The sound signal from the tape player or the radio receiver is extremely weak, so it cannot be heard from the speaker. The amplifier is a device to amplify the sound signal from the tape player or the radio receiver and to send to the speaker.
For a general radio receiver or tape player, an amplifier is built in.
Recently, some amplifiers are, however, used as a unit of the component audio system.
2.Construction of amplifier
An amplifier consists of a control amplifier (also known as a pre-amplifier) and a power amplifier (also known as a main amplifier). Some are independent and some are built in.
In the stereo broadcast, there are two types of signals so two amplifiers are needed. For the four speaker type, the stereo system has four amplifiers.
The control amplifier is an amplifier needed to control the power amplifier well. It is located before the power amplifier. It switches the input signal between the radio and the tape player and controls volume, balance and tone, etc. Generally, the tone control consists of two tone controls for bass and treble. In this case, the strength of bass and treble can be controlled separately.
The power amplifier amplifies the signal from the control amplifier at the constant rate and sounds the speaker. Therefore, when the signal from the control amplifier is weak, the sound from the speaker is low, and when the signal from the control amplifier is strong, the sound from the speaker is loud.
The output indicates how loud the amplifier sounds the speaker and “W” (watt) is the unit used. Therefore, the larger the number is, the louder amplifier can sound.
In the case of car audio, the required output when the user listens to it is only a few watts, but a 20 to 30 watt amplifier is used. It is because using a large output can produce the low strain and comfortable sound.
The speakers convert the signal that is amplified at the amplifier into sound.
A speaker system includes low-range woofers, mid-range squawkers, and high-range tweeters as well as full-range speakers.
In addition, there are two-way speakers and three-way speakers: the former separates the playback frequency into two ranges, low to middle and high and sound by the woofer and tweeter to create the high quality sound with a speaker. The latter, on the other hand, separate the frequency into three, low, middle, and high range.
2.Construction and principle of speakers
The magnetic force caused by magnet is transmitted to the plate and the center pole and it is intensively lead to the cylindrical gap between them. On the other hand, there is a moving coil that can move up and down freely in the gap. The moving coil is connected to the vibration plate (cone). When the signal (current) amplified by the moving coil is allowed to flow, the moving coil moves up and down according to the current, causing the cone to move and sound is produced.
3.Impedance of speaker
This indicates a resistance value of the speaker against the input signal, and is a value seen from the input terminal side.
The value shows the characteristic as shown in the left chart and this becomes the maximum value at a certain point in the low range.
The impedance whose frequency is higher than the maximum frequency and the impedance that first becomes the minimum are called nominal impedance.
Generally, the values of 4Ω and 8Ω exist and it is necessary to match the output impedance from the amplifier.
4.Maximum tolerate input
This is an index of the maximum momentary output limit that will not break the speaker, and “W” (watt) is used as the unit. Therefore, the larger this number, the larger the amount of electricity the device can receive. If the maximum tolerate input value is too small, the speaker easily breaks. So when installing a non-specified amplifier or speaker, conduct the operation with great care.
Inspection of Speaker
Disconnect the speaker wire from the radio receiver or amplifier and check the following items:
1.Measure resistance of each speaker
Measure the speaker resistance between the positive (+) and negative (-) terminals.
4Ω speaker: Approx. 4Ω
8Ω speaker: Approx. 8Ω
The position of the connector terminal differs depending on the type of radio, so refer to the Repair Manual.
2.Check insulation resistance between each speaker wire and vehicle body