Audio amplifiers play a vital role in the functioning of audio systems such as the shopping mall’s public address system, a disco bar’s sound system, and even your computer’s sound card.
Most often, audio amplifiers are considered to be the power amplifiers of loudspeakers. But this should not only be the case. Audio amplifiers are available on the market from various brands like Sansui, Philips, Sony, Yamaha, etc. With the car amplifier, digital amplifier and stereo amplifier for sale on the market nowadays, it is imperative that we review the audio amplifier basics.
Generally, an audio amplifier is any device that changes, usually increasing, the amplitude of a reproduced sound. Its three major types are:
- Vacuum Tube (Valve)
- Bipolar Junction Transistor (BJT)
- Field Effect Transistor (FET)
Each has its own strengths and weaknesses, but keep in mind that none is perfect. All audio amplifiers rely on passive components like resistors, capacitors and inductors to function.
While being the first audio amplifier from way back in 1906, the valve has survived its way into modern times. Enthusiasts often choose these tube amplifiers for the high quality sound that they produce and the ability to introduce low order harmonic distortion, creating a “warm” sound. Valves also have negligible distortion at low levels. However, valves tend to act like microphones, distorting audio signals when sound from the speakers gets in contact with the amplifier. On the other hand, BJTs are quieter than valves and will not act as a microphone. Thus, room noise will not distort the sound quality. The FET, however, is not as good as BJTs in minimizing sound distortion, but add-ons can be used to improve an FET’s operation.
Valves have wide bandwidth, capable of driving heavy loads where others blow up or get heartburn. On the other hand, a BJT’s bandwidth is wider, more noticeable at the lowest frequencies than valves, because no transformer is involved. A BJT won’t tolerate overloads even for a short moment. It will be an instant failure when this happens. FETs suffer during an overload also.
Valves are costly to maintain and easily broken with their thin glass envelopes. Furthermore, valves have a limited life. Even if well-handled, valves fail to work when minimal amounts of air enter their vacuum. Additionally, the valve’s output transformer is expensive and introduces its own sound distortion disadvantages. On the other hand, professionals find BJTs very reliable, for they will last many years even without service maintenance. However, experts say that FETs are more versatile and can survive in outer space due to their great resistance to radiation.
Valves are a hassle to maintain. You have to make sure that the typical high power amp of 600V DC doesn’t get into valve bases. Additionally, correct temperatures must be maintained to operate valve cathodes. A low heater voltage will make the valve useless. Professionals, however, find BJTs much more efficient than valves. BJTs only require lower voltages and zero heat. But for a BJT to work on high impedance, additional circuits are required to allow them to perform satisfactorily. However, when high impedance devices are introduced into a BJT, noise becomes a problem. If your schematics expect super high impedances, the FET is ideal for the job with the least noise. Additionally, FETs can tolerate more heat than the BJTs.
Whether setting up for your disco sound system or just the sound card of your computer, it is vital that you understand the differences of the various audio amplifiers so as to know which ones to use in certain situations.