Skip to content

Add Class D Audio Amplifier HAT tutorial #654

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
junn-dev wants to merge 1 commit into
base: main
Choose a base branch
from
+202 −0
Open

Add Class D Audio Amplifier HAT tutorial #654

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
202 changes: 202 additions & 0 deletions docs/tutorials/class-d-audio-amplifier-hat.mdx
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,202 @@
---
title: Class D Audio Amplifier HAT
description: Build a Raspberry Pi HAT around a PAM8403 stereo Class D amplifier with volume control and speaker terminals.
---

import CircuitPreview from "@site/src/components/CircuitPreview"
import TscircuitIframe from "@site/src/components/TscircuitIframe"

## Overview

This tutorial builds a compact stereo Class D amplifier HAT using a PAM8403.
The PAM8403 can drive small left and right speakers at up to 3W per channel from
a 5V rail, making it a practical choice for simple Raspberry Pi audio projects.

The HAT includes audio input pins, a dual-gang volume control, the amplifier IC,
speaker terminal outputs, and local decoupling for the power rail.

## How Class D Amplification Works

A Class D amplifier rapidly switches its output transistors instead of operating
them in a continuous linear region. The speaker receives a filtered version of
that switching waveform. This approach is efficient, produces less heat than a
linear amplifier, and works well for battery-powered or compact boards.

## Circuit Requirements

The board needs:

- PAM8403 stereo Class D amplifier
- 5V and ground from the Raspberry Pi HAT header
- left and right audio inputs
- volume control before the amplifier inputs
- left and right speaker terminal outputs
- decoupling capacitors near the amplifier supply pins

## Final Circuit Preview

<TscircuitIframe defaultView="3d" code={`
import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
<RaspberryPiHatBoard name="HAT1">
<chip
name="U1"
manufacturerPartNumber="PAM8403"
footprint="sop16"
pinLabels={{
pin1: ["LIN"],
pin2: ["RIN"],
pin3: ["VDD"],
pin4: ["GND"],
pin5: ["LOUTP"],
pin6: ["LOUTN"],
pin7: ["ROUTP"],
pin8: ["ROUTN"],
pin9: ["SHDN"],
}}
schPortArrangement={{
leftSide: { pins: ["LIN", "RIN", "SHDN"], direction: "top-to-bottom" },
rightSide: { pins: ["LOUTP", "LOUTN", "ROUTP", "ROUTN"], direction: "top-to-bottom" },
}}
pcbX={0}
/>
<chip
name="RV1"
manufacturerPartNumber="dual 10k audio potentiometer"
footprint="pinrow6"
pinLabels={{
pin1: ["L_IN"],
pin2: ["L_WIPER"],
pin3: ["L_GND"],
pin4: ["R_IN"],
pin5: ["R_WIPER"],
pin6: ["R_GND"],
}}
pcbX={-18}
pcbY={0}
/>
<chip
name="J1"
manufacturerPartNumber="audio input header"
footprint="pinrow3"
pinLabels={{ pin1: ["L"], pin2: ["R"], pin3: ["GND"] }}
pcbX={-28}
pcbY={0}
/>
<chip
name="J2"
manufacturerPartNumber="left speaker terminal"
footprint="pinrow2"
pinLabels={{ pin1: ["L+"], pin2: ["L-"] }}
pcbX={18}
pcbY={6}
/>
<chip
name="J3"
manufacturerPartNumber="right speaker terminal"
footprint="pinrow2"
pinLabels={{ pin1: ["R+"], pin2: ["R-"] }}
pcbX={18}
pcbY={-6}
/>
<capacitor name="C1" capacitance="10uF" footprint="0805" pcbX={-5} pcbY={9} />
<capacitor name="C2" capacitance="100nF" footprint="0603" pcbX={4} pcbY={9} />
<resistor name="R1" resistance="10k" footprint="0603" pcbX={-8} pcbY={-8} />

<trace from=".HAT1_chip .V5_1" to=".U1 .VDD" />
<trace from=".HAT1_chip .GND_1" to=".U1 .GND" />
<trace from=".J1 .L" to=".RV1 .L_IN" />
<trace from=".J1 .R" to=".RV1 .R_IN" />
<trace from=".J1 .GND" to=".RV1 .L_GND" />
<trace from=".J1 .GND" to=".RV1 .R_GND" />
<trace from=".RV1 .L_WIPER" to=".U1 .LIN" />
<trace from=".RV1 .R_WIPER" to=".U1 .RIN" />
<trace from=".U1 .LOUTP" to=".J2 .L+" />
<trace from=".U1 .LOUTN" to=".J2 .L-" />
<trace from=".U1 .ROUTP" to=".J3 .R+" />
<trace from=".U1 .ROUTN" to=".J3 .R-" />
<trace from=".C1 .pin1" to=".U1 .VDD" />
<trace from=".C1 .pin2" to=".U1 .GND" />
<trace from=".C2 .pin1" to=".U1 .VDD" />
<trace from=".C2 .pin2" to=".U1 .GND" />
<trace from=".R1 .pin1" to=".U1 .VDD" />
<trace from=".R1 .pin2" to=".U1 .SHDN" />
</RaspberryPiHatBoard>
)
`} />

## Step 1: Add the HAT Base

Use `RaspberryPiHatBoard` to start with the expected HAT outline and 40-pin GPIO
header. The amplifier can use the 5V and ground pins from this header.

<CircuitPreview splitView={false} hidePCBTab hide3DTab defaultView="schematic" code={`
import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
<RaspberryPiHatBoard name="HAT1">
<chip
name="U1"
manufacturerPartNumber="PAM8403"
footprint="sop16"
pinLabels={{
pin1: ["LIN"],
pin2: ["RIN"],
pin3: ["VDD"],
pin4: ["GND"],
}}
/>
<trace from=".HAT1_chip .V5_1" to=".U1 .VDD" />
<trace from=".HAT1_chip .GND_1" to=".U1 .GND" />
</RaspberryPiHatBoard>
)
`} />

## Step 2: Add Volume Control

A dual-gang potentiometer lets one knob adjust both channels. Route the left and
right input signals to the potentiometer inputs, then route each wiper to the
matching amplifier input.

## Step 3: Add Speaker Outputs

The PAM8403 uses bridge-tied-load outputs, so each speaker connects between a
positive and negative output pair. Do not connect either speaker terminal to
ground unless the amplifier datasheet explicitly allows it.

## Raspberry Pi Audio Configuration

For a Raspberry Pi analog audio source, route left, right, and ground from your
audio output connector to the HAT input header. If you use I2S audio, add a DAC
module before this amplifier stage and feed the DAC's analog outputs into the
volume control.

Example `/boot/firmware/config.txt` setting for analog audio:

```txt
dtparam=audio=on
```

Then use `raspi-config` or your desktop audio settings to select the analog
output. Keep the Pi output volume moderate and use the HAT potentiometer for
listening-level adjustment.

## Layout Notes

Place the 10uF and 100nF capacitors close to the PAM8403 supply pins. Keep the
speaker traces wider than the signal traces, separate speaker output routing
from the low-level audio inputs, and keep the volume-control traces short to
reduce noise pickup.

## Bill of Materials

| Reference | Part | Notes |
| --------- | ---- | ----- |
| U1 | PAM8403 | 3W per channel stereo Class D amplifier |
| RV1 | Dual 10k audio potentiometer | Left/right volume control |
| J1 | 3-pin audio input header | Left, right, ground |
| J2, J3 | 2-pin speaker terminals | Left and right speaker outputs |
| C1 | 10uF capacitor | Bulk supply decoupling |
| C2 | 100nF capacitor | High-frequency decoupling |
| R1 | 10k resistor | Pulls shutdown/enable high |
Loading