High-performance dual-band wireless microphone receiving circuit diagram
High-performance dual-band wireless microphone receiving circuit diagram
The author used the FM radio part of the old car radio to add an XR1075 audio processor, redesigned the printed board, and produced a stable and reliable dual-frequency wireless microphone transceiver system with excellent electrical performance. The transmitting part adopts the BA 1400 dedicated FM transmitting integrated circuit. The electromechanical principle is shown in the figure below, and the production process is now introduced as follows.
It can be seen from the figure that the circuit is composed of four parts, namely the FM head, intermediate frequency amplification, audio processing and power supply.
The basic principle is that the signal induced by the antenna is input from the pin of the FM head. After internal high-amplification and local oscillation mixing, the intermediate frequency signal of 10.7MHz is output from the pin. The C1 is input to T1 for intermediate frequency pre-amplification and filtered out by JT1. The 7MHz intermediate frequency signal is sent to the pin of IC1, which is internally limited, amplified, and discriminated to be demodulated as an audio signal to be output from the pin, and then coupled to C2 for amplification by C8 to meet the level requirements of IC3. The audio signal is input from the pin of IC3 and output from the pin after digital processing of the internal frequency division delay. The pin of IC1 is a 2.25V reference voltage source, and the pin is the output of the tuning instruction, which is used as noise suppression in this circuit. The principle is: when the pin has a 10.7MHz intermediate frequency signal input, the pin is low level, T3 is cut off, and the audio signal of IC3 pin is output without loss; otherwise, the pin is high level, the power supply is through R11, D2, R13 provides bias to T3 and T3 is saturated, so that the audio signal passes through the C and e poles of T3 to the ground, so as to achieve the purpose of noise suppression. L1 and C form a 10.7MHz frequency selective network. It is also the load of the second intermediate amplifier of IC1. C2 and C3 are the bypass capacitors of the intermediate frequency. W1 and W2 are the treble and bass gain adjustment potentiometers of the audio processor, respectively. See related articles in "Electronic News".
During installation and commissioning, find two bad car receivers and receivers (requires that the tuner contains a FM head), take out the circuit board and the tuner from it, and solder a 10.7MHz filter JT1, intermediate frequency filter (the appearance is like a middle circumference, and the magnetic cap is general (Light blue), key parts such as TA7640, FM tuner (see the upper right corner of the figure for appearance) are spares. Make a printed board according to the size of the chassis. The printed board should use epoxy board and be grounded in a large area. The components can be soldered when ready. T3 and T6 are installed after the whole machine is debugged. Turn on the power (take one way as an example), the pin voltage for measuring IC1 should be about 6.5V, the FM head pin should be 6V, and the pin should be about 0.15V (M47 type meter measurement, digital meter measurement is 1.9V), Adjust R1 and R10 so that the collector voltages of T1 and T2 are about 3V. Connect the power amplifier and the speaker. If the circuit is normal, the speaker should have a loud "rustle" sound. If there is no rustling sound, use a screwdriver to touch the IC3's foot and the T2 base electrode should have a hum, then touch the IC1's, , Foot, T1 base should have a loud "cluck" sound, otherwise you should check JT1, L1, IC1 and surrounding components. After everything is normal, rotate the FM head to receive a local FM radio station, and adjust the L1 magnetic core to make the sound quality clear. Then cooperate with the microphone to adjust the transceiver frequency (pay attention to avoid the local radio frequency), and finally use the microphone to adjust the W1 and W2 to the more familiar music with better sound quality so that the sound quality of the receiver is clear and natural. If the microphone is mainly used to pick up human voice, you can Increase the treble appropriately (adjust W2). The other way is adjusted in the same way. At this time, T3 and T6 are welded, the automatic noise suppression function is debugged, and the transmitter is turned off. The corresponding TA 7640 pin should be high; when it is turned on, it should be low, otherwise L1 must be readjusted.
Although this circuit does not use crystal oscillator frequency stabilization, due to the high stability of the FM head, the transmission and reception frequency of this wireless microphone is very stable, and there has never been a frequency deviation from summer to winter. The author uses the two microphones for Guzheng and voice respectively, subjectively feels Guzheng The string music is very crisp and beautiful, and the vocals have obvious tooth sounds. As long as the quality of the components is guaranteed, the wireless microphone can be comparable to hundreds of thousands of yuan of finished products. Of course, interested readers can also add harmonic generators at the output of IC1 and IC2 to improve the clarity of the sound. This machine uses a 9.6V rechargeable battery as the main power supply, and an external 16V power supply is designed for battery charging. Due to the current limiting and voltage stabilizing effect of R31 and D4, the external power supply can be connected to the machine for a long time.
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