A sheet feeder comprising a platform for stacking sheets and feed head assembly at the front of the platform for acquiring individual sheets from the stack and feeding separate sheets into a sheet handling machine. The feed head assembly is comprised of a vacuum plenum having a port plate, across which a perforated belt(s) moves in a closed loop. The port plate includes ports wherein the air flow through some of the ports is restricted by an intermediate plate positioned within the plenum which, in turn, has a restrictive passage therein through which air from the restricted ports must flow into the plenum.