Do you mean the amp send? No. Go from either: Studio Pre send, Studio Pre main outs A or B, Studio Pre recording outs A or B into your .50Cal+ return. You obviously have to plug your guitar into the Studio Pre. I suppose the .50Cal+ has a parallel fx loop and I don't know if it could be an issue. I think it's better to set all pre-loop controls (gain, drive, bass/mid/treble...) to 0 even if you haven't got anything connected to the amp input. Remember that if you use the Studio Pre send to feed the .50Cal+ poweramp, the A & B output controls on the Studio won't have any effect, since they only control main outs' and rec outs' level.