Thanks for the response on the input protection diodes.I should add that this 1974 amp is using the very old and gray LM307's. Good for 1968 but they got to go. This amp is a gem in the rough because it was Leo Fender and Tom Walker who were behind Music Man's products and this amp is built like a tank. Chrome plated chassis and huge transformers. (4) El34's for the output and 12AX7 for the phase splitter/driver 100Watts output. I am converting the input to OPA-627's because they are well regarded on the fanatic websites. I maybe buying the Analog Devices AD-843 instead, as a result of some of the postings on HeadWize . I understand this chip is renowned for it's " Bass impact", sounds good, I want some. If anyone is reading this and can comment on a choice between the two I welcome your input. I can use the OPA627's for my CD player. KMcC