Class B Audio Amplifier Tina Shaw Kendall James Andrew Cruz
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.
Today’s Topics • Overview of Class B Amplifier • Final Parts Update • Schematic • P-Spice graphs and simulations • Analog measurements • Elvis Simulations • Budget • Resources
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
Parts • Two Twelve Volts Batteries • Dual TL082 Op Amp • 10K Potentiometer • Resistors • 2 Capacitors – 1000 microF • Speaker 8Ω 5W • Bipolar Transistors with Similar ß (hfe)
Circuit Schematic from PSpice DC Power Source Pre-Amp Speaker ClassB amp
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).
P-Spice Preamp Analysis Potentiometer set to 0 resistance Amplification = R3/R4 + 1 = 28 Gain(dB) = 20log10(Amplification) = 29dB
Elvis calculation of low 3dB point (2KHZ signal = 6.89V RMS )
Elvis calculation of high 3dB point (2KHZ signal = 6.89V RMS )
Voltage at 2kHz 2V / div Signal = 6.2V Freq. = 2KHz
Voltage at 6 Hz 2V / div Signal = 6.2 *.707 = 4.4V Freq. = 6Hz
Voltage 70KHz 2V / div Signal = 6.2 * .707 = 4.4V Freq. = 70 KHz
Distortion Avg. of 100 points
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
References • Douglas Self, Audio Power Amplifier Design Handbook, Newnes, 1996 • Audio Power Amplifier Fundamentals. Retrieved September 1st,2004,from http://www.rocketroberts.com/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/potentio.htm • Dr. Mankowski • D-Spice