dragonworks said:
Watts are watts. But a tube amp with a certain wattage rating will be capable of producing louder, more pleasing music than a solid state amp of equivalent wattage.
Watts RMS indicates how much an AC signal can generate, regardless of the shape of the wave.
If you look at any audio amp's output rating, it will indicate X amount of watts at Y-frequency with no more than Z% distortion (probably across a certain frequency range).
Once you hit the limits of the amplifier, driving it past that point results in rapidly increasing distorion as the circuit begins to clip.
The quality of the distortion of a tube amp is much more pleasing to the ear in comparison to the quality of distortion in a transistor amp pushed to the limit. Also, in many tube circuits, the rate of distortion increase is not very steep, but gradual. In solid-state circuits, the distortion is like a cliff, you reach a point and you cross the line and the circuits distortion increases dramatically.
Tube circuits tend to have compression as the maximum power level is reached. This tends to increase apparant loudness as well.
Another difference found between tube and solid state amps is the application of negative feedback. Many solid state amps have very high open-loop gain and rely on large amounts of negative feedback to linearize the circuit globally. Once clipping is reached, the stability of the feedback circuit is pretty much gone, again resulting in harsh, unpleasant sound.
The typical tube amp uses relatively small amounts of negative feedback or perhaps none at all. The effect is similar and again contributes to a smoother transition into clipping, increasing appearant loudness.
So what you hear is an appearant loudness difference, rather than actual difference in electrical energy output. Loudness is a psychoacoustical phenomena, not a physical one. From the standpoint of physics, "watts is watts"
