Mini Amplifier with 2 Watts Output

Parts List

The objective of the design is to build an amplifier circuit that can be contained in a small loudspeaker box while producing a power output of 2 Watts.

• BC560 – a PNP epitaxial planar Silicon enclosed in a 24-pin dual in-line package or 3-pin TO-92 package typically used for switching and AF amplification due to its low noise and high voltage features
• BC337 – a small signal NPN Silicon 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
• TIP31 – a standard type of NPN bipolar junction transistor used for medium power linear switching applications

The assembly of the circuit did not include and integrated circuit intentionally and in order to achieve behaviour of good harmonic distortion by using an assembly in an old fashioned way which can also help in avoiding components that are hard to find. A wall plug-in adapter with 12 V rating can provide a voltage supply for the amplifier.

A bass-boost is provided by closing the SPST switch SW1 and simultaneously increasing the control of the volume for the compensation of power loss during higher frequencies. To provide minimal crossover distortion at the audible signals, the resistor R9 should be regulated cautiously. The distortion is always consistently present with minimal quiescent current consumption that is being measured. It would be better to set the quiescent current at approximately 10 mA to 15 mA. A DC current meter is wired temporarily in series with the collector of Q3 to measure the quiescent current.

The total harmonic distortion differs from the type of speakers used wherein 0.5% is obtained from 2 Ohm with 2 W speaker, 0.3% from 4 Ohms with 2 W, and 0.2% from 8 Ohms with 1 W. the frequency response at 1 dB gain is ranging from 30 Hz to 20 KHz.

This 2 W amplifier can feed small electronic gadgets such as CD players, Walkman, iPod, Mini-Disc, computers, and other devices similar for as long as the headphone output will be fitted on them. They can also be used for self-powered 2 Ohms, 4 Ohms, & 8 Ohms loudspeakers.

Source:redcircuits.com/Page33.htm