A compact printed circuit board assembly includes a printed circuit board (PCB) and a preamplifier subassembly. The preamplifier subassembly includes a preamplifier and an insulating endcap abutting one another and arranged in a plane parallel to the PCB. An electrical via formed within the first insulating endcap provides an electrical connection between a decoupling capacitor and the PCB to reduce noise detectable in current flowing between the preamplifier and a current source.