Car amplifier
Car amplifier is car power amplifier, to enlarge the car stereo power, to achieve the ideal vehicle effect. Power amplifier circuit by the forward voltage amplifier stage, drive, power amplifier, speaker and so on, prestage is voltage amplifier stage. The last level is power amplifier stage, from the prestage signal power amplifier, gain enough power output to the speaker, drive level is to provide the power output level required larger input signal power.
The necessity of car amplifier
Car audio equipment as well as home audio, also want to use the power amplifier. The people new to the car stereo, for also installed power amplifier in the car, or even to install multiple power amplifier, that incredible. So why do you want to install power amplifier? Because car power supply voltage is 14.4 V, power voltage (U) (P) = x up current, if only the host's own power amplifier, can reach 4 x55w, most can only promote the power of small speakers, distortion, and large volume will be sounded stiff, lack of flexibility. Ear hearing has a limit, the lower limit of less than can hear the volume of the upper limit, which is why the music is always at the beginning of a feeling. To make any sound is rather difficult to achieve the most realistic state. The windshield, inner decoration, engine and car chassis and the tyres of the noise when driving on the road, have great influence on listening environment; After low pressure level and low level power is also a very big defects, unable to replay music all the information.
work power. This value is only can truly reflect the working state of the equipment. Many people think that the main factor that cause the speaker coil burned is caused by the power amplifier's power is greater than the speaker. So for equipment collocation, used the power of the speaker is bigger than the power amplifier. This is a very common mistake. In fact, continuous output power of the power amplifier value is less than the continuous output power of the speaker is easy to cause the destruction of the speaker.
After the connection system. Once the volume knob, the output power is controlled in lOOW, power amplifier has been in a state of full capacity. The speakers still has a lot of allowance, once the user has to continue to increase the volume, then the output power than the power amplifier of continuous output power value, also is the moment when the distortion begin to produce. Distortion of what is known as the "clipping distortion", in the professional audio industry is called "speaker killer". This kind of distortion of signal, even il/power/b can produce similar dc electrical signals, can be easily burned loudspeaker coil. For a continuous output power 200 w speakers, distortion rate of 50% of 150 w electrical signal is worse than the 300 w signal without distortion.
So in the field of professional audio, keep the power amplifier "margin" is the important factors in the match system. Practice to ensure the continuous output power of the bass power amplifier output power continuously for the speakers of more than 2 times. In car audio, because the car's power extremely limited, each 1 w power is valuable, so to ensure the continuous output power of power amplifier slightly larger than the continuous output power of the speaker is the best choice. Don't let the continuous output the power amplifier to drive continuous output power is too small a great speaker. To do so, attention should be paid to control volume, to prevent the emergence of clipping distortion.
2 the impedance matching
Despite the boring theory knowledge, simple explanation is speakers with an impedance of power amplifier can bear a certain range. Only pick up on the pa speaker impedance in this range, power amplifier to safety work and provide the most ideal power output.
Different models of the impedance of the power amplifier can bear is different.
3 frequency matching
Power amplifier is usually divided into full frequency power amplifier and bass special power amplifier. Bass special amplifier distortion in the signal frequency is 250 hz can guarantee is less than 1%. And when, after more than 250 hz frequency distortion has soared, the output power is reduced sharply. So don't try to use special bass power amplifier drive tenor and soprano speakers. Full frequency power amplifier is usually USES the class AB amplifier design, power loss is larger. So the filter out low frequency signal, only promote the tweeter will be save power, the best choice to guarantee the quality.
As long as to master the equipment collocation principle, basic can guarantee the speaker and power amplifiers in a safe state, and can produce pure and no distortion.
The classification of automotive amplifier
1, class A power amplifier (also known as class A amplifiers)
Class A amplifier output stage in the two group (or two) transistors in A conducting state forever, that is to say, no matter whether they all keep the conduction current signal input, and make the two peak current is equal to the alternating current (ac), the communication in the case of the maximum signal into the load. When no signal, two transistor each the same amount of current flow, so there is no imbalance in the center of the output current or voltage, therefore, no current input. When the signal to the anode, the line at the top of the output transistor allowed into the more current, at the bottom of the output transistor is relatively reduced current, due to the unbalanced current start, then flows into the speaker and speaker voice. The workings of A class A power amplifier has the best linear, each output transistor amplification signal full wave, simply does not exist in the Distortion (Switching Distortion), even if they don't use of negative feedback, its open loop Distortion is still very low, so is known as the ideal sound amplification circuit design. But this kind of design, class A amplifiers put the biggest drawback is low efficiency, because there was no signal when there is still A current flows, full power all into A high quantity of heat. When the signal level is increased, some power into the load, but many still turn into heat.
Class A power amplifier is the ideal choice of replay music, it can provide A very smooth timbre, tone and warm, high transparent, open these advantages to compensate its drawbacks. Class A power amplifier calorific value, in order to effectively handle the cooling problem, class A amplifier must adopt large radiator. Because of its low efficiency for electric equipment must be able to provide sufficient current. A 25 w class A power amplifier for electrical ability enough to at least 100 watts class AB amplifier is used. So the volume and weight of the class A machine than class AB, this let the manufacturing costs have gone up, price is more expensive. In general, the price is about the same power of the class-a power amplifier class AB borne power amplifier twice or more.
2, class B power amplifier (class B power amplifier)
Class B power amplifier amplification works when no signal input, output transistor does not conduct electricity, so not consumed power. When there are signals, each pair of output tube the waveform zoom in half, one on one off each other to rotate to complete a full wave amplifier, when two output transistor rotation work occurs in the distortion, thus form a nonlinear. Pure class B power amplifier is less, due to the serious distortion when the signal is very low, so the distortion makes sounds rough. Class B power amplifier efficiency is about 75% on average, the heat generated by the relatively low class A machine, permitted use smaller radiators.
3, class AB amplifier
Compared with the former two types of amplifiers, class AB amplifier can compromise in performance. Class AB amplifier has two bias, usually in the absence of signal also has a small amount of current through the output transistor. It in signal hours with A kind of work mode, get the best linear, when the signal to A certain electricity automatically converted to A class B at ordinary times working mode in order to obtain higher efficiency. PuTongJi 10 watts class AB amplifier about within 5 watts work with class A, because listening to music when the required only A few watts, so the class AB amplifier is to use most of the time in class A power amplifier working mode, only in the event of A music into A class B transient forte. This design can obtain excellent sound quality and improve efficiency to reduce quantity of heat, is a rather logical design. Some class AB amplifier dispatch deviation is very high, make it in A wide range of power with A kind of work, make the sound close to pure class A machine, but the heat generated by the relative increase.
4, class C power amplifier (class C power amplifier)
This kind of power amplifier less heard, because it is a very high power amplifier distortion, is only suitable for use in communication purposes. Class C machine output, high efficiency, but not the HI - FI applicable
5, class D power amplifier (D class amplifier)
This design also called digital power amplifier. Class D power amplifier amplification transistor once open directly to the load and for electrical connection, but no voltage of the transistor current circulation so no power consumption. When the output transistor is closed, all the power supply voltage that appeared on the transistor, but no electricity, so also not consumed power, so the theoretical efficiency of one hundred percent. The advantage of class D power amplifier amplification is the highest efficiency, for electrical appliances can be narrowed, almost does not generate heat, so no big radiator, airframe significantly reduce the volume and weight, low distortion, theoretically linear. But this kind of power amplifier work complex, the increasing number of the line itself is also hard to avoid has a deviation, so the real success of products, price is not cheap.
The installation of car amplifier
Power amplifier match choose good after work completed only half of it, the other half is installed. Good installation can fully protect the power amplifier, prolong service life, and improper installation, in addition to often dyed ailment, also an understandable things, the following detailed introduction to the installation of power amplifier.
Here are some key points include the installation power amplifier main steps, as long as the correct matching and installation, power amplifier can achieve the best effect,
Point 1: assuring
Requirements: connected to the power amplifier, easily broken wire, influence system effect.
Fixed point 2:
Requirements: must be screwed on both ends of the power amplifier, all around, such as fixed on the board, board should be fixed.
There are two reasons: random is not fixed, harm:
One, the damage to the equipment, easy to crash.
Second, the damage sound quality.
Point three: coated
Requirements: terminal with good insulating tape coating, not way out of the copper wire.
Reason: 1, security, prevent short circuit.
2, shielding effect, preventing signal interference.
Point four: heat dissipation
Requirements: add extra fan, protective ventilation
Reason: high temperature inside the car, especially in the summer, there's not a good cooling measures, power amplifier is in the high temperature for a long time, although the high power amplifier has a protection system, but not so for a long time.
