Make: Radio

47Experiment 2: A Real Radio

ADDING AUDIO POWER

Although the transistors that you installed in the circuit provide some

amplification, they do not deliver enough power to drive a speaker. For that

purpose, you can now complete the circuit of AMR2 by adding an LM386—an

old-school chip that can amplify its input by a factor of 200.

Adding the LM386 is very easy: Just disconnect the earphone and add the

new horizontal yellow wire visible on the right in Figure

2-16

.

Notice the long, red power-supply wire in this figure, which is necessary

because the positive bus has been reserved for filtered power to the

transistors. Pin 6 on the LM386 happens to ...