Hearing Aid Circuit Help Needed

[vinylhalide]

Hi,

I want to build an electronic circuit shown in the diagram below. I'm a little unclear as to what each component does. Each transistor, capacitor etc. Could someone break the circuit down and explain it to me?

 

[Brevor]

There are close to 20 components in your diagram. It would be very time consuming to explain each one individually. So to keep it short, All the transistors amplify the audio signal. All the resistors (except the 1K at the top) bias the transistors to set their operating point. The 2 small capacitors connected to the negative supply limit the high frequencys. The other 2 small capacitors couple the audio signal between the transistor stages and block the DC bias voltages. The large capacitor on the far left works along with the 1K resistor at the top to isolate power for the first transistor stage from the 2nd and 3rd stages. Thats about it.

 

[audioguru]

On Colin's Talking Electronics site, it is called a Spy Amplifier. My son bought a Chinese one with the same circuit and it works very poorly.
It has the same output as normal hearing so it has no gain. It muffles high audio frequencies. Most deaf people need boosted high audio frequencies.

 

[vinylhalide]

Thank you Brevor
And audioguru, yeah that's true :-/ The output isn't amplified like it ought to be.