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

I noticed the same thing on my Pass X250,5.After 3 days being on,it sounded too bright and underpowered.The regular1 hour warmup sounds a lot better.

Amps ofen need to warm up to sound their best, I also leave mine on all the time

I agree with Rockvirgo. I don't think the caps have anything to do with it.

Amps with no global negative feedback have no choice but to let the bias drift. Without feedback, thermal changes cause an imbalance in the bias and that imbalance grows with temperature and time. Pass amps are known for needing to have the bias readjusted every so often to account for the average increase but maybe after a few days of being left on, it can peak and run the transistors out of headroom. I knew a guy who readjusted the bias on his X350 every few months, for example.

PS, I think the bias is class A at first in some amps due to current inrush and not deliberate design. See JA's measurements for high bias amplifiers and you can see this effect. One of my buddys has a Gryphon ST-100 amplifier that will burn the skin off your hands the first half hour after turn on.

Arthur

Overhang, I personally don't consider the amplifier warmed up if it is just being left on. Doesn't matter on for 3 days or on for 3 weeks. It will not sound the same as if it had played music for 2 hours. With your amp it makes very little difference between on and standby. A signal needs to pass through. That's been my experience with the X250.5. I've left it on and not playing. But it sounds better when I just turned it on and ran some music for an hour or 2 before listening.

Arthur, Pass amps are known for needing bias adjustments every so often? Is it official?

As recommended in the owners manual, my Plinius 8200 mk II integrated is left on all the time (unless I won't be listening for greater than 5 days). Pliniius states the amp needs atleast 24 hours of warm-up to sound it's best.