Originally Posted by FEAST
All modern amps of equivalent power, Class D, A, A/B (unless something is wrong/the amp is old) - sound the same - with exception of tube amps. If not then something is wrong.
Don't let anyone tell you otherwise. I own a Schiit Valhalla, HD600's, and a Cambridge Audio DAC. Yes, the amp and DAC sound almost exactly the same as my motherboard output. I live and breath audio every day, I write and produce my own music (you can hear it if you want).
I have sat down and flipped between many, many different amps. They sound the SAME. I too, once believed that amp quality effects sound. Don't listen to anyone. Setup a side by side comparison and see for yourself.
Headphones make a massive difference in sound quality. Almost all modern DAC's (last 4 years) sound the same.
Buy something as cheap, small, and powerful as you can.
Originally Posted by chinesekiwi
Not as simple as that. Circuit implementation is still key and things like output impedance affect audio equipment.
This is a great point, kiwi - I'd also add that one of the characteristics of a well-designed amplifier is tolerance to noise from other sources; everything from the circuit board layout to the power supply design could be allowing in noise from outside sources, and that has an impact on amplifier performance.
FEAST, unless you do your listening inside a faraday cage your audio device is the only thing plugged into a high quality filtered power supply, even the exact same circuit implemented two different ways could yield quite different performance. Almost any modern (or even older) amplifier topology can be implemented well, but there is more to that implementation than seeing that the thing is Class D with your desired output power and declaring it to be the best possible option.
That by no means says that all the spectacular claims made by some of the specialist audio manufacturers are real and valid - often times, they have almost no engineering merit - but there is more to a high quality amplifier than its mode of operation, output power, etc.
Douglass Self has many great publications on sources of distortion in audio amplifiers - they're worth a read if you're interested in learning a little more (and have some electronics aptitude).
I'd agree 100%, though, with your sentiment that the transducer itself (aka our headphones, speakers, etc) makes the single largest difference in the overall "quality" of an audio system.