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Battery Powered Portable Amplifier for Headphone Use

2015-01-01 16:17  
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Figure 1 

Part List
The circuit was designed for high performance unit as it serves as a portable amplifier for headphones while being powered with 3 Volts.

Amplifier – an electronic device used for intensifying the amplitude or power of a transmitted signal by manipulating the output to counterpart the input signal but with larger amplitudeBC239 – anNPNgeneral purpose transistor used for general purpose switching and amplification due to its low current with maximum 100 mA, low voltage with maximum 45 V, and enclosed in a T0-92 & SOT54 plastic packageBC337 – a small signalNPNSilicon AF medium power transistor used for general purpose switching and amplifying applications with features such as TO-18 manufactured package, suited for AF driver stages and low power output stages, and divided into three group types

Several headphones of different models can be tested with this circuit. They may either have separated impedances which come in the values of 32, 100, 245, 300, 600 & 2000 Ohms. Only the left channel is being shown by the diagram where a common channel is shared by battery B1, single pole single throw switch SW1, 3 mm stereo jack socket J1, and capacitor C3. The default value of resistor R3 in this circuit is set for headphone impedance up to 300 Ohms. The increase in resistance of the load for about 600 Ohms or higher, will cause the value of R3 to change to 100K Ohms.

The circuit may be upgraded by using a lithium ion prismatic rechargeable battery with a nominal voltage of 3.7 V and 1200 mAH current rating. When using a 32 Ohm impedance and 3.7 V, the exact value of R3 will be 100K Ohms. The amplifier at this specific stage will be delivering an approximately 3 V peak-to-peak value of undistorted output. This would signify that a supply of 3 V would make the output power on 32 Ohm load to be almost double the original output. This would also result to a 40 mA of current being drawn. The battery will last for approximately 15 hours when powering an amplifier that is a stereo version.

The portable headphone amplifier may be directly connected to tape recorders, tuners, and CD players. It will provide more volume and better audio quality to overcome the low output power of any audio player by delivering rich audio without distortion, hi-fi sound enhances high, mid, & bass ranges, decreases the battery drain on audio players, and it drives headphones with 16 Ohms to 600 Ohms. Aside from portable players like iPods, it can also be used on laptop computers and electronic toys and games.

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