This is my TA7642 TRF receiver that I’ve made it so far after I’d found some old electronic components among my stuff. It took me several hours a couple of days to make but I enjoyed. It reminded me an interesting hobby of mine I used to do years ago, assembling electronic kits. Furthermore, now I have something to listen to, which was made by myself.
TA7642 is a single chip AM radio receiver in TO-92 package from TOSHIBA. This IC is low power and works with a voltage down to 1.2V and maximum 300uA quiescent current. The output voltage is lower than a couple of 10mV, so the output must be amplified to drive a small 0.5W speaker.
The circuit is obvious – antenna circuit, receiver IC, and audio amplifier. I used a ready-made 10 cm ferrite rod antenna with a 90 turns coil in parallel with the variable capacitor, and a 20 turns coil connected to external antenna and circuit ground. The 1K AGC resistore mentioned in the datasheet didn’t provide a proper gain in my circuit, so I used a potentiometer to specify the AGC resistor before I’d used a 4.7K fixed resistor.
The amplifier circuit is different from the datasheet and I used another circuit with two transistor to amplify detector output signal. The supply voltage was increased to 3V to improve the output sound level with an 8 Ohms speaker. The 1000uF capacitor and 470 ohm resistor just stabilize the voltage of the receiver stage when the speaker is loading the supply.
Below are the link to the radio output sound sample and TA7642 datasheet, the schematic, and some photos of assembling.
