I have a little road gear amp to power an 8 inch sub for my home stereo. i tryed powering it from a car battery and all i get is a big buzzing noise. I can barely hear any music coming from the sub because of the buzzing
i am not sure i fully understand because if this amp does not make contact with the ground and hot on the battery then it wont work. thats how it was made and the manual says dont hook to car body ground
What are you using to get music or a signal to the amp or have you not progressed that far? Does the amp hum when only it is hooked to the battery and then to the speakers?
You're confusing me a bit. If you are trying to take the source signal (say from the CD portion of the system) to run to the car amp, that is the most likely source of your ground loop. All parts of the system have to be at the same ground potential or you will have a ground loop. Your's is the difference in ground potential between a bookshelf system plugged into an AC outlet and the car amp running off the car battery.
It's impossible to tell you and be certain the "fix" will work when dealing with a car amp in the house. The first thing I would try would be taking the power for the car amplifier from a 12 volt inverter which you should be able to find at most car audio shops.
There are quite a few threads devoted to using car amps in the house. Cruise through the past thread archives and see if you can find a better answer.