maalleh (sorry you didn't sign)--I just got my 12000 after having HVs since 1992 & you will LOVE Janome! Soooo user friendly. I've bought 3 different Janomes in the past month (actually dh surprised me with the FM 725). I still have Ruby but I am a convert. You will not be sorry.
As for pre-wounds I can't say for sure as my test may have been a top thread issue but changed both top & bobbin just to be sure.

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Vicki Jo

I get my Janome 12k on Saturday, upgrading from a Viking Designer SE. I
am so excited. I have many prewound clear plastic bobbins. My dealer
assures me that there is an adapter made for Brother machines that will
work in the Janome so that I can use up all my prewound L bobbins. Cost
is about $10. Will purchase new bobbins for the Janome once these are
used up. If that does not work I will transfer the Viking prewounds to a
Janome bobbin.