Quote Originally Posted by Dalebert View Post
Q 44 Can a sorcerer / bard us an instrument of the bards (the magic item) as a focus for his sorcerer spells?
A44: Doesn't seem like it.

PHB page 164. In the multiclass section:
Spells Known and Prepared

Each spell you know and prepare is associated with one of your classes, and you use the spellcasting ability of that class when you cast the spell. Similarly, a spellcasting focus, such as a holy symbol, can be used only for the spells from the class associated with that focus.