If I can afford one good cable, which component?


I'm vinyl only so it's either my LDR preamp or my Rogue Atlas amplifier. Phono stage is battery powered...
dhcod
Follow the musics signal>>Source>Pre>Amp>Speaker. If you have not addressed power from the wall and conditioning, you could also start there.>>Outlet>Power Cable>Conditioner or Regenerator> Power Cable to Source etc.
Post removed 
In my experience, putting the best power cord on preamp or integrated is the way to go. Not on the source, not on the power amp. And the rest of the cables, yeah, follow the signal. However, as Elizabeth said, it might be different in different set-ups even if only to a certain degree. Current from the wall and regenerators/conditioners is another subject.