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Audio Circuit With Voice-Over Capability

2016-01-16 23:43  
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Figure 1 

The purpose of the design of the circuit is to demonstrate the effectiveness of the preamplifier circuit and microphone over any audio signal.

In the entertainment world, the term voice over refers to the narrative method or technique by which a film maker places the sound of a human voice or voices over images, which may or may not be related to the images being shown.

The use of preamplifier is to amplify the low level signal to line level. Included in the list of common low-level signal sources are microphone, turntable or other musical equipment. Compared to a one way intercom, the amplifier switches from being an music output device to being an voice output device. The voice over component itself is a simple microphone and a switch mechanism attached to an amplifier, where the output from the microphone will take precedence to the audio signal upon pushing the push-to-talk button. This device is intended to function away from the main amplifier while the voice signal travels across the long cable. The change over switch consists of a relay with a single contact.

LM380 will be utilized because of its features such as low distortion, standard dual in-line package, high peak current capability, wide supply voltage range, fixed voltage gain, high input impedance and low power drain. It is widely used for consumer applications as a power audio amplifier. The connection between the amplifier, switching unit and microphone requires three wires.

The preamplifier consists of two BC109C transistors whose general purpose is switching and amplification. Using a long cable is possible because of the blending of high gain and low output impedance, which makes it invulnerable to noise & hums. The type of microphone used is electret condenser that uses a permanently charged material to supply power. The use of 1 K ohm resistor is to eliminate the DC component on the audio output while the potentiometer controls the volume of the audio input.

These type of equipment is now being used in malls and supermarkets to call the attetion of the shoppers and buyers. ?t may also be used in the campuses, hospitals, airports and other public and government premises.


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