A combination amplifier design using the concept of continuous current in both the positive and negative polarity output devices found in class A designs coupled with class B’s turn-off of unused output devices with the result being an amplifier that only allows very minimal current flow through output devices when signals of the opposite polarity are being created. he class AB amplifier maintains current flow at all times so that the output devices can begin operation nearly instantly without the lags that doom class B amplifiers. However, complete current is not allowed to flow at any one time thus avoiding much of a class A design’s inefficiency. Class AB designs are about 50 percent efficient (half of the power supply’s power is turned into output to drive speakers) compared to class A designs at 20 percent efficiency. hink of three cars at a stop light. The class A car keeps the engine running at full power and full RPMs ready to take off at any time. The class B car shuts off the engine entirely and must re-start and get in gear before it can take off at the green light. The class AB car keeps the engine running at idle with the gear in drive using some power but not as much as the class A car and being much quicker off the line than the class B car. Class AB amplifiers are the most commonly used amplifier designs thanks to their attractive blend of reasonable efficiency and high-quality output (low distortion and high linearity close to but not equal to class A amplifiers).