Popping and cut out from sub. Using 350 watt desktop PSU - AVS Forum
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post #1 of 23 Old 04-30-2013, 03:23 PM - Thread Starter
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So i had an old sub from my car and wanted to hook it up to my theater system. I didn't want to buy a pre configured AC to DC adapter so i used a 350watt PSU from a computer. I ran two(for safey) yellow 12v wires to the positive on the amp, a ground to the ground connection and jumpered the 12 to the middle connection(pretty unfamiliar with audio stuff). Im unsure of the watt rating on the sub but it's thumped more in my car and the amp is 300 watt.

The issue: there is a constant popping or crackling noise coming from it and when id expect loud bass it cuts out.

if the psu is 350 watts and the amp 300, doesnt that mean 650 peak watts going to the sub? is that too much?(its 15" but kinda sealed in the box so i cant really get more info)
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post #2 of 23 Old 04-30-2013, 03:41 PM
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a computer ps is not going to let the amp have the kind of amperage it needs to work properly
i have a 120vac to 12vdc power converter i use at home for testing speakers hooked to a 300 watt mtx amp. my power supply has a max of 15 amps output and even that isnt enough , i draw more power then converter can supply even with the 300 watt amp

best bet would be to go buy a real amp and not try to use a car audio amp
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post #3 of 23 Old 04-30-2013, 04:12 PM - Thread Starter
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What if i were to add another 300 watt psu?

also, wouldnt changing the level on the amp adjust the power intake enough that this wouldn't happen?
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post #4 of 23 Old 04-30-2013, 04:17 PM
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Quote:
Originally Posted by Dan Maloney View Post

What if i were to add another 300 watt psu?

also, wouldnt changing the level on the amp adjust the power intake enough that this wouldn't happen?

The problem is computer PSU's don't output their full current over the 12Volt rails, or rather, there's very few that do.
So relying on a PSU that's already probably 70-80% efficient to power an amp probably isn't a good idea.
i've done it with my friend before too, same problem. It's not really worth the trouble.
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post #5 of 23 Old 04-30-2013, 04:39 PM - Thread Starter
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so if i run EVERY 12v cable to it youre saying 350 watts isnt enough for a 300 watt amp? i dont really want to spend any money on it, so this is my option.

350 watt psu and 300 watt psu combined equals 650 watts(more than the 120% amp wattage i read was suggested) however, that gives me 24 volts right? then i'd need a resistor?

the purpose of am amplifier is to increase watts or volume, and car batteries give like 40 amps. so if i wanted to power this i'd need 40 amps at a minimum of 360 watts?(the amplifier being 300 watts)
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post #6 of 23 Old 04-30-2013, 05:03 PM
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Originally Posted by Dan Maloney View Post

so if i run EVERY 12v cable to it youre saying 350 watts isnt enough for a 300 watt amp? i dont really want to spend any money on it, so this is my option.

350 watt psu and 300 watt psu combined equals 650 watts(more than the 120% amp wattage i read was suggested) however, that gives me 24 volts right? then i'd need a resistor?

the purpose of am amplifier is to increase watts or volume, and car batteries give like 40 amps. so if i wanted to power this i'd need 40 amps at a minimum of 360 watts?(the amplifier being 300 watts)
car batterys cab supply in excess of 500 amps
and ur looking at the wrong thing , u need to be looking at amperage not watts , not sure what amp u are trying to use but my bet it either has a 20 or 30 amp fuse in the side of it . if its a 20 amp fuse u would need about 15-17 amps to get full power out of it , if it has a 30amp fuse u need more like 25ish amps to get full power out of it

if memory serves me corectly most computer power supplies are only going to put out about 5 amps

ur best bet is to buy one of the plate amps or go on ebay and pay 150 bucks for a musicsys 4500 amp or 119 bucks for the musicsys 2500


the 4500 does about 350w rms @ 8 ohms 500w rms @4 and 750@2 ohms off the top of my head
i use one to run my main speakers and it works pretty damn good for a very cheap amp , much better then any of the pyle offerings
the 4500 is not bridgeable

the 2500 is but i dont have the specs infront of me
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post #7 of 23 Old 04-30-2013, 05:07 PM
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heres the specs on the 2000 made a mistake this amp isnt bridgeable either only the 6000 model is bridgeable
Momentary Peak Output 2000 Watts

1000 Watts @ 2 Ohms

500 Watts @ 4 Ohms

250 Watts @ 8 Ohms


those are peak numbers

and the 4500
Momentary Peak Output 4500 Watts
2200 Watts @ 2 Ohms
1100 Watts @ 4 Ohms
550 Watts @ 8 Ohms

again those are peak numbers

and i misspelled the name its musysic
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post #8 of 23 Old 04-30-2013, 05:18 PM - Thread Starter
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yeah, kind of expensive for me. but if i buy http://www.newegg.com/Product/Product.aspx?Item=N82E16817170019 which has a single 12v rail at 25A chances are it would be enough?

the amp is at a friends house so i cant look at it but i remember its mtx and i looked up the model and it was a 300 watt.

or i could get many others with higher 12v amp ratings still for under that 119. so if i have the model of the amp i can get see what fuse is in it and i want at least just under that many amps for my 12v?
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post #9 of 23 Old 04-30-2013, 05:21 PM - Thread Starter
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side note: when i plugged it into my reciever with rca cables there was only one jack on the reciever so i went with only left. while looking for info on this i saw that you should buy a Y spliter to have both L and R in the amp and the Y in the reciever
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post #10 of 23 Old 04-30-2013, 05:32 PM
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Quote:
Originally Posted by Dan Maloney View Post

So i had an old sub from my car and wanted to hook it up to my theater system. I didn't want to buy a pre configured AC to DC adapter so i used a 350watt PSU from a computer. I ran two(for safey) yellow 12v wires to the positive on the amp, a ground to the ground connection and jumpered the 12 to the middle connection(pretty unfamiliar with audio stuff). Im unsure of the watt rating on the sub but it's thumped more in my car and the amp is 300 watt.

The issue: there is a constant popping or crackling noise coming from it and when id expect loud bass it cuts out.

if the PSU is 350 watts and the amp 300, doesnt that mean 650 peak watts going to the sub? is that too much?(its 15" but kinda sealed in the box so i cant really get more info)

PC PSUs split their power up among the various voltages that they produce. One 350 watt I looked at was speced like this:

3.3V@28A, +5V@35A, +12V@15A, -5V@0.5A, -12V@0.8A, +5VSB@2.5A

+12 is limited to 15 amps which is just 180 watts. This is pretty typical, as much of the power that is drawn by a modern PC comes out of the 3.3 and 5 volt outputs. The 12 volt power is mostly for hard drive and optical drive motors.

If you want to use PC or other current-limited power supplies to work better with audio power amps, add a large value such as 10,000 uF 25 volt capacitor across the 12 volt leads. This helps compensate for the typically spikey current drain pattern of audio power amps.
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post #11 of 23 Old 04-30-2013, 05:36 PM
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if ur running the amp in bridged mode then yes u need both input channels hooked up

u need something like this
http://www.ebay.com/itm/Goldsource-DF1790-1310-DC-Regulated-12-13-8V-13-8-V-Volt-Power-Supply-10-Amp-/150746830061?pt=US_Radio_Comm_Device_Power_Supplies&hash=item23193614ed
but larger
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post #12 of 23 Old 04-30-2013, 05:38 PM
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this would be decent
http://www.ebay.com/itm/Goldsource-DF1790-1310-DC-Regulated-12-13-8V-13-8-V-Volt-Power-Supply-10-Amp-/150746830061?pt=US_Radio_Comm_Device_Power_Supplies&hash=item23193614ed
rember car amps only produce rated power at 14.4 volts not 12 volts. so u want a regulated power supply as close to 14.4v as possible
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post #13 of 23 Old 04-30-2013, 05:45 PM
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post #14 of 23 Old 04-30-2013, 07:30 PM
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What Arnyk said except that the 12v rail is the primary in all PC or server supplies. The amperages for the voltages other than +12 are all roughly the same for all wattage supplies. It's the 12v rail that scales up on larger supplies (for overclocking cpus and large GPUs). Look for ones with a single 12v rail as well.

plus...Dont tie typical PC power supplies together. The one with slighty higher voltage will try to drive the other negavtive IIRC...they will either shut-off if they have a protection circuit or meltdown.

If you can find a "good" redundant server power supply then you might be in luck. Most redundant supplies (the ones with passive backplanes) are diode isolated, so tying them together isnt much of an issue if you get more than one.


I am now running an old CV car amp (300w x2 @4ohm) off of a server power supply. My server supply puts out 70A of 12v and runs the amp fairly well.
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post #15 of 23 Old 04-30-2013, 08:32 PM - Thread Starter
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Thanks for the info. its quite clear what i need in order to run an amp off a computer psu now or for that matter the general power supply's you linked. I wonder why its still so less expensive to buy something like you linked than something thats specifically meant for the job.
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post #16 of 23 Old 04-30-2013, 10:08 PM
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This might be an option as well: http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-315
It's adjustable between 10 and 13.5 volts.

The trick with computer supplies will be finding one with all of it's amperage on a single 12 volt rail at a reasonable price.
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post #17 of 23 Old 05-01-2013, 06:01 AM
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Quote:
Originally Posted by MoFinWiley View Post

What Arnyk said except that the 12v rail is the primary in all PC or server supplies. The amperages for the voltages other than +12 are all roughly the same for all wattage supplies. It's the 12v rail that scales up on larger supplies (for overclocking cpus and large GPUs). Look for ones with a single 12v rail as well.

plus...Dont tie typical PC power supplies together. The one with slighty higher voltage will try to drive the other negavtive IIRC...they will either shut-off if they have a protection circuit or meltdown.

If you can find a "good" redundant server power supply then you might be in luck. Most redundant supplies (the ones with passive backplanes) are diode isolated, so tying them together isnt much of an issue if you get more than one.


I am now running an old CV car amp (300w x2 @4ohm) off of a server power supply. My server supply puts out 70A of 12v and runs the amp fairly well.


Interesting.

Here's the current ratings of a 600 watt PC power supply:

+3.3V@36A, +5V@30A, +12V1@18A, +12V2@18A, +12V3@18A, +12V4@18A, -12V@0.5A, +5VSB@3.0A

Repeating what I posted above for the 350 watt PS:

3.3V@28A, +5V@35A, +12V@15A, -5V@0.5A, -12V@0.8A, +5VSB@2.5A

You appear to be right - the major upgrade to the 600 watt PS is the additional 12 volt supplies. No corresponding increase in the 3.3 or 5 volt supplies.

Counter intuitive, but true.

I also agree with your comments about the slings and arrows of trying to parallel regulated power supplies. Not a good idea, to say the least!

One possible but certain saving grace may be that with many PC supplies, the 12 volt suppl(ies) may not not regulated at all. In fact if you pull more current from the 5 volt supply on many PCs, the 12 volt supply would often increase its voltage! Or not.

Like so many things in life, don't count on this unless you test it and know for sure that it is true.

Hooking high performance audio amps to overcurrent protected power supplies is not a good idea. We are kinda being forced into going there with all the other attractions of switchmode power. We've been there for years with aftermarket audio power amps that typically had switchmode DC-DC up converters.

Take their lead - they generally have a good sized storage cap on the PS output to handle short momentary demands for lots of power.
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post #18 of 23 Old 05-01-2013, 06:03 AM
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Quote:
Originally Posted by Dan Maloney View Post

Thanks for the info. its quite clear what i need in order to run an amp off a computer psu now or for that matter the general power supply's you linked. I wonder why its still so less expensive to buy something like you linked than something thats specifically meant for the job.

It is all about economies of scale. Same reason I can buy a 5.1 AVR with all sorts of good stuff, bells and whistles for less money than a stripped-back 2 channel receiver.
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post #19 of 23 Old 05-01-2013, 10:06 AM
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As mofin stated high end computer power supplies have most of their amperage on the 12 volt rails for video cards, because that's where the power needs to be in a modern gaming pc.
Where as peripherals and such don't necessarily draw much more than they used to.

The Radeon 6950 I have in my machine for instance probably makes up around 60% of the total power draw for instance.

A server supply may fit the bill but I wouldn't think a supply with 70 amps on a 12v rail would be at all cheap and looking at server psu costs at newegg they don't seem to be as suitable for what your trying to do in the 40-50$ price range.

I'm not entirely sure if it's neccesary to reach 14 volts: http://www.caraudiohelp.com/newsletter/amplifier_power_and_voltage.htm

The cheap 12v, 30 amp supply Davece listed may very well be similar to the one Partsexpress is offering but do the research to make sure so you avoid the risk of getting a cheap knockoff.

Computer power supplies should be quite regulated to avoid damaging components. Cheap supplies can of course be far worse at supplying tightly regulated power but the really cheap brands tend to go up in smoke from what i've read.
Quote:
It is all about economies of scale. Same reason I can buy a 5.1 AVR with all sorts of good stuff, bells and whistles for less money than a stripped-back 2 channel receiver.

^Output Power comes into play there, if your comparing home theater recievers to power amps.

If your intent on finding a deal by buying a computer power supply, you might want to read up on your choices using review sites like this: http://www.hardwaresecrets.com/page/power

Good luck and I hope you find a cost effective way to do this because i've been considering doing the same.
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post #20 of 23 Old 05-01-2013, 11:01 AM
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Quote:
Originally Posted by arnyk View Post

It is all about economies of scale. Same reason I can buy a 5.1 AVR with all sorts of good stuff, bells and whistles for less money than a stripped-back 2 channel receiver.

Well, good computer PSUs like this one http://www.newegg.com/Product/Product.aspx?Item=N82E16817151111
Are still pricey. 71A single 12v rail. Modern large capacity hard drives can pull quite a bit of current. And when you have 24 hdd in a 4u server chassis, you had better get a PSUS with at least 60A 12v rail. Single rail PSUs are better.
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post #21 of 23 Old 05-01-2013, 11:01 AM
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Quote:
Originally Posted by Mik James View Post


...A server supply may fit the bill but I wouldn't think a supply with 70 amps on a 12v rail would be at all cheap and looking at server psu costs at newegg they don't seem to be as suitable for what your trying to do in the 40-50$ price range...

very true...The retail cost of the supply I am using is in the $500 range...I just happen to have a few lying around, among other things.
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post #22 of 23 Old 05-01-2013, 01:23 PM
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Quote:
Originally Posted by Dan Maloney View Post

so if i run EVERY 12v cable to it youre saying 350 watts isnt enough for a 300 watt amp?

You're forgetting about efficiency - assuming it's good for the whole 300W, that amp isn't going to be 100% efficient. That's not even getting into instantaneous current draw transients that may be well in excess of what the power supply is rated for on the 12V side of things. Cheap power supplies are also usually group regulated, meaning you need a load on the 5V side of things to get stable 12V output.

I review computer power supplies for a living... a good many of them can't take this kind of abuse. I personally fried a 700W unit with a car amp only good for 250W output. They're not designed for this kind of thing, but the larger server grade units can do it.

But... by the time you buy something like that, you're already almost spending as much as an amp designed from the ground up to operate at wall voltage.

My advice? Forget the computer PSU and car amp idea and just find a proper 120V AC amp.


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post #23 of 23 Old 05-01-2013, 03:45 PM
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You haven't really mentioned why you want to use a car amp vs a power amp?

I was looking into using one because they're dirt cheap per watt on the used market, but once you throw in the 50$ 30 amp 12v supply meant for the job, it doesn't sound so reasonable.
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