receivers don't "sound" different.
I'm surprised to hear people say that. I mean there are component level difference that can affect the sound. Weaker DSPs, inefficient transformers, crappy implementation of codecs. Isn't this one of the reasons why (legitimate) size and weight was a consideration in the non-digital days? Heat generation/ dissipation was a huge consideration in amplifier design. It's been ages since my classes, but poor implementation certainly would affect the sound.
Good points, Hansang, and I agree. I'll just add that the quality and type of the power supply, circuits, op-amps, chips, boards,wiring, analog connectors, caps all affect sound quality, which can often be audible especially in receivers or pre-amps. How well each amp, pre-amp or receiver has been designed to handle and dissipitate heat will also impact sound. Electro-mechanical characteristics of audio components are greatly affected by heat.
One other thing. Linear frequency response and low distortion are very important however those two parameters alone do not ensure optimum sound reproduction. Ask any designer and he will tell you there are many considerations in designing a great receiver, pre-amp or amp. And each designer has a unique vision for the component and sense for what compromises are necessary in order to achieve that vision. Accordingly, not all components including receivers are created equally or sound the same. The old advice of listening to a component in your home if you can and trusting your ears still applies.
