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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.
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MorryiseN1 month ago
Hae I had my amplifier connected to a psu which supplied 10 amps but it stopped working on the 3rd day... The amplifier is rated at 36 amps.... What could be the problem?

I don't know if you being sarcastic or not, but your psu was really weak and it broke.

IsaacS161 month ago
But how many Watts should the cps be?
High... I have a audiobank aab 4560.4k 4channel amp with 2 25A fuses... So I would guess that that is the min A needed... But my psu is only rated 16A... I have 2 of these nd neether switches the ap on.... I was wondering if its possable to use both on one amp combining the amperage? This might be a daft question though but boh psu is 450w
JesusE1 made it!2 months ago
I forgot to mention its all connected to four 6.5 kicker speakers. Not sure the watts but definetly 4ohms each. Amp is 4ch set up w 10a fuse. See pics. I guess my question is do i need a smaller cpu rated at less amps. Im guessing i need to rewire the whole system with thicker wires and group the wires better on cpu. I also connected the blue wire from amp directly to radio remote wire. Led lights were connectd to smaller separate yellow and black wires off cpu. I guess i over loaded the CPu
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JesusE12 months ago
Great article. I myself have tried to build a self powered speaker tower with a cpu rated 16a, 10a radio with front and rear preamp rca connections. They are wired with 16 guage wires. I also connected three led lights. The system is powerfull but the cpu blew at around two hrs. The amp is a inexpensive plye marine amps with leads and no terminals. I taped everything temp. Where did i go wrong. Can you help me? Im really excited to find such usefull information and want my project to be a success. Thank you.
Does any of the power supply electrical noise get through to the speakers or is it relatively clean power?

I get noise, I used an ATX power supply and my 8" Bazooka picks up hum from the power supply.

GobiiI rccipriani2 months ago

That may be due to the psu being a switching power supply (which
sometimes lets a tiny tiny small amount of ac current through like 0.5v)
so you need to ground the power supply. that should fix your problem.

Depends on the brand of the power supply I'm sure, but computer circuitry usually requires a very even input voltage. I would be surprised if any noise got through, but an electrolytic capacitor wired in parallel with the yellow and black wires should help even it out if there is.

If a power supply hum is present, it's possible that the system isn't grounded correctly.

ddvniek4 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)  ddvniek4 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.
Ilikeaudio eh10803 months ago
Hey, a question, if u have two 25a fuses on a four channel sony xplod 500 watt xm-504z, would u have to get a power supply to equal both fuses or just one? I want to bridge a 10" 300 watt sub and connect two speakers, how much amperage would i need, equal one fuse or both?
Im looking at this psu, what do u think? http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=8438086&CatId=1079
ddvniek eh10804 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.

An electrical component only draws the amps it needs as dictated by its impedance, and a car's rubber tires do not affect its ability to ground because it doesn't get electricity from the power grid. Its ground is its chassis, which is connected to the negative terminal of the battery.

Is your multimeter dead because you bridged a high amperage power source with it? Using the unfused side of a multimeter to short a circuit which could potentially deliver over 20 amps is a bad idea.

The potential for current spikes from the alternator is a good point, though.

Si mon carnalito I have four of the 12v yellows connected together reading 13.4

eh1080 (author)  ddvniek4 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.
ThomasT7 eh10804 months ago

Thicker conductor is necessary for higher current, whereas thicker insulation is necessary for higher voltage. A car battery only supplies 12 volts, but it can pour out an enormous 200 amps. The current from the outlets in your walls probably won't ever exceed 15 amps, since that's what most household circuit breakers are rated for. However, the 110 volts needs more rubber around the wire.

Wire gauge also changes for the length of the connection. If you're just running a short connection from a power supply directly to an amplifier on top of it, you can get away with a slightly lower gauge wire. However, when wired up in your car, the wire has to worm its way from the battery and through the chassis and into the trunk. This extra distance will benefit from a thicker gauge to keep the wire from heating up.

This is why jumper cables are made with such thick wire. 200 amps going across ten to twenty feet requires a lot of copper.

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.
ThomasT7 ddvniek4 months ago

The people at Yahoo probably thought you meant shorting all the yellow wires directly to the black wires without a resistive load in between, like your amplifier. This most certainly would blow the power supply, and probably throw a breaker somewhere in your house.

Alternatively, you could buy some thicker gauge wire, solder all the yellow wires to one at the source, then solder all the black wires to another similar thick-gauge wire, and run just those two from the power supply to the amplifier. You really don't want to just use two of the original wires from the power supply. Running too much amperage through a single, thin wire is a fire hazard.

jeffrey.oraye3 months ago

upgrading my cps from 550watts 25amp to 800watts 35amp will it give more kick on my 12" subwoofer?i have 400watts car amp powering 1 12" sub,2 10" mids ang 1 bullet tweeter..

hi guys if i buy active subwoufer whit amp allrdy inside and i hooked it up whit 450 w cps (computer power supply) will it work normal or should i buy 600 w,400w,250,200

which one is the best for 300 wat ground zero GZIV 120XACT ???

for a 300 watt amp, you should use a 300 watt or higher supply. Amps are usually rated for their root mean square (RMS) wattage, which is a somewhat deceptive rating for the amp and the circuit usually won't draw this much power. However, spikes do happen and it might help to have a little wiggle room with the wattage, especially if you intend to use it often at full volume with low impedance speakers.

400 should be ample for a 300-watt amplifier.

Antwon078 months ago

Ok, so i have on my receiver a mono channel rca plug for my subwoofer line out. I know that is going to be running at 8 Ohms. If i get an rca splitter and plug both lines into the rca line inputs for left and right side on the amplifier, will that drop both sides down to 4 ohms and be ok to run my subwoofer?

ThomasT7 Antwon074 months ago

The amplifier combines both the left and right channel for a mono output. This shouldn't affect output impedance in any way. Are you talking about using the RCA splitter to hook it up to a signal source, or are you talking about hooking up a single subwoofer driver to both output channels?

Just to clarify something. You sad the "stereo puts out an 8 ohm signal" that's incorrect. If the speaker is 8 ohm then the stereo will put out a specific voltage and amperage. How ever many volts x amps the stereo puts out is dictated by the resistance of the speaker. A 4 ohm speaker with an av reciever can be bad because the 4 ohm load can make the reciever over work itself. Because the resistance went from 8 to 4 than the power is now doubled! Look up ohms law its pretty cool.

Actually since we're on the topic of clarification and being incorrect, what you said is about halfway correct:

"A 4 ohm speaker with an av reciever can be bad because the 4 ohm load
can make the reciever over work itself. Because the resistance went from
8 to 4 than the power is now doubled!"

I recommend reading ohms law as well, it is pretty neat, because a 4 ohm load from a SVC driver to an 8 ohm amplifier = a 6 ohm load, so the resistance is not entirely dictated by coil impedance from the speaker(s).

I would go into more detail but you get the point, no one likes to be corrected, especially on an irrelevant/trivial piece of information that doesn't effect the outcome of what they're trying to accomplish by reading it. That being said, nice article to the author.

russ_hensel7 months ago

Just a note to let you know I have added this instructable to the collection:
Encyclopedia of ATX to Bench Power Supply Conversion
>> http://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/
Take a look at about 70 different approaches to this project.

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

DilawarS8 months ago

i have an amp(alpine class D mono car amp) with 8 voltage dc input and 25 amp fuse so can i use this amp with 12 voltage dc ??

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