I love to listen to FM radio. The radio line used before is very ordinary. It is nothing more than CXA1019, 1238, TA8122, 7640, 7358, 7343. It always feels difficult to be elegant, so I always think that the performance of DIY is quite powerful. Radio, I am more concerned about the sound quality, selectivity can be second, brewing for a long time, extensive reference to each machine line, choose its easy to make superior performance and take it, slowly accumulate parts, look at the time is ripe, this year, make use of leisure time Carefully planned production, so the birth of this hole board DIY radio, is a dream of round HiFi radio.
The following describes the circuit architecture of this machine.
The high-frequency head is taken from the finished product of an Alpine car. The internal part is composed of the line with the TA8116 chip as the core. The triple-coupling, balanced mixing, and the antenna input part are designed with BPF, so the selectivity should be ok. A Mizmi uses the high frequency head of the LA1193 chip, and the performance is slightly better.
The pre-intermediate part refers to the Yamaha TX-950 line, using two levels of differential amplification, using three Murata GDT varieties of ceramic filters, I am quite satisfied with this combination.
Several modules are designed in the middle and frequency section. It is connected with other lines, so that the circuit performance and sound quality of different IC architectures can be compared. The four chip circuit modules of LA1235, HA11225, TDA1576 and LM1965 are used respectively. . The result of the actual audition comparison is: the same is similar. The performance of the national half LM1965 chip circuit is the most distinctive. The sound quality of Hitachi's HA11225 seems to be more resistant, the intermediate frequency is full, and the high frequency is delicate and moist. The double tuning midweek used was removed from the waste radio head.
Stereo Decoder Chip I chose HA12016, which has excellent performance. The standard 2.54 pitch can match the hole board, and I don't have to pursue the LA3450, which is expensive and difficult to buy and has comparable performance. After decoding the output, the LPF is connected and removed from a lion-long radio head.
The power supply part uses 1117 chip voltage regulation for power supply, frequency discrimination and stereo decoding, 7808 chip power supply high frequency head, and the other tuning voltage is obtained by TL431 voltage regulation. After taking the 1117 chip, the 8.5V tuning voltage is guaranteed to be pure and stable. Connect multiple potentiometers to adjust the platform.
The power transformer is disassembled by the Yamaha radio head. The total measured current consumption of the whole machine is 113mA, which is about 1.5W. It is not bad.
The whole machine strives to select all the parts to ensure the quality and performance is stable. The power filter capacitor is removed from the smart sports car. It is obtained by connecting six patches 470uF in parallel. The electrolytic capacitors of the other circuits are almost all ELNA varieties.
The circuit board uses three pieces, the power supply and the stereo decoding are put together, and the glass fiber double panel is used. The edge part of the board is provided with a pin header for connecting the tuner and the pre-intermediate module, and the middle frequency discriminating module. It plays the dual role of fixed and electrical connection, and it is convenient to assemble, disassemble and replace.
Level meters, audio output, tuning potentiometers, antennas, etc. are also designed to be connected by pin headers, which can be inserted and removed at will, and are still simple and orderly.