hi, some might say you should try to do it yourself. there is an example in the pd documentation in audio examples/G02 for a recirculating delay. however, all pass filters are trickier so here is an allpass abstraction i've modified from my library to be vanilla-compatible, You cannot modulate the delay time. it's taken from this set up: https://ccrma.stanford.edu/~jos/pasp/Allpass_Two_Combs.html#fig:fbffcf

this might be useful too:
https://ccrma.stanford.edu/~jos/pasp/Schroeder_Reverberators.html

you may also want to check out the example G08 in the pd help files, as well as rev1~, rev2~ and rev3~ in the extra folder

I've included a recirculating comb filter abstraction as well that works the same way for convenience..
schroeder-abs.zip