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I just built a PT2399 delay with a BM tonestack in the regen path, tweaked for flat response in the middle, bass boost one end, treble boost the other. It sounds great - repeats can get progressively darker or progressively tinnier. Love it. Anyway, it's got me thinking - what else can we stick in the regen path to progressively...................the repeats? Octaves maybe......other stuff? Any other ideas? Maybe I'll experiment with adding a buffered effects loop......

I've been working on a design for an add-on feedback loop for delays. That would serve the same function as this, except it would be a separate box. I was planning on having treble cut, bass cut, and distortion to simulate an analog delay, as well as an effect loop. If you threw another delay in the loop, you could probaly get some neat reverb-ish sounds.

I built a delay that progressively ringmods the repeats 
it sounded pretty nuts!

where exactly is the regen path? they dont give much info on the datasheet.  is it coming from pin 14?

it's the feedback path. where delay output feeds back into the input at variable amounts. stick fun stuff in-between!

The A/DA analog harmonizer pedal, would use the delay regeneration path to create "bell tree" type effects, such that each iteration was shifted up or down a specific interval.

Effects loop in the regen path. Put any effect you like there.

I was kinda thinking that and read through the comments. I was thinking you could easily do a 'datasheet' delay with a send from the delay output, and a return back to the input, and even add in an input mixing or tone section. Then you could, exactly as stated, stick anything in you wanted... even have  a whole delayed and repeated side chain.

On a side note, Rick...  I DID take an octave up circuit ran out of the delay, but not repeated. I was hoping that I could simulate a guitar accompaniment. I haven't gone back and tried it, but I think the Little Angel could make it work properly. It sounded like just a delayed distortion, dry... dull. I was thinking that maybe if you come to something close in your feedback experimenting but it's lacking, try a little warble and see if it livens things up.

A second PT2399?  Could this be a way to get longer delay times cleanly?  I'm thinking set the first up for a single repeat, then send that to the input of the second, then use that output and the original dry signal for the final sound.   

thats how you do it, put them in series
but each stage adds to the background noise and quantization artifacts
and last, you need a way to synchronize the delay time on each chip. Think of current mirrors, vcr's, etc

BTW, here's the little layout I used, fits nicely on the tabs of the tone pot:




The configuration of the tonestack is just about flat at mid position with a 6dB drop. At either end it cuts bass or treble. I'm still deciding if I want to recover gain with a little booster, or if I'll get it back by tinkering with the regen path resistor/pot. Here's some graphs too:

I removed  the resistor right after pin 14 of the PT2399 (10k in the delay design I'm using), and replaced it with the tonestack.

The 2k7 one. Or you could replace the 15k which is orange on the schematic.....that's probably what I'd do.