Have you asked about this over at diyaudio.com ? That would be the first place I'd look.
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I used to be a close personal friend of Sao. Perhaps 15 years ago my telephone numbers failed to reach him and once I failed to find him in the telephone book. I would suspect that if Soundsmith has no circuit diagram, either they didn't need one to rebuild them or they don't want to be involved for some reason.
I will try DIY.
I had heard Sao was 'uncontactable' from a number of sources.
Peter probably doesn't want to be involved with the SDT preamp rebuilds anymore because he has his own product now.
I would love to give this box a "birthday"..components are historic and I think the cartridge (good as it is) is being held back hugely.