Car Amps on a PC

[YMK]

I have recently modded my case with a full paint job, a steel 120mm fan and two 50w RMS car amplifiers. One will be connected to the front of the SB live, the other to the rear. During this mod the floppy controller on my motherboard died. My hard drive now makes strange noises. Well I am getting both replaced for free. I bought a 25.5V 2A center tap transformer from radioshack. I am aware that I am running the transformer much harder than it was designed to run. I connected it to a homemade regulator circuit. Aside from the huge amount of heat it produces, there is another problem with the transformer (I think). I am worried that inside the case it will wreak all sorts of damage (electromagnetic fields) on my hard drive which is about 8 inches away. If anyone can help me I would be grateful.

[YMK]

oh by the way this transformer will also be powering a 200 watt subwoofer amplifier connected to a Polk EX 12" Subwoofer. Should I just leave the transformer out of the PC? It would be nicer to have it inside but leaving it out may be my only choice. Any thoughts?

[thekingofpain]

Are you trying to get GREAT sound from your PC to provide sound to a room or what? Killed/fried a m/b and hdd in the process from your mods?
AND they are gonna replace the components for free you fried???? (incredible support at times from manufacturers these days)
You did say SB Live right?
Just trying to understand what you're saying here as im sure others are as well...

[big_block_buick]

lmao, wouldnt it be better to buy a kick **** speaker system..obviously money is no object. so buy the best..

[YMK]

Well the motherboard is not dead. It works except for the floppy disk controller which died for no apperent reason. The disk light comes on but no data gets read. The hard drive just has a few bad sectors. These have probably gone bad due to physical shock and static shock but I don't know... I refuse to use up a card slot for a floppy controller so its covered under the 1 year warranty.

[MiKe85]

YMK!

You live in the thriving metropolis of Lancaster, Pennsylvania!!

Where in "Amish country" do you live? I used to live in Ronks.

[YMK]

Yep that's exactly where I live. Manheim Township to be more specific. No amish where I live.

[MiKe85]

ohhh well your missing out.. http://www.sysopt.com/forum/wink.gif

If i still lived in PA, i'd be going to Pequea Valley High School right now..

[MiKe85]

ahhh double post!!! http://www.sysopt.com/forum/frown.gif

[This message has been edited by MiKe85 (edited 06-26-2001).]

[YMK]

I ran a little test with the transformer. I put a couple of files on a disk and then I put it near the transformer. I plugged the transformer in and then I tried to read the disk to see if the transformer destroyed it and it did. I think I'll run the amplifiers off of the computer power supply. I realize I won't be getting the full 100 watts, but that much power through satellite speakers is enough to make your ears bleed so I don't think I'll be cranking it up too much.

[mds]

If you plan on running you amps off of the puter supply you better plan on buying a new computer soon, becouse as the car amps draw more current while under a load you ps volts with spike and flux alot fring your mobo,prossesor,hard drive's, and more. Also the inductance from a transformer can do unbelievible damage-plus all the added heat it will produce will make your prosessor run extremly hot. If you must use car amps locate them away from your computer a ways and buy a heavy duty 12v 50A power supply the results will be much better with less distortion and no damage to your computer. Also you need to put a line spike surpresser on before the amp to make sure you don't get a spike back from the amp during power up/down becouse it will blow your sound card. I have my puter hooked up to a Kenwood reciever/amp with output as 250w per channel running a set of Bose 501's, and it rocks the house.

[Warthog]

Why are you using car amps to begin with?

Warthog

[alondra]

warthog, excelent question. this micky mouse setup is frought with problems, inside a comp case is no place for magnetic fields and extra heat. not to mention destroying components, even if the company will replace them. duh. just the power supply for car amps are a problem they require clean DC. (like from a battery) from a rectified and filtered supply.) why not just use a sterio amp inputed from the comp. or a CD in the sterio. fella says "you dont milk a horse or ride a cow" http://www.sysopt.com/forum/smile.gif http://www.sysopt.com/forum/smile.gif IMHO

[YMK]

I am using two Optimus XL-50 Amps mounted on the left side of the PC. These amps contain no transformers. Not even one. There is only a tiny step up toroid coil. These amps are VERY efficient with power. I have tested them. When idle they use only 20ma. When playing very loudly they use 800ma (average). I have scrapped the idea of using the transformer at all. Oh by the way the amps have a built in protection from recieving or sending voltage spikes. The input is super high impedence (we're talking millions of ohms) so there is zero chance of the soundcard taking damage. These are baby amps and your question is why did I use them? Well how many people have done any modding on their cases beyond some stupid blowholes or paint jobs? Maybe a fanbus or a fancy fan grill. That's about it. My PC now has a panel of speaker wire clips on its rear. It can power speakers very well without a receiver or what have you. I use sony 4" as my front speakers and pyramid 3" as my rears. I'll use the transformer to power the Polk subwoofer. You don't need 12v and 50 amps to power amps. Thats 600 watts. the RMS rating for the baby amps alone are about 80 combined but I'll never play them that high anyway. Why put car amps on a pc? why not?

[YMK]

ooops double post

[This message has been edited by YMK (edited 06-27-2001).]

[alondra]

sorry, but I am having dificulty relating your last post with the first. maybe its me. oh well, hope it works for you.

[Warthog]

Why not? Because it's a pain in the @$$, that's why.

I have a stereo reciever...I simply ran a cable from the reciever to the sound card and viola! I have instant awesome sound.

And what kind of subwoofer can you have with that little power? http://www.sysopt.com/forum/frown.gif

It can power speakers very well without a receiver

...that's because you are using car amps... http://www.sysopt.com/forum/smile.gif

Warthog

[YMK]

I guess I didn't make myself clear. The two baby amps will run off of the case's PS. The subwoofer amp (Phase Linear PL200 125wRMS) will be powering a 12" subwoofer (Polk EX12) from a regulated power supply which will be plugged in the wall AWAY from the PC.

[RobRich]

MDS is correct with his statements above. At peak levels, you indicate your 50 watt amps pull 800ma a piece. That would be 1.6 amps from the 12v side of the PS. You have to consider that a PC operates with a switching power supply, not a linear feed type. This means the PS dynamically supplies enough energy to meet minumum needs.

As each amp moves from nominal (40 ma) to peak (1.6 amps!), say during a bass beat, then the power demands increase rapidly. It could be rapid enough that the switching supply can not meet the power needs, thus the amps will pull power away from other critical PC devices. While problems may not initially occur, this could cause component burnout due to brownout conditions. A switching power supply is not expressly built to rapidly respond to rapid power changes, as a PC usually retains a nearly consistent power demands.

Switch the amps to an standard power supply, then your problems should disappear. A small 2-4 amp transformer should be readily available for around ~$10 at most electronics supply vendors. I run my Audio Gods 400watt (Class A digital) amp off of an inexpensive ~$40 regulated 8 amp (12 amp surge) power supply with no problems.

Good Luck,
Robert Richmond

[YMK]

Yes. Like I said before, I have a transformer with enough power to run all three amps but I am worried about the EMF given off by it. Heat should be no problem though since the air in the case gets changed once every 5-10 seconds by the fan. The amps have built in capacitors of decent size. These amps won't be putting out any bass beats because I have capacitors in series between the amps and the speakers. That's what the subwoofer is for. As for brown outs, I have 2 100,000mf caps, but I don't think the PSU would like them or would it?

[DanU]

YMK,
Running two 50W car audio amps off of your computer power supply is very risky. A typical 300W ATX power supply can deliver about 120W into the +12V rail (10A). Assuming a 100% efficient audio amp, the two amps will consume 100W, leaving only 20W for the rest of the computer's +12V components! When you factor in the typical inefficienies of a class A or AB audio amp, you actually fall short of even powering the amps by themselves.

Don't think for a second that your amps will only draw 800ma max. If they do, then radio shack is guilty of fraud, cause 800ma * 12V is only 9.6watts. To drive two 50W loads at 12V, you'll need at least 8.33amps. Factor in the amplifier efficiency (~25% for class A, ~65% for class AB) and you may need ~30 amps for class A and ~13 amps for class AB.

Why don't you try installing a second (or even a third) ATX or AT power supply just to power your amps? It's a fairly common thing to do with high-power peltier units. Plus, people are practically throwing away AT power supplies, so you can get them for free if you ask around.

Don't use super-caps since a computer PS may not like such a large capacitive load. Super-caps are great when you're amps are connected the to horrendous electrical storm that is 12V auto power. A computer PS, on the other hand, is designed to provide highly regulated power to sensitive computer parts. They are orders of magnitude better than 12V auto power so a super cap isn't necessary.

Good luck with your project. Once you get it properly powered, it sounds like it will kick *****.

[YMK]

Thanks Dan, Its nice to hear some encouraging words rather than the negative feedback I got from 90% of the other people. You seem to have a good background in electonics. A second PSU is an option I haven't considered. What do you think of just a second transformer? How is a PSU sheilded so well? Would a steel or aluminum project box stop electromagnetic waves? OK. When my amps are idle they consume about 20ma each. When they are blasting, they average about 2.8 amps RMS. I'm sure the peak draw is a lot higher. I like to set them at a level where musical peaks don't sound distorted. Unless I play a square wave really loud I don't think they will pull 8 amps constantly (well, the fuses are 7.5 Amps). I would have to chop up my case for that second PSU right? I have a set of 4 stereo wire clips in the back of my pc kind of like on a reciever (8 clips total). They connect to the amps mounted on the left panel of the PC (on the outside) with a 12 pin molex connector. I will post some pictures of the case as soon as possible. Are there any interference issues or EMF problems with the amps mounted on the outside of the case? Will they wreck my HD? I know they have a high frequency DC-DC converter inside. Thanks Dan.

[DanU]

Using a traditional transformer + rectifier + linear regulator for a power supply works OK for low wattages, but at higher wattages you start to suffer from high heat dissipation and the weight of the transformer. Switching power supplies like a computer PS are really the way to go unless you have a specific need for a traditoinal linear power supply. They're far more efficient, cooler, and weigh much less.

The switching PS inside a car audio amp is very similar to the switching PS inside a computer power supply. Both are generally well shielded by their metal cases. I doubt they will cause any interference with your hard drives or anything else for that matter. Then again... I guess anything is possible. It just seems very unlikely since a car amp is usually built inside of a beefy aluminum enclosure that doubles as the heat sink. As a precaution, try mounting your HD as far away from where the amps are going to be.

[hamsterstan]

What ever you do don't put the amps and its transfomer inside your computer case, spend a bit more money and put them in there own case. I install systems into cars and even then if you put an amp to close to the head unit it will pick up interferance. So if it is any where near your HD and Mobo it will create some BIG problems.
And don't use a Switch mode power supply for them get a suitable transformer, rectifer, regulator and filter.

Stan the man with a mini van

[YMK]

The amps are on the outside of the case. I'll probably use an AT 350W supply since I have one in the basement somewhere... I'll try to post pics soon.

[DanU]

hamsterstan,
Why the bias against SMPSes? Sure, they're not as clean as a linear regulator, but it's WAY cleaner than what you get out of a car's electrical system. Besides, there's no way you can avoid having an SMPS because EVERY high power car audio amp has a boost converter built into it! Without it, we'd be limited to a measly 18watts per channel at best. P = (V^2)/(2R), V=12V, R=4 ohms.

YMK,
You may need to put a medium-sized resistor as a dummy load on the +5V line in order for the PS to properly operate. In general, most like to see a load that draws 10% of the rated maximum. Assuming a 25A max capability, you'll need a 2 ohm dummy load to draw 2.5A on the +5V line. Two flameproof 1 ohm resistors in series should do the trick. Practically every radio shack has them. You MIGHT be able to get away without this, however. Try it first and see.

[YMK]

Dan, I am using an AT power supply. Both amplifiers turn on with no problem when the PSU is turned on. I haven't put any sound through them yet. Should the resistor draw 10% of the PSU's total power or just the power on the 5v rail? I'm thinking of controlling the AC line to the AT PSU by a 12v relay connected to the +12v of the ATX PSU so that both turn on and off together.

[This message has been edited by YMK (edited 06-30-2001).]

[DanU]

In general, most (but not all) SMPSes have a minimum load requirement for each source that is 10% of the maximum power available from each source. If the loads for each of the sources draw less than that, then the power supply may regulate poorly or may not even start at all.

Take for example a typcial 250W AT power supply. It can supply up to 25A for the +5V rail (125watts) and 10A for the +12V rail (120 watts). The remainder of the power is used for the low power -5V and -12V rails, but we can disregard these because there is usually no minimum load requirement for the negative rails.

A 10% load would consist of two separate loads. One would be connected to the +5V rail and draw 12.5W (2.5A), the other would be connected to the +12V rail and draw 12W (1.0A). The total load of 24.5W is close enough to the magic 10% of 250W.

That said... i've tried using computer power supplies as cheap high current +12V sources plenty of times. Some work just fine without any load on the +5V rail, some can get away with a 2% load (10 ohm resistor), others need the full 10% load on the +5V rail.