Simple LM317 Audio Amplifier Circuit

This Simple LM317 Audio Amplifier Circuit is a kind of like small trick for make speaker sound louder.

LM317 chip usually is used to control voltage but here it works like small music booster amp.

Not very strong amp but still help give little more sound from the music source.

It can work, yes but not same like real audio amplifier but it have some limits.

Good for learning project but if want big sound or serious audio better use other amplifier.

Circuit Working:

Parts List:

Audio signal come from input like phone or MP3 player which connects into LM317 chip using 10µF 25V capacitor.

This capacitor stop any DC from input and only let audio signal connects through.

LM317 work like constant current source and 5k pot variable resistor that set the current.

This resistor change bias of LM317 and control how much current move in the circuit.

LM317 also act like voltage regulator and keeps output voltage stable at pin 2 or across 10Ω resistor which is around 4.5V.

Stable voltage is important for amplifier to work good.

Then amplified audio connects to speaker through another capacitor 470µF 16V.

This second capacitor stop DC again and so only audio signal connects to speaker.

This amp is class A type and can give around 1 watt power which is not super strong but sound quality is nice for less distortion.

So this LM317 class A amp is easy and cheap way for small audio boost with good sound.

Formulas:

This circuit use LM317 voltage regulator chip to make a simple audio amplifier.

Even though LM317 main job is to control voltage but it can also work as amplifier in some setups.

Power Output:

To estimate maximum power output it uses this formula:

Pout = (Vrms²) / R

where,

• Pout is the output power in watts
• Vrms is the RMS voltage across the speaker
• R is the speaker impedance which is 8 ohms here.

Note:

This formula does not consider efficiency losses but it can just give a rough idea of power.

If we want better performance like think about using an IC made just for audio amplifying.

This will usually give better efficiency, less noise and clearer sound.

How to Build:

To build a Simple LM317 Audio Amplifier Circuit follow the below mentioned steps:

Circuit Design:

• Connect LM317 like constant current source and set output using 5k pot variable resistor.
• Use 10µF 16V capacitor to cut noise from input sound.
• Add one more 10µF capacitor to help keep output voltage stable.
• Put 470µF 16V capacitor at output side this send audio signal to speaker.

Circuit Assembly:

• Put all parts on PCB like in circuit diagram.
• Be sure all wires, capacitor sides and LM317 pins connect right.

Final Step:

• After everything work fine put LM317 on heatsink so it do not get too hot.
• Tight all parts good so they stay fixed for long use.

Note:

• Be careful when working with electric stuff and always check before putting the power ON.onents and circuits.

Conclusion:

To conclude Simple LM317 Audio Amplifier Circuit is easy and cheap way to make sound louder for small power use.

By setting LM317 like class A linear amp it gives good sound with low distortion.

But it is important to use heatsink because LM317 gets hot and heatsink help it work safe and for long time.

References:

Datasheet IC LM317

Simple Class-A Amplifier with an LM317