[raoultrifan]

Feel free to replace the cheap wires with better cables with a decent shield. At least in theory cross-talk could decrease.
 
First opamp is the Voltage Amplification Stage, the other 2 opamps are paralleled and used as output buffers...hope this helps.

 

[dukefx]

I don't think NwAvGuy ever said that opamps do not matter. As far as I can recall it was more about price/performance and drawing a line where "better" opamps wouldn't result in an audible improvement.
 
As for the roles: the one next to the potmeter (2068 by default) amplifies voltage. The pair operated in parallel on the side is the output and supplies your headphones with the juice required. The 4th has nothing to do with the sound, it's for the battery and overall protection.

 

[leeperry]

Fair enough, what he said is "CAN I UPGRADE THE OP AMPS? You could, but it would be a waste of money and might degrade the performance. I tested nearly two dozen op amps and the O2 is optimized for the op amps that proved best."
 
OK sounds good thanks, I got a whole bunch of LME49990, ADA4627 gizmos to roll but apparently my revA mayflower comes with 1X/3.3X gain and that seems very very low, oh well I don't expect much so I can't be disappointed I guess. I also got a spare 2A 16VAC PSU that sounds great on Mimby, can't hurt ^^

 

[dukefx]

The proper statement would be I tested nearly two dozen op amps and the O2 is optimized for the op amps that proved best from what I had at hand. 
 
 
Gain depends on your input. 1/3.3x is excellent for a 2.1V input (ODAC). 3.3x is actually a tiny bit more than it can safely handle. Mine's at 1/3.2x and I don't really need the gain button. If you use a >1V onboard soundcard output with hungry headphones it's low indeed.

 

[leeperry]

MStage sounds best in many ppl's experiences with 10X gain, I would use Mimby and ODAC but I bet its ancient Tenor/9023 chips won't make me too happy

 
Anyone tried that O2 booster board? http://www.agdraudio.com/o2%20booster%20board.html

 

[dukefx]

No, but Alex will storm in and tell you all about it XD I'm happy with the OPA1688s.

 

[ostewart]

I posted my review up of the Head "n" HiFi desktop kit: https://www.head-fi.org/showcase/head-n-hifi-objective2-desktop-version.22677/reviews#review-19254

 

[adydula]

I have two O2's, one with OPA 1688's and one with AGDR's booster board that has 827's installed plus a few other things.
I also have a bone stock O2 and have done many listening tests..and they all sound pretty much the same.

I dont think that 99% of people would be able to tell any real world differences in the sound ....

I am down to only 9 head and three dacs, I switch back and forth every few days and each time the amp being put into use
sounds really good for a few days.....lol.

Alex

 

[leeperry]

Well AGDR main sales argument is that distortion is much lower when you start listening at 120dBA

Any internal pics of the masdrop units around? I guess the desktop version is using some crappy wires to reach the back jacks and some ghetto kludge for the 6.35mm HO?

 

[Jimster480]

The proper statement would be I tested nearly two dozen op amps and the O2 is optimized for the op amps that proved best from what I had at hand.


Gain depends on your input. 1/3.3x is excellent for a 2.1V input (ODAC). 3.3x is actually a tiny bit more than it can safely handle. Mine's at 1/3.2x and I don't really need the gain button. If you use a >1V onboard soundcard output with hungry headphones it's low indeed.

I feel the same way. I just leave it on 1x most of the time and its fine!

 

[UNOE]

If I have (2.5x / 6.5x) gain unit. Can I just remove the 6.5x resistors to have (2.5x / 1.0x)? Or do you have to remove the 2.5x to get 1.0x.

http://www.jdslabs.com/pdf/O2_LowGain.pdf

 

[dukefx]

Whichever pair you remove will turn to 1.0x.

 

[Arkady Duntov]

Whichever pair you remove will turn to 1.0x.

+1

Removing one pair changes the gains to 1.0/2.5x and removing the other pair changes to the gains to 1.0/6.5x. I checked with JDS a long time ago, and they'll do the removal for a relatively small fee. (My ODAC+O2 is from JDS.)

 

[Jimster480]

+1

Removing one pair changes the gains to 1.0/2.5x and removing the other pair changes to the gains to 1.0/6.5x. I checked with JDS a long time ago, and they'll do the removal for a relatively small fee. (My ODAC+O2 is from JDS.)

Yep I did custom gain at build time. Its def worth for lower impedance headphones. I use my o2 all day every day now.

 

[UNOE]

+1

Removing one pair changes the gains to 1.0/2.5x and removing the other pair changes to the gains to 1.0/6.5x. I checked with JDS a long time ago, and they'll do the removal for a relatively small fee. (My ODAC+O2 is from JDS.)

So it is a yes to my question "Can I just remove the 6.5x resistors to have (2.5x / 1.0x)?"