A record player's needle makes a very small signal. A phono preamp boosts it to the level an amplifier or powered speaker expects on its line input. Many record players have one built in. You need a separate one in two cases.
Your record player has no built-in preamp, like the Fluance RT82, Fluance RT85 and Rega Planar 1, and your amplifier or speakers have no phono input.
You fit a moving coil cartridge. Its signal is smaller again, so it needs a preamp with an MC setting, even on a record player with a built-in MM preamp.
For moving magnet (MM) cartridges
These take moving magnet cartridges only, the type fitted to most record players.
We take these details from the makers' own websites and check them carefully, but makers change parts and part numbers, and we may miss an update. Before you buy, check the part on the maker's official website. If you spot an error, please tell us.