Demand Peripherals     Robotics and Automation Made Easy

AAMP: 1.2 Watt Class-D Audio Amplifier

The Audio Amplifier Card (AAMP) uses the Maxim MAX9700B Class D amplifier to give over one Watt of audio power.


- Maxim MAX9700B
- 1.2 Watt output
- Power efficiency over 90%
- Total Harmonic Distortion less than 0.1%
- 5 Volt input power using rugged screw terminals
- Optional FPGA card connection for tone generation
- Industry standard 3.5mm input jack



Class D amplifiers have a high frequency (relative to audio frequency) digital output. They use Pulse Density Modulation to make the average signal over a short span correspond to the audio output. The high frequency digital output is low pass filtered by the inductance in coil of the speaker. A digital output is what gives Class D amplifiers such great efficiency and such low distortion.

Even if the average is low, the instanteanous output is at full power for brief periods. Underrated speakers can catch fire when driven to full power by a Class D amplifier. This is why you must use a 1.2 Watt (or higher) magnetic speaker with the AAMP card.

The schematic and layout of the AAMP are shown below. The Eagle schematic, board, and bill-of-materials are available here: aamp.sch, aamp.brd, and aamp.txt.




Note that the connection to the FPGA has three resistors arranged as a asumming network. The resistor values are a decade apart. This means that the FPGA must give each output a PWM signal that can take on one of ten different pulse widths. Three PWM signals each a decade apart in volume gives the circuit about 10 bits of dynamic range. However since the resistors are not matched the linearity of the circuit might not be very high.

If you want stereo output and computer controlled volume you might want to consider building a circuit that combines the MAX9744 with EI2C peripheral and daughter card.

FPGA Defined Peripherals
User Interface
FPGA Configuration
FPGA Buttons & LEDs
Text LCD and Keypad
Quad WS2812 Interface
Quad Slide Pot
Tone Generator
IR Recv/Xmit
6 Digit LCD
RC Decoder
Keyfob RF Decoder
Rotary Encoder Interface
Motion Control
Dual DC Motor Controller
Dual Quadrature Decoder
Quad 13 Bit Servo
Bipolar Stepper Controller
Unipolar Stepper Controller
Simple Input / Output
Quad Binary Output
Quad Binary Input
Octal Input/Output
32 Channel Binary Output
32 Channel Binary Input
Octal 12-bit ADC
Quad Ping))) Interface
Octal SRF04 Interface
Quad Event Counter
Generic I2C
Generic SPI
Octal 8-Bit DAC
Quad Digital Potentiometer
Quad PWM Output
Quad PWM Input
4 Bit Pattern Generator
Real Time Clock
Dual Watchdog Timers

Interface Cards
User Interface
Audio Amplifier
IR Recv/xmit
Six Digit LCD Display
Keyfob RF Receiver
Rotary Encoder
Quad Switch Card
Text LCD / keypad
Quad Slide Pot
Motion Control
Dual 7-amp H-bridge
Quad Open Drain Driver
Quad 10 Amp Relay Card
Input / Output
Octal 8-Bit DAC
Quad Digital Potentiometer
Octal 12-bit ADC
Octal SRF04
Generic I2C
Generic SPI
USB 2.0 Hub
Real Time Clock
Slot Expander
Octal Input/Output
32 Channel Input
32 Channel Output
Power Distribution Card
15 Amp Power Distribution
5 Volt Switching Regulator
ATX Power Break-Out Card
Disk Drive Power Break-Out
MP43 Aluminum Mounting Plate
WW2 Prototyping Card
WW1 Small Prototyping Card