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Project #240
Power Amp
OBJECTIVE: To check stability of power amplifier with
When you turn on the slide switch (S1), the power amplifier should not
oscillate. You should be able to touch point X with your finger and hear
static. If you do not hear anything, then try touch point X with one of the
snaps on any part. High frequency clicks or static should be coming from
speaker indicating that the amplifier is powered on and ready to amplify
signals.
The power amplifier may oscillate on its own. Do not worry, this is normal
with high gain high-powered amplifiers.
Project #241
Electronic Kazoo
OBJECTIVE: To show how electronic feedback can be
Use the circuit from Project 240 shown on the left.
When you place one finger on point X and a finger from your other hand
on the speaker (SP) snap that is not connected to the battery, what
happens? If the amplifier starts to oscillate it is due to the fact that you
just provided a feed back path to make the amplifier into an oscillator. You
may even be able to change the pitch of the oscillation by pressing harder
on the snaps.
This is the principle used to make an electronic Kazoo. If you practice and
learn the amount of pressure required to make each note, you may even
be able to play a few songs.
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