Requirements to the source selection:

• connection of the wanted signal inputs with the desired signal outputs
• routing of the signal within the preamplifier
• since the switching elements are part of the signal path, the switching process should perform as neutral and exact as possible.

Regularly the user owns a couple of different source devices. The switching matrix, that connects the desired source device to signal conditioning stages and the following devices may consist of mechanical switches, electromechanical actuators or electronical switches.

Mechanical switches come in many different shapes and price classes.

The contact quality can be very high. A disadvantage can be that the contact may not be located physically close to the optimum position and that it requires longer cable or PCB trace runs.

Electromechanical actuators are mechanical contacts moved via electronic control means, for example motorized switches or relays. The latter have the advantage that the contacts may be positioned in close proximity to the ideal position, often hermetically encapsulated, partly filled with inert gas, and that they come in small sized casings with highquality contacts. Costs can be considerably high.

In electronic switches mostly integrated circuit technology is used featuring MOSFETs as switching transistors.

Simple control circuits, a huge number of different models and types and soft ON- and Off-switching behaviour are a plus.

Disadvantages are the typically lowish signal voltage limit, height and non-linearity of the On-resistance, as well as parasitic effects like switching capacitances and cost of high-quality types.

Of main importance remains the PCB layout. Short and low-ohmic traces are the prime target.