Amplified Ear: Build a Sensitive Sound Amplifier

Description

This circuit, connected to 32 Ohm impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard. You can also listen to your television set at a very low volume, avoiding to bother relatives and neighbors. Even if you have a faultless hearing, you may discover unexpected sounds using this device: a remote bird twittering will seem very close to you.

Circuit Diagram:

Parts:

Circuit Operation :

The core of the circuit is a constant-volume control amplifier. All the signals picked-up by the microphone are amplified at a constant level of about 1 Volt peak to peak. In this manner very low amplitude audio signals are highly amplified and high amplitude ones are limited. This operation is accomplished by Q3, modifying the bias of Q1 (hence its AC gain) by means of R2. A noteworthy feature of this circuit is 1.5V battery operation. Typical current drawing: 7.5mA.

Notes:

1N4148

The 1N4148 is a general-purpose diode, frequently used as a rectifier in power supplies or as a switching diode. It's a silicon diode with a typical forward voltage drop of 0.7V at a current of 1 Ampere. This component facilitates unidirectional current flow, effectively blocking current in one direction while allowing it to pass in the other. Its reliable performance makes it suitable for various circuit applications, providing both protection against reverse polarity and efficient current routing.

BC547

The BC547 is a general-purpose NPN bipolar junction transistor. This transistor is commonly used in switching and amplification applications. It features a moderate gain and is often selected for its small size and readily available supply. The BC547's widespread use stems from its versatility and its performance characteristics, making it a popular choice in both amateur and professional electronics projects. Its performance is influenced by factors like temperature and bias conditions, which can be adjusted to optimize its operation for specific needs.

BC337

The BC337 is another common NPN bipolar junction transistor, favored for its relatively high current gain and moderate voltage rating. It's frequently found in applications requiring intermediate amplification or switching. This transistor is known for its predictable performance, making it a reliable choice in many electronic circuits. The BC337’s performance is influenced by factors like temperature and bias conditions, which can be adjusted to optimize its operation for specific needs. Because of its characteristics, it is often preferred in circuits demanding moderate power handling and robust performance under varying conditions.