In the old days you had to put a delay in a mixer feedback loop and look for the sweetspot for a few hours to get that effect, I've been told
I've gotten exactly the same sound, even the sound when the effect is changed live, by:
making a feedback loop with my sound interface, standard channel two line-out to channel two instrument in (preamp, gain control). For software I just had a pitch shifter and added flanger or phaser to get the resonance.
Yep, that gives you delay, digital to analog to digital feedback loops are different than other fb's
I have sound samples if someone doesen't believe it, hehe.