[Cankin]

Someone recently asked my opinion about O2/Odac and if this combo have no bass.
I guess it depends on that person's preference, it is not hard to see some members would try as hard as they can to color the sound.

On the other hand, there are some of us who prefer their DAC and Amp have no or very little coloration. To my ears, O2 & ODAC achieve my requirement of "colorless".

In fact, I wanted one immediately right after I heard it, regardless of price. It sound just like another DAC I wanted for a long time.

You may ask which is the other DAC? The other DAC is Apogee Symphony, which is not often talked about on Head-Fi.

How do they sound like? Nothing. They are so transparent that they sound like nothing.

I guess you can say my decision is purely based on my subjective experience, nothing objective lol.

In conclusion, I would not recommend O2/ODAC if you are trying to color your sound or cover flaws of your badly mastered recording. But if you want something that let you enjoy how your music and headphone sound, you should get them.

 

[goober-george]

This may be a dumb question but, is there any cable that would allow me to hook up my O2 DAC/AMP to my Mad Ear with no rca inputs and only a micro usb port? Some sort of micro usb to rca input cable?

 

[Dark_wizzie]

Mike has possibly discovered a THD issue with the original O2 with the volume pot being at mid way etc..AGDR has been analyzing this and thinks he knows what the issue might be. Its still below audible hearing etch.

You can read the techie stuff again over at DIY Audio.

That said none of this affects the sonic equality at all but AGDR being a perfectionist has continued to make improvements to the ODA. None of them really would be audible but makes the ODA better, safer from line input transients and more easy to build. So the latest V2.1 boards are going to be sent out shortly after he gets parts from Mouser. The 2.1 can be seen in this thread above and photos.

Details on the 2.1 revisions are listed in great detail on agar's Google drive under the 2.1 area.

I will be updating my 2.0 ODA with a few of the component updates, one being a transport across the AC power inputs to help with any surges, two regulator capacitors from 10uf to 22uf..based on data sheet errata, no sonic issue here, just one of a corner case oscillation possibility.... and a Pico amp fuse in series with one of the ac line inputs.

Also the big news is that agar asked me to share he will be offering ODA BOARDS with the small hard to solder SMD parts' Here is his post:

"In other news I have decided to sell ODA boards with just the SMD stuff soldered on for an additional $39 labor fee plus the $32 or so worth of SMD parts. All as time permits, lol, which will probably mean weekends, just doing them as ordered. If you run into anyone in your travels wanting a through-hole only ODA, feel free to point them to the posting:"

You can send AGDR a pm directly and/or read the post at diyaudio in the vendor area.

THD is total harmonic distortion, yes? I'm not such a techie like them but I don't understand how midway point of the volume knob presents special problems with THD... Only two things I think of in this case is: 1) Volume knob set too low, channel imbalance problem 2) Volume knob too high, hear noise floor, distortion increases (But won't be specially apparent at halfway point).
Also worth noting... Although the O2 can probably drive the HE-6, the ODA can definitely drive the HE-6 IIRC. So is AGDR making a finished product or is he selling parts? Thank you for sharing this news with us.

   
Argh, it's so difficult to figure out the best gains when you have to take so many things into consideration. :/ I ordered a 1x/5x config, but reading the last few posts was just about to attempt to change my order to 1x/3x. Then you wrote about replaygain, which I use too. So I guess suddenly 1x/5x would be fine with me? Even more so if I change to a pair of 300ohm headphones in the future?
 
lol, anyway, I think I'll just wait for my 1x/5x O2/ODAC to arrive and see how it goes. Worst comes to worst I'll change the gain resistors.
 

I don't really see how a person needs more than one gain setting for only one pair of headphones. For the majority of people, the defaults are more than enough. They're the defaults for a reason.

 

[hekeli]

Regarding the midway pot... it's funny that something is broken in my O2 in such way that there's a loud hiss on other channel, but only when midway..

 As soon as I hit max it disappears.. so maybe my fault is revealing the THD problem?

 

[liamstrain]

  This may be a dumb question but, is there any cable that would allow me to hook up my O2 DAC/AMP to my Mad Ear with no rca inputs and only a micro usb port? Some sort of micro usb to rca input cable?

 
I'm not quite sure what you are trying to do. If you use it as a DAC from your computer, then it is a USB connection, and no RCA would be needed. 

 

[adydula]

AGDR is selling ODA boards on eBAY. I posted this in the ODA thread in this site.
 
http://www.ebay.com/itm/Objective2-O2-Desktop-Headphone-Amplifier-ODA-PC-Board-V2-1-/191284729783?ssPageName=ADME:L:LCA:US:1123
 
FYI
Alex

 

[adydula]

In regards to the THD at midway volume pot settings AGDR thinks he understands what is happening and is asking an engineer with a dScope to take a look at this with an 02 compared to the ODA.
 
 
I can share this:
 
"Apparently many of the op-amps have input impedance non-linearity that produces distortion with increasing source resistance, with the op-amp looking back into the source."
 
There is a lot of techie stuff about the impedance changing etc I have links to this stuff etc. Doug Self etc.
 
If this is the case its possible that this is one area the designer missed, There aren't any 1/2 volume THD measurements in his blog that I can find.
 
When and if the O2 is measured I will be glad to share the THD measurements etc.
 
FYI.
Alex

 

[JacobLee89]

  This may be a dumb question but, is there any cable that would allow me to hook up my O2 DAC/AMP to my Mad Ear with no rca inputs and only a micro usb port? Some sort of micro usb to rca input cable?

 
If it isn't any special DAC/AMP combination you're using. It really should be like so:
 
PC (usb cable) ---> Objective DAC / Objective 2 (3.5mm jack cable)  -----> Headphones
 
Though I believe what you're trying to do is connect your MAD EAR amp to the DAC side of your O2/ODAC
 
In this case you'll need to connect a 3.5mm to RCA cable from the input side of the O2/ODAC, and plug it into the MAD Ear. 

 

[Dark_wizzie]

  AGDR is selling ODA boards on eBAY. I posted this in the ODA thread in this site.
 
http://www.ebay.com/itm/Objective2-O2-Desktop-Headphone-Amplifier-ODA-PC-Board-V2-1-/191284729783?ssPageName=ADME:L:LCA:US:1123
 
FYI
Alex

Ahh... I see. Unfortunately assembling this is way beyond my league. I can only wait until somebody sells a finished product. 

 

[XIX47]

Never a good idea while posting half awake.....

 

[Faemix]

Hey folks.
I will order a O2/Odac combo. I'm actually using a Q701.
Should I modify gain or stick with default settings ?
I'm not sure I need 6x...
 
Is a 1x gain is enough for Q701 ?
 
Thanks for help !

 

[adydula]

You do not need 6x at all for Q701's...I had them for awhile etch... works well with unity gain or 2.5x.
 
Alex

 

[Faemix]

  You do not need 6x at all for Q701's...I had them for awhile etch... works well with unity gain or 2.5x.
 
Alex

Thanks for reply, Alex.
If I don't need 6x, should I use another value or just don't care about that ?

 

[adydula]

Faemix,
 
The stock gain settings from JDS Labs is 2.5 and 6.5 I believe.
 
You never really will need the 6.5 for your headphones....
 
You could just leave it like it is and try the 2.5x settings and see how you like that and where the volume control settings are,.
 
If you think the 2.5x is too much you can snip some resistors and get unity gain where the 6.5 setting was... this is what I did on one of my O2's.
 
I don't use earbuds etch and only run headphones and have not found any headphones that unity or 2.5 can't drive well.
 
There are some really inefficient headphones that would be an issue with the O2 but they are far and few between etch.
 
Give John Seaber a call at JDS Labs and discuss with him....
 
FYI
Alex

 

[Faemix]

  Faemix,
 
The stock gain settings from JDS Labs is 2.5 and 6.5 I believe.
 
You never really will need the 6.5 for your headphones....
 
You could just leave it like it is and try the 2.5x settings and see how you like that and where the volume control settings are,.
 
If you think the 2.5x is too much you can snip some resistors and get unity gain where the 6.5 setting was... this is what I did on one of my O2's.
 
I don't use earbuds etch and only run headphones and have not found any headphones that unity or 2.5 can't drive well.
 
There are some really inefficient headphones that would be an issue with the O2 but they are far and few between etch.
 
Give John Seaber a call at JDS Labs and discuss with him....
 
FYI
Alex

Many thanks Alex.
I will go with unity and 2.5x then and switch transistor to get a 6x if I need this someday.
 
Thanks again. Really helpful.