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300 Watts Output High Power Audio Amplifier
The circuit has been designed to produce an audio amplifier that can be used for low efficiency speakers or outdoor sound systems since it can deliver 300W of power.
- Power Amplifier – a type of amplifier built and designed for the purpose of delivering and supplying sufficient and maximum high output power to directly drive loudspeakers or loads, within a given percent of distortion
- BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections
- MJ15003 – a ballasted epitaxial-base silicon NPN high power transistor used for series and shunt regulators, solenoid drivers, power switching circuits, high-fidelity amplifiers, and other industrial and commercial use due to its features such as high gain at high current, maximum safe-area-of-operation curves, low saturation voltages, rugged design, and high dissipation capability
The construction of the circuit consists of three parts which includes the input stage, the power stage, and the power supply. The input stage produces the high gain as it functions as the low power driver while it comprises of transistors Q1 to Q9 while the output stage provides massive power gain although it only has a voltage gain of four. The input stage has its own current source in each side as it functions as a complementary differential network. A collector current of approximately 0.7 mA is used to run the transistors at the input stage. The improvement of linearity and gain stabilization is done by the emitter resistors.
The transistors Q7 & Q9 are virtually two constant-current sources that conducts at 7 mA and is driven by the output of Q1-Q5. An out of phase modulation is performed by these virtual current sources during an input signal, where the collector current of one decreases while the other increases. A sufficient amount of gain is provided by this configuration.
Within the virtual current sources is the transistor Q8 that functions as the thermal sensing bias transistor with a voltage regulated by TR1 as it sets the quiescent bias current for the output stage. The output stage has a gain of five, consisting of Q10-11, Q13-14, and Q16-17, which are set by R44, R28, and R29. The reverse biasing of Q10-11 is prevented by the presence of diodes D4 & D6, which could limit the output otherwise.
Q12 & Q15 provides the protection of the output transistors and monitors both voltage and current in the output transistors while the base current is bypassed if the limit is exceeded. The RC networks R31/C10 and R46/C15 and the combination of capacitors C6, C11, and C12 provide the stabilization of frequency. The upper frequency limit is set by C6 while the lower frequency response of the amplifier is set by C1 and C7. As an alternative option, a balance/bridge and DC protection circuits can be used.
An aluminum box should enclose all the transistors that are inside the interrupted line while attached to a suitable heatsink. Isolated from this group are the transistors Q7-11, Q13-14, and Q16-17.
The 300 W power amplifiers are widely optimized in commercial installations, video conferences systems, houses of worship, hotels or motels, for driving small & medium-sized live PA systems, for bars, clubs, & restaurants, for live sound venues, and for industrial & retail stores. They are mostly preferred since they deliver reliable power, low distortion, and clean output in any occasion and in any time of events.