Originally Posted by Ishcabible
Ugh I don't really want to get into this, but nobody's pointed it out for some reason. Why would you try to amplify an amplifier?
Of course you don't hear a significant difference; what you're doing is amplifying a source that isn't good in the first place. What you're doing is trying to resize a 5x8 picture into a wall-sized picture and complaining that the result doesn't look nice. The O2 is doing its job. It's amplifying the source. You're plugging the O2 into a laptop headphone jack. The O2 could not possibly improve the sound because the sound it's receiving is already degraded; amplifiers aren't magical devices that can somehow improve something that's been degraded.
The O2 could in fact easily improve the sound by preventing the built-in amplifier of the laptop from degrading it while driving a headphone load, rather than the input of the O2, which is much easier. Onboard audio often has problems like high output impedance that can be fixed by adding a low impedance amplifier. Also, running the laptop at 100% volume (or whatever its maximum is without clipping), and using the O2 as an attenuator can reduce noise with sensitive headphones. Another thing to consider is that the laptop jack might be switchable between line and headphone mode. But even if it is not, the popular belief that "double amping" cannot improve the sound is not correct, as explained above.
Finally, there is not really such thing as an "unamped output": even line outs are driven by amplifiers, just - typically - low power ones not designed for transducer loads. However, it is technically possible to design a headphone output that is good enough for both purposes (except for a minority of headphones that need more power than what can be provided by a good buffer op amp like the NJM4556 and ~2 Vrms full scale voltage). In fact, many sound cards have "headphone jacks" with specifications closer to that of a typical line output.
Edited by stv014 - 2/26/14 at 8:58am