[shadow419]

Cool, I haven't even run on batteries yet.  You have the latest suggested values then.  My batteries should be here by this weekend, and I should have time to test the shutdown performance.

 

[wdahm519]

Quote:

Cool, I haven't even run on batteries yet.  You have the latest suggested values then.  My batteries should be here by this weekend, and I should have time to test the shutdown performance.

Well, listen for the obvious distortion that heard when the batteries get really low.  I'm using Tenergy 9.6V 200mah batteries and got roughly 8ish hours out of it with Westone UM3x IEM's.  If you're using bigger headphones that require the volume to be cranked up I'm sure it'll be shorter.  Either way, it'll be really apparently if you start getting distortion because it'll sound like pink/white noise in with the song playing behind it. 
 
I hope its not doing damage when the voltage is that low.

 

[mikeaj]

What voltage do the batteries measure at when it's having issues?

 

[shadow419]

Quote:

Well, listen for the obvious distortion that heard when the batteries get really low.  I'm using Tenergy 9.6V 200mah batteries and got roughly 8ish hours out of it with Westone UM3x IEM's.  If you're using bigger headphones that require the volume to be cranked up I'm sure it'll be shorter.  Either way, it'll be really apparently if you start getting distortion because it'll sound like pink/white noise in with the song playing behind it. 
 
I hope its not doing damage when the voltage is that low.

 
 
 
 
 
 
I wouldn't worry about damage, you're just getting clipping when your batteries are low.  The increase in distortion is as good a sign as any to charge up the batteries.

 

[Billyk]

OK here is a quick subjective comparison. O2 vs mildly modded Crack with Speedball.
Source = PC-> Foobar-> Wasapi-> AMB Gamma 2
Cans= HD595
Tunes+ Vince Guaraldi , A Charlie Brown Christmas, Fur Elise, The Christmas Song, Greensleeves
 
Had the wife help out. She would change the amps while my back was turned and start the song. I could tell the difference clearly, the Crack was smoother with more seeming detail, wider sound. The sound was kinda towards the rear and spread beyond the outside sides of the headphones. The instruments seemed to be a bit more clearly defined in the space. Bass was full and clear, mids good and cymbals and brushes were smooth and crisp. O2 did really well though, crisp sound, a bit forward and closed in, the sound was confined to my head. Definition was very good bass was deep and well defined but not as rich, mids good, cymbals and brushes were not as lush(?) and brighter.
 
Overall the O2 did a remarkably good job, it was fun to build, a great price and sounds very good. I mean the 6NS7 chrome top cost more than two boards and all the parts for two O2s... not to shabby!
 
Pardon my lack of description, my very first review of this type.

 

[Shike]

The output impedance difference would likely explain the differences you heard.  If I'm right the Crack amp is OTL which could definitely change the sound of a lot of cans - especially Sennheiser since they're known for quite reactive headphone loads (see - low damping factor).

 

[Head Injury]

The HD595 in particular has the largest impedance curve I've seen in a dynamic driver. Up from 50 ohms to over 200 ohms at 100 Hz, a four-fold increase. I think only its updated HD598 brother has a larger one.

 

[fishski13]

Quote:

The output impedance difference would likely explain the differences you heard.  If I'm right the Crack amp is OTL which could definitely change the sound of a lot of cans - especially Sennheiser since they're known for quite reactive headphone loads (see - low damping factor).

the Crack has an output impedance of around 120R.  socketing and rolling output resistors in the O2 would be easy to compare.  
 

 

[Head Injury]

Quote:

the Crack has an output impedance of around 120R.  socketing and rolling output resistors in the O2 would be easy to compare.  

Ouch. Basically a 7 dB boost to 100 Hz. Hard to believe that wasn't really obvious, actually.

 

[kingoftown1]

Ugh, so after deciding to replace the inputs and outputs on my board, I've only got one channel working.  All my new connections are testing fine.  I noticed that there's very little resistance between the left and right channels of the gain switch.  Am I correct in assuming that's entirely wrong and shouldn't be happening, or should I be looking elsewhere?

 

[mikeaj]

From the diagram...
 
Looking at the bottom (solder side) of the board, batteries facing you, then the six pins of the switch are 1-6 starting from the upper-right and going clockwise**.  2 and 5 are connected to each other and to ground.  With the switch one way, 2 is connected to 1 and 5 to 4.  With the switch the other way, 2 is connected to 3 and 5 to 6.  If they're connected, then yeah they're supposed to have next to no resistance between the points.
 
**edit: I apologize if it's upper-left and going counter-clockwise, or it's something else...need sleep sorry...
 
Anyway, the gain switch is probably the last place you should be looking, since if there's no connection at all ("infinite" resistance to ground), then you'll just have 1x gain for that channel.  It shouldn't be that you get no sound at all.
 
 
What are the DC outputs when powered on, for each channel?  Check the supply voltages at the op amps.  If the op amps are socketed, I'd also try swapping the 4556s (U3 and U4) to check if which channel is bad also swaps.

 

[Willakan]

@BillyK
Now just change the O2's output impedance and flog the Crack to the highest bidder

 
@kingoftown
NwAvGuy has just added a more comprehensive trouble-shooting section to his blog, including voltages for any point on the board. Give it a look and you'll probably find your problem.

 

[kingoftown1]

Thanks so much guys, I'll give it a look later today.

 

[shadow419]

Got my panels yesterday, and batteries today.  Going to solder the battery terminals and see if I can recreate wdahm's problem.
 

 

[fordgtlover]

The O2 sounds great to my ears. Good stuff.