Instructables

Car Amplifier and Subwoofer Powered By a Computer Power Supply

video Car Amplifier and Subwoofer Powered By a Computer Power Supply
Background Information:

For starters, your car amplifier is meant to receive its voltage from a 12 volt DC source which is your car battery. Common households use approximately 120 volts AC. So you can see that we two problems. The first is that we need 12v and not 120v, if this was the only problem it wouldn't too hard to solve. However the real problem is that we need DC electricity instead of AC. So why not use a simple transformer, like a cheap laptop charger that supplies 12v DC?

The problem with using some type of transformer is not that it puts out 12v but its the amperage. A typical car amplifier requires anywhere from 10-30 amps. (You can check how much amperage you need by looking at the fuses usually located close to the inputs on your amplifier.) So if you were to use a simple transformer that delivered 12v DV, it would most likely work at very low volume but it would get destroyed by the power needs once the volume starts to get louder and the amplifier requires more amperage. So, do they make transfers at a high amperage at 12v DC?

Yes, but they are often very expensive, easily on the upwards of a few hundred bucks for a quality one. So what's the best solution thats also more economical?

The best solution is to convert a computer power supply (CPS) to work at 12v DC and deliver high amounts of amperage. This is the most effective and possibly also the simplest way to get your amplifier working at full capacity. The process isn't too complex, it would be beneficial to have some knowledge of basic electronics and circuitry, and also be able to solder.

Tutorial:

To begin, first know how many amps your amplifier needs. Do this by looking online or checking the fuses on your amp. Ideally you would want to exceed the amperage on the fuse so that your not constantly working the CPS too hard. This is the one i used, its rated at 24 amps for the 12v output. (http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2475867&CatId=1078) Once you have your CPS, search the serial number with additional words such as pinout to locate your models pinout sheet. Its typically not too hard to find pinouts of a CPS. Once located, you want to find the pin that says something like "PS_ON" or "PS_OK", typically located on the "Main Power Connector" plug. Most of the time the wire will be green but I have seen a few that have been purple or other different colors (typically older power supplies don't use green). Once you've located that wire, connect it to any of the black ground wires. What this does is allows the CPS to turn on properly. So once you've connected these two wires, try to turn on your CPSband it should work.

Now that you have your CPS working, unplug it and take the cover off. The orange wires usually supply 3.3v (good for wiring any LEDs if you want) and the red wires usually supply the 5v source, both in DC voltage of course. If your only using the CPS to power your amplifier, then trim all the orange and red wires. KEEP the Yellow and Black wires, those are the ones used to supply the voltage and ground the amplifier. Once down, group all the yellow and black together separately. I used zip ties so they weren't a mess.

I STRESS that it is needed to wire all the yellow wires and all the black wires to the amplifier. When running this high of voltage, just one or a few wires going to the amp may work great at first but it will lead to problems. Think about the wire thats used to connect the amplifier to your car battery, those wires are thick. Its not only a strong fire hazard but also keeps the voltage flow more open and puts less stress on the amplifier by wiring them all together.

Now you need to find a way to attach a bundle of wires to a small terminal on your amp. The best solution i found was to use a fork wire terminal for two reasons. (1) it makes a great connection. (2) it doesn't look sloppy. You can buy these at your local hardware store, automotive store and just about anywhere that has a hardware section. I would encourage you to solder the wires together into a bundle before crimping to terminal on. This ensures that every wire is connected and makes it hard to pull the wires out from the terminal. For extra precaution i heat shrinked the connection as well.

Additionally, you will want to bridge a wire from the 12v source on your amp to the "REM" or "REMOTE" terminal on your amplifier as well. This bridge allows the amplifier to turn on.
So connect the 12v, ground and REM wires to your amp and it should be good to turn on. Don't connect it to your subwoofer right away though.

Lastly, im sure you know how to connect your amplifier to your subwoofer but you need to know how to connect it to your stereo. This is a little complicated because of the amount of ohms your amplifier receives and the amount of ohms your stereo puts out. It almost all cases, your home stereo receiver will put out a 8ohm signal and your amplifier will require a 4ohm signal. This problemcan be easily solved by using the speaker level inputs on your car amplifier. Simply connect both channels of the speaker level inputs on your amplifier to just one pair of terminals on the back of your receiver. This splits one 8ohm signal into two even 4ohm signals for your amplifier. Double check your ohm ratings to be sure though.

Now, give it a try.

Additional Information:

Be careful, electronics can be fragile in the right environment and you don't want to damage something and spend hours or maybe days trouble shooting or having to re-buy something. There's no shame in posting a comment if your unclear about something and need help.

I have had offers to build the CPS unit already converted and ready to hook up. I have no problem doing this for a bit extra than what it costs for materials and shipping. Send me an email to work something out.
This is something what i need to try nice one!

The amount of disinformation in this post is amazing. (just as the first reply said).

Basic Electricity facts:
The lower voltage, the thicker wire it needs. The higher voltage, the smaller diameter wire needed.
EXAMPLE. Car amp vs Home Amp, given that both give same power output.
Car amp needs ticker wire because its feed by lower voltage (12v). Home Amp has less thick wire to feed it because its 127v. Voltage helps on "pushing efficiently" power.

WIRE SIZE, for overcoming voltage loss over longer wires.
At lower voltage, the thicker wire it needs to travel farther to reduce voltage loss. At higher voltage, less wire diameter because voltage drop is less.
Car amp needs thicker wire because at lower voltage, there is more voltage losses over shorter amounts of wire.
Home amp needs to be fed with slimmer wire because 127v; The higher voltage feed, the less voltage drop in every yard of wire.
______________
The same stuff applies on every electricity conducting wire.

Transporting electricity through hundreds of miles, requiere very high voltages for two things:

1) So slimmer wires can be used (slim for the amount of energy transported)
2) So there are less voltage drop over every yard, mile, etc.

The opposite applies for car (12v) installations:
The Lower voltage, and the more voltage drop per yard (because lower voltage), THE THICKER WIRE IT NEEDS.
______________________
USING THE FULL AMOUNT OF AMPS over each 12v, 5v or 3.3v wires,
IF THERES THREE 12V wires (yellow), its needed to join them togheter to achieve a "thicker wire" through using the three.
__________



XsSPL7 months ago
There is SO much misinformation in this comments section it is scary. The reason a computer power supply can use a 16 gauge wire to transfer say 20 amps is because the current is going a very short distance so there is very little resistance. Resistance causes the wire to heat up and reduces the amount of current (amps) that can go through the wire. Another important reason car amplifier wires are so big is they have heavy duty insulation on them to make it harder to "short" them or have the electricity go where it's not supposed to go and ruin things or cause a fire.
The writer of this instruct able seriously needs to learn something about basic electricity before posting. Yes computer power supplies make great cheap basic power sources, but what you are recommending is likely to cause a fire in someone's house.
can someone tell me if i have a 400 watt power supply what size amp i would need ??
tsidoti5001 year ago
I'm not sure of the description of how to convert the amp to 8ohs. im going to hook it to my receiver with rca cables. do i still need to link the speaker outputs.
Does any of the power supply electrical noise get through to the speakers or is it relatively clean power?
12amedle2 years ago
i have a 100 whatt amp and 2 house speakers that have subs in them already. it sounded great in my 98 tahoe but i bought new speakers and subs. anyway i hooked this up in my basment but the subs are not kicking as hard as they did in my truck. i think i need a head unit to make it work better. i just pluged an rc cable to the amp then straight to my i pod. So what iam asking is, if i connect a head unit will i get better bass??
hsmith-luck2 years ago
Nothing quite like seeing the head unit & amp boot up -- Cheers, bud!
IMG_2292[1].JPG
misk02 years ago
I'm powering my amp this way , years and years ago . . . but , my amp eats pwr s. like candys hehe :)
tsiddiqui3 years ago
Hi. I am having a problem. My car amplifier is 500watts which comes out to about 41amps at 12v. I have found some cps's that put out that much power but they have not one but 3-4 +12v wires or rails. And they are not evenly powered.

For example: I am getting a really cheap CPS which is 650watt and has 4 12v rails. +12v1/18A, +12v2/16A, +12v3/18A, +12v/3A. Now in a situation like this where there are 4 +12v outputs with different current output, do I still connect all of them together. I feel like if I am to connect all of these together the CPS would blow out. Also, would the amps accumulate (18A+16A+18A+3A) and give me a total of 55Amps? Would this work??? Please let me know cuz Im lost at this point. Thank You.
vision3583 years ago
What do you do about the RCA cables and inputs?
markzielon3 years ago
I know this is an older post so this question might not get answered. But it's worth a try I guess.

I'm having a little bit of trouble getting my CPS and amp to work together nicely. My amp draws 250W at 12V (which works out to max. 21 amps), and according to the label, my CoolerMaster CPS can throw out 550W (46 amps) total, or 360W (30 amps) at the 12V level only. So from these measurements only, this should be more than amperage to run the amplifier.

I connected the green and a black wire, and the CPS turns on and runs fine without anything attached.

I connected all the yellow wires together, and all the black wires together. I connected the yellow wire to the +12V input on the amp, and the black wires to the ground. I bridged the 12V and Remote inputs as shown.

However, when I turn on the CPS, the fan starts up and everything looks fine for about 2 seconds. All of a sudden, the CPS and amp both shut down unexpectedly. I'm starting to think that it's almost like the amplifier is somehow pulling too much from the CPS and shutting it down, but I honestly don't know enough about this sort of thing to take much of an educated guess.
annanearl3 years ago
The reason for the disparity with wiring from domestic to car is due to the diference in current drawn by a high or low voltage system.

Hmmmm.....didn't make much sense.....ok, in a car the maximum available voltage is 14 volts, the average being 12 volts. In a House supply, the voltage is 110 or 240 (USA OR UK)

The higher voltage allows for lower current use. Meaning wire size can be smaller. Which is good for keeping bills down. And installation costs down.

In a car the voltage is low, so the current drawn will be higher, hence the wire has to have a greater surface area. In amplifiers, the current drawn can be quite high, hence the larger size of wire. Especially for woofer drivers.

If you need to know relative currents and wattage:

100 watts at 12 volts = 8.3 amps available. So 400 watts is 4 x 8.3 = around 33 amps.

However, as eh1080 has said his system works so sometimes just doing it works.

As mentioned by ddvniek, the higher current causes heating so bear in mind a car battery can source 300 amps in certain conditions. Thats about 3.6 kilo watts of power. Nice if you want a brew, ( Tea, for our American friends) not much good if you want to keep things cool.

Bunching the wires at the CPS causes them to present a lower resistance, so lowering heating under load conditions. (Kirchoff's Law)

I hope this has helped. Great idea, in the spirit of re-using otherwise scrap units. Splendid.
Mindhunt3r3 years ago
nice 'ible! I have a couple of questions for you, I would like to try this but my amp needs 62 amps at 2 ohms and I'm not sure if my cps will push that many amps, what do you think? The cps is 400 watt, could you possibly run two cps to achieve the amps/watts you need?
ddvniek3 years ago
Hi. I have recently hooked up my Amplifier to a PCU. But I only used one black and one yellow wire of the PCU to power it. You said to connect all the yellow wires to each other and all the black wires to each other, and to use them that way. But when I asked if I must connect the yellow and black wires together (Like you did) on Yahoo Answers, people told me I will blow my amp and PCU if I did that. Why I don't know.... Can you please tell me if I will blow it or not.
My PCU supply's 14A on 12V+
It's a 450W
Please help
eh1080 (author)  ddvniek3 years ago
Thats a great question. After some additional research, it appears that the standard wire size for a computer power supply is 18awg. According to various sources, it seems that 16A would be the maximum for an 18awg wire.

However, there is a lot of information that skews this 16A rating. Each situation has their own variables that need to be considered specifically for that application.

Personally, i have had this set up for about two years now and use it daily. I've also built many more of these conversions and have never had or heard of any problems.

This question leads me to wonder why the power cable in your car for an additional amplifier is so huge (like 4-8awg). It just doesn't add up to me, why you would be able to use an 18awg wire in your house and then have to use something like a 4awg wire in your car.

Theres clearly something i'm missing here, ill keep doing some research in my down time and see if i can figure this out.
Maybe because theres no alternator being cranked by your car and sending direct current? not really sure, thats my take at it. I custom built my conversion with a nitrious switch, as a On / off switch, its pretty sweet. i would make my own instructable but the nitro switch isnt exactly easy to disassemble. and is almost permanently soldered together, but then again i think the switch could handle 120Amps.
ddvniek eh10803 years ago
Hmmm.... Yeah you're right. Maybe the power cables in a car is so huge because the car's battery Amp's are way bigger than the 16A of a CPS. I've read that a normal car battery gives round about 30A out. Thus the cable's need to be bigger to carry that type of current. Otherwise the cables could over heat and short out. Imagine 30 Amps running through a 18awg wire in a car.
Actually I'll give you a big hint.. there is a diffrence between House/Home electronics and Car Electronics.. It's called the Alternator.

Basically car electronics are typically 'over engineered' because unlike house hold appliances which typically can be certain that they are going to get a constant supply of power that isn't surging all over the place a Car can't.. you can actually watch this on (older) Cars simply by watching the Battery meter if your alternator starts to flux, the volts being thrown out by your battery also begins to flux as well, not to mention that cars have FUEL in them and are on rubber tires and don't ground easily.. it's better to over engineer their requirments there then to go 'oh damned we just blew up the car'

as for the actual output on the White PSU 12V and it's output Has any one actually bothered sticking a multimeter on a SINGLE plug and seeing what it's throwing out? My Multimeters dead atm so I can't.
eh1080 (author)  ddvniek3 years ago
Yes thats correct that they can give out something around 30A.

However though, the amount of amps running through the cable will only be what is needed by the amplifier at that instant. Especially for a smaller amp that would only require something like 15 or 20A at max. The size of the wire required even for a small amplifier is still something like 4 or 5 times bigger in diameter.

It might be partly due to the fact that the wire is running a long distance and that there would be a small voltage drop due to inefficiency with a small wire. However the increase in size due to the voltage drop would not account for that big of an increase of size for a wire only like 10-15ft.
Thicker wire has less resistance. Less resistance menas better sound.
Pro

Get More Out of Instructables

Already have an Account?

close

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!