ABSTRACT
Distortion from the small-signal stages kept to levels that prove negligible compared with distortion from a closed-loop output stage. The first distortion, non-linearity in the input stage, cannot be totally eradicated but its onset can be pushed well above 20 kHz. The second distortion, non-linearity in the voltage amplifier stage, can be effectively eliminated by cascoding. Large-signal nonlinearity increases as load impedance decreases. In a typical output stage loaded with 8 Ω, closed-loop Large Signal Nonlinearity (LSN) is usually negligible, the THD residual being dominated by high-order crossover arte-facts that are reduced less by negative feedback. Switching distortion depends on several variables, notably the speed characteristics of the output devices and the output topology. THD in the LF region is very low, well below a noise floor of 0.0007", and the usual rise below 100 Hz is very small indeed. The usual nonlinear distortions generate most of their unwanted energy in low order harmonics that NFB can deal with effectively.
