Tons of audio noise problem

hutacars · 09-21-2009, 05:32 PM

I just got my carputer up and running today, but I'm having major problems with my amp. I know it's not the amp's fault, as I tested it beforehand and it was running fine.

As a temporary solution, I've simply hooked up a cigarette lighter cable running from the back of the amp into the lighter, until I get some relays/other stuff I need to do a more permanent install.

I have a short (8") cable running directly from the audio output on my Mac Mini into the RCA inputs on the amp. When the carputer is on and the amp has power, there is just a wall of noise. If I play music, I can hear it playing, but only just. When the carputer if off but the amp is on, there is just a loud whine. I was going to hook up an MP3 player to the other input, but that likely wouldn't make a difference since it makes noise even with the carputer off.

Any ideas are appreciated. Thanks!

thewizard · 09-21-2009, 06:52 PM

I know that you said this wiring setup is temporary, but until you run your amp's power all the way back to the battery you are going to experience the noise issue. That is in all likelihood your biggest problem.

hutacars · 09-21-2009, 06:59 PM

I now have an even bigger problem. I tried booting the computer with the amp already on, and it was only exhibiting low levels of noise, until suddenly the noise ceased completely. I looked down and noticed that the red light to indicate the cigarette lighter cable was in use was off. I plugged in a GPS, and it worked fine, so I guess the lighter is working fine, but I blew out my amp somehow. Likely next weekend I'll pop it open and check it out. Hopefully it's something simple such as a fuse. Once I fix it, I won't hook it back up that way, and instead make a point of purchasing everything I need and hooking it up properly.

PaulF · 09-21-2009, 08:58 PM

Or you blew the fuse that is built into the cig lighter cable. Most have fuses built into the connector.

hutacars · 09-21-2009, 09:22 PM

That's not possible, considering I was able to plug in my external GPS and it powered on like it was supposed to when the car came on, and asked me if I wanted to standby when I shut the car off. It has to be something related to the amp.

PaulF · 09-21-2009, 09:26 PM

Does the GPS use a different cable than than the one you are using to hook up the amp?

hutacars · 09-21-2009, 09:37 PM

Oh, I understand, I thought you meant there was a fuse built into the cable behind the cigarette lighter itself. I did not check for a fuse in the cable leading to the amp, but I shall tomorrow.

PaulF · 09-21-2009, 09:40 PM

If the cable itself has a light on it, I guarantee it has a fuse in it since it is more than just a simple connector.

That fuse is rated at 10 amps... 120 watts. You're trying to power a computer and amp off that. No way that will hold up.

hutacars · 09-21-2009, 09:44 PM

I figured the light just might come on only when it has a load, but you have a point. It's not powering the computer as well (that's powered directly off the battery), but I suppose even the amp alone could have exceeded 10A. There's no labels anywhere to suggest what it's rated at.

PaulF · 09-21-2009, 09:50 PM

How many watts is the amp?

The amp probably has a fuse on it. Whats the fuse rated at?

hutacars · 09-22-2009, 06:27 AM

It's a 400 watt amp. There may be a fuse inside it, but I have not opened it yet. Then again, maybe not, considering it was a cheap amp from China

I'll check the fuse in the cable first, and if need be I'll pop open the amp and have a look.

PaulF · 09-22-2009, 06:39 AM

Volts x Amps = Watts

Car electrical system ~ 12 volts.

400 watts at perfect efficiency is 33.33 amps.

33.33 is over 3 times what a lighter socket can handle. You definitely blew the fuse in the cable. Run it to the battery.

hutacars · 09-22-2009, 08:16 AM

I thought watts of audio output were different than watts of power draw? It provides 400 watts of audio output, but I don't know the power input, because as I said earlier, there's no label that tells me, nor can I find any information about it online.

The amp is designed to be used with a cigarette lighter cable, so it *shouldn't* draw more than one of those cables can pull... right?

ik632 · 09-22-2009, 09:45 AM

Most amps aren't designed to run off a cigarette lighter plug. You need to connect it all correctly and then see if the issue is still there. If your signal cable is running next to the power cable you will get a lot of noise too. Try running the amp with an mp3 player connected to the input. The input level will be about the same as from the computer so get it roughly setup using the mp3 player and then you should be good. Save your self some time and frustration now and just run the proper cables. For a 400 watt amp, you should be fine with some 8awg from the battery. Be sure to fuse at the battery and then fuse again before you go to the amp. For ground, you can connect to somewhere near where the amp is mounted. Finally, you'll need remote turn on either from the computer or some other source that you are using.

soundman98 · 09-22-2009, 10:05 AM

i think some of this is assuming that the amp truly puts out 400 watts-- if it is just a cheap china amp, i would have to say that the wattage is wrong (or measured at 24volt input...).

it used to be true for car audio amps of any caliber that you could use that formula, but these days, it seems that alot of the companies have strayed to their own measurement system--mostly the cheap amp producers. for these amps, the formula does not work.

but on the other side of the coin, there is CEA certification, and higher end companies that pride themselves on selling exactly what they market (alpine and jl are 2 of the more popular companies that do this).

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