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46
Project #124
Project #126
When you turn on the slide switch (S1) the trombone should start playing.
To change the pitch of the note, simply slide the adjustable resistor (RV)
control back and forth. By turning the slide switch on and off and moving
the slider, you will be able to play a song much like a trombone player
makes music. The switch represents air going through the trombone, and
the adjustable resistor control is the same as a trombone slider bar. The
circuit may be silent at some positions of the resistor control.
When you turn on the slide switch (S1), the power amplier IC (U4)
should not oscillate. You should be able to touch point X with your
nger and hear static. If you do not hear anything, listen closely and wet
your nger that touches point X. High frequency clicks or static should
be coming from speaker (SP) indicating that the amplier is powered on
and ready to amplify signals.
The power amplier may oscillate on its own. Do not worry, this is
normal with high gain high-powered ampliers.
Trombone
OBJECTIVE: To build an electronic trombone that changes
pitch of note with slider bar.
Power Amplier
OBJECTIVE: To check stability of power amplier with open input.
Use the circuit from project #124 shown on the left, but change the 0.02μF
capacitor (C1) to a 10μF capacitor (C3). Make sure the positive (+) mark
on the capacitor is NOT on the resistor (R2) side when you snap it in.
When the slide switch (S1) is turned on, you should hear a very low
frequency oscillation. By sliding the adjustable resistor (RV) control up and
down, you should be able to make the sound of a race car engine as it’s
motor speeds up and slows down.
Use the circuit from project #126. When you place one nger on point X
and a nger from your other hand on the speaker (SP) snap that is not
connected to the battery (B1), what happens? If the amplier starts to
oscillate it is due to the fact that you just provided a feedback path to make
the amplier 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.
Project #125
Race Car Engine
Project #127
Feedback Kazoo
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