House Amperage vs Stereo Amperage

15 amps at 115 volts represents 1725 watts...more than your toaster! Think what this would do to the tender voice coil of your speaker. Obviously the average power delivered to the speaker is only a few watts. Speaker sensitivity typically runs about 90 dB for 2 watts. 90 dB is quite loud.

Feedback around an audio amplifier enables it to properly follow the signal input even if the "rail" voltages fluctuate. If the rail voltage diminishes, the transistor (or tube) is just turned on more. I am sure everyone is familiar with the way that a power amp will continue to play for several seconds after it is turned off. During these several seconds the rail voltage "sag" is catistrophic, but there is little immediate audible effect.

Chipman...A good observation. I suppose one could have an amp with ten volt rail voltages that could put out 150 amps, which would be 1500 watts. It would probably work better as a welding machine than an audio amp.

sean...About circuit breakers...when a tree next to my house was struck by lightning almost every fuse in the house blew, but not a single breaker opened. (Give me fuses any day).

About rail voltage sag...if the audio signal peaks at 35 volts this can be output by a 70 volt rail voltage with the transistor conducting 50 percent, or by a 60 volt rail voltage and the transistor conducting 58 percent. Because the rail voltages are heavily filtered in the power supply (and sometimes regulated) the "sag" (as the name suggests) will be at very low frequency, which any feedback loop can easily follow.