The Amplifier

The Amplifier, also known as the Amulet of Metaspell Influence is a magical enchanted amulet that will give mages wearing the item some extra spellslots. This can be gained when the party kills Razamith in Baldur's Gate. This can be done during a subquest.

In-game description
"Amulet of metaspell influence: 'The Amplifier'. Known for its ability to enhance spellcasting, the Amulet of Metaspell Influence is highly sought after by magic practitioners. It was created by Elairdrin Mellwith who resided in the Star Mountains. His reason for fabricating such an item stemmed from his womanizing habitats, and to this extent the Amplifier served his purpose well. It was later taken from him by a mage with a more destructive intent, but records detailing the change of hands vary widely."