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This is the 25W Class-A power audio amplifier circuit. The output devices are MJL4281A (NPN) and MJL4302A (PNP), and have high bandwidth, fantastic SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, using the power transistors having a 230W dissipation and the drivers are 50W. 25W Class-A Power Audio Amplifier Circuit Diagram  The supply voltage must be a maximum of ±25V. This supply is simply obtained from a 20-0-20V transformer, recommended current is 1A.  All resistors ought to be 1/4W or 1/2W 1% metal film for lowest noise, with the exception of R9, R10 and R15 which ought to be 1/2W varieties, and R13, R14 have to be 5W wirewound.  Using the suggested and advised 25V supplies, Q4 will typically not need a heatsink. The output drivers (Q5 and Q6) recommended to use a heatsink, even though it doesn’t have to be big.

I have built this amplifier and it does sound good. It requires a preamp as it hasn't got much gain. It requires big heat sinks and a large transformer and a great power supply and careful wiring, but in the end it is xtremely simple and it sounds very good. The zener diode rejects any ripple coming from the power supply, But you still only want a ripple of 10mV max. The ripple reaching the input is amplified, so the zener diode gets rid of that, but whatever ripple there is will still reach the power stage.  10 to 14W Class A Audio Amplifier Circuit Diagram

With LM4651 & LM4652 The combination of the LM4651 driver IC and the LM4652 power MOSFET Class D power amplifier IC provides a high efficiency amplifier solution, suitable for self-powered speakers, subwoofers and quality car boosters . The LM 4651 is a fully integrated conventional pulse width modulator (PWM) driver, containing undervoltage, short circuit, overmodulation, and thermal shutdown protection circuitry. The IC features a standby function which shuts down the pulse width modulation, minimizing supply current. The LM 4652 is a fully integrated H-bridge Power Mosfet IC in a TO220 power package. The IC has a built in temperature sensor to alert the LM4651 when the die temperature exceeds the threshold limit. Used together, the LM4651 and LM4652 form a simple, compact, efficient, high quality power audio amplifier solution complete with protection, normally seen only in Class AB amplifiers. The maximum efficiency of this circuit is 85% at 125W with a standby attenu...

This is the 25W Class-A power audio amplifier circuit. The output devices are MJL4281A (NPN) and MJL4302A (PNP), and have high bandwidth, fantastic SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, using the power transistors having a 230W dissipation and the drivers are 50W. 25W Class-A Power Audio Amplifier Circuit Diagram  The supply voltage must be a maximum of ±25V. This supply is simply obtained from a 20-0-20V transformer, recommended current is 1A.  All resistors ought to be 1/4W or 1/2W 1% metal film for lowest noise, with the exception of R9, R10 and R15 which ought to be 1/2W varieties, and R13, R14 have to be 5W wirewound.  Using the suggested and advised 25V supplies, Q4 will typically not need a heatsink. The output drivers (Q5 and Q6) recommended to use a heatsink, even though it doesn’t have to be big.