25 W Hi-Fi power amplifier circuit is a one of simple design that’s build by transistor NPN and PNP. The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, with the power transistors having 230W power dissipation and the drivers are 50W. The amp may also be operated at lower supply voltages for less power, but I do not recommend less than ±18V, which will provide around 15W into 8 ohms. This supply voltage (approximately) may be obtained by using a 15-0-15V transformer. This figure is show the circuit and operation of the circuit.
The supply voltage should be a maximum of ±25V. This supply is easily obtained from a 20-0-20V transformer. All resistors should be 1/4W or 1/2W 1% metal film for lowest noise, with the exception of R9, R10 and R15 which should be 1/2W types, and R13, R14 must be 5W wire wound. The bootstrap capacitor (C5) needs to be rated at least 25V, but the other electrolyc can be any voltage you have available. The potentiometer (VR1) must be a multi turn type, as the current setting is critical. Each of these amps will require a 0.25°C/W heat sink (very large). Consider using a fan or even water cooling to keep temperatures as low as possible.
The supply voltage should be a maximum of ±25V. This supply is easily obtained from a 20-0-20V transformer. All resistors should be 1/4W or 1/2W 1% metal film for lowest noise, with the exception of R9, R10 and R15 which should be 1/2W types, and R13, R14 must be 5W wire wound. The bootstrap capacitor (C5) needs to be rated at least 25V, but the other electrolyc can be any voltage you have available. The potentiometer (VR1) must be a multi turn type, as the current setting is critical. Each of these amps will require a 0.25°C/W heat sink (very large). Consider using a fan or even water cooling to keep temperatures as low as possible.
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