The Boss GT-6 is a guitar effects processor with a built-in COSM modeling engine. Unusually, the GT-6 has an external jack loop that can be used to add an effects loop to the signal chain. This is primarily designed to allow a guitarist to replace the built-in overdrive or distortion effects with a separate guitar pedal. The effects loop is only active if the overdrive and distortion settings are set correctly.
Connect the guitar to the Input port of the Boss GT-6 using an instrument cable.
Connect the guitar amp to the L (Mono) output port on the GT-6 using an instrument cable.
Connect the guitar effects to be used in the effects chain with pedal cables. The input port on the first effect and output port on the last effect in the effect chain should be open.
Connect the Send port of the external jack loop on the Boss GT-6 to the input port on the first effect using an instrument cable.
Connect the Return port on the GT-6 to the output port on the last effect using an instrument cable.
Turn on the guitar amp and Boss GT-6 guitar effects processor.
Turn the dial on the GT-6 under the label “OVERDRIVE/DISTORTION” to the setting marked “CUSTOM/EXTERNAL.” This will have the processor use the external jack loop in place of the built-in overdrive or distortion effect options.
Press Pedal 2 on the GT-6 to activate or deactivate the effects loop. The red light on the pedal indicates whether or not it is currently active.
Using the external jack loop on the Boss GT-6 guitar effects processor as an effects loop prevents using any of the built-in overdrive or distortion options. There should be a distortion or overdrive pedal in the effects chain if that effect is to be used. All of the other effects or options on the GT-6 can still be used normally.