In final year project we are making power amplifier. We discussed lots of ideas, but out of them , our lecturer selected power amplifier of 200watt. We searched lots of circuit ideas on internet. But some few were only 20w or some circuits components were no t clear. So we picked IC based project. So shat one IC can complete our requirements. First of all we will make project then there is audio input option. Output will be on speakers.
The term amplifier is very generic. In general, the purpose of an amplifier is to take an input signal and make it stronger (or in more technically correct terms, increase its amplitude). Amplifiers find application in all kinds of electronic devices designed to perform any number of functions. There are many different types of amplifiers, each with a specific purpose in mind. For example, a radio transmitter uses an RF Amplifier (RF stands for Radio Frequency); such an amplifier is designed to amplify a signal so that it may drive an antenna. This article will focus on audio power amplifiers. Audio power amplifiers are those amplifiers which are designed to drive loudspeakers. Specifically, this discussion will focus on audio power amplifiers intended for DJ and sound reinforcement use. Much of the material presented also applies to amplifiers intended for home stereo system use.
The purpose of a power amplifier, in very simple terms, is to take a signal from a source device (in a DJ system the signal typically comes from a preamplifier or signal processor) and make it suitable for driving a loudspeaker. Ideally, the ONLY thing different between the input signal and the output signal is the strength of the signal. In mathematical terms, if the input signal is denoted as S, the output of a perfect amplifier is X*S, where X is a constant (a fixed number). The “*” symbol means” multiplied by”.
This being the real world, no amplifier does exactly the ideal, but many do a very good job if they are operated within their advertised power ratings. The output signal of all amplifiers contain additional (unwanted) components that are not present in the input signal; these additional characteristics may be lumped together and are generally known as distortion. There are many types of distortion; however the two most common types are known as harmonic distortion and intermodulation distortion. In addition to the “garbage” traditionally known as distortion, all amplifiers generate a certain amount of noise (this can be heard as a background “hiss” when no music is playing). More on these later.
All power amplifiers have a power rating, the units of power are called watts. The power rating of an 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 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 power output of an amplifier is understood to be its maximum output, it in no way means that the amplifier can only be used at this output. For example, if an 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. More on this later.
In the early days, audio power amplifiers used devices called vacuum tubes (referred to simply as “tubes” from here on). Tubes are seldom used in amplifiers intended for DJ use (however tube amplifiers have a loyal following with musicians and hi-fi enthusiasts). Modern amplifiers almost always use transistors (instead of tubes); in the late 60’s and early 70’s, the term “solid state” was used (and often engraved on the front panel as a “buzz word”). The signal path in a tube amplifier undergoes similar processing as the signal in a transistor amp, however the devices and voltages are quite different. Tubes are generally “high voltage low current” devices, where transistors are the opposite (“low voltage high current”). Tube amplifiers are generally not very efficient and tend to generate a lot of heat. One of the biggest differences between a tube amplifier and a transistor amplifier is that an audio output transformer is almost always required in a tube amplifier (this is because the output impedance of a tube circuit is far too high to properly interface directly to a low impedance loudspeaker). High quality audio output transformers are difficult to design, and tend to be large, heavy, and expensive. Transistor amplifiers have numerous practical advantages as compared with tube amplifiers: they tend to be more efficient, smaller, more rugged (physically), no audio output transformer is required, and transistors do not require periodic replacement (unless you continually abuse them). Contrary to what many people believe, a well designed tube amplifier can have excellent sound (many high end hi-fi enthusiasts swear by them). Some people claim that tube amplifiers have their own particular “sound”. This “sound” is partly due to the way tubes behave when approaching their output limits (clipping). The onset of output overload in a tube amplifier tends to be much more gradual than that of a transistor amplifier. A few big advantages that tube amplifiers have were necessarily given up when amplifiers went to transistors. First, tubes can withstand electrical abuse that would leave even the most robust transistor completely blown. Also, tube amplifiers use an output transformer to interface to the speaker; such a device provides an excellent buffer (protection to the speaker) in the case of internal malfunction. Modern amplifiers (with no output transformer) occasionally fail in a way that connects the full DC supply voltage to the speaker. If the amplifier does not have adequate protection circuitry built in, the result is often a melted woofer voice coil.
An amplifier’s main purpose is to take a weak signal and make it strong enough to drive a speaker. Power amplifiers get the necessary energy for amplification of input signals from the AC wall outlet to which they are plugged into. If you had a perfect amplifier, all of the energy the amplifier took from the AC outlet would be converted to useful output (to the speakers). However, in the real world no amplifier is 100% efficient, so some of the energy from the wall outlet is wasted. The vast majority of energy wasted by an amplifier shows up in the form of heat. Heat is one of the biggest enemies to electronic equipment, so it is important to ensure adequate air flow around equipment (especially so for those units using convection cooling). Most amplifiers in the 200 watt per channel range (and up) have forced air cooling (via fans) in order to prevent excessive heat buildup.
Many amplifiers have a number of features to help monitor the status of the amplifier and also to protect speakers (and the amplifier itself) in the event of an overload condition. Some features include power meters, clipping indicators, thermal overload shutdown, over current protection, etc. Features vary from manufacturer to manufacturer. In addition, there are many variations in how protection circuits are implemented and how much “safety margin” they allow. For example, I tested the clipping indicator on one particular amplifier. The clipping indicator did not come on until there was a substantial amount of clipping actually occurring (as viewed on an oscilloscope). In this case, I did not notice a significant degradation of the sound quality despite the clipping. The manufacturer in this case chose to “allow a little more volume” before actually lighting up the warning light.