An assembly for passing controlled impedance electrical signals between two different environments via feedthroughs in a feedthrough block. The feedthrough has a signal coupling, a dielectric surrounding the signal coupling, and a ground coupling surrounding the dielectric. An electrically insulating block has an electrically conductive signal link and discrete electrically conductive ground links surrounding the signal link. An electrically conductive block has a separate dielectric spacer and signal link through the spacer. The junctions between the block, links, and spacer are sealed to hermetically separate the two environments. In one method, the components are press fit, leaving no gap between adjacent components. In another method, potting material is forced into the junctions between components.