I just discovered this little funny thing by accident.

Connect the line out of your 404 to the line in of your 404 and
apply an effect to the ext. source. Now play your pattern and FX freak it like there's no tomorrow. Of course now you can use only the headphone output to hear/record stuff. Nothing big but I had some fun playing with this.

hey this is feeeeeeeeedback!)

isnt it dangerous a little bit?

i also haven't tried to put 404sx between microphone, overdrive and guitar combo with crunch - microphone feedback is very loud u know

Yes it might be.. some effects made horrible noises. My 4o4 still works great though. Anyway I'm not going to buy anyone a new sampler or pair of ears if something happens