Sony XM-3040 Operating Instructions Manual page 9

Level Adjustment Control
The input level can be varied with this control.
Use it to adjust the input sound level when
using source equipment of other manufacturers.
Be sure to set the control to SONY STD if the
unit is connected to a SONY car stereo. Turn it
to 0.1 V when the input level of the cassette car
stereo or CD player seems low.
SONY STD O.,