What Is a Stereo Receiver?

Stereo radio A radio that can receive stereo broadcasts and has a stereo playback effect. Stereo radio as the name suggests, the sound effect of stereo radio is stereo, and the sound quality is better than that of ordinary radio, which will bring us the sound that sounds like the sound we hear in the place where the microphone is placed.

Stereo radio A radio that can receive stereo broadcasts and has a stereo playback effect. Sound broadcasting systems include FM stereo and AM stereo. Therefore, there are FM stereo radio and AM stereo radio, respectively. But because the latter is in the development and trial broadcasting stage, most of the stereo broadcasts are FM stereo broadcasts, so stereo radios are generally FM stereo radios.

FM stereo radios are available in two and four channels. Two-channel stereo radio is used to receive two-channel stereo programs. A four-channel stereo radio can receive signals from four different directions. At the program transmitting end, the sound signals corresponding to the left front, right front, left rear, and right rear directions corresponding to the listener's position are compiled into two composite signals each containing four information by an encoder group, and then two-channel stereo is used. The broadcast system sends. In a four-channel radio, the two composite signals demodulated by the stereo tuner are restored to the front left and right by the decoder. The signals of the left and right rear channels pass through four independent power amplifier sections and are sent to four corresponding speakers for playback. Because the circuit of a four-channel stereo radio is too complicated, FM stereo uses dual-spectrum. ^[1]

If you want to feel the depth and orientation of the sound source, the sound system must be able to provide different information to the left (L) and right (R) ears. If the sound transmitted by a system consisting of a microphone, an amplifier and a speaker can be heard with one ear, then the sound transmitted by a system consisting of two separate microphones, two amplifiers and two speakers Will bring us the sound that sounds like the sound we hear when we are actually where the microphone is placed.

The actual stereo recording process is much more complicated. It is often not just two-channel recording, but four-, eight-, or more-channel recording. After processing, two channels are recorded on the tape. Only a two-channel recorder is required for playback. Can restore stereo sound.

When listening to stereo music, where you listen is important. In addition, the place where the sound is played and the layout of the speakers have a great impact on the sound effect.

The distance between the two speakers (or speakers) of a general dual-channel stereo playback system is about 2.5 meters. The best listening area is near the mid-vertical line, which is 3 to 4 meters from the midpoint of the line connecting the two speakers. When it is too close, too far, or too far to the left or right, the clarity of the sound image will be reduced accordingly, and in severe cases, the direction of the sound image will be blurred. The sound image group expands, also known as the body sound widening. In the case of two channels of stereo playback, crosstalk feedback measures of equalization and delay circuits are adopted, so that the two channels can obtain a proper amount of crosstalk signals with opposite phases to each other. This measure is often used in a cassette stereo recorder to improve the problem that the stereo sound is not strong because the two speakers in the unit are too close. ^[2]

Structure and working principle of FM radio

The structure of the front-end circuit of the FM radio is the same as that of the AM radio, except that the frequency of the signal is different. The signal received by the antenna is subjected to high frequency and mixing processing to output the intermediate frequency signal with the frequency difference of the local oscillator signal, and then FM demodulated by the intermediate amplifier, limiter and frequency discriminator to demodulate the audio signal modulated on the carrier wave. .

When the mono FM receiver receives the FM stereo radio signal, the composite stereo signal output by the frequency discriminator is directly filtered by the de-emphasis circuit, and the difference signal and pilot signal outside the audio range are suppressed, and only the stereo composite signal is output; After the synthesized signal is amplified by the audio circuit, a mono signal is output to achieve compatibility. For stereo receivers, the composite stereo signal output by the discriminator must be sent to the decoder first. The composite stereo signal is separated into the left and right channel signals, and then the high-frequency signal is attenuated by the de-emphasis circuit, and then the dual-channel audio The circuit is amplified to drive the left and right channel speakers to play.

The decoder is a key part of the stereo receiver. It separates the left and right channel signals from the stereo composite signal. There are many types of circuits. At present, the integrated circuit switch and phase-locked loop decoder are commonly used. There is also a stereo automatic switching circuit and a stereo indicating circuit in the integrated circuit decoder. Their function is to automatically cut off the subcarrier channel when receiving a single channel signal or the stereo signal level is too low (or the signal-to-noise ratio is too small). Only the single-channel signal is sent to the left and right channels evenly; when the level of the received stereo signal is high and the signal-to-noise ratio is high, the subcarrier circuit is automatically switched on, and the decoder is in a normal decoding working state, and the stereo The indicator light is on, indicating that the receiver is in stereo receiving state. ^[2]

Stereo radio radio circuit

The AM and FM radio circuits of medium and high-end cassette recorders are basically the same as general FM AM radio circuits, that is, the AM section includes frequency conversion, mid-amp and detection; the FM section includes high-frequency tuner (high-amp, mixed-frequency) , Local oscillator), amp, frequency discrimination and stereo decoder. These parts are now integrated.

Stereo radio recording and playback circuit

The stereo recording and playback amplifier circuit can be divided into two or more channels, and each channel is mainly composed of three parts, that is, a preamp, a recording and playback equalization amplifier, and an audio amplifier (voltage amplification and power amplification). Each channel has its own amplifier. Generally, the playback channel and the recording channel share an amplifier circuit, and the working state is switched by the recording and playback switch. The two-channel stereo recorder circuit can be considered as a combination of two mono recorder circuits with the same performance. Due to the development of integrated technology, most of the recorders currently produced use integrated circuits. ^[2]