The relay race

With the advent of remote control for high-end stereo equipment, relays became the input selector of choice. Where once we used a wiping rotary selector and stressed over contact materials for best sound, suddenly the game changed yet again. The advantage of a relay are two fold: instead of a hand turning a knob or punching a button, relays work with a pulse of electricity, and they can be placed next to where they are needed (as opposed to a mechanical switch that must be positioned where it is accessible). But they too have their disadvantages. A mechanical switch tends to be self cleaning, while relays are not. Every time you turn a mechanical switch or push a mechanical button, the contacts are cleaned by the wiping action of the switch. Relays are different. They do not wipe. They slap. Here's a picture of a relay's contacts. Note the round button. This is the contact area that slaps together making connection (it's also partly responsible for the "click" you hear when it engages). Once connected there's little difference in performance between the mechanical switch and this contact. They both rely on the contact material: rhodium, gold, silver, and exotic brews for improved conductivity and long oxidation-free life. For the curious among you, relay's work like loudspeakers—using a magnetic field to pull them in one direction or another. The electrical pulse activates a coil of wire, similar to the voice coil of a woofer, and pulls the contacts closed or open. So, we've covered the two types of physical switches employed to select inputs. Tomorrow, the electronic switch.