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Review: NwAvGuy's O2 DIY Amplifier

Discussion in 'Sound Science' started by shike, Aug 25, 2011.
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  1. Satellite_6


    You could just look a FR graph and figure out who's right. . . 
  2. mikeaj
    I can appreciate different preferences and perceptions of what the sound is, but for a quick sanity check, figuring out the frequency response would be very easy and doesn't require any expensive equipment.  Something like "boosted bass" doesn't leave much other room for interpretation, so that can be readily confirmed or denied.
    You can test output voltages with a decent multimeter using 0 dBFS (or any level) test tones and record the result.  If the result is different at different frequencies and your multimeter can actually measure voltages correctly across the audio frequency range, then the FR is not flat.
    If it's a 2-channel amp, then you could just use RMAA loopback through the amp.  A 3-channel Beta22 or M^3 wouldn't appreciate the active ground being shorted to the sound card line in ground though.  Most people probably don't have an interface with a floating ground input.
  3. zzffnn
    @ Satellite_6,
    ^ No offence, but have you compared the FR between O2 vs. Gs-1 vs. M^3 vs. Beta22? I bet you 5 bucks that all 4 amps produce ruler flat FR from 20 Hz-20k Hz.
    My 2cents:
    1) flat frequency response alone may not mean neutrality to ears. An amp with rule flat FR may not sound neutral to ears (that flat FR amp may sound edgy / bright or warm / musical), because of distortion, slew rate, sound decay or circuit design.
    2) FR graph is not music. Let your own ears judge and do not just rely graphs alone. Your individual preference is likely determined by 100s of graphs, which no one can predict.
    3) We are reviewing an amp here to help future / potential buyer, so it is probably irrelevant to argue what is neutrality or if neutrality is always preferred. It would be up to an individual's preference eventually (e.g., Some people may be sensitive to treble while some love treble).
    4) To be helpful in providing an impression, I suggest that we compare sound of amps in relative terms, e.g.,  "amp X has more perceived treble presence than amp Y". 
  4. palmfish


    Amp performance is influenced by the load it's driving too. A "neutral amp" may sound warm driving a low impedance headphone that has a mid-bass region impedance hump.
    Personally, I never understood the attempt to find "synergy" between an amp and headphone. Why do I read so many comments about folks who have a bright and crisp headphone and then they try to warm it up with an OTL amp and EQ?
    If your amp is neutral with low output impedance, then you're free to choose a headphone that sounds right to you out of the box. This is why I like the O2 so much
  5. mikeaj
    I think that's the point being made.  And I think all of these have fairly low output impedance, so it's not going to depend on the headphones too.
    The next questions are then about if those listening impressions are consistent, and why people may hear one to have more or less bass, treble, or whatever presence or quantity or whatever (some aspect of the performance characteristics other than FR, or imagined?).  If there's a difference and if we understand why, then we can subjectively review the amps more accurately and give better amp recommendations in the future, taking this into mind.
    There's a distinction between "sound neutral" and "neutral" that's been discussed previously of course, but I'd emphasize that you can't listen to amps without transducers and I'd agree that different people have different ideas of what sounds right, so "sounds neutral" is a lot more difficult to define.  I think it's better for everybody to converge on the same reference points and terminology, so subjective reviews are more consistent between different people (of course it'll never be close to exact) and thus useful.  Defining what's most mathematically neutral as the reference point, would be the natural way for a number of reasons.
  6. maverickronin

    EQ is a pretty useful tool.  I wouldn't dismiss so quickly.
    From a practical and economic point of view I think the best way to find "your sound" is to start with the headphones.  They have more affect on the final sound then all the rest of your hardware combined.  In theory the DAC and amp are just as important but in practice the variation between different models of DACs or amps is almost always miniscule as compared to the differences between of headphones so excepting models that require unusual amps like 'stats or the K1000 and HE-6 always pick the headphones first.  Even if you have an unlimited budget there are only so many models of headphones to choose from so finding one that's perfect for you out of the box requires a lot of luck and you might need more tweaking.
    Next I'd try modding the headphone since the mods will "follow" the headphone and affect its sound from any source.  Depending on your skill, confidence, and budget (not many people will want to try and mod expensive flagships) you might not be able to get satisfactory results.  I think its still worth mentioning for those with an adventurous streak.
    The next step is software EQs and DSPs but they aren't a panacea either.  Even if your computer is your only source they don't "follow" everything perfectly as they're usually set up in a single program and not "system wide" affecting everything you might play.  Despite that limitation I place them here because they're usually free or pretty cheap.  You can spend thousands on name brand professional mastering VST plugins if you want to though.
    After that I'd try hardware filters, EQs, or DSP boxes.  They can be used with more sources than a purely software solution but often they're more expensive and aren't as customizable so I place them after the software types.  Example of these such as crossfeed circuits and tone controls seem to be the most common and accepted of these sorts of tweaks among the head-fi community.  The Smyth Realiser is now making a strong case for hardware DSPs as well but its price keeps it a niche within a niche.  Hardware EQ boxes seem nearly unheard of on here though.
    Only after all that would I consider looking for "synergy" between a headphone and an amp or DAC.  Clean and neutral components take many variables out of equation and give you a blank slate to create your desired sound.  As the Objective2 shows they can be a lot cheaper as well.  Even after factoring in a large budget for professional VST plugins or hardware DSP boxes you'll likely save as compared to something like a TOTL tube amp plus a tube rolling budget.
    Of course your preferences might actually lead you towards a "synergistic" DAC or ampin the end even if you try all the other steps I listed.  No off the shelf product I know of will replicate the sound of a specific amp and unless you're Bob Carver you probably aren't going to be able to do it yourself either.  There are other factors besides the just the sound that some may consider as well.  Besides practical features I think tube amps just look amazingly cool.  It's only the fact that making one which sounds as clean as the O2 would be monstrously expensive that keeps me from using one instead.
    In the end what you like is what you like (assuming it's actually real and not just in your head anyway) and there's nothing wrong with that.  I just think that from a cost perspective jumping to a new amp or DAC to change the sound usually be at the bottom of the list of things to try.  There are plenty of people here who don't have to worry about that sort of thing and can pretty much buy whatever they like.  If you know what you're getting into then go right ahead.
    What I hate is when newbies are given the impression that you have to spend big bucks on a DAC and amp for a good headphone to sound better than a cheap one.  The endless, "oh its your amp/DAC no wonder you think audiophile headphone X sucks" sort of comments around here convince people to spend money on things they don't need or want.  Even if their DAC or amp really does suck that's probably still not why they don't like headphone X.  The sort of differences most people in this hobby care about are tiny on an absolute scale.  They get blown out of proportion on here and some people keep spending money on upgrades waiting for a revelation that never comes.  For the most part plugging a new pair of good headphones straight in your iPod is the biggest revelation you're going to get.  If someone doesn't think that's worth the money then they sure aren't going to think the smaller improvement a better amp may bring will be worth it either.
    This wandered quite a bit, and most of it isn't really even directed at palmfish, who I quoted, but I felt like a rant today for some reason...
    LizardKing1 likes this.
  7. Satellite_6


    Meaning they should probably probably all sound the same in terms of neutrality. I'm not sure how distortion and circuit design can affect neutrality if the FR is flat. I can't see how listening to the same music at the same volume with the same headphones through an amp with the same flat FR is going to result in different neutrality. I think my preferences are going to remain with headphones and not listening to amps. We could compare in relative terms through subjective impressions (with conflicting opinions all over the place no doubt) or we could figure out through measurement which amps change the sound and which do not, or if they should all sound the same. Sorry, I'm just talking hypothetically and being argumentative, so I'll stop now anyway. 
  8. zzffnn
    I can see that we all agree on certain things, although not all things.
    I agree that headphones (transducers) tend to affect sound more than amps. Of course, we should try to compare amps using the same headphones, if possible.
    I am not sure you can compare sounds of amps by comparing measurements alone; I am not saying that measurements are not important, I meant that you should also take a good listen because measurements do not always tell the full story. I bet that you would not be able to compare amps very well, If you just compare FR graphs. Case in point here is that all the 4 amps mentioned above should be dead neutral / flat according to FR, but ears tend to believe M3/Beta22 sounds slightly warmer than O2/GS-1.
    I guess neutrality according to Satellite_6 should be always measured by machine. I was mainly talking to Upstateguy, because his neutrality is apparently based on ears not scope.
    Example for distortion affecting neutrality (perhaps I should say PERCEIVED neutrality here):
    one example is that odd-order distortion may impart some PERCEIVED brightness to sound, even though an amp that produces the odd-order distortion reveals ruler flat FR; in this case ears may think that said odd-order-distortion-producing amp is bright instead of neutral. Conversely, even-order distortion may be perceived as warmth by ears. 
    Examples for circuit design affecting neutrality:
    The MOSFET in M^3 is usually consider to be warm sounding. Another example is that OPA627s / 637s in M^3 are usually considered warmer or more laid-back sounding that AD8610s (which some considered as cold/bright) or AD843s in otherwise the exact same circuit of M^3.   I heard OPA627s vs AD843s in M^3 and have to agree that OPA627s sounded warmer and more laid-back.


  9. palmfish


    I wasn't dismissing EQ and never said it wasn't useful.
    What I said was that EQ should not be thought of as a band-aid for "fixing" headphones that you don't like.
    If you don't like bright, sibilant sound, don't buy a pair of Grados and hope you'll find a "warm" amp to tame the treble. Just buy headphones that aren't sibilant.
  10. thehadi
    Hello all,
    I bought JDS Labs O2 and i would like to buy HD800. For a while i will use iBasso DX100 as a source. May be in a few months i will buy a proper DAC.
    How is O2 with Senn HD800? Should i look another amp or O2 is well with it?
  11. Maxvla Contributor
    I'd like to know as well. Considering a HD800 and will get the objective amp + dac when it's released, primarily for my UERM.
  12. upstateguy


    Grasshopper, you couldn't be more incorrect.
    If you were to ask Ti Kan, he would tell you that 637/627s sound exactly the same as 8610s in an M^3.
    In fact, more than a few years ago, I sent him WAVs of the 637/627s and the 8610s so he could hear the differences himself.  He nulled them with audacity and sent me back the difference which was at -45dB (instead of complete silence),  because he had to invert and line up the wave forms by eye.
    Now what?
  13. zzffnn
    I guess if you don't think HD800s are too bright and like them to start with, then O2 amp may suit you.

    Please take my comment with a grain of salt. I prefer slightly warm and laid back sound (I am sensitive to treble). I do not like HD800s to start with, so I would prefer HD800s on OTL tube amp to obtain warm coloration. If I have to go with solid state amp, I would prefer M3 with OPA627s or Beta22 over Objective2 or GS-1; in other words, I prefer "treble polite" amp with HD800s.
  14. zzffnn

    Firstly I am not Grasshopper.

    Secondly, if you want to discuss opamp rolling with M^3, I invite you to continue on the thread for M^3. Not here.

    Thirdly, opa637 requires different gain value than opa627. Are you sure your WAC files are volume matched to start with (gain value affects volume).

    Fourthly, I would like to know how Ti Kan proved that those two opamps "sound the same". Please continue with me on PM if you care. Let us not go off topic.
  15. Draygonn

    I enjoy my 02 with the HD800s. The E9 lacked soundstage and detail with the HD800s. The O2 seems to do everything right. It sounds a little thin compared to the WA2 for obvious reasons but I don't have an expensive SS amp for comparisons. Too bad we didn't get Naim's O2 vs V200 comparison.
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