Class A power amplifier designed by three-terminal regulator LM317

The power amplifiers that have been successfully produced with the voltage regulator set are of no positive significance for electronic enthusiasts as an attempt to develop ideas. The circuit works for pure class A, and uses low-noise tube for voltage amplification. Therefore, THD, NF and other indicators are good, and the output power can reach 30W.

As shown in the figure, the transistor VT1 is amplified as a voltage. Since the input impedance of the voltage-stabilizing integrated circuit IC1 is high, it is sufficient that the operating current is only 0.6 mA. R1 and C3 are power supply decoupling, and C4 is used to prevent parasitic oscillation. The R3 and R4 partial voltages provide bias and AC-DC feedback to VT1 to improve linear and DC stability. VT2, R5, R6 and diode form a constant current source to improve the efficiency and output power of the circuit and increase the output dynamic range.

Because the circuit is particularly simple, the components can be lap soldered. The constant current of the constant current source can be set at 10~15mA. When debugging, the output voltage of the LM317 can be adjusted to half of the power supply voltage. The quiescent current is about ten milliamperes. The power transformer T1 power must not be less than 50W.

The three-terminal regulator IC selects LM317, and the triode VT1 selects 9014. VT2 selects 8050 type, diode VD5, VD6 selects 2CP20, the power of transformer should be greater than 50.

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