It's one most of the time. I shut down if I know I'm not listening for two days or if a storm approaches. I use it almost every day.
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Pro: Leaving any component on all the time tends to keep everything thermally stable and avoid thermal shock: light bulbs fail most of the time when they are first turned on.
Con: Some amplifiers (e.g. Krell class A rather than class AB push pull) run so hot in idle that turning the amp off while idling is recommended by the manufacturer.
Since I recently switched from a 300 wpc amp to a 100 wpc (both 8 Ohm), I leave it on and do not turn the voulume down. My amp only runs slightly warm. BTW, since I've been leaving the amp on full time, my stereo system sounds its best at all times. All my other components have standby modes. Cheers. Craig
Jmcgrogan: If you've never had your Threshold powered up for at least 3 days consecutive, you've never heard what it can do. Honest.
High bias designs are the most sensitive to thermal cycling / sonics. The lower the bias on the amp, the less differences that you'll notice if cycling power off an don as needed. Higher biased amps ( these run hot at idle ) will always sound better when leaving them turned on. I do agree that it is a good idea to kill the power to them if you will not be around for an extended period of time or if you are expecting severe storms.
I have six amps ( four Threshold products and two Perreaux's ) in one room that idle at about 120* - 130* each. These stay on all the time.
I have two amps ( modified Kinergetics KBA-202A Platinum mono-blocks ) that idle at about 110* in my office system. These stay on all the time.
My HT amps ( Sunfire Signature & Sunfire Cinema Grand Signature ) stay on all the time although these draw VERY little current at idle. As such, they run cool to the touch unless pushing them hard. I could power these down and not really notice much of a difference after about a half an hour of use.
My bedroom amps ( two Quad 405's ) stay on all the time.
My tube based system is powered up and shut down as needed. I am a firm believer in letting tubes "heat up" prior to passing signal. I also let them "heat down" prior to shutting off.
So, do i get the "wattage waster" award or what ??? : ) Sean
Leaving the amps on generally makes 'em sound better, but some do stabilize after an hour or so to the point where leaving them on longer makes no difference. Depends what you have; my Levinson mono's sound their best after 24 hours, my ARC peaked out an hour after start, and my Forte seemed to get better day after day after day. Similar differences with other amps I had - the Class A's took a lot longer to settle in than the A/B's.
If your amp has a current inrush limiting (soft start)circuit, then daily on/off should not "stress" components. However, if your lights dim or if you hear a buzzing on start up, then leave it on. That's stress.
The only problems I see with leaving them on all the time is a) it's not a good idea when not at home, and b) the premium on your electric bill if they're Class A.
Sean, maybe I'm wrong, but I was under the impression that leaving class A amps on all the time would significantly lower their lifespan. I've seen many used Threshold/Coda and other class A amps on the used marketplace where the heatsinks have discolored from black to like a bronze or purple. I don't know if this is from abuse or leaving powered up all the time. Since the IGBT's in my T400 are irreplaceable, I don't want to risk wearing them out. I also believe that it sounds better quicker than other SS A/AB amps that I've owned (Classe, Coda, Aragon). It sounds as good 1 hour after power up as it does after 8-10 hours, IMHO. The other amps (A/AB), I used to leave powered up, but they didn't run so damn hot and they also would take 2-4 hours for the sound to warm up.
Unless your amp has an "idle" feature, leave it on all the time. For the rear channels of my system, I use an old Marantz PM94 integrated amp, which is left on all the time. Everyone who I've ever spoken to who owns one of these things has found that they blow up after a period of time--the result of heat cycling. Not my PM94. It's been working continuously for nearly 8 years. Heat cycling is bad news for solid-state equipment.
John: My guess is that the amps that you speak of were were probably shoved into an enclosed rack, not allowing proper heat dissipation. These amps require open sides and at least 12" of space above them. Otherwise, you can expect them to cook themselves to death.
I have some of their amps with IGBT's in them also. They do not get turned off. My experience with circuits like this is that you have a greater chance of in-rush current smoking the outputs. On top of this, you now have tremendous thermal swings that occur over a relatively short period of time. This can result in uneven gain characteristics from output device to output device, resulting in reduced stability. Leaving the units powered up reduces all of the above problems to a minimum.
Obviously, one has to take into account that these amps will generate a good amount of heat and have them installed in a manner that will allow more than adequate ventilation. This is true whether the amp is cycled off and on or left on all the time. If placing the amp in a rack, keep in mind that heat rises. This will "warm" the shelf above it, which could transfer heat into the component above the amp.
If you are truly worried about such things, you might want to remove the top lid of the amp. This will allow greater cooling of the insides via natural convection. If you are worried about RFI or small fingers inside of the amp, it would not be hard to fabricate some screening that would act as both a shield and "guard". Sean
Sean, thanks for the post. You make some valid points. I may try leaving it on. Ventilation is not a problem. My system sits on Lovan Sovereign AVR rack, which is 43" wide. The Threshold shares the top shelf with my turntable. So there is about 4+ feet of clearance between it and the ceiling. I always wondered what could cause those amp heatsinks to discolor so much. I thought it was being left on all the time or being run beyond their capabilities. I hadn't thought of poor ventilation, although that very well could have caused it.
I keep mine on 24/7.
I put the NAD components into "standby" and the Plinius just stays on (per Plinius' recommendation and my listening pleasure). If I turn off the NAD stuff completely for a couple of days, they warm up in a few hours. However, the Plinius takes a frikkin' week! I'll never turn it off, unless I absolutely must (e.g., storm)!