You'd be surprised. :)

I'll post a note term sheet that I raised money on last year once I find it but notice the prepayment clause here: http://startuplawyer.com/convertible-notes/convertible-note-...

When you're raising on a convertible note, you're essentially taking a loan from the angel. You're promising to "pay them back" at the next financing by converting their money into stock equal to the principal + interest they've accrued on that note. If you really wanted to (and the term sheet doesn't preclude a payback), you could pay them back for only their principal & interest instead of converting them to stock.