This is the distortion at 20kHz of a standard class-B amplifier with output stage quiescent current set to 6mA. Large crossover spikes can be seen.Standard class-B circuit.
This is the distortion at the optimum quiescent current setting of 10mA. Crossover spikes can still be seen. Even a small variation in the current gave a rapid increase in distortion. Thermal effects make it difficult to keep the current accurately at this optimum value.
Above the optimum quiescent current the distortion increases again. This is the distortion at 60mA. Increasing the current further would eventually eliminate the distortion and the amplifier would then be operating in class-A at this signal level.
The modified circuit with feedforward error correction gave this remarkable result for any quiescent current over 15mA (a maximum of 120mA was used in the tests). The 'distortion' was not visibly different with the 20kHz test signal switched off, and is primarily the noise of the amplifier and test equipment.
The full details and circuit diagram of the design are presented here. The idea is very simple, but appears not to have been discovered previously. It was published in Electronics World, April 1998, with the title "Class-B in a New Class".