Distortion in audio amplifiers

Summary form only, as given. The evolution of amplifiers will be put in perspective by starting with vacuum valve designs. The cost of gain stages kept valve amplifiers out of transient interncdulation distortion. The low cost of gain stages, and later of integrated circuit operational amplifiers, led to the use of large amounts of negative voltage feedback to reduce The:enin's impedance and distortion of output transistors. The result was transient intermodulation distortion which sounds much worse than the device non-linearity the feedback was intended to reduce. Practical bounds on gain within each feedback loop will be given as a basis of the amp1ifiers contribution to the distortion budget.