This project is a typical project of electronic world. You can connect this in parallel with the telephone line and hear the conversation clearly with short tone. This project is a boon for children as well as elders in the house. If its sound is increased little bit more it can be heard throughout the room.
TECHNICAL DESCRIPTION AND WORKING
This project has been developed and tested O.K. in our TV Engineers Technical Lab. The components and PCB used in the projects published in our books are available for sale at resonable price.
This project is a modern age project. Because revolution in the telecommunication, telephone network has been spread over in our villages and towns. Here we are giving a telephone amplifier circuit through which you can enjoy hearing sharp and clear voice. This project is very helpful for young and old to hear the voice clearly. In this project we have used IC BEL 1895 developed by Bharat Electronic Ltd. BEL IC 1895 is a eight pin small size IC. It works as a audio preamplifier as well as audio output amplifier. Positive supply is given on pin no. 8, pin no. 6 & 7 are earthed. Input signal is given on pin no. 4 & on pin no. 5 changing the value of resistance 470E and 1mfd/63V condenser. We can increase or decrease the gain. Amplified audio signal available on pin no. 2 of IC is given to speaker connected at the output. We obtain very clear output signal from the telephone amplifier. This IC works on 3Volt to 9Volt DC power supply. The output of 1 Watt can be received by using a 6V supply and speaker of 4E impedance. Circuit given is workable of 3 Volt DC.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT :-
- Use a 3V cell to avoid humming noise, Eliminator should not be used. In case transformer of Eliminator get shorted, there is every possibility of 230V AC supply touching the telephone line.
- Don’t increase the volume control, whistling will be heard, it is due to feed back.
- IC should not be soldered directly on PCB, because the parts get damaged due to leakage current from the soldering iron.
LIST OF COMPONENT
PCB [Code 5TP05] =1
120K=1, 470E=1, 1E=1, 10K TONE =1
220mfd/16V=2, 100mfd/16V=1, 1mfd/16V=1, 0.1pf/400V=1, 100pf=1
IC BEL 1896=1, IC BASE [8 pin]=1
Speaker [8E] =1, Battery Cell [1.5V]=2, Wire = 1 Meter