Dual 105mW Headphone Amplifier with Digital Volume Control and Shutdown Mode

This is a low noise Headphone Amplifier capable of delivering 105mW per channel of continuous average power into a 16Ω load with 0.1% (THD+N) from a 5V power supply. The project is based on the LM4811 chip from the boomer series. The board provides high-quality output power with a minimal number of external components. It features a digital volume control that sets the amplifier’s gain from +12dB to −33dB in 16 discrete steps using a two−wire interface or onboard 3 tactile switches. On-board jumper implements the shutdown feature. The chip also has an internal thermal shutdown protection mechanism.

Connector CN1 Audio Input

• Pin 1 Audio Signal Input 1
• Pin 2 GND
• Pin 3 GND
• Pin 4 Audio Signal Input 2

Connector CN3 Power Supply

• Pin 1 +5V DC Input
• Pin 2 GND

Others

• Connector LS1 and LS2: Optional Speaker or Headphone Connection
• Connector CN4: 3.5MM Stereo EP Female socket for Headphone
• Connector CN2: External/Optional 2 Wire Gain Control
• Jumper J1: Closes = Enable, J1 Open Shutdown
• LED D1: Power LED
• Switch 1: Clock Input, Increment Steps
• Switch 2: Volume Down Operation
• Switch 3: Volume Up Operation

Features

• Operating Power Supply 5V DC
• Output 105mW Stereo
• On-Board Power LED
• Digital Volume Control Range from +12dB to −33dB
• “Click and Pop” Suppression Circuitry
• THD+N at 1kHz, 105mW Continuous Average Output Power into 16Ω 0.1 % (typ)
• THD+N at 1kHz, 70mW Continuous Average Power into 32Ω 0.1 % (typ)
• Low Shutdown Current
• 3 Tactile Switches to set the Gain
• Optional 3 Pin Header Connector for 2 Wire Interface for Micro-Controller for Gain
• On-Board Stereo EP Socket for Easy Headphone Interface
• Optional 2 x Header Connector for Headphone/Speaker Connections
• Header Connector for Power Supply
• Jumper for Shutdown
• PCB Dimensions 39.21 x 37.47 mm
• 4 x 2.5MM Mounting Holes