Since the sound from the heart showing small signal thus in amplifying the signal of the heart sound, power amplifier circuit is needed.
The op-amp chosen to be the amplifier is LM-386 since it amplify low noise, and the amplifier cater for low noise voltage amplifier. So, it is suitable for this project and it will make the sound audible.
Since the gain are from 20-200, then it is effective enough for the amplifier to amplify the heart sound since the heart sound frequency is in that range.
The figure below shows the 8 pin-out including labels of the op-amp.
The inputs are ground referenced while the output
automatically biases to one-half the supply voltage.
The quiescent power drain is only 24 mW when
operating from a 6-V supply, making the LM-386 is ideal for battery operation.
Moreover it make it more suitable for this project since, this product is going to get the power supply by 9V battery.
Amplifiers can be thought of as a simple box or block containing the amplifying device, such as a Transistor, Field Effect Transistor or Op-amp, which has two input terminals and two output terminals (ground being common) with the output signal being much greater than that of the input signal as it has been “Amplified”.
Table below shows the classification of amplifiers.
| Type of Signal | Type of Configuration | Frequency of Operation | |
| Small Signal | Common Emitter | Class A Amplifier | Direct Current (DC) |
| Large Signal | Common Base | Class B Amplifier | Audio Frequencies (AF) |
| Common Collector | Class AB Amplifier | Radio Frequencies (RF) | |
| Class C Amplifier | VHF, UHF and SHF Frequencies |
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