Class B Audio Amplifier

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Class B Audio Amplifier

• Tina Shaw
• Kendall James
• Andrew Cruz

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Criteria Overview

• Using commonly available operational amplifier to
  build the DC coupled Class B Audio Power
  Amplifier
• Take measurements from both Physical Instruments
  and Virtual Instruments.

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Todays Topics

• Overview of Class B Amplifier
• Final Parts Update
• Schematic
• P-Spice graphs and simulations
• Analog measurements
• Elvis Simulations
• Budget
• Resources

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Output Class B Configuration

• Two transistors
• One transistor provides power to the load during
  one-half of the wave form cycle
• Second transistor provide power to load for
  another half of the cycle.
• Neither transistor remains on for entire cycle
  which allow them cool down during the waveform
  cycle

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Parts

• Two Twelve Volts Batteries
• Dual TL082 Op Amp
• 10K Potentiometer
• Resistors
• 2 Capacitors 1000 microF
• Speaker 8? 5W
• Bipolar Transistors with Similar ß (hfe)

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Circuit Schematic from PSpice
DC Power Source
Pre-Amp
Speaker
Class B amp
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Transistors

• Current producing devices and have a relatively
  low input impedance.
• Two types NPN,PNP
• Current Gain (Beta)
• Ratio between collector and base current is call
  Beta (Hfe).

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P-Spice Preamp Analysis
Potentiometer set to 0 resistance Amplification
R3/R4 1 28 Gain(dB) 20log10(Amplification)
29dB
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P-Spice Frequency Response
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Labview Input Signal
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Signal After Pre-Amp Section
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Elvis calculation of low 3dB point
(2KHZ signal 6.89V RMS )
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Elvis calculation of high 3dB point
(2KHZ signal 6.89V RMS )
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Voltage at 2kHz
2V / div Signal 6.2V Freq. 2KHz
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Voltage at 6 Hz
2V / div Signal 6.2 .707
4.4V Freq. 6Hz
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Voltage 70KHz
2V / div Signal 6.2 .707
4.4V Freq. 70 KHz
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Max Output Signal (ELVIS)
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Max Output Clipped (ELVIS)
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Distortion
Avg. of 100 points
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Elvis Distortion Limitations
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Natural Noise
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Amplifier Specs
Analog

• 4.8 Watts peak , 2.4 Watts RMS
• 6Hz 70 KHz
• Max. Output Signal 6.2V peak
• 11.9 Watts peak , 5.59 Watts RMS
• 0Hz 100KHz
• Max. Output Signal 9.76V peak
• THD .65

ELVIS
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Gannt Chat
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References

• Douglas Self, Audio Power Amplifier Design
  Handbook, Newnes, 1996
• Audio Power Amplifier Fundamentals. Retrieved
  September 1st,2004,from http//www.rocketroberts.c
  om/teachart/amp.htm
• Class B audio amplifier. Retrieved September
  1st,2004,from http//www.allaboutcircuits.com/vol_
  6/chpt_6/10.html
• Basic Car Audio Electronics. Retrieved September
  13th, 2004, from
• http//www.eatel.net/amptech/elecdisc/potenti
  o.htm
• Dr. Mankowski
• D-Spice

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END

• Question???