From the preamp, the signal goes to an onboard effects loop switch, which routs the signal either directly to the guitar's volume control or to Garcia's effect (via a TRS jack), and then back into the guitar (through the same TRS jack) to the guitar's volume control. From there, the signal finally goesout the main output The genius of this wiring is that it allowed Garcia to keep full volume going to the pedals while controlling his output volume from the guitar. The advantage is that the tone and response of the pedals would not change with the guitar's output volume, as it normally would if Garcia plugged directly into them. The wiring also allowed for a true bypass of the effects when they weren't in use.