I have a Subdecay Proto Series Echobox, DOD FX91 & Digitech PDS-1002 that all self-oscillate nicely. All of these are digital- the DOD & Digi boxes have internal trimpots that allow this but the Sub does it stock(
AFAIK- I got it use & haven't popped the hood). Oh yeah- I also have an old Ibanez Soundtank Echo Machine that SO's HUGELY- this pedal is convinced it's analog.