some op amps are bad from the word go. the plus and minus power supply must be the exact voltage to work correctly. Bob Carver has info on this, he and others were duped into using op amps that were defective. A lot of kenwoods, sansuis used these op amps , They sounded distorted, this could not be fixed without redesigning the preamp circuit. this is where the bad rapport came from. Op amps are supposed to sound good if done right.