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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. Anaxilus


    You can cross off the E5, it's about as transparent as politician.
  2. wakibaki

    Nobody said it was going to be fair.
    So we're now asking if a well-made cmoy is indistinguishable from the Benchmark DAC 1 pre's headphone output? It's unlikely unless perhaps the cmoy is built with an AD8397 or similar high-current opamp. Most cmoys (most opamps) have a high enough output impedance to have an audibly non-flat frequency response with many phones. The O2 isn't far removed from a cmoy though, the main difference is the gain stage preceding the volume control, it's not inconceivable that with the right opamp and gain the difference will be inaudible in many phones, particularly ones without sufficient sensitivity to reveal low levels of Johnson noise at the input.
  3. estreeter
    Getting back to the Objective 2, anyone received their EHP-02 yet ? I dont want to pester Oliver - just interested as I believe this was the week he indicated when I emailed him several weeks back. I suspect that he has orders galore.
  4. frenchbat
    I suppose he does have a decent amount of orders. When I asked him about the lead time as of last week, he told me "end of January". I guess things are gonna get better after the holiday season, he deserves his rest like anyone else. 

  5. maverickronin

    A cmoy could possibly pass that test into certain loads.  One like Voldermort tested with the two 9V batteries and the 4556 seems like a good candidate.  Something with more current capacity like the AD8397 could be even better if someone has a brilliant hack to keep it stable and from blowing itself up when the TRS jack shorts it or something.  I'm not versed in all the options, especially if you go surface mount, so there be a better option.
    Of course the more gain you try and wring out of single stage design like that the worse the distortion gets so it may end up having so little gain its useless as anything but a buffer to reduce output impedance.  It could be transparent in some situations, but those would be more limited and make the design less useful.
  6. fubar3

    I got a different understanding from reading regulator datasheets.  Even though regulators are robust and easy to use, the designers realize they cannot anticipate every circuit that users may invent.  After all, the regulators are complex active circuits that interact with the circuit topology.  Therefore, the application designers have final responsibility for the regulator deployment.  The notes about bypass caps are intended as helpful guidelines, not absolute rules.
  7. mikeaj
    Well IMHO assuming the DAC and ADC are fine, Audio DiffMaker should be more interesting than a DBT anyway.
    Out of curiosity, have you pinpointed differences between those amps with Audio DiffMaker, or was that just an idea for possible future plans?
  8. cheapskateaudio


    I basically agree with your view. My issue is that I've built two of these, and I've heard the amp's output quality degrade after 1-3 hours on both of them, depending on ambient temp, volume, input levels, and headphones. From my experience with electronic devices if performance changes over a long period of time it's probably heat related, so I poked around a bit with a thermometer and found one v-reg at nearly 80C and the other one at only 50C. Devices perform differently at different temps (fact), so I think the smearing harshness that starts to rear its head over time is related to the v-regs having performance characteristics that deviate further as their temperature deviates further. The fix of course is to get some helpful direction from the datasheet.
    I've checked the amp several times with a DMM and everything is normal. I don't see evidence of a short or any other problem with parts. I've followed the O2 build guide and troubleshooting posts on diyaudio as well. 
    I built two of these amps, I modded them both, I didn't do that because I thought they sounded fabulous stock. Even the fully modded amp is not that great as the difference is relatively subtle, but the HD650's have more of that dark signature they're known for using the modded amp. 
    I just don't see/hear what's special about this amp and I recommend that people who build it look at it as a cheap starter rather than a real contender as a reference amp. You know, the O2's builder acts like he invented the low noise/distortion amplifier. As if nobody else could take a datasheet phono circuit and recreate that same low noise amp. Then [Mod Edit: Inappropriate] backs this nonsense because it is presented in a factual manner and they fell for it. 
    When you design an amp to actually drive headphones so that they sound good, compromises are inevitably made. I think that is the real lesson of the O2. Amplifier performance is not dictated by noise or distortion, it's dictated by how it responds to a REAL LOAD. 
  9. shadow419
    Continuing the discussion : Are you absolutely positive that everything in the power supply section is operating correctly, and that output opamps are working correctly as well?  I'll say it again, the regulators on my O2 don't come anywhere near the temps you are reporting (80C).  I'm getting low 40-45C with a real headphones plugged in.
  10. kiteki
    I'll compare it to the E6.
  11. cheapskateaudio


    The wall plug shows 18.1v
    C2 & C3 show 24v
    U5 & U6 show 24v on the input & approx 12v on the outputs.
  12. Fred_fred2004 Contributor
    I've just finished building 2 of these amplifiers it only took a couple of hours once I got the parts sorted.
    I'm using the AKG 600ohms at the moment and they sound brilliant, I'm not real flash with the descriptions of the sound, but it'll do me :)
    We owe the designer of this amp a big thank you not just for doing the leg work but for freely releasing it so we can all very cheaply have a great sounding new toy, the compact design, all on one board is a master stroke and makes the construction a doddle
    the only thing is why use those sky blue jacks??
  13. Currawong Contributor
    I've removed all the personal attacks, abuse and off-topic nonsense from the last couple of pages of this thread. For the most part, if you don't agree with the OP (of any thread), don't crap all over their thread. Start your own.
    DIY is supposed to be fun and people involved are supposed to be helpful. The behaviour from some of you has been disgusting and totally against the spirit of what DIY is. Someone pointed out that another forum was more helpful, and it's no wonder with the roughly 2 pages of crap I've had to remove from here why they felt that way. 
    Back on topic please, starting with the post immediately after this one. 
    olor1n and Groundloop like this.
  14. Anaxilus


    There is definitely (relative) truth to this statement.  I've heard some $1K shiny aluminum boxes fail quite miserably at this.

    Was wondering about this myself.  Can't imagine it's anything but aesthetic or maybe cheap because it's overstock nobody wants.
  15. upstateguy


    I'll be using a North Star 192 MKII dac and my computer line in, if I can hear differences between the O2 and the GS-1.
    I don't have my O2 yet, but am expecting it soon, so no comparisons have been made.
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