Audio Power Amplifier

Measure voltage across the 1k resistor connected to the input stage and Vcc. The DC voltage should be about 2 volt, or 2 mA of current through this resistor. Eg, if Vcc is at 24 volts, the side of this resistor connected to the 2N5210 transisor ought to be at about 22 volts. Turn the variable resistor slowly until the amplifer`s current consumption is approx 50 mA. Turn slowly
Audio Power Amplifier - schematic

and be careful. if you turn too far you could damage the output transistors. Conect an oscilloscope to the output and apply a low amplitude 20 kHz square wave to the input. DO NOT connect any speakers during this test. This test should be done without the 330 pF capacitor installed. The amp should output a 20 kHz square wave with very little "ringing". It should not oscillate. Shut off the power, connect audio input and a speaker. Make sure the volume is turned all the way down. Apply power. watch current meter again and shut off the power immediately if the current jumps to something much higher than 50 mA. Slowly turn up the volume and see if the amp works. DO NOT turn it up very much. the amplifier should not be operated with a supply less than +/- 30 volts. It should never be used for high volume output without a power supply rated for at least 2 amps of current (8 ohm load). After this initial test with +/- 24V at 200 mA (current limited) only a proper power supply should be used which can provide enough current.

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