I have a pretty draining sound system, with a 5 farad cap and i just have the stock alternator. I've never had any problems yet and my stereo is almost always all the way up. I'm using one of those optima red top batteries though. I don't know if that makes any difference. I think my stereo draws about 130 amps at full power, which means at a musical peak, so I'm betting it doesn't draw anywhere near that much power most of the time, even when all the way up. If anyone has noticed a difference in the sound of their stereo since adding a high output alternator please let me know.