  So far, the masses of excited states of mixed orbital symmetry and in
particular those of nonstrange $[{\bf 70},1^-]$ baryons derived in the $1/N_c$
expansion were based on the separation of a system of $N_c$ quarks into a
symmetric core and an excited quark. Here we avoid this separation and show
that an advantage of this new approach is to substantially reduce the number of
linearly independent operators entering the mass formula. A novelty is that the
isospin-isospin term becomes as dominant in $\Delta$ as the spin-spin term in
$N$ resonances.
