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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. khaos974
    Apparently http://www.head-fi.org/t/584202/epiphany-acoustics-join-head-fi-with-the-ehp-o2-portable-headphone-amp
  2. Anaxilus


    Alright, when mine comes in I'm going to post shots w/ my IR thermometer.
  3. mikeaj

    Take note of the AC adapter used and the line voltage produced, for a fair comparison, or at least a reference point.
    With the RC filter mod, there's some voltage drop across the resistor, so the voltage into the regulator is a little less, so it should heat up a little less I guess.  Even without that, it really shouldn't get dangerously hot...and these regulators are often operated much much hotter in many applications, since they're specified to work properly at such temperatures.
  4. estreeter
    I guess I shouldnt have been surprised, but all the plugpacks in my little town in northern NSW use some form of DC switching - the exact type of wallwart that Voldemort loathes in cheap amps. Fortunately, we have a new-fangled contraption called the internet, and all is not lost.
  5. deadlylover
    No, the Dark Lord loathes them because that's the wrong type to use in his creation. [​IMG] You need an AC transformer, not something that spits out DC.
    I think you can get one from Jaycar, pretty pricey though at like 25 bucks. I just threw one together for 10 bucks or so.
  6. qusp Contributor


    fixed, i think he lost that possibility some time ago now......
    continuing to use such extreme subjective terms and kinda desperately wanting people to believe the design as a whole and not just his botched build is flawed, is really getting old. 
  7. upstateguy
    Someone should start another O2 thread in the portable amp section.
  8. Willakan
    I am pondering doing a giant, multi-page O2 review, but I can't think of much use for it - I don't believe in subjective amplifier description silliness and am incredibly biased (I like NwAvGuy, I like the amplifier design, I like the reasons behind it, I like what it is doing) so it would just be a load of rambling about the history of the amp until you finally got to the "Listening Impressions" section, which would read "See Measurements."
  9. mikeaj
    Short of somebody else with an AP / dScope / whatever...I'm still waiting to see a real-world evaluation using a reasonably decent audio interface (line out and line in) and maybe audio differencing.  I'm not sure what could be covered that hasn't been covered before, but it would be an interesting comparison to see what the changes are in the time domain.
    So play some revealing music--whatever you think "revealing" counts as, or that may be challenging to reproduce--with the following setups, and record it:
    0)  original music file, do nothing
    1)  interface out -> interface in
    2)  interface out -> O2 (loaded with headphones via Y-splitter) -> interface in
    3)  interface out -> another amp (loaded with headphones via Y-splitter) -> interface in
    And of course match up the start times and make sure the amplitudes are the same before and after recording.  With a reasonable interface, 0 and 1 should be very very similar (indistinguishable by listening even with just 16/44.1 if done well enough).  Then you can analyze the results, or distribute the files for analysis and/or ABX testing.
    This is the kind of thing I'd like to see in any amp review though, especially those with more exotic designs (i.e. not this one).
  10. DRUB


    Just got my Epiphany Acoustics built O2 today. Works perfectly and its aesthetically very minimal, which is nice - diminutive black metal enclosure that feels reassuringly heavy. As for the sound, well that would be a bit redundant as Willakan has stated. Wire with gain. One change I've noticed (in admittedly sighted listening) is a difference in the way bass sounds compared to my Asus Essence ST headphone out (which had the output impedance mismatch). Will need to do a blind comparison before I can be sure though, which will have to wait until some friends come back to college for next term!
  11. estreeter
    Guys, personally I don't think there is a problem with saying 'I like what this amp does for bass impact with my phones/music' or whatever - its when people like 6Moons start ranting on endlessly about some minute difference between the kit under review and their gold-plated, 15K 'reference' amp that it ye olde subjective review gets a bit silly.
    What stuns me about HF is how each new set of impressions are accompanied by an array of requests for someone to test the amp with headphones X, Y and Z - if its truly a 'wire with gain', there should be absolutely no need to do this with anything other than the extremes - high sensitivity IEMs and very low sensitivity planars. I believe Voldemort tested his prototype with the HD650, and that's about as 'big' as I believe a portable amp needs to drive - as always, that might not be enough for some on Head-Fi.
  12. wdahm519
    Has anyone else had problems with the O2 not shutting down on low battery like Voldemort said it would?
    I just did a test run while studying for finals here, I had the amp running on battery power for roughly 8 hours.  Right around that mark the music was distorting, first very slightly and about 15-20 seconds later it was distorting a lot.  I knew instantly that this was batteries low time, so I plugged it in, and the great sound returned.
    But, it never shut off?  What gives!?
    EDIT:  Yes my amp is built with all standard parts, I didn't go experimental on it, its built correctly, blah blah blah, I know what I'm doing [​IMG]
  13. micmacmo
    Did you work your way through the post-build tests, specifically the low-voltage shutdown test? 
  14. shadow419

    There have been a few folks who have had this issue in one way or another.  Most have had a power on/off cycling as the load on the batteries is removed/re-applied.  There was an update to the  values of a pair of resistors.  R25 1.5M ohms R9 33K ohms.  From what I understand it's a battery induced change to account for different batteries.
  15. wdahm519


    I used the parts from the "latest" BOM that was hosted online.  I'm not sure if the resistor values were changed there.  As for post-testing, I have no had time to do test yet so I might find something there.  I'll look into it in a few weeks when I have some more time again.  For now, I'll just run it for 6 hours or so and then make sure I charge.
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