Amplifier principle circuit diagram

Below is the schematic diagram of the Amplifier Circuit.

This 2x50W audio amplifier, designed for low-cost yet high-quality sound, costs less than 30 yuan. It can cover an area accommodating up to 600 people in open spaces like squares, delivering impressive sound reproduction. In Figure 1, a key feature of the design is the addition of negative current feedback via R4, R5, R6, and C2. This helps eliminate distortions caused by the speaker's voice coil inductance, improving overall sound quality. Adjusting R9 changes the operational mode of the device: increasing its value shifts the output toward Class A operation, while reducing it brings the output closer to Class B. When R9 equals 43Ω, the device operates in both Class A and Class B modes.

For selecting transistors, use a 500-type multimeter to ensure that the β values of Q5 and Q4 are similar, as well as those of Q6 and Q7, and Q1 and Q2. Q1, Q2, and Q5 utilize domestic N5551 transistors, while Q3 and Q4 employ N5401 types. Q6 and Q7 use Darlington transistors (model D1277), which cost about 2 yuan each. Resistors R6, R14, and R15 should be 5W ceramic types, and other components such as capacitors and inductors have standard specifications.

Once assembled correctly, the amplifier functions flawlessly, producing 50W of output power across two channels. Using two sets of dual-channel configurations with matching speakers ensures durability outdoors and provides excellent sound quality.

Components like Q1, Q2, and Q5 are built using domestically produced N5551 transistors, whereas Q3 and Q4 are made with N5401 types. Q6 and Q7 employ Darlington tubes (D1277 model). Resistor R6, along with R14 and R15, are selected from 5W ceramic resistor models. Other resistors and capacitors do not require any special characteristics. If soldered properly, the system operates smoothly, delivering a total output power of 50W over two channels. With two pairs of speakers, it performs reliably in outdoor settings and delivers satisfying sound quality.