What qualities do you look for in a good amp?

Hmmm, I am not into silver yet, so I look for black faceplates. =)

This is like asking literally for "ice cream" when you walk in Baskin Robbins.

Seriously, I try to "listen" more than look. I will "look" at the spec sheet but that doesnt mean much. I like to look inside and see large and well constructed torodial power supplies, first and foremost. Then all the other "guts" like, voltage rails, cabling routing, Caps, boards, output terminals, output devices, etc. etc.

I think of a power amp as the producing element in my system. Preferably it will be the strong, silent type which can execute the most demanding of tasks without complaint or hesitation. Extending the analogy, the front end source component is the talent and the preamp is the director. The rack, cables, cords, spikes and room treatments are the props. The speakers are the stage.

My decision tree when auditioning a power amp flows from one must-have aspect to another. It begins with philosophical considerations:

1. Solid-state. For me, this is a cost, stability and reliability issue. If the best tubes were perfectly matched and cost the same as sparkplugs I'd reconsider.
2. Reputation. I take comfort believing there is a designer behind the product with experience and talent. An amp's popularity is a plus.
3. Pleasant appearance. The amp must look purposeful. Flimsy looking or unfinished parts convey weakness in execution.

Physical considerations:
4. Rows of external heat sinks. These are reputed to be expensive. Mounting them on the outside of the chassis seems to be the preferred method.
5. Sheer weight. Real-life power supplies are heavy. If it specs at 200 watts a channel but weighs only 25 pounds somebody's kidding somebody.
6. Number of output devices. More is better. While I admire an amp that can squeeze alot of performance from a minimum of parts, in the long run my money's on the unit that has so many muscles it never breaks a sweat.
7. Connectors. With the amp in place they must be reachable and not too difficult to tighten. With its own allure, gold plating is the icing on the cake.

Sound:
This subjective element is the hardest to pinpoint. When an amp is doing its job for me, it will sound smooth, effortless, unforced yet unrestrained, balanced, limitless, fast, quiet and balanced. All combined it will sound magical.

Enjoy your search.

I like the ones that just get out of the way.This is one that changes the signal the least from input to output. I like the romantic sound but not on every recording.Quiet is a major plus...no hum in the speakers. So far the ones that seem to do this the best IMHO are digital amps. They don't weigh much but are 50% more efficient than the average amp.Which means they only take in what the speakers need.Instead of giving half of their stated power to the atmosphere in the form of heat.

Good Luck with the Hunt

Look for an amp that doubles it power (watts) as the ohms are halved. This is a sign of a stable amp that will drive almost any speaker load.

IE:
200 watts @ 8 ohms
400 watss @ 4 ohms
800 watss @ 2 ohms etc.,etc.

Like Rockvirgo said, the heavier the amp, usually the better... this translates into a larger power supply and more $$$.

Short list to start with: Audio Reserach, Bryston, Krell, Mark Lenvinson, Pass Labs.(only to name a few) These are all high quality, well made amps, by 1st rate manufactures.

The final choice is what sounds best to YOU, not the BS the salesperson tells you. Good Luck!

I agree with rockvideo.Let me add some specifics.Some of the amps mentioned by Ig40 did not work for me.You need an amp with big dynamic range no feed back and reputed to be reliable.I have been happiest with Gryphon and YBA amps.