Quoted from hawknole:
How do you switch between the mixes on pinsound?
You turn the volume down to zero a few times and then you’ll hear a chime, which indicates the mix is switched. If you have the headphone jack, just twist the knob back and forth a few times. If not, use the buttons in the coin slot to move the volume up and down to zero a few times. You might be able to do it with the volume knob on the Pinsound board itself, too, but that is obviously less convenient.