My oldest Series bass is a 1976, which was produced just after the end of the "mil spec" era described by Edwin. The electronics are still original (and by the way the bass is dead quiet). I don't hear a difference between that bass and any of my 4 string Series basses (one of which has the newest electronics). If there is a measurable difference between the old and new electronics it's not something that anyone would ever hear in a mix, live or recorded. As far as the noise upgrade goes, as I am sure Mica has or will tell you, some basses will benefit from it while others don't need it.