Forgive me, but what circuit, where?
When I look at the site, I see something about CDTV clockport adaptors, SIMMfonie, Melody 1200 and Twister 1200, but nothing about clockport adaptors for the A500 (or is it just the same as the CDTV one?). Or is the fact that I can't spot the circuit diagram due to my lack of German?