If you're on a budget, a passive preamp is a serious option if you run shortish interconnects and your source and poweramp match. Passives, if made right, are transparent. So, they may change your previous sound, depending on whether and how your previous preamp colors the sound. If your previous preamp is hiding some flaws in your other components, the change may be for worse. But don't blame the passive for that!
Look into Odyssey's new passive preamp (ca. $350, but it's not on their US website yet; Google "Odyssey Etesian" and call Odyssey) or a used FT Audio Little Wonder (hard to come by used, though). Demos of Creek OBH-12 can be had cheap (ca. $250); the new OBH-22 is a bit more expensive (ca. $450).
Also search the AudiogoN amp/preamp forum; I remember reading older threads recommending good preamps, passive and active, of older vintage that can be had cheap used.
Look into Odyssey's new passive preamp (ca. $350, but it's not on their US website yet; Google "Odyssey Etesian" and call Odyssey) or a used FT Audio Little Wonder (hard to come by used, though). Demos of Creek OBH-12 can be had cheap (ca. $250); the new OBH-22 is a bit more expensive (ca. $450).
Also search the AudiogoN amp/preamp forum; I remember reading older threads recommending good preamps, passive and active, of older vintage that can be had cheap used.