Even at the higher gain settings with the O2 your not going to get any audible hiss......if there is some its from your recording.
(or from a noisier DAC/audio out such as that implemented in the STX). The O2 is a 'black' amp, but back when I had it plugged in to my Realtek Audio chipset in my laptop, there was hiss at high volume with nothing playing.
Of course. Good amps/DACs don't improve the signal, they just degrade it as little as possible. In other words: even a perfect amp could not improve/reduce the noise generated by the DAC, it just wouldn't add more noise.
Part of the high performance of the O2 is the fact that the volume control comes after the gain stage. So the noise generated by the gain stage will be attenuated if you turn the volume control down.
The STX has entirely digital volume and gain control, and therefore the software "gain switch" does not affect the noise floor or the distortion of the headphone output at matched levels at all. The only things that do affect the noise floor are:
- software problems on Windows (16-bit volume control, etc.)
- hardware problems like interference, bad power supply, or ground loops
- the sample rate (48/96/192 kHz is 6-7 dB less noisy than 44.1/88.2/176.4 kHz because of the re-clocking performed by the C-Media chip in the latter case)
- the impedance and efficiency of your headphones (use 250+ Ω HD6xx, DTxx0, etc., and there should be no audible noise, with the additional benefits of a high damping factor and low distortion)
If high gain sounds better to you, that can be because of two possible reasons: either you did not match the volume properly (and therefore provided another example of how higher gain fools people into thinking the sound quality has improved, when in fact it did not), or there is some problem in the Windows drivers (for example, under certain circumstances, software dynamic compression is applied to the audio output to avoid clipping, but that should not normally happen at 50% volume).
I agree, generally speaking the less gain an amp runs the quieter it is, and less prone to distortion. As above, if you need to wind the volume past 12 o'clock you could probably do with a bit more gain. Aim for ~50% on the volume dial as the maximum volume you will use.
There is nothing wrong with using low gain on the O2, and more than 50% volume.
Well i use unity gain in my O2 and half volume is my comfort level with Grados, with Sennheisers i use 2.5x gain as half volume is also the most i can comfortably listen to. Reason for aiming for 50% on the volume pot is because that is the sweet spot for channel balance.
This may be a stupid question but I'm considering the Magni and noticed it only uses stereo RCA's for input. If I connect an Xonar DGX with a mini to RCA to the Magni will I lose the Dolby Headphone 5.1 surround effect since the signal is being "split into stereo"?
The headphone surround effect is encoded into the stereo output of the sound card. But you need to select "Headphones" instead of "2 Speakers" in the Xonar Audio Center, and enable Dolby Headphone. Note that some Xonar cards that have separate (amplified) headphone and line outputs (specifically, the Essence ST/STX) do not support Dolby Headphone on the line outputs.
edit: But if you're interested: something like a receiver's headphone jack has a high output impedance. This causes, for example, a bass boost and loose bass with dynamic headphones. Planar magnetics are pretty much purely resistive loads so they don't really care about the output impedance.
So, if you switch from the Magni or O2 to a receiver with a HD555 you will hear a huge different in the bass, with a HE- or LCD or other planar magnetic headphone you won't.
It seems like the Modi is preferred over the ODAC due to the Modi sounding less bright; the O2 is preferred over the Magni for the same reason. Receivers are preferred over both for open dynamics due to a greater effect on the bass. For those that prefer warm and bass-heavy headphones, it seems to me like it would be easier to go with a set of dynamics and an AVR receiver (albeit without 0 ohms impedance), enjoy the bass, and forgo the entire M&M vs O2/ODAC transparency debate.
xnor mentioned AVRs providing more bass than the low-end Schiit and JDS sets. I'm thinking of getting a set of the Fostex T50RPs (probably won't ever mod them); since they're orthodynamic, I'd like to know that the two sets mentioned in this thread will be sufficient to drive the set without leaving out bass due to brightness bias. I have mentioned which three receivers and which speaker amp I had in mind (all of which were manufactured within the last three years), but I'll leave any debate of those particular sets in their own thread.