Originally Posted by cfull
If all an amp does is boost the power that is being output, how can that possibly change the sound (all these comments about improved bass/midrange/soundstage/etc)? I am genuinely curious, because it seems to me an amp built cheaply can fulfill the same output criteria as these 400 dollar and up jobs people spend money on. Is there any sort of science behind the notion that SQ is somehow improved, other than it makes the can louder? I don't want to start a flamewar or anything, and I'm sure this question has been debated before in some way or another on this forum, but I genuinely want to know. I just got a pair of DT880s and my emu0404 usb struggles to drive them, and i'm looking at options.
Your E-MU 0404 doesn't have a dedicated headphone out, right? If so, the line out may be able to produce sound through your headphones, but it is electrically limited (current supply), may distort and roll off the bass, as it's designed to «drive» a high-impedance load (such as >10 kΩ) instead of a headphone.
A headphone amp has an output stage specifically designed for this purpose. So it represents a better precondition than the (line) outputs of soundcards, even those with a dedicated headphone out. Extrapolating from my E-MU 1212M, I suppose that the 0404 has decent sound quality – as a source. Depending on your sonic demands, an outboard DAC would be a higher-quality option, or a DAC/amp combo (→ Meier-Audio, HeadRoom...).
There are cheap and expensive amps around. Roughly spoken, expensive amps use better parts and may have more sophisticated designs for better sound quality. It's just a rule of thumbs, and there are exceptions to the rule. People on this forum usually buy the amps after audition; so they chose the one that suits their sonic preferences best. This «best» amp isn't necessarily the most neutral and accurate amp, but maybe the most euphonic amp or the one with the best synergy with the existing gear. Some people don't care for neutrality.
From my wording you can deduce that different amps sound different. Yes, they do, at least to my ears (and I'm not alone). I wouldn't have spent ~$1000 if I could have got away with $200 to get the same sound quality. I still have some other (older, cheaper) amps around; compared to the Symphony and the Opera they just don't have the same finesse and resolution. Even between Symphony and Opera there's a difference in favor of the former. Although some recordings benefit from the slightly smoother, more forgiving presentation of the latter.
Technically the sonic differences are hard to verify. There are measuring differences, but they are very small, since 95% of modern solid-state amps have a virtually ruler-flat frequency response and very low distortion (< 0.01%). That's why the sonic differences are somewhat disputed in certain circles.
It really depends on your own demands. You may be satisfied with a $100 or $200 amp..