Dwight Diller's advice to me, which helped my banjo a lot, was to take a cloth or sponge and roll it extremely tightly. Push it between the head and the dowel stick as near to the neck as you can. This works well to remove hollowness from the tone. Making a banjo sound modern is not necessarily a good thing - the best bluegrass banjo players want theirs to sound like prewar Gibson mastertones, while Old Time clawhammer players want theirs to sound like a Fairbanks or Bacon fom around 1900.

Cheers
Ray