I have the Center Posotive plug, and I have a couple ports that I can switch to 12v. I recall (maybe?) you saying that as long as the Truetone isn't maxxed out, the ports will share the overall power.The LA-1a needs 12 volts and at least 1amp. Center positive plug. If a power supply can deliver that you should be OK. When in doubt, contact Effectrode.
Using a center negative plug will do damage to the unit and you will likely see smoke as your poor compressor is ruined requiring repair.
