that Boss Delay schematic look a little too schematic.

IC14 ("LFO" - Low Freq Oscillator) feeds the "Clock Gen" only in chorus mode. In echo mode it gets a second control knob but sits there doing nowt. There is something implicit they aren't telling you.
BDB looks like yer main delay (Bucket Brigade Device - delay set by "Clock Gen"), set by the clock frequency, but FCF beats me. Is it a Fully-Connected Filter (?) or a Frequency Correlation Function (aka a phaser?). The circuit diag doesn't give me much more.

It would be interesting to know.