How to Build a Class-D Audio Amplifier: TPA3116, Power Supply, and Speaker Matching

Introduction

A Class-D audio amplifier is the most efficient way to drive speakers from a DC power source. Unlike traditional Class-AB amplifiers that waste 50%+ of power as heat, Class-D amps use pulse-width modulation to achieve 90%+ efficiency, meaning a small amplifier board can deliver 50W or more to a speaker while staying cool enough to touch. The TPA3116D2 from Texas Instruments is the gold standard chip for DIY audio — it is cheap, sounds excellent, and powers everything from desktop speakers to portable boomboxes. This guide covers the complete TPA3116 build: power supply selection, speaker impedance matching, Bluetooth integration, enclosure design, and tuning for the best possible sound.

What You Need

• TPA3116D2 amplifier module (dual 50W or 2.1 channel with sub)
• DC power supply: 12V-24V, 3A-6A depending on target output
• Speakers: 4Ω or 8Ω full-range drivers or component set
• Bluetooth audio receiver module (optional)
• Enclosure: 3D printed, wood box, or repurposed speaker cabinet
• Speaker wire, heat shrink, connectors

Understanding Class-D Amplification

Class-D amplifiers do not amplify the audio signal in a linear analog path. Instead, they:

1. Convert the analog audio input into a high-frequency PWM square wave
2. Amplify the square wave using MOSFET switches (very efficient)
3. Filter the output through an LC low-pass filter to reconstruct the amplified analog signal
4. Send the result to the speaker

The TPA3116D2 switches at ~300kHz, well above audible range. The output filter removes the carrier frequency, leaving clean audio.

Step 1: Choose Your Amplifier Module

TPA3116D2 Dual-Channel (Stereo)

• 2 × 50W into 4Ω at 21V
• 2 × 30W into 8Ω at 24V
• Best for: Desktop speakers, bookshelf systems, portable audio

TPA3116D2 2.1 Channel

• 2 × 50W (left/right) + 1 × 100W (subwoofer)
• Built-in crossover: sub gets frequencies below 200Hz
• Best for: Full-range systems with dedicated bass

TPA3118 (Lower Power, Lower Cost)

• 2 × 30W into 8Ω
• Single-channel option available
• Best for: Small desktop speakers, battery-powered projects

Step 2: Power Supply Selection

The TPA3116 performs best at 18-24V. Higher voltage = more power, but exceeding 26V damages the chip.

Voltage vs. Power Output

Supply Voltage4Ω per channel8Ω per channel 12V15W8W 18V30W18W 21V50W25W 24V50W (current limited)30W

Power Supply Options

• 19V laptop brick: Perfect for TPA3116, widely available, 3-6A
• 24V LED power supply: Cheap, high current, but may have audible switching noise
• 18V drill battery: Portable option, works with Ryobi/Makita battery adapters
• 12V lead-acid battery: For car audio or outdoor events

Current Requirements

Formula: Current = Total Wattage / Voltage / Efficiency

For 2 × 50W at 21V with 90% efficiency: 100W / 21V / 0.9 = 5.3A minimum

Step 3: Speaker Selection and Matching

Impedance

• 4Ω speakers: Maximum power output, but amplifier runs hotter and needs beefier power supply
• 8Ω speakers: Lower power but safer for the amplifier, better for battery-powered builds

Driver Types

• Full-range drivers: Single driver handles all frequencies. Dayton Audio DMA45, Tang Band W3-1876, Visaton FR8. Simple, no crossover needed.
• Component systems: Separate woofer + tweeter with a passive crossover. Better frequency response but more complex.
• Subwoofer: Dedicated low-frequency driver. Needs 2.1 amplifier or active crossover.

Sensitivity

Measured in dB at 1W/1m. Higher sensitivity = louder at same power:

• 85dB: Needs more power, common in cheap drivers
• 88-90dB: Good all-around range
• 93dB+: Very efficient, excellent for low-power builds

Step 4: Wiring the Amplifier

Basic Stereo Setup

1. Connect power supply VCC and GND to amplifier module
2. Add a 1000μF+ capacitor across power input near the board
3. Connect audio source to 3.5mm input or RCA jacks
4. Connect left speaker to L+ and L- terminals
5. Connect right speaker to R+ and R- terminals
6. Turn volume to minimum before first power-on

Gain Setting

The TPA3116 has a gain pin (GAIN0, GAIN1) that sets amplification:

GAIN1GAIN0Gain LOWLOW20dB (10x) LOWHIGH26dB (20x) HIGHLOW32dB (40x) — most common HIGHHIGH36dB (63x)

32dB is the sweet spot for most line-level sources. Higher gain introduces more noise.

Step 5: Add Bluetooth

Bluetooth receiver modules make your amplifier wireless:

1. Purchase a Bluetooth 5.0 audio receiver with 3.5mm or line-level output
2. Wire module VCC (3.3V or 5V) and GND to a regulator off the main supply
3. Connect audio output to TPA3116 input
4. Pair with your phone — audio now routes wirelessly

Popular modules: MH-M18, MH-M28, or CSR8645-based boards.

Step 6: Enclosure and Acoustics

Enclosure Design

• Sealed box: Tighter bass, simpler design. Volume = driver Vas × 1.5-2.0
• Bass reflex (ported): More bass output, lower extension. Requires port calculation
• Transmission line: Complex but excellent bass from small drivers

Materials

• MDF (12-18mm): Best acoustic properties, easy to work with
• Plywood: Good alternative, lighter than MDF
• 3D printed: Convenient for small speakers, use 3+ walls and high infill to reduce resonance

Internal Damping

• Line walls with acoustic foam or polyester pillow stuffing
• Reduces standing waves and cabinet resonance
• Fill ~50% of empty volume for sealed boxes

Step 7: Tuning and Testing

First Power-On

1. Start with volume at zero
2. Power on the amplifier
3. Slowly increase volume while playing music
4. Listen for distortion, clipping, or buzzing
5. If you hear distortion at moderate volume: gain is too high or power supply is insufficient

Measuring Output Power

1. Play a 1kHz sine wave at known input voltage
2. Measure AC voltage across the speaker terminals with a multimeter
3. Power = Voltage² / Speaker Impedance

Heat Management

• The TPA3116 has built-in thermal protection at 150°C
• Add a heatsink to the chip for continuous high-power use
• Ensure ventilation in the enclosure
• At moderate volumes, the chip stays cool to the touch

Troubleshooting

• No sound: Check power LED, verify input connections, test with different source
• Humming/buzzing: Ground loop — use same power source for amp and source, or add audio ground loop isolator
• Distortion at high volume: Power supply sagging — upgrade to higher current supply, or reduce gain
• Overheating: Add heatsink, reduce volume, check speaker impedance (4Ω runs hotter)
• Bluetooth dropouts: Keep antenna away from power wires, add ferrite bead on power leads

Pro Tips

• Upgrade input capacitors to WIMA or Nichicon for better sound quality
• Use star grounding: all ground points connect at a single point to prevent ground loops
• Add a volume potentiometer (10kΩ dual-gang log taper) for analog volume control
• For portable builds, a 5S Li-ion pack (18.5V nominal) powers the TPA3116 for hours
• Bi-amp configurations (separate amps for woofer and tweeter) eliminate passive crossover losses

Conclusion

The TPA3116D2 makes high-quality audio amplification accessible to any maker. With a $5 amplifier module, a laptop power brick, and a pair of full-range drivers, you can build a speaker system that rivals commercial products costing 10x more. The keys are proper power supply sizing, speaker impedance matching, a well-designed enclosure, and attention to grounding. Whether you are building desktop monitors, a portable boombox, or a home theater subwoofer, Class-D amplification delivers the power and efficiency modern audio demands.