Quoted from mikeincali:
On the sound board inside the backbox there is potentiometor which looks like a round dial in the center of the board. Turn it counter clockwise to adjust the volume. It say sustain adj. next to it.
I hope I'm not wrong but in your photo - in the lower left quadrant is another potentiometer marked "Vol Adj" - I think this is the board output volume.
"Sustain Adj" should produce a "sustain" effect on the music notes - either lengthening or shortening the life of the note.
Try adjusting the volume control located on the coin door first.
Congratulations on getting such a fantastic game. Paragon is on my wanted list.