The MAX9744 amplifier can use between 5-14VDC power. The higher the voltage, the more gain you can get. So if you want 20W per channel, you'll need to supply 12VDC. The amplifier is a Class D - so it only draws current when its playing audio, but the voltage requirement is still pretty important. If you pick a voltage too low, you'll hear distortion on the speakers because the output is 'clipping'
There's two ways to get power into this board, either by the 2.1mm DC jack (on the left) or the 3.5mm terminal block breakout (in the middle). Both are connected up together so use whichever you like.
The 2.1mm DC jack is a 'standard' 2.1mm/5.5mm barrel jack, with center positive connection. The terminal block has markings showing which pin is positive and which is negative. If powering from a wall adapter, use the DC Jack, the terminal block is best for battery packs with wires coming out of them. You'll need to solder the terminal block into this spot, see the Assembly page for details
To the right of the terminal block is a polarity protection MOSFET, it will make sure you only provide positive voltages to the board! If the polarity is negative, it just wont work. Its more likely to happen with the terminal blocks but its always nice to have a protection circuit.
All the way on the right is a spot for a electrolytic capacitor. We include a 470uF capacitor in the kit. This capacitor helps smooth out the power supply. This isn't required when running off of batteries, but if you're using a wall adapter, especially a really old 'transformer' style one, this will be required. If you want the capacitor, solder it in using the instructions in the Assembly section
The MAX9744 board draws about 30-50mA quiescent current - that means that even when not amplifying audio you'll be drawing that much current from the power supply. On top of that, you have to add the current usage for audio amplification which will vary widely based on audio volume, speaker impedance, amplification, etc.
This audio amplifier takes in stereo audio, either using a 3.5mm stereo jack or terminal blocks. Line in audio is a-OK. The audio inputs are not differential! The ground connection is connected directly to the power ground, this chip simply does not handle differential inputs. However, the inputs do have blocking capacitors, so if your audio levels have DC bias, its OK to connect them up directly without extra audio blocking caps.
Line level audio (about 1Vpp) is suggested, but it can handle up to ~3Vpp inputs.
You got this amp to amplify, and this is where you get that amplified signal out! We use two dual 3.5mm terminal blocks for the speakers, Left and Right
The outputs are Bridge-Tied-Load which means you can only connect speakers up directly. Don't connect the outputs to another amplifier! And you can't "parallel" the two BTL outputs for one 40W load either.
To connect up the speakers you'll want to solder in the terminal blocks, see the Assembly section for details
At the very bottom, we break out all the pins you're likely to use with this amplifier. If you're using the amp in Analog Mode you don't need to connect to any of these, most likely. If you're using the amp in Digital Mode, you may want to connect to some of them. See the tutorials for each section on how to use the board in either mode.
Above the pinouts there are three solder jumpers (Analog / AD1 / AD2) and then on the left, a 3-pin breakout called Pot. Vol - these are used in analog mode, the solder jumpers are closed to tell the chip we'll be using a potentiometer to set the volume. The Pot Vol connection is how we wire up the 1K potentiometer. This is covered in more detail in the Analog Wiring section.
Starting from the left, here are what each pinout connects to:
- RIN - this is a duplicate of the audio input terminal block, right channel
- LIN - this is a duplicate of the audio input terminal block, left channel
- AGND - analog reference ground, the 'quieter' ground for audio signal referencing
- SDA - i2c digital signal data, if using Digital Mode to control volume over i2c
- SCL - i2c digital signal clock, if using Digital Mode to control volume over i2c
- Vi2c - the i2c voltage reference for logic. Only used in Digital mode - connect to 3V or 5V whichever your microcontroller uses
- SHDN - digital Shutdown pin. Connect to ground to turn off the entire chip and put it into low power mode
- MUTE - digital Mute pin. Connect to ground to turn off only the audio output stages, its faster than shutdown and keeps the digital i2c audio levels
- SYNCO - Sync output, this is the high frequency signal from the PWM generator, about 1.4MHz
- SYNC - Sync input, for advanced users who want to clock in their own PWM frequency, keep it above 800KHz.
- AD1 - I2C address select pin #1
- AD2 - I2C address select pin #2
- GND - Power ground
- VDD - 5-12VDC power, from the terminal block/DC jack after the polarity protection. You can use this to power your other projects that can handle 5-12VDC power input.
The solder jumper on the back allows you to connect AGND (analog ground) to DGND (digital ground)