AC dual 12-18V LM1876 power amplifier board with speaker protection (finished product)

LM1876 is a high fidelity dual channel audio amplifier chip produced by National Semiconductor in the United States. The operating voltage range of the integrated circuit is AC dual 12V - dual 21V, with a continuous average output power (8 Ω load) of 30 W per channel. The total harmonic distortion plus noise (THD+N) is only 0.112% at a continuous power of 30 WX2; The signal-to-noise ratio is as high as 102dB

In addition to two power amplifier circuits with the same function, the LM1876 integrated block also has various safety protection circuits, including overvoltage and voltage loss automatic power-off protection, overload and short circuit protection, and over temperature protection (automatic output shutdown at 165 ℃ and automatic recovery at 155 ℃), to protect the power amplifier IC from damage in any working state. LM1876 also integrates a power on mute circuit internally, overcoming the defect of LM1875 power on shock!

Board features:

1. Easy to install, LM1876 chip is designed on the right side of the board, making it very convenient to fix the chip.

2. Strictly adhere to the principle of grounding, separate the wiring layout for high current ground and low current ground, making the low noise of this board almost imperceptible.

3. The input terminal is closely adjacent to the input pin of the chip, making the input terminal wiring the shortest and minimizing interference.

4. The power supply of the relay is provided by a voltage regulator block and a heat sink, which is stable and reliable. General power amplifier boards use current limiting resistors to supply power to relays, which are easily affected by input voltage. When the input voltage is high, the relay generates more heat, and when the input voltage is low, the relay does not close tightly, resulting in high contact resistance.

In terms of materials:

1. The board is a 1.6mm fiberglass board with a one point grounding design. The board size is 120 * 72mm.

2. The rectifier bridge is an original SEP from Taiwan, the filter is a Japanese Nikon capacitor with 2200UF35V, the decoupling is a Japanese 100UF capacitor, the input coupling is Siemens from Germany, the Beryl circuit is Siemens, the negative feedback is ELNA blue robe, the resistors are all five ring gold film copper pins, the relay is Omron, and the chip is disassembled from the original equipment.

Installation and usage precautions:

1. The board integrates rectification and filtering transformers for direct power supply. It is recommended to use dual 15-18V transformers with a power not less than 60W for the power supply!

2. The output impedance of LM1876 is designed to be 8 Ω. If you want to drive a 4 Ω speaker, it is recommended not to exceed a dual 16V voltage and to increase the heat dissipation area.

3. This chip is TF version and does not require the installation of insulation particles or sheets. You can apply some silicone grease appropriately!

4. During power on testing, the signal input terminal on the board should be connected to the load and not suspended, otherwise there will be induced noise. Shielded wires should be used for signal lines as much as possible.

5. If the board is installed in the chassis, it is necessary to connect the outer shell of the chassis to the input ground wire on the board (short circuit J1 on the board with a jumper). If a front-end and back-end input ground are added, there is no need to connect the chassis again. Just connect the front-end input ground to the chassis. If both are connected, it will cause a ground loop and generate noise.