sumif non-number not equal to cell X

Object:
To add amounts in column A, where the corresponding row-cell in column B is not equal to cell B1, a non-number (i.e. "a").

When I put the value in the formula:
=SUMIF(B:B,"<>a",A:A)
it works.

But I need the cell number in the formula, so I can change the value in B1, and not have to change the formula.
But this:
=SUMIF(B:B,"<>B1",A:A)
does not work.

Any suggestions?

It works, thank you!

Can you explain?
Does the ampersand (&) indicate that what follows is a a cell reference?