Thanks for that link, I really had no idea dual power was a requirement for anything, ever. This all must be done internally in the TR-808 or TR-909s.
I am glad you sent me that page, because I was quite confused by the schematic from Eric Archer, his schematic has some generic capacitors across to ground. I then looked at a PCB built by jmej and the board has two electrolytic caps to ground on the dual voltage.
I see the same pattern from the link you pointed to -> using electrolytic caps
Jmej
https://www.muffwiggler.com/forum/userpix/1043_808bs_sc_2.jpg
