# PC power driving car amp?



## Bilbo (Dec 13, 2007)

Time to pick your technical brains again, you zombies....

I want to run a mic through a car amp I'm no longer using to either speakers or a sub (or both). I don't have a car charger I can use so was thinking of trying the PC Power supply.

I know the supply runs 12 volts but usually only about 10 amps, right? My sub is 900 amps but I don't need it loud, just enough to use for my Magic Mirror.

It's a lost cause, right? I need to find a charger to run it right? The plan was to run the mic through my computer (voice changer), to the amp and then to the sub to make my voice ominous.

If you have a better (easier, cheaper) route for me, I'd love to hear it!

Quick add... one thing I'm pondering if I use either the power supply or the charger, what does the remote wire get hooked up to??


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## hedg12 (Jul 6, 2008)

I'm guessing you mean 900 watts - 900 amps would melt some pretty big wires. That said, 900 watts at 12 volts is still 75 amps. Of course, that's the worst case scenario - full volume at max load. I'd imagine the amp will run at moderate volume on 10 amps. Just to be safe, you might want to put a 10 amp (or maybe even a 7.5 amp) fuse in line with the amplifiers + lead. That way if you get carried away with the volume, the fuse will blow before the power supply melts down.

edited to add: The remote wire needs +12 volts to turn the amp on. Just hook it up with the + wire of the power supply.


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## Bilbo (Dec 13, 2007)

Well hot diggety! Thanks Hedg, I certainly did mean 900 watts. I was typing after a very long day and missed that one.

I will certainly put that fuse in place, although the power supply was free from my brother in law still don't want to fry the thing.

Good to know about the remote wire needing 12v too. I lost my amp's manual so thought it was a lower voltage to trigger.

I'll write later tonight and tell you how it went.


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## corey872 (Jan 10, 2010)

You might be getting close to a power limit there...10 amps at 12 volts is only 120 watts of input power. Then figuring most amps are only 60-70% efficient so that only lets you run mid 70 watts max of acoustical power. Which then means running maybe 35-40 watts continuous - which I think is hardly going to be audible on a 900 watt speaker.

Maybe you could ditch the 900 watter in favor of a speaker around 20-30 watts. Or maybe use a battery and a good charger to keep up with the power requirements.


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## Wildcat (Nov 3, 2007)

On the power output of the car amp. I know a lot of amps will claim big wattage but the easy way to tell the truth is look at the fuse in the amp. A 30 amp fuse will only draw 360 watts no matter how you do the math. 
So check the fuse on the amp to get the required amperage.

As mentioned above, a battery would probably be a better option if available to run a high wattage audio system. Another option would be to go to a car audio installation shop to see if they would part with stock audio equipment that they remove from cars. An average car audio head unit can put out more than enough power for most haunt situations. On the plus side most stock audio systems could be run from the PC power supply.


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## hedg12 (Jul 6, 2008)

corey872 said:


> You might be getting close to a power limit there...10 amps at 12 volts is only 120 watts of input power. Then figuring most amps are only 60-70% efficient so that only lets you run mid 70 watts max of acoustical power. Which then means running maybe 35-40 watts continuous - which I think is hardly going to be audible on a 900 watt speaker.
> 
> Maybe you could ditch the 900 watter in favor of a speaker around 20-30 watts. Or maybe use a battery and a good charger to keep up with the power requirements.


The wattage rating of a speaker refers to the maximum power the speaker can handle, not the amount of power necessary to drive the speaker. (There's no regulating body that oversees these ratings, so take the specs with a grain of salt.) The spec that matters is the efficiency of the speaker - the output of the speaker when driven with 1 watt, measured at a distance of 1 meter. An inefficient speaker will be in the 75 - 80 db range. A doubling of power should result in a 3db gain, which is considered a doubling in acoustical output. So if you could get 32 watts out of the amp and the speaker had a 75 db at 1w/1m efficiency, 32 watts would give 93 db output. 93 db is about like an obnoxious Japanese car with a fart can muffler in a tunnel - plenty loud.



Wildcat said:


> On the power output of the car amp. I know a lot of amps will claim big wattage but the easy way to tell the truth is look at the fuse in the amp. A 30 amp fuse will only draw 360 watts no matter how you do the math.
> So check the fuse on the amp to get the required amperage.


We used to refer to inexpensive car audio amplifiers as being rated in "watts ILS", or If Lightning Strikes. Like I said, there's no regulation for these ratings. Manufacturers can put anything they want on the equipment just for the cost of the label.

I agree that a battery and charger would be a better option, but a PC power supply should work OK in a pinch.


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## Bilbo (Dec 13, 2007)

I must have been asleep when I sent my original message.... My amp is a 900 watter, not my sub like I said. Not sure of the power level of the sub, but I did hook it up using the suggestions I got here (thanks to all!!!) and it kicked out more than enough volume to satisfy my needs. 

Who knows? I might even be able to run some led spots off the same supply?


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## Bilbo (Dec 13, 2007)

Thanks once more to all who helped. That's what makes communities like this great!


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