I think voltage gain is measured either in dB or as a ratio (eg. 3.5x), not in V directly, since gain is Vout/Vin, but maybe I'm wrong with this, nevertheless lets assume that I have only odac+o2 and some "voltage hungry" hp which will need 7V. So I will have these two options - change the O2...

Regarding O2 power capabilities I have one question - according to designer's site, O2 is able to produce 7.15V when powered from AC. In a same time designer states that max input voltage before clipping is 7.15 / GainValue. Does this mean that when used with ODAC, which has 2V output and...

Not really, in fact voltage requirement is depended only on headphone's sensitivity which doesn't necessarily correlates with hp's impedance curve. Look here: http://doctorhead.ru/upload/iblock/efd/fr.png At 500 Hz it has higher sensitivity than on 1 kHz despite being higher impedance on 500...

I don't know about matrix, but E9 and magni has more power, but the real question is, if you really need that more power? Simple answer is no, you don't, because O2 can drive 99% of all headphones to crazy  volumes.. (That can be calculated with quite simple math)

I'm using HD 600 with O2+odac and I simply love that combination. Difference between those two is that hd 600 are more neutral/linear, easier to drive and more comfortable for long listening, HE-4 has better bass.

It's not a bass boost and you really shouldn't be using higher gain with ODAC (only in special circumstances), because it can make distortions / clipping. The problems you described earlier sounds just like that to me. Higher gain is meant to be used with low power devices like mobiles etc..

That's correct - with volume slider at 100% I measured 1.999V,  at 90% - 1.588V 80% - 1.336V 70% - 1.060V and so on   EDIT: I did full plot from 100% to 0% on volume slider in Win at 5% steps if anyone is interested:

  Yes, I used simple DMM at 50Hz sine wave @ 0 dBFS.

  That's strange, cause I didn't hear any difference between 2.5x vs 6.5x with HD600 or HD800. You just have to be sure to lower the volume in pc if you wanna use 6.5x, so the output from odac is 1V max, if using AC adapter. In case of batteries it's even lower (cca 0.7V). According to my...

Those measurements for LCD-2 and LCD-3 seems strange to me. lcd-3 should definitely be more sensitive.. Maybe I'm wrong, but didn't you swap it?

Quote: There shouldn't be any audible difference between 3.5->3.5mm vs 3.5->rca, but i prefer rca simply because it seems to be more robust.. I'm using BJC MSA-1 and I can only highly recommend it. And yes, you can use your headphones directly from odac.. true, it's far from being ideal...

Quote: Sorry, but are you paid for defending ODAC and/or O2 ?

Quote: Of course you are right, you can't set anything on ODAC. By "5% volume" I meant setting PC volume slider (labeled as odac) to 5%.   The point is, you get 2V RMS only when this slider is set to 100%.  And by previous post I wanted to say, that with O2 amp with 1x gain, you...

Quote: I'm not sure if that's a good idea. According to NwAvGuy, peaks in audio at standard listening volumes can be as high as 110 dB for which you will need ~2.5V from amp with HD 600 or 650. But O2 set to 1x gain with ODAC would be able to deliver only 2V. I think it's just easier to...

Quote: Use lower gain, higher can cause distortion if used with desktop sources. Higher was made for lower voltage sources, like mobiles/daps..