That's a correct definition - but isn't it incomplete? For instance, if I overdrive the input will it not cause distortion, even if it's not completely audible? From this MSB page on Preamps. I don't know why a headphone amp would be any different: Active preamps add gain. Signal levels can exceed the preamps capability in two ways. If the output clips, sound is distorted at high volumes. If the input clips, sound is distorted at all listening levels. http://www.msbtechnology.com/faq/how-can-you-avoid-preamp-clipping/ Am I misunderstanding something?