Distortion is the phenomenon that the input signal and the output signal are proportional to the amplitude, the phase relation and the waveform shape change. The distortion of audio power amplifier can be divided into two categories: distortion and distortion. The distortion is caused by the circuit, and the distortion is caused by the loudspeaker. The types of electrical distortion include: harmonic distortion, intermodulation distortion, transient distortion. The main distortion is the distortion of AC interface. According to the nature, there are nonlinear distortion and linear distortion.

Linear distortion refers to the change of the amplitude and phase of the signal frequency components, only the amplitude and phase distortion of the waveform. The nonlinear distortion is the distortion of the signal waveform and produces a new distortion of the frequency components. Audio power amplifier distortion generated by the following points:

Harmonic distortion

This distortion is caused by the nonlinear elements in the circuit, the signal through these elements, the new frequency components (harmonics), these new frequency components interfere with the original signal, this distortion is not consistent with the output waveform signal waveform of the input signal, the waveform distortion.

The main methods to reduce the harmonic distortion:

1, the right amount of negative feedback.

2, select the characteristics of high frequency, low noise coefficient and good linearity of the amplifier.

3, improve the power reserve, improve the filtering performance of the power supply.

Two, intermodulation distortion

Two or more different frequency signal through the amplifier or speaker after difference to form the new frequency and shoot, this distortion is usually done by the active device in the circuit (such as transistors, electron tubes produced). The size of the distortion is related to the output power, because the new frequency components are not similar to the original signal, so the less intermodulation distortion is easy to be perceived by the ear.

Method for reducing intermodulation distortion:

1, the use of electronic frequency division, limiting the amplification circuit or speaker bandwidth, thereby reducing the generation of beat.

2, choose a good linear tube or circuit structure.

Three, transient distortion

Transient distortion is an important index of modern acoustics, which reflects the ability of the power amplifier circuit to keep track of the transient signal. This distortion makes the music lack of level or transparency, there are two forms of expression:

A, transient intermodulation distortion

In the transient signal pulse input, because the output of the capacitors in the circuit output voltage can not be due immediately, and the negative feedback circuit can not get timely response, the amplifier's open-loop state at this moment, the output moment overload causes clipping, the clipping distortion called transient intermodulation distortion the distortion is more serious, in the stone on.

Transient intermodulation distortion is a dynamic index of power amplifier, which is mainly caused by the negative feedback of the amplifier. Is arch-criminal influence stone sound, lead to "transistor sound" and "metal sound". The main methods to reduce the distortion are:

1, choose a good device and adjust the operating point, as far as possible to improve the open-loop amplifier gain and open-loop frequency response.

2, to strengthen their own negative feedback amplifier, cancel the negative feedback loop.

B, distortion caused by low conversion rate

The above mentioned, the high level input pulse causes the amplifier to produce the clipping and the transient intermodulation distortion. Will the low level input pulse cause distortion? This depends on the response time of the amplifier, due to the rapid changes in the response time is too long to change the amplifier output signal amplifier with no input signal caused by transient distortion, distortion is called conversion rate is too low. It reflects the response speed of the amplifier to the signal, the distortion of the small amplifier, the playback of the sound resolution, sense of hierarchy and positioning are very good.

Four, AC interface distortion

The distortion of the AC interface is caused by the back electromotive force (which is produced by the speaker 's vibration when cutting the magnetic field lines).

Improvement methods are:

1, reduce the output impedance of the circuit.

2, choose the right speaker, so that the damping coefficient is more reasonable.

3, reduce power supply resistance.