Intermezzo: Class-D amplifier
The first amplifier, for testing, was a “lowly” LM386. In order to get decent sound, we used a TBA820 that was originally made for a different project.
One of the goals of this project was to have a radio that can run for a decent amount of time on a set of batteries, so I wanted to do an experiment with a class D amplifier.
Class D amplifiers are more efficient than “classical” amplifiers, because they are built on the principle of switching power fully on or fully off.
The amplifier selected for this project was Maxim’s MAX4295. It’s a mono amplifier, up to 2W of output power, and it can work on a 5V supply.
Here are the datasheets:
The schematic (from the evaluation kit) is shown here:
The following image shows the prototype amplifier as built on protoboard:
The signal and power enter at the bottom side. The signal is fed into the amplifier, and converted into an amplified, PWM-type signal. At the top of the PCB there are two inductors and some passives to convert the PWM signal back into an analog signal suitable for the speaker.