Editing Audio power amplifier (section)

==Power output stages==
[[File:Micro amplifier (booster) FIIO Fujiyama for smartphone etc. headphones.jpg|thumb|A micro audio amplifier for boosting the output of [[line level]] sources to [[headphone]]s or small speakers. Edge length 4{{nbsp}}cm, mass {{val|16|ul=g}}, power output about 100{{nbsp}}mW into a 32{{nbsp}}Ω load.]] 

The final stage of amplification, after preamplifiers, is the output stage, where the highest demands are placed on the transistors or tubes. For this reason, the design choices made around the output device (for single-ended output stages, such as in [[single-ended triode]] amplifiers) or devices (for [[Push–pull output|push-pull]] output stages), such as the [[Amplifier#Power amplifier classes|class of operation]] of the output devices is often taken as the description of the whole power amplifier. For example, a class-B amplifier will probably have just the high power output devices operating cut off for half of each cycle, while the other devices (such as differential amplifier, voltage amplifier and possibly even driver transistors) operate in class A. In a [[Output transformerless|transformerless output stage]], the devices are essentially in series with the power supply and output [[Electrical load|load]] (such as a loudspeaker), possibly via some large capacitor and/or small resistances.