This PA amplifier circuit is like a super powered bullhorn for your voice!
It takes your voice from a microphone and makes it much louder so a whole crowd of people can hear you clearly.
This is perfect for big places like schools, offices, stadiums or even parties where you need everyone to hear the same message.
Circuit Working:
Parts List:
| Category | Item | Quantity |
|---|---|---|
| Resistors | 56k | 1 |
| 1M | 1 | |
| 12k | 1 | |
| 220Ω | 1 | |
| 33k | 1 | |
| Potentiometer | 10k | 1 |
| Capacitors | Ceramic 0.1µF | 2 |
| Ceramic 0.01µF | 1 | |
| Electrolytic 10µF 25V | 1 | |
| Electrolytic 100µF 25V | 1 | |
| Semiconductors | IC LM380 | 1 |
| Transistor BC547 | 1 | |
| Others | 8Ω Speaker | 1 |
| ON/OFF Switch | 1 | |
| Electret MIC | 1 | |
| Battery 6V 4.5Ah | 1 |
This circuit is designed to be used like a public address amplifier, particularly in noisy environments where it can help reduce the strain of giving vocal speeches.
It utilizes the LM380 power amplifier IC which provides a 2 watt output suitable for giving speeches in public areas.
The amplifier is compact and can be enclosed within the speaker box along with the battery making it portable.
The circuit includes a preamplifier stage using the NPN transistor BC547 and a power amplifier stage using the LM380.
An external collar microphone can be connected to the input using an audio jack.
The voice signals are amplified by transistor T1 and fed to the LM380s input through the volume control VR.
Capacitor C3 helps reduce undesirable howling from the speaker.
The LM380 is a versatile audio amplifier with a fixed gain of 34 dB.
It is designed to be short circuit proof and includes internal thermal limiting for added protection.
The IC operates on a DC voltage range of 5 to 22V and is available in a dual in line package.
To assemble the classroom microphone system circuit you can use a common PCB.
A 9V PP3 battery can be used to keep the unit compact but for extended use a 6V 4.5 Ah rechargeable battery is recommended along with a provision for a charger input.
It is advisable to use a small high quality 8 ohm speaker.
If the output power is insufficient consider using a higher power amplifier IC in place of the LM380.
Electrical Characteristics of IC LM380:
| Parameter | Symbol | Conditions | Min | Typ | Max | Units |
|---|---|---|---|---|---|---|
| Output Power (RMS) | POUT(RMS) | RL=8Ω, THD = 3% (2) (3) | 2.5 | W | ||
| Gain | A_W | 40 | 60 | V/V | ||
| Output Voltage Swing | V_OUT | RL=8Ω | 14 | Vp-p | ||
| Input Resistance | Z_IN | 150k | Ω | |||
| Total Harmonic Distortion | THD | 0.2 | % | |||
| Power Supply Rejection Ratio | PSRR | 38 | dB | |||
| Supply Voltage | V_S | 10 | 22 | V | ||
| Bandwidth | BW | RL=8Ω | 100k | Hz | ||
| Quiescent Supply Current | I_Q | 7 | 25 | mA | ||
| Quiescent Output Voltage | V_OUTQ | 8 | 9.0 | 10 | V | |
| Bias Current | I_BIAS | Inputs Floating | 100 | nA | ||
| Short Circuit Current | I_SC | 1.3 | A |
How to Build:
To build a Simple Public Address Amplifier Circuit you need to follow the below mentioned connections steps:
Preparation:
- Gather all the components and tools needed for soldering and assembly.
Circuit Design:
- Refer to the circuit diagram for the audio amplifier.
- Ensure you understand the connections and component placements.
PCB Layout:
- Design or obtain a PCB layout that matches the circuit diagram.
- This will guide you in placing the components on the board.
Component Placement:
- Begin by placing the IC sockets followed by the resistors, capacitors, transistors and other components on the PCB according to the layout.
Soldering:
- Solder the components onto the PCB ensuring good connections and avoiding solder bridges.
Wiring:
- Connect the microphone, volume control, audio jack and speaker to the appropriate points on the PCB as per the circuit diagram.
- Once the circuit is assembled test it with a power source and audio input to ensure it functions correctly.
Enclosure:
- If desired, place the PCB, battery and other components inside a suitable enclosure such as the speaker box for protection and portability.
Final Testing:
- Test the amplifier again in its enclosure to ensure everything works as expected.
Finalization:
- Secure all components and wires in place and label any necessary controls or inputs.
Note:
- Remember to follow safety precautions when working with electronic components and soldering equipment.
- If you are unsure about any step, it is best to seek guidance from someone with experience in electronics assembly.
Conclusion:
The goal of a public address amplifier circuit is to amplify the audio signal from a microphone or other input source and deliver it to one or more speakers with sufficient volume and clarity to be heard by the intended audience.
The design and power output of a PA amplifier circuit depend on the size of the area to be covered and the expected ambient noise level.