Post by DocSpeed on Sept 12, 2005 13:39:35 GMT -5
Amplifier Classes
Class A: The transistor amp conducts for the entire cycle of input signal. The conduction angle is 360 deg. These amps run hot, as the transistors in the power amp are on all the time, but the upside is high sound quality.
Class B: In this amp, the positive and negative halves of the signal are dealt with by different parts of the circuit. The output devices continually switch. These amps run cooler, but the sound quality is not as pure.
Class AB: These amps work by biasing the transistor amp at a non-zero DC current much smaller than the peek current of the signal source. The second transistor conducts during negative half cycle of waveform and the currents from the 2 transistors are combined at the load. A compromise between sound quality of Class A and efficiency of Class B. Most modern amp designs employ this method.
Class D: Analog and Digitally Controlled
Analog-Controlled Class D: Switching amplifiers with an analog input signal and an analog control system. Normally some degree of feedback error correction is present
Digitally-Controlled Class D: Amplifiers with a digitally generated control that switches a power stage. No error control is present. Those that do have an error control can be shown to be topologically equivalent to an analog-controlled class D with a DAC in front.
You should remember:
1.Class A amplifiers are very inefficient and produce lots of heat because there is a large amount of current flowing through the output transistors even with no audio signal.
2.Class B amplifiers are more efficient but will have a 'notch' distortion.
3.Class AB amplifiers are moderately efficient (depending on bias current) but notch distortion is eliminated by the idle (bias) current.
4.Class D amplifiers are very efficient but are generally used for non high fidelity or subwoofer applications.