There is no switch on the E-202 and the manual is of no help because subwoofers didn't exist at the time. The manual does address using a separate amp (which I realize the subwoofer actually is in this case), but the signal did not appear to be going to the sub. My repair tech said that using the preamp outputs would automatically disconnect the amplifier section, but I don't agree with that because when I did connect the sub, the unit continued to work as normal, other than no output to the sub. The amp has been out of circulation for several months due to my having the barrier strips for the speaker outputs replaced with binding posts and I want to get this issue with the sub resolved before hooking it back up.