Electricity usage of amps

[Ding Dong]

this may sound stupid, but I was wondering if the amount of power that an amp uses is more a function of the volume setting or of the amount of signal going through it.
For example, which would use more power (in regards to my electric bill):
A: I leave my guitar amp or powered monitors on, with the volume at ten, but with no signal going in for an hour, or
B: I set the volume of my amp at 4 and play music through it for an hour.

thanks.

 

[boingoman]

It depends on the class of the amp. A class A amp is always operating at max current draw whether the amp is on 0 or 10, signal or no signal. Other classes don't work that way, and will draw more current when they are fed a signal (assuming the amp is used to drive a speaker)

 

[dementedchord]

boingo is right... assuming it's a solid state amp in a non classA it will use next to nothing when idleing... a tube amp on the otherhand can use shit loads wheth working or not... in your example B would use the most power unless A was a class A amp... one of the things that's confusing for alotta people is we're used to thinking "class A" means top notch... and that's not neccessarily the case...

 

[Ding Dong]

Thanks- i apriciate you clearing this up for me. What you say makes sense, because I've noticed my yamaha CA1000 hifi amp gets really hot when set to class A, even if it's silent. Because of this I never use the class A setting.

So my KRK monitors say they have 100 watt dynamic power. I assume this means non-class A? So i can leave them on for a while without too much worry? These are the ones I was specificly wondering about. thanks guys.

 

[mshilarious]

So my KRK monitors say they have 100 watt dynamic power. I assume this means non-class A? So i can leave them on for a while without too much worry? These are the ones I was specificly wondering about. thanks guys.

Very few solid state power amps are going to be class A. It would simply waste tremendous amounts of power. You see it in audiophile designs, but generally only at relatively low output ratings.

Tubes are so woefully inefficient because of the need to feed their heaters that it matters somewhat less, but even so, a lot of tube output stages are class AB push-pull designs.

I am pulling these numbers out of my head, but generally a class AB amp is 40% efficient, class A is 15% or so, and a tube amp is usually in single digits.

Class D amps, or switching amps, are starting to catch on in audio as quality is being improved greatly. Efficiency of a class D can be very high, up to 80%.