2. Project Outline
The goal of this project was to build a plasma
speaker that will amplify an electric guitar
sound.
Build an audio oscillator circuit using an
ordinary speaker
Test speaker performance compared to
equations on data sheet
Replace speaker with auto ignition coil to
create a plasma arc
Replace audio oscillator with an Audio
Power Amplifier
3. Hypothesis
I hypothesize that an Audio Power
Amplifier will be capable of magnifying
the output of an electric guitar through a
plasma arc.
The values of the measured frequency and
duty cycle will match the equations on
the data sheet for the oscillator circuit if
built correctly.
5. Constructing the Audio Oscillator
Circuit
Create the audio oscillator using the
ICM7555 CMOS timer following the product
data sheet
Add amplifying transistors from example
circuit
Example circuit from: http://geocities.com/CapeCanaveral/Lab/5322/fbt2.htm
7. Testing the Audio Oscillator
Circuit
Connect speaker to the output
Attach a 9 Volt battery
Frequency and duty cycle are changed by
adjusting the two potentiometers and the
value of the capacitor
Take measurements of frequency and duty
cycle using an oscilloscope and an electronic
tuner
Compare to calculated values
8. Frequency and Duty Cycle
Connect oscilloscope
and take measurements,
T1 and T2
Use ohm meter to
measure RA and RB
Adjust potentiometers
and repeat
measurements
Measured:
F
1
T2
T1
T2
Calculated:
D
T1
T2
F
1.38
( RA 2 RB )C
D
R A RB
RA 2 RB
9. Creating a Plasma Speaker
Replace speaker with auto ignition coil
Connect wires from the primary coil to the circuit
board
Attach wires to the secondary high voltage coil
Adjust spacing between wires to create a small gap 2 to 5mm worked best
When the circuit is energized, the air between the
electrodes is ionized and becomes a plasma
A new spark is created with every oscillation of the
circuit
Your ear hears this as a musical tone
The frequency or note of the tone can be adjusted
using the potentiometers
10. Creating the Plasma Powered
Guitar Amp
A second copy of the circuit was constructed, replacing the
oscillator chip with a low voltage audio power amplifier
The gain of the amplifier was increased to 200, which gives a
square shaped wave form
The spark also produces a sound, but now the frequency
corresponds to the note being played on the guitar
C6 = 1046.5 Hz
C5 = 523.25 Hz
11. Audio Oscillator Diagram – With
Coil
9V
POT1
10K
RA
RESISTOR
1K
RESISTOR
330
T
Auto Ignition Coil
POT1
10K
NMOS
7
RB
8
4
RESISTOR
NPN
ICM7555
RESISTOR
1K
2
C
0.1 or 0.01
GND
6
1
RESISTOR
10
3
100
IRF510
2N2222
17. Conclusions
Measured values of frequency and duty
cycle were only two significant
figures, resulting in less accuracy
The electronic tuner was more accurate
than the oscilloscope because the
tuner, like an ear, can hear smaller
differences in frequency – verified by
comparing the pitch to a piano
The plasma guitar amplifier produced a
satisfactory sound, but the volume and
sustain could be dramatically improved