Car amp in dorm room? What kind of power supply?

[Dojo2000]

I'm trying to find a way to take my subs and amp out of the car and use them in my dorm room while I'm up here for college.

It's a Jensen XA1120. I know I need a 12V-13.8VDC power supply, but I'm just not sure how many amps I'm going to need. The stock altenator puts out 105 amps so I don't think the amplifier will need an ungodly amount of power.

Right now I'm looking at this one from over-priced Radio Shack. It rated at 25 amps. It that overkill, or not enough?

[ July 08, 2003: Message edited by: Dojo2000 ]</p>

[Dojo2000]

A guy at Radio Shack (I'm guessing a Physics major here at App) said I would need at least 18 amps. He said a 20 amp power supply would be what I needed. This sound about right?

[Distephano]

20 amps should be more than fine. 20 amps are what most household (110 volt) circuits are. So, for just an Amp, 20 amps should do the job just fine.

[youngcamarokid]

<blockquote>quote:</font><hr>Originally posted by Distephano:
20 amps should be more than fine. 20 amps are what most household (110 volt) circuits are. So, for just an Amp, 20 amps should do the job just fine.<hr></blockquote>

ARGH!!!!!

20 amps might be what a household circuit is, but that's at 120volts! That means the wattage is about 2400watts!!!!! GRRRRRRRRRRRR you can't compare a household ampere to an automotive ampere...well you can, it's just most people think in watts....and 20 amps at 12 volts is only 240 watts!!!

Question #1) How many watts is your amp

take the wattage, divide it by 12, and there's your amperage rating.

Yes, I say "12", because a bench power supply will actually output 12 volts, instead of 13.7, which is common in cars.


Finally, overrate the supply by 15%. so if your amp draws 20 amperes at full capacity, overrate the supply and get one at 23 or more amps.

[Darknight]

When you step-down and rectify high voltage AC to low voltage DC, the current compensates automatically according to how much demand you place on it. It is true that 20 amps at 120 volts is more wattage than 20 amps at 12 volts, but the load will pull the additional amps needed through the rectifier. However, you have to make sure the circuit can handle that additional current load.

Look at it this way, an amp is an amp, is an amp. It's a unit of electrical charge, like a gallon of water. Now, pump that gallon up to 200psi through a pipe, and you have high voltage. Make the pipe diameter larger, and the pressure(voltage)drops, but the current remains the same. Now, imagine having a vacuum at one end of the pipe, and normal pressure at the other end. The pressure difference will still be great, and the water will still come shooting through at great force, as it if were pumped through.

That's how high load demand works. It's like having an electrical vacuum, and the normal 12volt supply suddenly has more current being pulled through. Is the pipe large enough to hold it? You better hope.

My amp has a 30amp fuse for every 200 watts. How many watts is your amp rated for, and how high do you run it?

By the way, I used to work at the Shack. When they talk about "high-power" car stereos, they mean between 200-500 watts. I'm betting this is designed to work in that range.

I personally have a Radio Shack Optimus 400watt amp, which puts out good power. I'm not looking to cause an earthquake, though. It sounds good through a couple 10s. Plenty of thump for the buck.

DK

[ July 09, 2003: Message edited by: Darknight ]</p>

[Dojo2000]

I took Physics for two years. I should have known that formula [img]graemlins/dunce.gif[/img]

220 watts / 12 = 18.3A
Just like the guy at Radio Shack said.
He said I should go for about a 20A power supply.

My amp is rated at 220 watts and I usually run it at about 3/4

My local radio shack didn't have that amp from the website, so now I'm looking at some power supplies off Ebay. The main one I'm watching is a 25 amp continuos power supply.

If any of you guys know of a place to get one dirt cheap please let me know.
___________________________

Also, I do have a stereo receiver I'm borrowing from a friend that supposedly rated at about 200 watts. I've thought about hooking my subs up to that, but the problem I see is my subs are wired in series and bridged on my car amp, and I'm not sure how to hook them up to the receiver. My two 12"s are in a single chamber box so they wouldn't sounds too good hooked up to seperate channels. I'm not sure if I should try hooking them up or not. I had planned on using a small 12VDC power converter to power my x-over.

[youngcamarokid]

check www.nutsvolts.com

ask if anyone wants to sell a power supply for cheap

Also, you need to take a look at the surge draw of your amp, it's MAX rating that it can push in one thump. Actually, that's not technically the surge rating, but you'll be good from there.

Make sure the surge rating is high enough on the power supply to handle that thump.

If i had to do it?

Use a car battery. Have a switched charging supply for the battery. Engage it when the amp is not in use.

[Dojo2000]

I don't know what the surge rating on it is. I don't have the manual anymore, I can't find any power specs of it on the internet, and there's nothing like that on the amp itself.

Being a college student, even $60 for a power supply is kind of steep for me.

A battery would definetly have the amperage for the amp, but how long would it actually last? I've seen it done before, but the battery died in less than a minute hooked up to a amp no more than 500 watts. What kind of charging supply would I need, like a regular battery charger?

Does anyone know if hooking the subs up to my reciever would work?

[AllTheGoodNamesAreGone]

"Does anyone know if hooking the subs up to my reciever would work? "

it will work.. just look at the specs on your reciver before you do it make sure the speaker impeadence is higher then the recivers lowest rated impeadence..

its probably not the best idea in the world.. but it will work fine assuming it cranks enough power to really move those subs..

[Dojo2000]

<blockquote>quote:</font><hr>Originally posted by AllTheGoodNamesAreGone:
"Does anyone know if hooking the subs up to my reciever would work? "

it will work.. just look at the specs on your reciver before you do it make sure the speaker impeadence is higher then the recivers lowest rated impeadence..

its probably not the best idea in the world.. but it will work fine assuming it cranks enough power to really move those subs..<hr></blockquote>


<blockquote>quote:</font><hr>Also, I do have a stereo receiver I'm borrowing from a friend that supposedly rated at about 200 watts. I've thought about hooking my subs up to that, but the problem I see is my subs are wired in series and bridged on my car amp, and I'm not sure how to hook them up to the receiver. My two 12"s are in a single chamber box so they wouldn't sounds too good hooked up to seperate channels. I'm not sure if I should try hooking them up or not. I had planned on using a small 12VDC power converter to power my x-over. <hr></blockquote>

Not sure if you read this, or thought I was talking about my car receiver.

My basic concern is how to wire the subs up to the receiver. The subs are those cheap *** Road Gear 12"s from Wal-Mart [img]tongue.gif[/img] (they don't sell them anymore)

Right now there's four 6x9's hooked up to the receiver, and it's just not giving me the thump I want ;)

[AllTheGoodNamesAreGone]

"The subs are those cheap *** Road Gear 12"s"...

OMG.. you acctualy use those?

i bought one as a joke one time.. and but it in a plastic bucket and wired it with and old lamp cord.. it was the funnyest thing ever..

Those subs use like little to no power.. so i guess you could run it off your head unit/ reciver.. it will sound like crap though without a cross over..

[ July 09, 2003: Message edited by: AllTheGoodNamesAreGone ]</p>

[96firebird311]

So you plan on using your HOME reciever for this amp. Using speaker level inputs I'm assuming? Does the amp have speaker level inputs? Or are you gonna use a line output converter?

[Dojo2000]

There's actually two topics going on in this same thread. Sorry about the confusion.

My first question had been how many amps would a 12VDC power supply need to handle to power my 220 watt car amp. I've determined it's about 20-25 amps. That would make for an expensive power supply (I'm a poor college student.) I'm watching a couple on Ebay, but I don't think I'm going to find one cheap enough.


My second question was refering to a JVC home stereo receiver I'm borrowing from a friend. I don't know the specs on it, but he says he thinks it's rated at around 200 watts. I would use this instead of my car amp.

I would hook up my two subs to the receiver. Problem I see is my subs are wired in series because they're in a single box. My car amp was bridgeable so it wasn't a problem. I'm not sure how to wire them to the stereo receiver; left channel, right channel, does it even matter? Am I making a problem out of nothing?

Right now the stereo receiver is hooked up to four 6x9's. I run a head-phone jack-&gt;RCA plug to the receiver from my computer. I had planned on hooking up my car cross-over to the RCAs. The cross-over would be powered by a 12VDC power converter I was going to splice into.

[youngcamarokid]

It's not a problem at all to run them off your stereo receiver.

Check the impedence of the receiver's outputs, it probably actually has a 4 ohm out. If your subs are 8 ohm, wire them in parallel, run them off the left channel. If they're 4 ohm, wire them in series, run them off your left channel.

Is your crossover active or passive? If it's active, you know it needs to go before the amp, right? If it's passive, you have no problem.

If it's active: you can probably jurryrig the crossover with a tape output, then send the input into the spot that says "tape 2 monitor". Mine all have that input, it's usually for checking the gain on your recording device, but you can use it as a loopback input.

[Dojo2000]

<blockquote>quote:</font><hr>Originally posted by youngcamarokid:

Is your crossover active or passive? If it's active, you know it needs to go before the amp, right? If it's passive, you have no problem.

If it's active: you can probably jurryrig the crossover with a tape output, then send the input into the spot that says "tape 2 monitor". Mine all have that input, it's usually for checking the gain on your recording device, but you can use it as a loopback input.<hr></blockquote>

My crossover is active. I have RCAs running from computer to the receiver's CD In, and I can place it on them. I have a line-out converter laying around here that I could have used anyway.

Thanks for the help guys. I'm still not exactly sure what I'm going to do, but I'll probably go the receiver route unless a power supply falls into my lap.