This 2x50W audio amplifier, with its low cost and excellent sound quality, costs less than 30 yuan. It is suitable for venues hosting gatherings of up to 600 people, delivering impressive sound reproduction. Figure 1 presents the circuit diagram. One notable feature of this design is the inclusion of negative current feedback through R4, R5, R6, and C2, which helps eliminate distortion caused by the inductive voltage from the speaker's voice coil, thus enhancing the device's sound quality. Adjusting R9 changes the operational mode of the amplifier: increasing R9 shifts the output towards Class A operation, while decreasing R9 moves it closer to Class B operation. A resistance value of 43Ω represents the transition point between Class A and Class B modes. When selecting transistors, ensure that the β values of Q5 and Q4 are close, as well as those of Q6 and Q7, and Q1 and Q2.
For the transistors, Q1, Q2, and Q5 use domestic N5551, Q3 and Q4 use N5401, and Q6 and Q7 utilize Darlington tubes D1277 (a disassembled product costing around 2 yuan each). Resistors R6, R14, and R15 should be 5W ceramic types, while other RC components do not require special specifications. As long as the soldering is done correctly, the unit operates reliably, producing an output power of 50W. Two sets of dual-channel configurations form the system, utilizing two speakers. The amplifier proves durable for outdoor use and delivers satisfying sound quality.
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Below is the circuit diagram of the Amplifier schematic circuit diagram.
