A few years ago, I decided to build a solid-state stereo FM receiver. My 8-tube
FM receivers were quite a success, but I wanted to try my skills at a solid-state version. Among the many FM radio ICs (integrated circuits) on the market, I wrongly focused on the TDA7088T
FM tuner, the TDA7040T
stereo decoder and the TDA7050T
stereo amplifier. These SMD (surface-mount) ICs were hard to obtain and difficult to solder, so my project ended up on paper and never saw the light.
I was searching the internet for receiver projects one day when I landed on Patrick Cambre's website. Patrick described a 2-IC stereo FM receiver he built with the SMD (Surface mount) version of the TEA5711T and TDA7050T ICs. His receiver was based on the application circuit of the TEA5711T, which was simple and easy to implement. Patrick used a printed circuit to connect the miniature ICs, but since I was going to use Manhattan style
construction, I decided to use the DIP (Dual inline) version of the ICs for my receiver. Obtaining the larger TEA5711 and TDA7050 was not an easy matter as they were out of production, but I eventually located and purchased a bunch of them with the help of a friend in Germany. I was finally ready to build my first solid-state stereo FM receiver!
My receiver is built around the larger TEA5711
ICs. The receiver section of the TEA5711 features high selectivity with distributed IF gain, good strong signal handling, AFC (automatic frequency control) for drift-free reception, a mute circuit to decrease static on weak stations, and an MPX decoder for stereo reception. The TDA7050 features low distortion and is rated at 75 mW output per channel. The application circuit uses 3 volts to power the receiver, but I decided to run my receiver with 4.5 volts for increased audio output.
I have received stereo transmissions all the way from Cyprus, 240 km (150 miles) away. This attests to the high sensitivity of the TEA5711. The AFC functions well and provides drift-free reception. AFC level can be controlled with the value of the capacitor at pin 20 of the TEA5711. Adjacent channel selectivity depends on the two ceramic filters used, which plug into sockets in this receiver. I tested a few of these and settled for the narrow filters with 150 KHz bandwidth with very good results. I tried a ceramic filter in place of the ceramic resonator at pin 5, as Patrick did in his receiver, but the sound was distorted. A ceramic resonator is definitely the way to go here. I used 0.47 uF capacitors at pins 2 and 3 instead of the suggested 0.1 uF in the application circuit, to improve base response. Stereo separation is a function of signal strength, and is similar to that in my stereo MPX decoder
wich has 45 dB separation. With good quality headphones, the sound is rich with deep base and high treble and offers hours of enjoyable stereo music. All in all, this receiver turned out to be a good performer and a pleasure to listen to!
The receiver is housed in a 7 x 5 x 2 inch aluminum chassis. Controls from left: on/off, balance, volume, stereo/mono and tuning. High quality stereo headphones with 32 or 60 ohms impedance can be used with the receiver. A 6 to 1 miniature vernier drive offers smooth tuning. Stereo reception is indicated by the small red LED. The stereo/mono switch allows clearer reception of weak stereo stations. The balance control comes in handy for transmissions with slightly flawed balance. A removable telescopic antenna can be swiveled, extended and collapsed for best reception.