ABSTRACT
The power amplifier gives more distortion with heavier loading, that is, with a lower load impedance. This chapter looks into why that happens and tries to fix it. A solid-state amplifier gives more distortion with heavier loading. The extra distortion component large signal nonlinearity would not exist. Such an amplifier gives no more distortion into 4 Ω than 8, and it has 'Load-Invariant to 4 Ω'. The loading qualification is required because, the lower the impedance, the greater the difficulties in aspiring to load-invariance. A Blameless Class-B power amplifier design gives a distortion performance into 8 Ω that depends very little on variable transistor characteristics such as beta. This is because at this load impedance the output stage nonlinearity is almost all crossover distortion, which is primarily a voltage-domain effect. Large signal nonlinearity is clearly a current-domain effect, dependent on the magnitude of the signal currents flowing in drivers and output devices, as the voltage conditions are unchanged.
