Sometimes I see the SP-12 photographed with a (15Henry?) choke in the power supply, sometimes not...Mine doesn't have a choke, I have no evident power supply noise on even 99 db./meter horn speakers, is there any reason for me to add a choke? I'm pretty much of the "If it ain't fixed don't break it" camp, mainly I'm curious why some kits shipped with it and some without. Later revision?