This has been covered many times in the archives. There are some threads that contain various explanations / points of view as to why some of us feel the way that we do. I would suggest taking a look at those answers, digesting that info and then doing some simple testing for yourself. For your convenience, here's one covering Class A amps, but most of the info can be carried over to high bias AB amps also. Sean
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comments & first hand experience with leaving amps turned on
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comments & first hand experience with leaving amps turned on