Car amp question....

[se7en]

Hey all, i am new to the stereo section....


I am trying to test some car amps that I have..

one is a p4004 rockford fosgate(4 channel, specs are available online)
and the other is a sony exm702(2 channel, don't know any specs)

anyways, I am trying to fire them up inside with a 15volt-800mA dc power source... and neither one seems to work...

the sony one has a light that flashes, but that's it...no sound...(subs hooked up, and using laptop to send a signal to the amp..)

the Rockford one doesn't do anything....

I have test car stuff before with this setup, but maybe amps don't like 15 volts....or 800mA isn't enough....

Anyone have any input on this?


thanks

7

[Ryan]

You need an imput signal(variable), an 12 positive bias, a 12v ground, a 12v remote (tells the amp to turn on) and then your output wired correctly. Amps aren't much more complicated than that, unless you take it apart.

[se7en]

ya, I got that part already man...this isn't the first amp i have installed

I have never tested one inside before like this though....15 volts,800mA....is that toomuch? too little amperage?

[se7en]

Okay, using my electrical expertise I figured out that I think I don't have anywhere near enough watts of power coming out of the power source....15 volts x .8(800mA or 1 rounded up) = 15 watts ish....

no where near enough I guess

I will just have to install it in the car, and see how it works..

[Savin]

i was about to say.....800 milliamps is way too low. If you use ohm's law, you can probably figure out what kind of amperage you need to get the wattage you want, seeing as the p4004 rockford fosgate is rated at 400 watts, lol. for maximum watts you need like 26 amps? or something. 26x15=390 (close enough)

EDIT: I read from something that your sony amp is 140 watts per channel. I hope that helps.

[se7en]

ah, 140 per channel...that's nice I guess...I should bridge it then and run two 10's at 2 ohms, and it should run at 280watts? or more?

[tmac4t4]

IF your amp is designed to run at 2ohm stable, may overheat in the long run...and that 140 watts is peak wattage..you will be lucky to get half that wattage in RMS which is really all the amp can handle continuosly without fryin itself

[Ryan]

I'm quite sure you don't want 15 amps. I'm not sure exactly what system of amp they use nowadays, but you don't need an input equal to your output. My best guess is transistor amps, check out common emitter amps, and do some reverse calculations, since you know the RMS output. 15 sounds too high, and bridges won't quite double the output. Also, don't bridge it unless it says you can. Its pretty easy to toast amps... They're so complicated, I gave up trying to fully understand. I can build little ones, or simple ones for guitars, but car ones are too complicated. Also, the specs on the Rockford one say ~12 - 14.4 V.

[RS_OBD'oh_2]

This is kind of tricky.

Ohms law will not test for Power.
V=IR
Power is:
P=VI

Input does not equal output on an Amp. Hence the purpose of the amp. Without knowing specs of the amp it's hard to determine the input current needed to run the amp. 15V, 12V.. either should be fine. The Amp should still turn on and run. If the voltage is too high it may heat up faster and it should internally shut down the output to the subs. One needs to take in account Z, or impedance rather than resistance. The best way to check it is simply to install it. The Current draw of the amp is best unrestricted.

Good luck.