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Raspberry Pi HATs

Building a Class D Audio Amplifier HAT

Overview​

This tutorial walks through a Raspberry Pi HAT for a small stereo Class D amplifier. The design uses a PAM8403-compatible amplifier, a dual-gang volume control, local supply filtering, and terminal blocks for left and right speakers.

Requirements​

  • PAM8403 or compatible 3 W per channel stereo amplifier.
  • Dual-gang 10 kΩ audio potentiometer for volume control.
  • Left and right speaker terminal blocks.
  • 100 µF bulk capacitor and 100 nF bypass capacitor near the amplifier.

Step 1: Start with a HAT board​

import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
  <RaspberryPiHatBoard name="HAT1">
    {/* amplifier circuit goes here */}
  </RaspberryPiHatBoard>
)

Step 2: Add the amplifier and controls​

<chip name="U1" footprint="soic8" manufacturerPartNumber="PAM8403" pcbX={0} pcbY={0} />
<chip name="RV1" footprint="potentiometer_9mm" manufacturerPartNumber="Dual 10k audio pot" pcbX={-18} pcbY={0} />
<chip name="J1" footprint="terminalblock_2" manufacturerPartNumber="Left speaker" pcbX={18} pcbY={8} />
<chip name="J2" footprint="terminalblock_2" manufacturerPartNumber="Right speaker" pcbX={18} pcbY={-8} />

Step 3: Add filtering​

<capacitor name="C1" capacitance="100uF" footprint="cap_0603" pcbX={-6} pcbY={8} />
<capacitor name="C2" capacitance="100nF" footprint="0402" pcbX={-3} pcbY={8} />

Complete example​

import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
  <RaspberryPiHatBoard name="HAT1">
    <chip name="U1" footprint="soic8" manufacturerPartNumber="PAM8403" pcbX={0} pcbY={0} />
    <chip name="RV1" footprint="potentiometer_9mm" manufacturerPartNumber="Dual 10k audio pot" pcbX={-18} pcbY={0} />
    <chip name="J1" footprint="terminalblock_2" manufacturerPartNumber="Left speaker" pcbX={18} pcbY={8} />
    <chip name="J2" footprint="terminalblock_2" manufacturerPartNumber="Right speaker" pcbX={18} pcbY={-8} />
    <capacitor name="C1" capacitance="100uF" footprint="cap_0603" pcbX={-6} pcbY={8} />
    <capacitor name="C2" capacitance="100nF" footprint="0402" pcbX={-3} pcbY={8} />
    <trace from=".HAT1_chip .V5_1" to=".U1 > .pin4" />
    <trace from=".HAT1_chip .GND_1" to=".U1 > .pin2" />
    <trace from=".RV1 > .pin2" to=".U1 > .pin3" />
    <trace from=".RV1 > .pin5" to=".U1 > .pin5" />
    <trace from=".U1 > .pin1" to=".J1 > .pin1" />
    <trace from=".U1 > .pin7" to=".J2 > .pin1" />
  </RaspberryPiHatBoard>
)

Layout and test checklist​

  • Keep speaker output traces away from low-level audio inputs.
  • Use wider traces for power, ground, and speaker outputs.
  • Place speaker terminals at the board edge.
  • Verify there is no short between 5 V and ground before powering the HAT.
  • Start testing at low volume with inexpensive speakers.