# Sixth Lichuang Electric Competition# High-fidelity desktop 2.0 channel amplifier

Part of the circuit in this design refers to the circuit in @winton's "[Course Design] TPA3116+M18 Bluetooth Digital Power Amplifier". Hereby explain

1. Description

      1. Function description

             1), AUX audio input + Bluetooth two-in-one input, inserting AUX will automatically cut off the Bluetooth input

             2) TDA7492P13TR is a BTL class D audio power amplifier produced by STMicroelectronics, with an output power of up to 25W*2.

      Working voltage 8V-26V, THD + noise >0.4%.

             3) Bluetooth version 4.2, with high transmission efficiency and long distance.

       2. Parameter description

             1). Power supply voltage: DC-005 connector is used, power supply range: 13V-24V. After that, they are respectively stepped down by LDO and powered by the preamplifier circuit, Bluetooth module, and function selection circuit.

             2) Preamplifier circuit: The preamplifier circuit is borrowed from the circuit in @winton's "[Course Design] TPA3116+M18 Bluetooth Digital Power Amplifier". Powered by NE5532 single power supply. NE5532 mostly uses dual power supplies in conventional audio circuits.

      The audio input terminal adopts the input interface as shown in the figure. This interface has its own audio switching function. When AUX is inserted, the Bluetooth input to the preamp is automatically cut off.

         3). The M18 Bluetooth module is an existing module bought on Taobao and can be adjusted with 4 buttons.

         3. TDA7492 circuit introduction

             The chip has two working modes: silent and standby. This design only uses the silent mode, the silent control pin pin 21, the low-level silent mode. The Bluetooth module defaults to high-level silent mode, so a transistor is added for level conversion.

          The chip can be set externally for gain setting. In this design, a fixed gain is used, and the gain control is added to PIN 30 and PIN 31. Each is connected to the internal LDO of the chip. The gain is controlled at 33.6dB.

      Refer to the chip manual for the output low-pass network. Under 4Ω load, choose 15uH inductor and 470nF capacitor. Try to choose an inductor with a larger current capacity to avoid inductor saturation during bass.

2. PCB display

3D (contest logo needs to be verified)

3. Test

       There was no speaker and no high-power cement resistor was found, so I only tested the input and output waveforms under no load. See the video for details.

       During the test, the 15V power supply voltage used showed clipping distortion when inputting high amplitude in the low frequency band. Increase the power supply voltage and attenuate the input, and the distortion will disappear naturally.

      There is inconspicuous crossover distortion in the high frequency band, which is related to the input capacitance of the oscilloscope's test leads. It may disappear after adding a load. Test again after adding a speaker behind it.

4. Physical photos