￥The FD1N is nicknamed “British Edition”, while the FD3N carries the label “U.S.A. Edition”. It doesn’t appear that the EQs have been modeled after any specific British or American pieces of hardware, but Babelson Audio does mention some components that were used for the models:

 

FD1N British Edition: EF86 high gain valve, EZ80 rectifier valve
FD3N U.S.A. Edition: 12AX7 tube, “classic tube”, “warm tube”, “Class A tube”, “vintage tube”, “dirty vintage tube”