• Voltage comparator
• Precision voltage follower
• Noninverting amplifier
• High-impedance voltmeter
• 555 audio oscillator
• 555 ramp generator
• PWM power controller
• Class B audio amplifier
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Volume VI - Experiments » ANALOG INTEGRATED CIRCUITS »
Class B audio amplifier
• Four 6 volt batteries
• Dual operational amplifier, model TL082 recommended (Radio Shack catalog # 276-1715)
• One NPN power transistor in a TO-220 package -- (Radio Shack catalog # 276-2020 or equivalent)
• One PNP power transistor in a TO-220 package -- (Radio Shack catalog # 276-2027 or equivalent)
• One 1N914 switching diode (Radio Shack catalog # 276-1620)
• One capacitor,47 µF electrolytic, 35 WVDC (Radio Shack catalog # 272-1015 or equivalent)
• Two capacitors, 0.22 µF, non-polarized (Radio Shack catalog # 272-1070)
• One 10 kΩ potentiometer, linear taper (Radio Shack catalog # 271-1715)
Be sure to use an op-amp that has a high slew rate. Avoid the LM741 or LM1458 for this reason.
The closer matched the two transistors are, the better. If possible, try toobtain TIP41 and TIP42 transistors, which are closely matched NPN and PNP power transistors with dissipation ratings of 65 watts each. If you cannot get a TIP41 NPN transistor, the TIP3055 (available from Radio Shack) is a good substitute. Do not use very large (i.e. TO-3 case) power transistors, as the op-amp may have trouble driving enough current to their bases for good operation.CROSS-REFERENCES
Lessons In Electric Circuits, Volume 3, chapter 4: "Bipolar Junction Transistors"
Lessons In Electric Circuits, Volume 3, chapter 8: "Operational Amplifiers"
• How to build a "push-pull" class B amplifier using complementary bipolar transistors
• The effects of "crossover distortion" in a push-pull amplifier circuit
• Using negative feedback via an op-amp tocorrect circuit nonlinearities
This project is an audio amplifier suitable for amplifying the output signal from a small radio, tape player, CD player, or any other source of audio signals. For stereo operation, two identical amplifiers must be built, one for the left channel and other for the right channel. To obtain an input signalfor this amplifier to amplify, just connect it to the output of a radio or other audio device like this:
This amplifier circuit also works well in amplifying "line-level" audio signals from high-quality, modular stereo components. It provides a surprising amount of sound power when played through a large speaker, and may be run without heat sinks on the transistors (though you should experimentwith it a bit before deciding to forego heat sinks, as the power dissipation varies according to the type of speaker used).
The goal of any amplifier circuit is to reproduce the input waveshape as accurately as possible. Perfect reproduction is impossible, of course, and any differences between the output and input waveshapes is known as distortion. In an audio amplifier, distortion may causeunpleasant tones to be superimposed on the true sound. There are many different configurations of audio amplifier circuitry, each with its own advantages and disadvantages. This particular circuit is called a "class B," push-pull circuit.
Most audio "power" amplifiers use a class B configuration, where one transistor provides power to the load during one-half of the waveform cycle (it pushes) anda second transistor provides power to the load for the other half of the cycle (it pulls). In this scheme, neither transistor remains "on" for the entire cycle, giving each one a time to "rest" and cool during the waveform cycle. This makes for a power-efficient amplifier circuit, but leads to a distinct type of nonlinearity known as "crossover distortion."
Shown here is a sine-wave shape,...