The simplest triode audio amplifier circuit

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The simplest triode audio amplifier circuit involves adjusting the value of R1 to ensure that the signal remains distortion-free at maximum output, while also allowing for greater power output. If you have a multimeter available, you can fine-tune the voltage at the collector (C) to approximately half of the power supply voltage. This helps maintain optimal operating conditions for the transistor.



Figure 1 shows a fixed bias configuration, where the power supply voltage has a significant impact on the bias current. This basic common-emitter circuit is straightforward but sensitive to voltage fluctuations.



In Figure 2, the circuit incorporates negative feedback, which reduces the overall gain but makes the bias current less affected by changes in the power supply voltage. This type of voltage feedback configuration allows the circuit to operate over a wider voltage range, making it more stable and reliable.

This class A amplification design is known for its simplicity, although it has the lowest efficiency among amplifier classes. It's rarely used in low-voltage applications due to its limited output power. However, it is still commonly applied in power-driven circuits where both voltage and current amplification are required.