Simple Class AB Amplifier

Where are the amplifier? In: amplitude 5v, out amplitude 2v. Could you explain?

Ideally, this amplify would have nearly unity gain. I.E. the input voltage would be the same as the output voltage. This cannot actually be practical because some energy is lost to the BJTs. The important thing to remember is that this is not meant to act as a voltage amplifier, but rather it is meant to increase the maximum wattage of the signal. In other words, If I wish to drive my speaker system at high wattage, I cannot plug my music player directly into the speaker. Instead I must take the voltage signal from the music player and use an external source to amplify the maximum current it can output to the speaker, which is where power amplifiers like this one come into play.

Also, the output amplitude is actually 3.5~4V, so the amplifier does not attenuate as much as it appears. EveryCircuit does not do a fantastic job of marking output levels unfortunately.

Thanks for your answer. I apologize, but I really don’t understand what is the difference between voltage gain and current gain...

I don't know what your experience is with amplifier circuit design, but I'll try to give a simple and general answer: Current gain can be a little harder to define than voltage gain. What is important is that we are using a voltage source to control the amount of power supplied to a load from some external power bank. By using these BJTs as valves that we can open/restrict the flow of current through, we can supply the load with much more power than our initial source could, even at similar voltages.