Analysis of circuit diagram of small ear loudspeaker

This is a simple ear small amplifier or commonly known as hearing aid or hearing loss amplifier item. The circuit has been tested on some patients and resulted in significant improvements in their hearing. It consumes a very small amount of power in the 10 milliwatt range. In addition, the voltage requirements of each major component are in the range of 1.8V and 15V. Therefore, for portability, a 3VDC battery is used to power the circuit.

According to the recommendation of the TDA2822MIC manufacturer, the output unit of this project uses 32 ohm headphones. According to the IC's datasheet, this 32-ohm headphone will produce approximately 1.3 watts of output. In the above circuit, capacitors C11 and C12 are called coupling capacitors. Their function is to block any DC components in the preamplifier input and output. The preamplifier consists of R5 and capacitor c13, which decouples the power supply of the preamplifier stage, while capacitor C12 and resistors R2, R3 and R4 form a negative feedback amplifier with transistor T1 to stabilize the overall gain (A). Resistor R4 is known as the emitter flood resistor and it also increases the stability of the amplifier. A medium power amplifier amplifies the preamplifier's output to audible levels. It consists of the TDA2822MIC and those external components required to make the IC work properly. Other external components are capacitors C14, C15, C16, C17, C18 and resistors R6 and R7. Resistor R5 and capacitor C13 form an RC decoupling circuit and are connected across the power supply to eliminate noise. Finally a 32 ohm headphone was used in the output unit.

Ear Amplifiers: Parts List

The components used are: condenser microphone, 1=2.2kΩ, 2=330kΩ, 3=680kΩ, 12=33Ω,

5=10kΩ, 6=220Ω, 7=4.7Ω, 8=4.7Ω,, 1=BC547A, 1=0.01, 4=100, 3=47, 4=10, 5=0.01, 6=100, 7=0.1 , 8=0.1, V1=10kΩ, LED-Red, TDA2822M, switch and battery (3V) and headphones.

The components of the ear sound amplifier circuit were first assembled on a breadboard and tested. After finding that it worked as expected, the components were transferred to Vero boards for final construction.