In one embodiment, a mass spectrometer includes an RF drive circuit for generating RF signals, a quadrupole mass filter, and a fixed connection assembly for delivering RF signals from the RF drive circuit to the quadrupole mass filter, the fixed connection assembly representing the entire delivery path of RF signals from the RF drive circuit to the quadrupole mass filter. By avoiding flexible components such as a freestanding wires or flexible circuit boards, the need for retuning when parts are removed or disturbed for testing or servicing is reduced, and a modular instrument in which components and connections are standardized and therefore interchangeable is realized.