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O2 Build Complete: Let the objective, subjective listening tests commence!

Discussion in 'Sound Science' started by cheapskateaudio, Oct 27, 2011.
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  1. 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.
  2. wdahm519


    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.
  3. mikeaj
    What voltage do the batteries measure at when it's having issues?
  4. shadow419


    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.
  5. Billyk Contributor
    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.
  6. 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).
  7. Head Injury
  8. fishski13


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

    Ouch. Basically a 7 dB boost to 100 Hz. Hard to believe that wasn't really obvious, actually.
  10. 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?
  11. 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.
  12. Willakan
    Now just change the O2's output impedance and flog the Crack to the highest bidder[​IMG]
    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.
  13. kingoftown1
    Thanks so much guys, I'll give it a look later today.
  14. shadow419
    Got my panels yesterday, and batteries today.  Going to solder the battery terminals and see if I can recreate wdahm's problem.
  15. fordgtlover Contributor
    The O2 sounds great to my ears. Good stuff.
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