I'm going to help my friend set the gain on his amp this weekend but I've got a couple questions first. He has a TMA 500.1 that is rated at doing 500 rms at 2 ohms. However, he installed a new alt in his car yesterday and his car runs at 13.8 volts. The 500 rms is rated at 14.4 volts so my first question is, how much RMS is his amp putting out at 2 ohm on 13.8 volts. Is there an equation to determine the rms? My second question is should the gain be set according to this new amout of RMS the amp will be doing at the 13.8 volts or at the 500 rms it is rated at doing on 14.4 volts? Also as far as setting the gain's voltage I saw in the other thread that it is the SQRT (RMS/Ohm load) correct?
the output power of the amp depends on the type of power supply it uses. a tightly regulated switching power supply will put out the same 500 watts regardless of input voltage, within reason. If the power supply is unregulated, or loosely regulated, then the output varies based on the input voltage. Either way, the output wattage really has nothing to do with setting your gains on teh amp. the gain control on the amp is designed to match the input stage of the amplifier to the head unit's line voltage. Find out if your friend's head unit has 2 volt, 4 volt, etc.. line-outs. Then set the gain to match that output voltage @ the head unit.
If you still want to find out his "output wattage" accurately, the way to do that is by using a bench power supply (regulated switching AC to DC power supply, high current) along with a resistive dummy load, an oscilloscope, a source device with a 20Hz-20KHz test tone (white noise or pink noise) @ a known voltage, and a True RMS digital multimeter. Then, you can get a "birth sheet" power rating for the amp. Otherwise you're just talking estimated power ratings, anyway.
Alrighty, thanks for the info. I'll set it to the 15.81 volts on my dmm. His voltage stays pretty stable around 13.8. I helped him upgrade his big 3 and he's only running the one amp on a 90 amp alt, that is new.