Should an audio system be left on at all times?

12-02-08: Kijanki
Bigbucks5: electronic fail when you turn it on when it's not designed properly. You can turn on and off electronics thousand times a second for years and nothing will happen.

That's so much BS. I guarantee that ANY electronics will have a much higher failure rate when turned On/Off vs leaving it on.

You can leave electronics on for 20 years and no failures. But try turning it on/off every day, and you'll never get close to 20 years out of it before it fails. Power cycling is always worse than not power cycling, regardless of how it is designed. Sure, the better the design the better it will tolerate power cycling, but it is always worse than not cycling.

I guarantee that ANY electronics will have a much higher failure rate when turned On/Off vs leaving it on.

Your guarantee is a considerable over-generalization at best.

For starters, your guarantee totally ignores how often the equipment is turned on and off, how long it is left on when it is on, and how long it is left off when it is off. Your guarantee also evidently extrapolates from your experiences with certain equipment to all other possible equipment designs, part qualities, usage patterns, and environments, which is, to use your term, "bs".

All electronic and electromechanical parts, whether resistor, capacitor, inductor, transistor, analog integrated circuit, digital integrated circuit, relay, even printed circuit boards, have finite MTBF's (mean time between failure) if left on all the time. The MTBF is typically non-linear with the age of the component (i.e., older components fail more frequently). New components also fail more frequently, especially if they are not adequately screened and burned in by the manufacturer. As has been noted in some of the posts above, MTBF is typically temperature dependent, and will be shortened as operating temperatures increase. It will also typically be shortened due to the thermal stress of being powered up and powered down repeatedly, which is apparently a key basis of your statements.

As I indicated in my earlier post, an analysis that would balance and combine all of these factors for all of the parts in a piece of equipment, and define an optimum power-up/power-down duty cycle for even one specific design, is essentially an impossible task. Most of the responses above, including yours, are based on perspectives that just address a limited number of these factors, for a limited number of part types in a limited number of designs, and understandably don't present any quantitative trade offs.

As I said in my earlier post, as an experienced electronics design engineer I believe that the best approach (for solid state gear) is simply the common sense one of turning the system off if you don't use it frequently, and leaving it on if you do. If like many of us you are somewhere in the middle, and use the system neither very frequently nor very infrequently, then you won't be going very far wrong with either approach.

Regards,
-- Al

Blindjim: Yes original question was about longevity - read again

Bigbucks5: I don't know where you getting your information. Electronics that stays on is also constantly switched - electrolytic cap are geting sharp spikes of current, switching power supplies as wel as class D amps constantly switch on off etc. Rush current during power-up doesn't do anything to SS electronics.

Almarg: semiconductors, resistors, capacitors etc don't have MTBF (not in our lifetime). They operate practically forever (except electrolytic caps). LED diodes might loose brightness over time (structure recombines itself to non-emmiting junctions) but it's not a sudden failure and it takes probably 20 years for this to even notice.

People got impression that SS gear will fail most likely during power up/down cycle because of previous experience with tube gear, relays, switches, bulbs, hard disks etc.
The only case I know where SS electronic gets "tired" is with very high power SCR devices (thyristors) switching few hundreds of amperes and it takes very long to fail.

semiconductors, resistors, capacitors etc don't have MTBF (not in our lifetime). They operate practically forever (except electrolytic caps).

Not true at all, unless you are referring to a single part operating by itself, which you are not. The combined mtbf of the hundreds or thousands of semiconductor and passive devices (even excluding electrolytic capacitors) in a typical sophisticated audio system will be measured in decades at most, and quite conceivably in years (less than one decade). That is especially true when you consider the sharp increase in failure rate that occurs with older components, according to accepted reliability models, and is even more true when you consider that many amplifier designs intentionally run semiconductors at high junction temperatures in the interests of improving the sound quality.

Please take a quick look at some of the 205 pages of MIL-HDBK-217F, linked to below, which is the guideline document for reliability calculations for military systems. Note that it addresses just about every conceivable type of electronic component. And keep in mind also that these are typically components that are manufactured, burned in, tested, and screened vastly more rigorously than anything in most consumer audio systems.

http://assist.daps.dla.mil/docimages/A/0000/0005/3939/000000041349_000000020839_BTJRBUHXWM.PDF?CFID=18958726&CFTOKEN=fdbcdd5971174382-FEB22389-1372-548A-D368EF4CD631E514&jsessionid=063010dbe387801aa415

Regards,
-- Al

Kijanki
All 'lectronics is subject to failure. The metal interconnects used in ICs and discrete devices 'moves' under the pressure of the flow of electricity. The break will usually occur when the line goes over an edge, where the metal is thinnest and current density is highest.
When we (my company) introduces a part, especially a new technology/revision, part of the specification includes Lifetime. Parts are put thru a rapid aging cycle while under electrical stress. 1000 hours is typical and an industry standard. There is an accepted rate of failure, usually highest at lower hours.....so-called infant mortality.
That being said, I have never had a SS failure...cap, resistor, I/C, discrete device. My old amp was on as continuously as possible for 20 years. Other stuff switched as needed.
My company makes a line of 'HiRel' and some of our stuff even finds its way into output and power supplies.....and makes full-on class 'd' modules.
Everything has a MTBF, even if it is a HUGE number.
I personally count on Infant Mortality of new equipment. Do a run in for a couple weeks and call it good.

Doesn't current surge, the first 1/2 cycle to saturate a transformer count as stress?