M.T.H. premier M10000 Operator's Manual page 6

Manual Volume Control
To adjust the volume of all sounds made by this engine, turn the master volume control
knob located next to the rear truck of the power unit clockwise to increase the volume
and counter-clockwise to decrease the volume.
Proto-Sound 2.0
Volume Adjustment Knob
Figure 5: Proto-Sound Manual Volume Adjustment
6 Premier M10000 Locomotive Set