Reliabilty, Keeping Equipment Powered on or off?


I generally keep my system components powered on because the system does not have to "warm-up" when I sit down for a listen. I do know that reliability is usually calculated by POH (power on hours) however this calculation IMHO is a broad brush stroke. I do power down certain components that are not required to be left on to sound their best, such as a Luxman T-117 tuner and Wadia 171i Dock . However, my Krell IA, with the volume turned all the way down runs pretty hot, so hot you can't leave your hand on it. When turning the volume up on the Krell to reproduce the live event sound level, you can fry an egg on it, so I can only guess the Krell was designed to handle this kind of heat? However, back to the other components, such as DAC, SACDP, Headphone Amp, etc. Is keeping everything turned on asking for trouble or is leaving it on best to prevent thermal expansion and contraction which may be detrimental?
grm
skiroe

I can't speak to all equipment, but I am very familiar with Parasound as I have schematics for the JC1, JC2 and other products such as the 2200ii and P3. Although well designed (as good or better than most), there is no voltage transient protection besides filter capacitors. Transient voltage protection is typically not provided by most manufacturers and is left to sand alone outboard line filter and transient protection devices.
So many with different opinions.
IMHO, i would rather deal it a more scientific way. Generally, if the measured temperature on the chassis (using a temp probe) is less than 35 degree C, it is safe for equipment to remain on 24/7. If you need to be more specific, just open up the chassis and measure the heat of the components inside (i won't be responsible for any damages to your equipment and to your own safety), if the temp of the components is hovering around 40-45 degree C, it is still OK to be on for 24/7, BUT with one caveat , you gotta search for the lowest temp rating of internal capacitors. If it is rated at 70 degree C, then the internal ambient temp and\or components gotta to be less than half of that, i.e. 35 degree C or lesser. Capacitors life span and other electronic is affected by temp and their specification rating would drift faster over time due to heat.
I was told as rule of thumb the components that run hot - not just warm, should be left on at all times along with good line protection. I think this applies to most if not all power amps that operate in class A. Extreme temperature cycling puts a lot of stress on electronic components and can reduce their life expectancy even when they are designed to handle those conditions.
If they (audio equipments) are designed to handle those conditions, then of course , it should be left on without problems. It's those equipments that use poor quality parts that have "borderline" specifications on heat, current, mechanical tolerance (thermal expansion) etc..  that we should take note of irregardless they are running hot during idle or operating in Class A or not.
regards,
-phil
I've previously noted that leaving things on even at the suggestion of amp designers is the domain of wasteful boneheads who, as an example of wasteful boneheadedness (!), might also leave their cars running at all times to insure proper engine lubrication without that pesky "start up" stress, and leave refrigerator doors open to obviate door hinge wear, etc. I've since completely changed my stance on this issue (although I turn my rig off so I don't have to think about it blowing up when I'm not listening to it) as the rampant wasteful tendencies of people have irretrievably set our demise in motion, so you might as well waste whatever energy you can. After all, your audio playback standards can make you happier, and will help assuage any stress from, for example, an area of African farm land the size of Alaska recently being rendered unusable from rising sea water contamination. Who cares? Get yer Mahler on and you can let the kids worry about all the other stuff...