Do you DI guitar amps also incase their amp fails? I'm guessing not.You mean what brands of amps have I seen that became unusable on gigs? Aguilar, Ampeg, Eden, Fender, Gallien-Krueger, Marshal, Matchless, Mesa, SWR, and Vox off the top of my head. Nothing is perfect. Hell, even Lexus has a service department. If they were perfect, they'd just send all their customers to JiffyLube every 3 months.