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Mic and speaker
Today we are going to discuss about a Low cost, compact Audio Pre-Amplifier with Loud speaker. By using this device you can hear your voice loudly with a better quality. The circuit provides an output power of about 0.5 watts by just 5V supply. It can be used as a part of intercoms, walkie-talkies, pocket radio receivers etc… all the components used in this project are readily available in the market at low cost.







COMPONENTS REQUIRED

IC 1 – BEL1895


T1 & T2 – BC148 NPN


Loud Speaker 4Ω 1W


Condenser Mic


Battery 6v

CIRCUIT DIAGRAM

audio pre amplifier circuit




WORKING PRINCIPLE                                                                                                                                

For better understanding we can divide  the circuit  into two sections

1) High gain Mic Pre-Amplifier

2) A.F Power Amplifier


High Gain Mic Pre-Amplifier

It consists of a condenser mic, a variable resistor and two NPN transistors (BC148) with some passive components such as Resistors and Capacitors.

  • Condenser Mic

It is basically a transducer, used to convert  audio(speech) signals to electrical signals. The commonly used condenser mic’s are cylindrical in shape in which its top most part is enclosed by a sensitive diaphragm. The diaphragm vibrates with respect to our voice, hence the carbon granules filled inside it. This offers a variation in output resistance which in turn varies the voltage directly. This minute variation in electric voltage with respect to our voice is amplified in the further stages.

  • Variable Resistor

It is  a 10kΩ variable resistor, used to control the gain of audio pre-amplifier by adjusting this we can increase or decrease the output gain.

  • NPN Transistors T1 & T2

The circuit uses two stage RC coupled amplifier to increase the gain of signal coming from condenser mic. The transistors are biased by a voltage divider network to provide proper stabilization.


A.F Power Amplifier

Audio frequency power amplifier section consisting of IC BEL 1895, it  is a monolithic audio power amplifier designed for AM radio applications. It delivers 1Watt output power at 6V supply voltage. BEL1895 ic exhibits low distortion and noise with an operating range of 3-9V. The output is taken from pin1 which drives the loud speaker.

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  1. i want a ckt for audio amplifier to use two speakers and input through audio jack

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