Relay Switching
Audio is switched within a remotely driven relay
Latching Footswitch Control
A SPST latching switch can activate or deactivate a relay. The relay can be SPDT and can substitute for the footswitch in the half bypass scheme or it can be DPDT and have half bypass with a LED switched by the relay.
A DPDT relay can also make a full bypass scheme, and the LED can draw power from the relay's control voltage.
A SPDT or DPDT latching footswitch can also drive the relay. The SPDT provides two concrete positions instead of the simple open/closed action of the single throw. A DPDT may be wired with the two poles in parallel for redundancy and greater reliability.
Momentary Footswitch Control
A SPST non-latching/momentary footswitch may be used to drive an electronic toggle circuit that then drives the relay. See the next section for a discussion of electronic toggles.
Examples
The oldest relay controlled effect pedal I know of is the Univox Uni Fuzz. Crowther Audio of New Zealand, Line 6 (DL4), and Electro Harmonix (Deluxe Memory Man EC-2002) include relay switching within some of their effects, just to name a few examples.
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