How do you identify a good amplifier?

Question

I know that the most important thing is to plug in and test drive it, just like you do when shopping for guitars. But what should I look for when I’m plugged in? And what kind of features do I look for? I have a good ear for pitch but not for tone, so it’s often difficult for me to tell what kind of difference various knobs and settings make.

I’ve done enough research to know most of the basic amplifier effects and features, like gain, equalization, and reverb. I know all about the effects loop, the difference between the pre-amp and the power amp, and the difference between tubes and solid-state. However, there’s a lot more that I’m (mostly) clueless about, like presence and clean/dirty channels and tuner/aux outputs and such. I don’t have a good idea of what’s important or how to evaluate them.

Answer 1

A good amp, apart from sounding good, should have a long life before it. So check all the controls: do they make a solid impression? Do the pots move smoothly, nothing is loose, and nothing makes noises it shouldn't? If every change in settings comes with its own sequence of "snap, crackle, pop", then this won't get better over time.

How much noise does the amp make when you are not playing? How much noise does it make when you are playing at "I'm only using the amp because I would not hear the electric guitar otherwise" levels? Either by playing softly, or by having the volume set low?

What happens if you switch off/on while at a high volume setting? Loud noises?

How solidly built is the cabinet? What would happen if someone bumped into it? Sat on it? Can you put a foot through a speaker by accident? Through the cabinet itself?

How good are any holds for moving it? How reasonable is moving it?

Answer 2

Disclaimer: I'm one of those folks who always preferred multiple independent components over an integrated system for audio work. That said, I would go with stomp boxes and separate preamps for practically all tone control, and look for a power-amp&speaker box which is as close to the "wire with gain" paradigm as possible. Which means an amp that is as near to perfectly linear over the full audio spectrum as possible, and doesn't add and distortion or clipping to the input signal.

It's easy to mod the signal thru a pile of preamps and distortion boxes; why make the power amp to any of that?