  We study the amplitude and spectral tilt of density perturbations in the
simplest hybrid inflation models. We give an exact expression for the amplitude
of quantum fluctuations on all scales in the limit where we can neglect the
backreaction on the metric. This is a very good approximation for values of the
inflaton field well below the Planck scale and our results remain valid far
from the usual massless limit. We confirm that the primordial density spectrum
in this model has a constant spectral index n>1 over all observable scales. For
the small values of the tilt (n<1.4) required by observations, the results
remain close to those obtained using the quasi-massless approximation.
