From Lehle:

The Lehle 1at3 SGoS is a programmable True Bypass switcher that lets you switch backwards and forwards between up to three amplifiers, when you want, as often as you want.
In combination with jack socket C→B, output C can also be used alternatively as an effect loop for amp B, excluding all the effects you don't currently need from the signal path. A tuner can also be connected to output A, taking it, too, out of the signal chain. The gold-plated-contact relays feature active pop-and-click suppression, and switch not only the signal, but also the signal ground, making hum loops impossible when switching back and forth between outputs A, B and C.
Like all members of the SGoS family, the Lehle 1at3 SGoS can also be programmed unbelievably easily and intuitively. The slender, TRS format remote socket assists with programming, and can be used, via a stereo patch cable, to communicate with other SGoS switchers, or for direct contact with MIDI controllers. The Lehle 1at3 SGoS can be programmed as a stand-alone unit, or remote controlled using MIDI program change commands.