Does your powercenter have a provision for being turned-on remotely, by a jack somewhere on it? If it does not, then you have to make a simple relay circuit using a 12vdc wall wart, a 5vdc controlled relay rated for 12Vdc on the switched side, another relay controlled by 12vdc and rated for 120VAC and the necessary current capacity on the switched side, and a connector that will plug into your DC trigger on your preamp. You also need to fuse the 5vdc, 12vdc. If you don't want to do this, then you could build a simple TTL controller with a high voltage output relay. Either way, you will have to cut into your powercenter or cord to connect the relay to perform the switching. And both cases will be viewed negatively by the building inspector and the insurance company. If your house burns down and they see that homemade switcher, you're screwed. Also, if you don't already know about making these types of circuits, then you should stay out of it. Needless to say, you don't own a turntable. Most of us just get up out of the chair.