything worked as planned.
 
[...]

 
Just use one of the backside USB ports from your desktop (you need to use an USB port directly soldered onto the motherboard, no internal wires!); in case you're using a laptop as source, use an USB port not close to power plug.
 
Enjoy you new sound!

 

[Rado2]

Just to mention, that some computers have dedicated USB ports for audio or other purposes. I was quite surprised for example that my motherboard came with two of such, for which the manual (and the engineers staff) said are specially though over for clean power and data supply. I have no idea how true is that, but I ran from there my O2+DAC and USB Microphone. 

 

[dukefx]

Do a RMAA test to find. I haven't had the pleasure of testing such USB port myself, but I highly doubt it'd anywhere close to a linear power supply.

 

[raoultrifan]

Try finding a good scope and measure AC ripple and noise on the +5V for that USB port.
 
Thank you!

 

[chongky]

Will the O2 amp clip at loud volume for dynamic music like classical? I have a SMSL M8 DAC which has an output level of 2.15 Vrms, dynamic range: > 125dB, SNR: > 126dB. My headphones is the Beyerdynamic T90, impedance 250 ohm, sensitivity 102 dB SPL at 500 Hz at 1 mW. I plan to listen at the 1.0x gain.
 
I'm not a math guy and I wonder if listening to classical music Redbook CDs (mainly symphonic) my T90s will distort at high (but not ear-deafening) volume.

 

[raoultrifan]

It all depends on the gain setting used. Feel free to search within this thread, because there are lot of people explaining the correct gain calculation.
 
From what I know, max. output voltage for the O2 would be around 7.3V RMS, so if you'll devide this to 2.15 you'll get the max gain for your setup of 3.39X. That being said, I can strongly recommend you the highest gain setting of 3X and the lowest gain setting between 1X and 1.5X, depending on the headphones used.

 

[chongky]

Thank you for your speedy reply. I found a site after searching this thread:
 
http://www.digizoid.com/headphones-power.html
 
So I keyed in the impedance (250 ohms) and sensitivity (102 dB SPL/mW) of my T90, which in turn showed it requires ~ 4 Vrms to output to ear-splitting levels, i.e. 120 dB.
 
Which means it's more than loud enough, and still below the distortion inducing level of .7.3V RMS. Which means it ought not distort either at 1x or 3.3x gain (according to your calculations)?
 
Correct me if I'm wrong.

 

[raoultrifan]

There will be no distortions for gains up to 3X, no worries here; just be sure not to setup the gain to 3.5X or more, because 3.5x2.15=7.525 V RMS and the internal gain stage will start clipping. I recommend you MUSES8820 for your gain stage, to replace NJM2068, but only if you intend to start modding (most likely between the 2 opamps there's an inaudible difference for most people).
 
I strongly recommend you to read how much you can from this thread because you'll find many answers and thoughts.
 
Regards,
Raul.

 

[adydula]

I have several O2's and T90's....I hae gains from 1x to 6.5x and no issues at all at 1.0x or "unity" gain. The O2 will work fine with your T90's, which are my favorite cans over many, many others even those costing more!
 
Enjoy
Alex

 

[chongky]

  I have several O2's and T90's....I hae gains from 1x to 6.5x and no issues at all at 1.0x or "unity" gain. The O2 will work fine with your T90's, which are my favorite cans over many, many others even those costing more!
 
Enjoy
Alex

 
Thanks - that is really assuring. My O2 will take a while to arrive due to the Black Friday traffic but I'm sure it and the T90s will be a great pairing!

 

[dukefx]

My newest addition finally arrived. Had to replace 2 caps to make it fit.
 

 

[dukefx]

I joined the OPA1688 club. The difference is subtle, but noticeable. Don't even ask how I managed to fit them in.
 

 

[raoultrifan]

Guys, please stop teasing me!
I really have no time to do this mod right now and every post like this one makes me have nightmares.
 
P.S.: Nice one dukefx, any chance on an A/B test?