[Guangxi Normal University Competition] Practical Audio Amplifier

Team information: Chen Hao, Zhuang Wanxiu, He Dongyuan

Award information: First prize in school competition

Question requirements

1. basic requirements

(1) The sinusoidal signal input voltage amplitude of the amplification channel is 0.1~1Vpp; dual power supply DC power supply is used, and the voltage is not greater than +20V; when the equivalent load resistance R is 8Ω (the power amplification part is powered separately), the audio amplifier should meet: The maximum undistorted output power PoR ≥ 10W (distortion less than 10%), at this time the efficiency n ≥ 40%. Power amplification bandwidth BW≥ (40~20000) Hz. When the preamplifier input terminal is shorted to ground, the AC noise Vpp on RL=8Ω≤200m Vppo. The preamplifier has bass, midrange, and treble adjustment functions (the changes in bass and treble should be clearly heard during adjustment). With volume adjustment function.

(2) The preamplifier uses a conventional operational amplifier or triode, and no special preamplifier integrated circuit is allowed; the power amplification part is given priority to use discrete components.

(3) The circuit layout is reasonable and the interface is standardized and reliable. The signal source input uses a 3.5mm coaxial audio interface, and the power amplifier output interface uses an RCA "lotus head" female socket. The preamplifier and power amplifier parts can be tested separately; the preamplifier output interface and power amplifier input interface must be convenient for alligator clip (length 35mm) to access (the distance between GND and signal line in the interface is ≥5.00mm). Each module of the amplifier provides a GND interface for easy access with an alligator clip (length 35mm). All interfaces are clearly marked on the PCB using copper pours.

2. play part

⑴ Make a digital volume control circuit (special audio volume control integrated circuits are not allowed, and can be implemented with general-purpose digital circuits or single-chip microcomputer control circuits), and use light touch switches to increase or decrease the volume respectively, with a control level of no less than 8.

(2) Make a four-way audio source selection circuit and use a light touch switch to switch audio sources. 3. Function display, including but not limited to sound source selection display and volume level display.

(3) Make a sine wave generator for amplifier testing. The output frequency includes but is not limited to three frequency points: 100Hz, 1kHz, and 10kHz (frequency deviation ≤ ±5%). The output frequency is easy to switch or adjust.

(4) Others (such as homemade power supply, graphical display, wireless remote control, PCB touch buttons instead of tact switches, etc.).