Exile - well they had an album on Wooden Nickel (and maybe two more) before the Mixed Emotions album which I assume was the one you are referring to since it was produced by Chapman. They did have another pop album after that, but did not repeat the success of that one. They switched to country - logical choice since they were from Kentucky. Had 7 or 8 number 1 country songs. Members have written number one songs for Alabama and other country artists. They are still together playing fairs, the Grand Ole Opry, and other venues.This is easy. Three from the same producer.
The Knack, Nick Gilder and Exile.
No loss as far as The Knack goes but I hoped for more from Exile.
Also Zager and Evans from 1968 or 69.