USB Portable Speaker With Amplifier




Introduction: USB Portable Speaker With Amplifier

This is a very simple USB amplifier with just three components and a speaker, it can be used as a mono headphone amplifier too, the input powersupply is 5v obtained from the used this system can b used for listening songs while travelling and this circuit can work from powerbanks too. the component costs are so less too.

Step 1: Parts List

1 x common circuit board ( dot matrix board)

1 x 3.5 mm headphone socket

1 x 100uf electrolytic capacitor

1 x BC547 transistor

1 x 1K ohm resistor

Step 2: Circuit Diagram

complete the circuit according to the circuit diagram

Step 3: Conclusion

enjoy music all the way :), cheap and effective and can be made easily with very less components



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    2 Discussions

    Not very well. This is an old Class A topology popular in magazines and kits from the 1950's when transistors were very expensive for enthusiasts. It worked well enough for education and demonstration purposes but it was highly inefficient.

    However, the design presented is incapable of short term reliable operation and not recommended. In my testing, collector current with no audio input signal was 300mA which resulted in a power dissipation in the BC547 of 750mW. This is 125mW higher than the maximum device dissipation specified in the transistor datasheet, which is 625mW at 25 Deg C. 750mW power dissipation in combination with the thermal resistance of the plastic case will result in exceeding the maximum junction temperature of 170 Deg C in a matter of minutes. The amplifier may work for the short term but the BC547 will eventually fail. And that's before any music signal is applied. The circuit is burning 1.5W of power with no music to show for it.

    In this topology, a large amount of current is flowing through the speaker which causes the voice coil to heat up and the cone to be displaced from it's neutral position. This limits the amount of cone travel available for producing sound which reduces speaker efficiency and can damage the speaker.

    This is a Common Emitter amplifier without emitter degeneration resulting in an extremely low input impedance of around 18 ohms. You won't be able to drive the amplifier with anything other than another audio amplifier with sufficient power to drive a speaker.

    The temperature rise of the BC547 transistor makes the amplifier very noisy and overall gain difficult to predict.

    By any measure, the circuit described is not a practical audio amplifier. It's fine for a quick demonstration on what can be done with a few components, but it's not sufficient for regular use.