Turn it up and it becomes a Very distorted Echo in a culvert, to add to BLHagstrom's comment! Setting the SR-202W is like Brylcreem. a little dab'll do ya. Turn the main gain control all the way counter clockwise. This is the off or minimum setting. With the stereo on and the 202 connected and in the loop, advance the gain control VERY SLOWLY. You'll start hearing what sounds like a deepening of the sound (or an echo chamber effect) like you are in a large hall or arena. This is the best efect. Too much and it starts to distort the sound until you get garbled garbage out of the speakers. Ideally you'd set it to just as it's hitting the echo chamber sound, so it sounds like you are in a large hall or arena. With the 202, you can also connect two tape decks (tape loops). It gets complicated from there.
Larry