stereo making engine cut out

[roadkill69]

I recently installed a new stereo and amp in my 1970 c10. It's a 1200w jvc powering 2 8" subs. I noticed that when I hooked this up my motor will have a rough idle or cut out when driving while the stereo is turned up. I installed a 1/2 farad capacitor and that didn't seem to help. Obviously the stereo is pulling too much voltage from the motor. The alternator is a 100 amp acdelco brand new. Anybody know what could be causing this.?