How does an amp change the sound quality?

[bloodevil]

Definitely a newby question I know, but I can't understand how an amp can change the sound quality!
I obviously understand that it should amplify the sound volume, that's why it's called an amplifier, but what does it mean when I read that an amp sounds good?
I'm talking about Headphones specifically, does that mean that it doesn't distort the sound or it means that it makes the sound even better?

 

[Wes]

By introducing noise or distortion products. The latter include harmonic, intermodulation, and cross-over distortion to mention a few.

Some distortion products are often thought to be euphonic, or "better" in a sense. e.g. tubes introduce even-order harmonic distortion products.

Interestingly, I have never seen a scientific study showing that even-order harmonic distortion products actually are preferred by a listening panel...

Today, most amps will not alter the sound in any meaningful way, so it is the headphones you need to focus on.

 

[BDWoody]

Definitely a newby question I know, but I can't understand how an amp can change the sound quality!
I obviously understand that it should amplify the sound volume, that's why it's called an amplifier, but what does it mean when I read that an amp sounds good?
I'm talking about Headphones specifically, does that mean that it doesn't distort the sound or it means that it makes the sound even better?

The ideal amp would simply take a little signal and make a perfect copy in a bigger version, but all amps in the real world add some inherent base level of noise, and a level of distortion to the incoming signal. If those levels of noise and distortion are low enough that you can't hear them, you have an amp that would be considered 'transparent' to its source. This is generally considered good (around here at least).

It can't make the sound better than what came in.
(Edit: Defining better here as higher fidelity. ) With headphone amps, you want to have an output impedance low enough and power high enough to be able to comfortably drive your headphones to whatever level of volume you like and they require, without clipping, audible distortion or noise.

Fortunately, amps like the JDS Atom make that available to almost anyone. No magic, just good engineering.

 

[MRC01]

By introducing noise or distortion products. The latter include harmonic, intermodulation, and cross-over distortion to mention a few.
...

yes, and...

One more: by curving the frequency response. For example, an amp with high output impedance boosting frequencies around the headphone's peak impedance frequency range. A common example is a tube amp making it sound warm because the headphone's peak impedance is around 100 Hz.

One more: by introducing L-R channel imbalances, especially at low volume settings.

One more: by running out of power and clipping. This may be frequency specific, due to the power spectrum of the music and the headphone's uneven impedance vs. frequency.

 

[Wes]

headphone amps clip?

 

[MRC01]

Sure they can. Just hook them up to an HE-6