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

From the standpoint of safety, longevity and energy savings, it makes sense to power down everything.  This is particularly true of tube gear.  I can understand not wanting to power down amps which can take a really long time to come back up to song, but, these are exposed to the most heat from being left on, and these can do damage to speakers if something happens while you are not there to power them down.  As for thermal cycling, that is really not an issue because it happens relatively slowly.  If you look at rating of most parts, they include rating by operating temperature--the higher the temperature the shorter the life.

I only keep on what is meant to be on all the time.  That means I don't power down my music server/NAS.  It would take about 20 minutes to bring the server network back up if I turned it off (components have to be brought up in a particular sequence).

One thing not mentioned. Power line transients. The longer something is kept on and connected to the AC power, the more potential for damaging power transients to destroy components in your power supplies. If you have good line voltage protection (like a Furman line voltage filter, for example), then this is less of an issue. But also be apprised that many line voltage protection devices (like MOVs) have a limited number of transients they can absorb before they fail and you have no further protection.

Power brown outs may create similar problems. If you have frequent or constant power line drops, this can also be hard on equipment as it shuts down due to the low voltage then re-powers as the voltage levels are restored. All this may be happening while you are gone and unaware if you leave equipment powered up continuously.
My Rowland Cadence / Coherence preamp/phono doesn't want to be powered down, in fact there is nothing in the manual about turning it off, ever. Worse, if you power it down, you have to go through a whole blah-blah to start it up again properly, vis-a-vis the batteries in the power supply, and to top it off it forgets where it was. I turn the preamp down to zero, and that supposedly shuts down almost all of the internal circuitry.
A suggestion that I have deemed to worthwhile considering is the contention that amps,,etc  are most at risk for damage when a unit is turned on.   Inrush current.    While undoubtedly there are  electrical components in place to help counter any effects of the surge --It seems to make  a lot of sense to subject units to turn on current as little as possible.     That being said-- I am not leaving my tube amps on nor my s.s. amps on especially my class A amp.  I do leave a Trends amp on as it is quite economical to run.   It is more of a summer amp.     I am leaving my 2 tuners on that are used daily---especially considering they are vintage tuners and dont want to subject them day to day to inrush current .  I listen to my systems on a daily basis.  My Sonic Frontiers Line 1 has a standby and I use that.  If I am going away for overnight or even the entire day I usually shut it off completely.   As long as I am in town  I would not want to be powering it up every day subjecting the tubes to start up current of which it is known to subject tubes to more stress .    Re/power line failures.   I think a good portion  of the high quality equipment made  and even not in the higher price range comes with protection circuits for power failures and surges.    They have to design this into the circuits --it is part and partial of designing a quality power supply.      I recently bought a pair of Emotiva mono's  and am surprised at the lengths this company has gone to in protecting the circuity for a not much money at all considering what I paid for my Pass amp on the used market.  .     I leave the Emotivas  in standby and have been using them primarily in my main system as of late.   This with a  $5k plus (new) Pass amp sitting idle.       
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.