Thank you BOB I thought I was being ignored for awhile. I thank you for the information and I kind of remember it also used to keep opamps from locking-up. Sounds good . I'm convinced now that they will not be needed with the OPA-627's I am replacing the ancient LM307's. 1965 or so technology. I never see them (diodes in a differential config.) in any new designs and the output of a BASS guitar is not that much different than any other high level, high impedence source.