This miniature amplifier operates only on 1.5V battery. In case of application as Hearing Aid the battery shall be button cell. The headphone shall be of Mono type of 32 ohms impedance. All other components shall be SMT type to build the amplifier in a miniature size PCB. The PCB shall be approximately 1-square inch size.
AMPLIFIER: Sound detected by the electret microphone is fed to amplifier IC (ICL7611DCBA) through resistor R6 and capacitor C3 and C4. Resistor R3 and R6 determines the overall gain of the amplifier and C3 partially determines the amplifier’s frequency response. To ensure the proper operation using a single 1.5V battery as power supply and R4 and R5 simulates a null condition equal to half the power supply that feds to non-inverting input of the IC. The output of IC shall be transferred to emitter follower amplifier ‘TR’ via volume control R2. The high impedance input and low impedance output characteristic of the emitter follower matches the moderately high input impedance output of IC to a low impedance headphone load.
The amplification gain of the amplifier is determined by R6/R3. The normal gain is approximately 122. Though this 122 times gain is sufficient enough but, if the gain shall have to increase more, then R6 may be replaced by one 330K resistor and in this case the gain of the amplifier shall be approximately 183.
Now a days SMT soldering is much easier in home and the components are also available in the market. At the time of soldering of the SMT components proper enlarger Glass may be used to view and solder the components properly.