A Push-Pull Amplifier
Électronique / Electronic

We've said that electronic devices are made up of different basic circuits. One of these is the amplifier.

As its name tells your this circuit uses the transistor's ability to amplify weak currents. Look at the schematic and notice how the two 2SC transistors are connected together. This is called a push-pull amplifier. Can you guess how this amplifier works?

We'll tell you in a moment After finishing the wiring connections, connect the Earphone.

Put the power ON and speak into the Earphone. What do you hear from the Speaker?

This Project takes the weak current from the Earphone and amplifies it to a level you can hear from the Speaker. In a push-pull amplifier, both transistors "take turns" amplifying the signal from the Earphone. This lets both transistors do their job better and prevents distortion, what you hear from the Speaker isn't much different from what was spoken into the Earphone.

If you want to get higher gain, change the capacitor from 0.005 uF to 0.001 uF.

Amplifiers are very common circuits. How many devices can you think of that likely use an amplifier circuit? (Don't forget to record your guesses)

We've been using the Earphone so far both for listening to sound and also as a microphone. How do you think an Earphone works? (Here's a hint: it doesn't have any coils of wire nor any magnets at all) Give up?

Okay, here's another clue: it's known as a crystal Earphone. Take your best guess and we'll find out for sure later! See Radio Section