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Overview The circuit was designed to produce high quality and powerful audio amplifier that would provide 60W-90W power output. Terminology - MPSA43 – NPN high voltage transistor with low current and high voltage used for telephony, professional communication equipment, and telephony, and is the complement type of MPSA93
- MJE350 – a plastic medium power PNP silicon transistor designed for use in line-operated applications such as low power, line-operated series pass and switching regulators requiring PNP capability with features of high collector-emitter sustaining voltage, excellent DC current gain, and plastic thermopad package
- IRFP240 – an N-channel enhancement mode silicon gate power field effect transistor with an advanced power MOSFET designed, tested, and guaranteed to withstand a specified level of energy in the breakdown avalanche mode of operation used in applications such as switching regulators, switching converters, motor drivers, relay drivers, and drivers for high power bipolar switching transistors requiring high speed and low gat drive power due to features of high input impedance, linear transfer characteristics, nanosecond switching speeds, limited power dissipation, and single pulse avalanche energy rated
Circuit Explanation There are two diodes out of three that was replaced by a red LED in the original circuit where the three diode string was attached to R10 in a series connection. The replacement was done in order to achieve improved stability of quiescent current over a larger range of temperature. By means of an Avo-meter, the quiescent current can be measured by connecting the meter in series to the positive supply rail and no input signal. The transistors Q6 & Q7 should be fitted on a small and U-shaped heatsink while a larger heatsink is used to mount the transistors Q8 & Q9. For the regulation of voltage, the trimmer R10 is set to its minimum resistance which is made possible when powering ON the amplifier and then adjusting R10 until the drawing of the current reaches about 120 mA to 130 mA. If necessary, the current will need to be readjusted when after 15minutes, the current keeps on varying. In the parts used for power supply, the suggested value for capacitors C1 & C2 should be at the required minimum for a mono amplifier. The capacitance values may be increased up to 10000 uF when used in stereo configurations to achieved optimum performance. To eliminate ground loops and hums, an appropriate grounding is very essential. This will be done by connecting R1, R3, C2, C3, & C4 to the same point of the ground sides and the ground input wire while in the output ground, C7-C11 & R7 will be connected. Finally, the input and output grounds will be connected separately to the power supply ground. Application The 60W MOSFET audio amplifier may be used in automotive sound systems, home theater entertainment systems, and audio-video receivers to continually improve the quality of the audio. Source:redcircuits.com/Page100.htm
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