I love my DD-20, had it for a while now and know almost all there is to know about it....
Recently though, I read something somewhere about some dude connecting the stereo out jack to the stereo in jack with a cable... said something about "feedback looping" but that's all it said.. I'm wondering what this might do and if it would be harmful to the DD-20 in any way?
I have seen a similar thing done with an older Zoom 2020 multi-effects. (for use in delay mode). but I believe you would have to limit the amount of output signal, that you fed back into the input, with say a volume pedal or just a simple potentiometer/variable resistor, wired into the return cable.
This would give you better control, in case it went into runaway feedback.