Speaker

The MCB2130 includes a speaker controlled by the output of the on-chip D/A converter. The LM386M low voltage power amplifier (IC4) amplifies the D/A output to drive the speaker.

Jumper J13 connects the D/A output (Port 0, pin 25, P0.25/AOUT) to the input of the LM386M amplifier. Removing this jumper disables the speaker.