Small Discrete Audio Power Amplifier

Posted on Feb 4, 2014

This is a little audio amplifier, it is similar to the audio amplifier which is used in small transistor radio. This circuit draws about 30 milliamps from a 9 volt supply. This circuit consist of two stage. First stage is input stage (2N3053 transistor) and the other is output stage (2N3053 and 2N2905 transistor pair). Here is the schematic diagra

Small Discrete Audio Power Amplifier
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m of the circuit : Supply voltage is divided equally across the two complimentary output transistors which are slightly biased in conduction by the diodes between the bases because the input stage is biased. To stabilize the bias current so it doesn`t change much with different transistors and diodes or with temperature. This circuit uses a 3. 3 ohm resistor that assembled in series with the emitters of the output transistors. The voltage between the base and emitter decreased, because the bias current increased, so it is reduce the conduction. This circuit has voltage gain about 5 with an 8 ohm speaker attached and input impedance about 500 ohms. In the output stage, the voltage swing on the speaker is about 2 volts without distorting. The power output of this circuit is in the 50 milliwatt range. To provide more power we must use the addition of heat sinks to the output transistors and a higher supply voltage. With LM1875, we can build a low cost but high performance audio power amplifier. With 50V power supply, it can produce 20W output power for 4 or 8 ohm speaker. We can even get 30W output if we use 60V Continue reading †’. This audio power amplifier is very good for your portable devices, or for your headphones amplifier. The circuit of this audio power amplifier is very simple, consist of only seven components. Here is the schematic diagram of the amplifier circuit: Continue reading †’. The transistor is biased in...

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