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.
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Some class A/AB amps are designed so the bias adjusts more toward class A (class A = semiconductors on all the time) during warm up, theorectically so they won't sound like junk prior to thermal stabilization. Never heard of cap saturation in a negative context. It sounds like a good thing. Caps are the storage batteries for the amp. The worst case scenario with caps is insufficient capacity where they drain too fast when you need them. Keeping them filled is the big, heavy transformer's job. Like an automobile engine, the amp's system should work best over the long haul operating at its designed thermal equilibrium. I 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.
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?
I tried the " leave it on" for a day or two but all the amps I have from Krell 400xi, Parasound Hca 1000a, Bryston 4bsst seems sounds softer, warmer, more open but lacking of " edge" or sharp details and I really miss that . In my set up, I find it is best to have 30 to 60 mimutes warm up before playing any sources.
After many years in this hobby I don't see that leaving an amp on all the time provides any benefit vs. turning off if not listened to for extended periods. My solution is to turn on and off during the week if I listen in the evenings only and leave on during the weekend when I will spend more time listening. Also, I have never had an amp or other components go bad because of cycling off and on; I think the fear of premature wear, is highly overrated and unsubstantiated.
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.
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.