This is a 4 transistor audio amplifier circuit. Which is a 4-transistors complementary push-pull amplifier, that shows the basics of audio amplifier design.
You have a good power amplifier and speaker. You are listening to music. But the sound is very light. The problem has many reasons. One reason for the problem is…
This is Electronic Stethoscope circuits. Usually the stethoscope is a medical device that listens to the heartbeat. Which we can make it with the least amount of electronic equipment so easy to make.
These are two simple mini intercom circuit. They use IC-OP-amp as main parts.