Yes, I ALWAYS use a speaker cable with my SVT CL. BUT...someone in the space I share (with quite a few other bands) not only attempted to use my SVT amp without asking, but hooked it up with an instrument cable. Now, luckily I walked in just as they were starting and they played maybe half a song before i gave them the axe and shut my gear down. (Yes, they have been kicked out.). Now, I know the amp was only used for maybe a minute, but is there any chance that any damage was done to my amp? I'm always super careful with my gear, so this is a bummer.