Edit: Or you could just click the effect style knob (the one used to scroll through songs, as well). I thought I might have done it without the brake button. Ah well.
While researching the Denon S1200 turntables, I recall reading a review or two that complained about the interaction between the built-in effects and the scratch functionality. Because the jog wheel is used to both scratch and adjust the wet/dry of the effect, people simply couldn’t scratch with an effect active. I think I’ve found a workaround.
First, activate the effect and adjust it to the desired level. Then, double-tap the BRAKE button at the bottom. This enters then exits the brake activation menu. (You can actually use the DUMP and REVERSE buttons, too, but those interfere with playback.) Now, you’ve dropped back into simple playback mode and you can scratch to your heart’s content with an effect active. To disable the effect, just double-tap the effect button.
I like to add some flanger to beef up and texturize my samples. Filters also work well for some variety. Echo/Loop doesn’t really do much because applying pressure to the disc stops all sound and the echos seem to only be generated when the track is playing. Anyway, that’s two more effects than I had before, so I’m happy.