Well yes Externet. I found the Orban automatic stereo synthesizer block diagram but I couldn't make head nor tail of it. It seems to use a comb filter just as you said but how to use the information shown is beyond me. The 275A is called the blue face version I gather. I think it would take a lot of alteration to make use of it in my application but thanks for the suggestion. I found the circuitry on a different web page, by the way. There was no page 22 on the one you quoted.

 

Because of my doubts about what I want to do I've decided to give this subject a rest for a while. It was beginning to look as if I would need one sampler for every harmonic of the missing fundamental of the lower notes, say something like five harmonics per note and therefore five samplers per note. If there are say eight notes of this low frequency type that's forty samplers. Then there's the notes where there is a fundamental frequency present and these would each need a sampler. The whole thing is becoming much bigger than I expected. I need to think it out again.