Figure 1. Power Amplifier for the
Speaker
As shown in the figure above, the LM386M-1 amplifier device is powered by USB +5V. The gain from the power amplifier circuit is fixed to 20 V/V. The input of this circuit is the analog output of the 8-order low power filter for the DAC.
In front of the power amplifier, one variable resistor (VR1) and a couple of relative resistors construct a simple circuit for the users to adjust the loudspeaker volume.