  A single sandpile model with quenched random toppling matrices captures the
crucial features of different models of self-organized criticality. With
symmetric matrices avalanche statistics falls in the multiscaling BTW
universality class. In the asymmetric case the simple scaling of the Manna
model is observed. The presence or absence of a precise toppling balance
between the amount of sand released by a toppling site and the total quantity
the same site receives when all its neighbors topple once determines the
appropriate universality class.
