Will leaving an amp powered-up all the time...

I'm with Stevecham. Also if a amp manufacture is stating to keep a amp on all the time to sound their best, then it's a crutch and design flaw IMHO, I'd stay away. There are plenty of amps that sound great upon turn on.

If you have very revealing speakers and a quality ss power amp, letting it warm for at least an hour definately makes an audible difference. I can understand Kkm's thoughts that this may be a design flaw but have come up with my own theories on this. For example the Odyssey Stratos has a power switch on the rear obviously because the amp should be left on at all times to sound its best. I feel that the overkill on the Stratos's heatsinking delays the output devices from reaching a desirable operating temperature that would in turn keep them from sounding their best at least for awhile. So I would not view this as a design flaw but rather a careful design that allows the Stratos to operate at cooler temeratures even after warmup thus giving the amp longevity.

In Contrast the McCormack amp does not nearly have as much heatsinking as the Odyssey and it takes a shorter period of time to reach its optimum operating temperature for best sound but it does run much warmer than the Stratos even though both amps are biased up a bit.

There are some cases I have found that some amps actually do sound brighter if left on continously but some would say that the amp is not brighter but just more revealing & transparent. On the other hand there are some amps that just start sounding warmer when left on all the time. I suppose that is why we have an amp game.

Virtually all conventional solid state amplifiers will sound their best when left on continuously. The reason for this is that even at idle, an amplifier has voltage and current present which will keep capacitors charged and keep the dielectrics of everything (resistors, inductors, traces, point to point wires, etc...) formed to some extent. When you switch off your amp and leave it off for a number of hours or days, everything with a dielectric returns most of the way back to an unformed state. This is why amps sound closed-in and dynamically restricted at turn-on compared to thoroughly warmed up.

Tube amplifiers also benefit from being on but the cost of running the output tubes in a power amp 24 hrs. per day is too expensive to be practical. You would burn through a set of 2000 hour rated tubes in just 84 days.

As for any heat/biasing issues, if they exist, they are separate problems that don't apply to 99% of the other amplifiers in the world and are not normal. The heat issues can be solved with adequete ventilation and/or heatsinking.