I cannot help but compare my stereo's power amplifier to the new guitar amp. They're just so different yet they are meant to do similar stuff. And yes, I know it's not really a "stereo" system that I have, but I refer to it as a "stereo" system for a lack of a better word and for respect to the term hi-fi (a DVD player purchased from Aldi for $50 is not a hi-fi component, sadly, no matter how good it is value for money wise).
So how do these two amps compare?
On the stereo side I've got a genuine hi-fi component, a Hafler power amplifier. It can deliver up to 200 watts of continuous output to the speakers through its huge power supply, and since it has a Class A configuration it gobbles up electricity at a relatively constant rate of 850 watts.
That maximum output of 90 watts can be misleading, though. Most of the time the amp delivers much less power: My main speakers have an efficiency rating of 87, which means that 1 watt of output from my power amp will generate 87db of noise. Since 87 is quite a lot - it's a level a person should not be exposed to for more than a few minutes a day - this means that my amp is mostly "unemployed" and terribly inefficient: for the less than 1 watt of output its required to output most of the time, it consumes 850 watts on a regular basis. This 1:1000 rate is not what one would expect in most places and not what one would pay for under most circumstances, but in the hi-fi world this is the price you need to pay for a reliable reproduction of the original signal. The more efficient the amp was, the more distortion would slip through.
The guitar amp, a Fender rated to deliver 15 watts of output at its integral speaker, consumes just 38 watts from the grid. And it probably doesn't consume anywhere near as much most of the time.
I can't do the same ratio estimations I did for the Hafler on the Fender, because this one doesn't consume electricity at a constant rate and because I don't know its speaker's efficiency. But it's quite clear it is much more efficient as an amp; and the speaker is bound to be way more efficient than hi-fi speakers too. The reason is simple: In a guitar amp, you actually want distortion. You want it to clip (albeit a soft clip); you want the overdrive. And you even allow the speaker to get out of the boundaries of its coil, something you would never allow in hi-fi.
You can easily listen to it, too. If you set the guitar amp to its "high quality" setting you get a very mild amplification of the guitar, and it all sounds pretty much like a classic guitar. Turn the gain up and encourage it to clip, and you get this powerful noisy monster that would guarantee the wrath of every neighbor. And all at a fraction of the power consumption.
It makes the environmentalist in me shudder.