Amplifiers are one of the most popular electronics projects. Why? Because they are easy to build, cheap, sound good and can be customized to your needs.
One of the most diffucut steps involved in building your own amplifier is deciding what type of amplifier you need. This all depends on your skill, end application, heat requirements and sound quality you expect. This page will describe the types of amplifers and what their pros and cons are.
Choose a type of amplfier below, or scroll down the page:
• Gainclones
• Solid State
• MOSFET
• Transistor
• Vacuum Tube
• Amplifier Classes
• Power Dissipation
Gainclone: The gainclone is by far the easiest to build
.
They consist of a single chip (or in some cases such as bridged amps or
stereo amps, two or more chips. We will discuss this later), and a handfull
of resistor and capacitors. Experts and listeners frequently claim that the sound quality of a gainclone is superior to a traditional transistor amplifier due to the reduced part count and shorter signal path. A Brief History: Many people ask how it got it's name. The gainclone got it's name from the gaincard, made by 47Labs. Pictured to the left is the original Gaincard. For more info, visit the 47Labs website
After the gaincard, many companies designed chips that were like "clones" of the Gaincard, hence the name gainclone. National Semiconductor (www.national.com) is one of the largest gainclone amplifier chip manufacturers. The LM3886, LM3875, LM1875 chips, which are by far the most popular chips for beginners and professionals alike, are all made by National Semiconductor.
Today, the gainclone is becomming more and more popular, even in commercial equipment.
Packages:
Gainclones usually come in 2 different types of
packages.
To the right is the LM3886 chip, in a TO-220 non-isolated package. There
is also an isolated version of the chip. A non-isolated chip such as the
pictured LM3886T has the metal tab exposed. A non-isolated chip is covered
in in insulator so that there is no metal from the chip touching the heatsink.
The reason for the two types of chips is because the metal tab is connected
to the negative power supply. If the heatsink, was, for example, mounted
to a metal case that was grounded, then there would be a short between ground
and the negative rail. Notice that at the end of National Semiconductor part numbers, there is a 'T'. That tells you that it is a non-isolated chip. If it were
a 'TF' instead, then the chip would be an isolated package. If there is
any chance that the heatsink would come in contact with another conductive
surface, I recommend using the isolated version of the chip. Note that with
an isolated version of a chip, the thermal resistance will be higher and
therefore require a slightly larger heatsink.Solid State: Solid state amps use many individual transistors and components to amplify sound, rather than a single chip. A chip amp is basically a solid state transistor amplifier shrunk into a single silicone die. Since ther part count is much higher with a solid state amp, it is a much more complicated amp to build. If you are building your first amp, I would strongly suggest building a gainclone to get the hang of amplifier theory then progress into solid state amps.
The following are types of solid state amps:
.
MOSFET: The MOSFET is one of the best components for amplifier use. They deliver high-quality sound with less heat than standard transistors. MOSFETS are most commonly used in Class D switching amps as well which will be discussed later.
Transistor Amps: Transistor amps are the "original" type of solid stat amplifiers. They use standard high power PNP or NPN transistors to amplify audio.
Amplifier Classes: Amplifiers have different classes. The following is a brief overview of the classes and what type of amps fall into them:
• Class A - Class A amps are amplifiers that offer the best sound quality of all solid state amplifiers, but the transistors are always operating at full power. As a result, the efficiency is very poor and the amplifier always draws a large amount of power and runs hot.
• Class B - Class B amps are amplifiers that offer higher efficiency, but they suffer from more distortion than a Class A due to crossover distortion.
• Class A/B - Class A/B amps are combinations between Class A and Class B. They are related to Class B with their higher efficiency, and to class A with their higher quality. However, some very minor crossover distortion does still exist. Class A/B is by far the most common type of solid state amplifier.
• Class C - Class C is classification designed for RF (Radio Frequency) amplification.
• Class D - Class D amps use transistors differently than a Class A / B / AB amp. Instead of amplifying sound by using a transistor as a power booster, they amplify sound by rapidly switching the transistors on and off. This greatly reduces heat, while still allowing high output power.
A common misconception about Class D amps is that the D stands for Digital. That is not true.
One major disadvantage with a Class D amp is that the sound quality is not as good as with a class A / B / AB amp. That is the major reason Class D amps haven't replaced Class A / B / AB amps completely. Class D amplifiers are perfect for bass applications, however. Crisp, clean audio is not required by a subwoofer but high power output is. Class A / B / AB amplifiers that produce high wattage generate large amounts of heat and draw a lot of power. Class D, on the other hand, offers high power with high efficiency and low heat.
• Above Class D
New technologies in audio are emerging all the time. On of the most promising seems to be Class G. Class G combines tghe efficiency and low heat of a Class D with the better sound of Class A / B / AB amps.
Power Dissipation:
Power dissipation is how much heat an IC or transistor puts out, measured in watts. The higher the power dissipation of heat an amp puts out, the larger the heatsink needs to be, and vice versa.
This is a very basic introduction to audio amplifiers and the basic background information about them designed to get you started on Amplifier building.