Audio Power Amplifiers

This simple Audio power amplifier was originally designed for a circuit board workshop, conducted by the OSU IEEE Student Group. At the workshop, 20 audio power amplifier participants each constructed this audio power amplifier, by etching and drilling the single sided circuit board, soldering all audio power amplifier components, and attaching a pre-built heat sink assembly with the output audio power amplifier transistors.

Three audio power amplifier workshops were held between 1995 to 1996. Though the audio power amplifier design is simple, these audio power amplifier has impressive performance, with a frequency response to approx 40 kHz, very low noise, reasonably fast slew rate, and approx 50 watts (true "RMS" power) audio power amplifier with the proper +/- 40 volt unregulated power supply. The term audio power amplifier is very generic. In general, the purpose of an audio power amplifier is to take an input signal and make it stronger (or in more technically correct terms, increase its amplitude). Audio power amplifier find application in all kinds of electronic devices designed to perform any number of functions. There are many different types of audio power amplifier, each with a specific purpose in mind. For example, a radio transmitter uses an RF audio power amplifier (RF stands for Radio Frequency); such an audio power amplifier is designed to amplify a signal so that it may drive an antenna. This article will focus on audio power amplifier. Audio power amplifier are those amplifiers which are designed to drive loudspeakers. Specifically, this discussion will focus on audio power amplifier intended for DJ and sound reinforcement use. Much of the material presented also applies to audio power amplifier intended for home stereo system use.

All audio power amplifier have a power rating, the units of audio power amplifier are called watts. The power rating of an audio power amplifier may be stated for various load impedances; the units for load impedance are ohms. The most common load impedances are 8 ohms, 4 ohms, and 2 ohms (if you have an old vacuum tube amplifier the load impedances are more likely to be 32 ohms, 16 ohms, 8 ohms, and maybe 4 ohms). The power output of a modern audio power amplifier is usually higher when lower impedance loads (speakers) are used (but as we shall see later using low impedance loads just to get the extra power is not always recommended). The rated  audio power amplifier output of an audio power amplifier is understood to be its maximum output, it in no way means that the audio power amplifier can only be used at this output. For example, if an audio power amplifier is rated at 100 watts, the output can be anything between zero and this maximum rated value. Chances are that the amp can probably put out more if the input signal is overdriven, however the quality of the output will degrade rapidly.