Disclaimer: I know nothing about electronics or guitar amps.
(Actually, I do know one thing: that "wattage" is synonymous with "volume" when speaking about guitar amps and since watts are measured on a logarithmic scale, a 100 watt amp is only twice as loud as a 10 watt amp…I think.)
I am very confused.
My question applies to any guitar amp, but as a random example, I will use the Fender Blues Junior III amp.
According to the product description on the official Fender website (and all product descriptions of this amp online), it has 15 watts:
But, according to the plate on the back of the amp itself, it has 180 watts:
How come there are two different watts numbers with guitar amps? What does each number represent, and how can they both simultaneously represent the amp's "wattage"?
.jpg){kind=link}
Best Answer
Although both values are in watts, they are referring to two different power quantities. The "15 watts" refers to the audio output power, i.e. the power delivered to the speaker. This is the power that generates the sound that you hear. The "180 watts" listed on the back of the amplifier refers to the power drawn from the AC input line. This is the power supplied to the amplifier from the AC wall socket (120 volts at a frequency of 60 Hz). It needs this power to run its internal electronics which produces the 15 watts of audio output power. The AC input power will always exceed the audio output power since the amplifier cannot be 100% efficient. In this case, its efficiency is pretty low (15 watts out for 180 watts in or an efficiency of 8.3%).