i need to do a project which is about IR AUDIO TRANSMITTER AND RECEIVER to amplify the audio signal to headphone
the circuit is as follows.
http://www.electroniq.net/audio/wireless-ir-headphones-circuit-diagram-electronic-project.html
however, i dun know wt is the function of the three transistors in the receiver part exactly. can someone answer me?
also can u briefly tell me the working principle?

 

I have seen that old circuit before on other websites. I don't think the transmitter works because its first transistor has no base bias current and the red LED shorts the audio signal.

The first two transistors in the receiver are a preamp and the 3rd transistor is a class-A driver for the low impedance headphones.

 

yup, i know we should add a source to make a base current. but the second part still not work........do u know??

 

The transmitter circuit is a total disaster.

In addition to the first transistor missing its base bias current the red LED is shorting the audio signal so the second transistor in the transmitter does not modulate the current in the IR LEDs.

The receiver circuit is also a total disaster.
I forgot to mention that the receiver puts DC through the headphones which might cause them to burn out.

The circuit comes from a website in India where almost all circuits do not work.
http://www.electronicsforu.com/electronicsforu/lab/freecircuitslist.asp?id=26&title=Infrared Cordless Headphone

 

can you explain the circuit in detail including how all the values are chosen

 

old thread, now dead.
The topic starter can always ask a moderator to open the thread again.