auto amp

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paulrevelcet
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auto amp

Post by paulrevelcet » Sun Jan 23, 2005 10:35 am

What would be the best way to power a 400 watt amp. from the mains? it is a automotive amp (12v) and I would like to use it but I am not sure if it would be worth the cost. I need about 30 amps 12volt dc.

jimandy
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Re: auto amp

Post by jimandy » Sun Jan 23, 2005 10:57 am

I would think an auto amp would have good internal voltage regulation and filtering if it is designed to run off the wild and wooly auto 12V supply. So a power supply design for such an appplication would be minimal in parts as long as it had just brute force and a big "tank" cap.
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Chris Smith
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Re: auto amp

Post by Chris Smith » Sun Jan 23, 2005 11:29 am

For that large gas tank value, you might include a car battery leading the parade, followed by a large one farad cap. The car battery can be substituted by any battery bank of any type as long at it can deliver two to three times the surge draw. Car amps have a habit of drawing instant power when the base cuts in, lowering most power systems below the threshold voltage minimum which causes distortions.

Mike
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Re: auto amp

Post by Mike » Sun Jan 23, 2005 12:55 pm

http://www.radioshack.com/product.asp?c ... Fid=22-510<p>Its 25A, so pretty close. And you can get it for much cheaper I'm sure through any catalog.

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haklesup
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Re: auto amp

Post by haklesup » Mon Jan 24, 2005 2:40 pm

An automotive battery charger with at least 30A fast charge (start) setting would be the simplest power supply. Most of the cost will be wrapped up in an adequate transformer. You could add a filter capacitor across the output if you felt it was too noisy but jimandy is most likly right about the Amp having a well isolated internal supply.<p>On the other hand, depending on the AMP's built in filter to filter the ripple may disproportionately heat that filter in the AMP causing premature failure wheras an external filter cap would reduce ripple at the source. <p>The filter cap will have a low ESR and a modest value (<1000uF-2200uF) and be located close to the power supply. A storage cap will have a huge value (>1F or more) and be located close to the Amplifier. Both are probably optional and depends on the performance/price point you demand of the system.<p>Ultimately the amount of storage capacitance (like a 1F cap)(or a battery in parallel) depends on how much low end you want to support. Most of the instantanious power is needed in reproducing loud low notes.<p>Just like in a car, if you power the head unit (or any other audio source) off the same power supply, you will need to insert audio isolation transformers in the signal lines to prevent the AC ripple on the primary supply from spoiling the music.

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Re: auto amp

Post by jimandy » Mon Jan 24, 2005 4:44 pm

I would think that if the power supply has to provide heavy current over an extended period for a 400 watt amp, then the walls of the structure wherein the speakers are ensconced will soon be bending outward from the internal pressures generated therein. (forsooth).
"if it's not another it's one thing."

chapter30
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Re: auto amp

Post by chapter30 » Thu Jan 27, 2005 5:27 pm

I've ran audio amps on workbenches using the old (and expensive) HP variable power supplies. If you are going to run this in a home audio system you might want to run a supply like this but they are a little loud. <p>In the audio lab we had to put it in a closet during critical listening.

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Re: auto amp

Post by Dean Huster » Sat Jan 29, 2005 7:51 am

Remember that in high-power amps designed for 12v systems, fully 2/3 to 3/4 of the space inside is taken up by the power supply converter that boosts the 12v to around 40 to 80 volts. To eliminate all of the high-current stuff you'd have to do to power the thing up, you could just get into the amp, find out the amp-proper's supply voltage and make a supply to produce those from 120v. Current requirements will be a fraction of what will be required with the 12v option.<p>If you do choose the 12v supply option, you may find that you can buy a standard household amp cheaper at Wal-Mart than you can buy the stuff to power the car amp ... and it'll take up a lot less room, weight a lot less, not look so ugly, not involve battery acid in the living room, be more efficient and you won't have to worry about how to get rid of all that hum from the battery charger -- which, by the way, may not be able to handle your current requirements at 100% duty cycle.<p>Dean
Dean Huster, Electronics Curmudgeon
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Re: auto amp

Post by Mike » Sat Jan 29, 2005 1:25 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Dean Huster:
If you do choose the 12v supply option, you may find that you can buy a standard household amp cheaper at Wal-Mart than you can buy the stuff to power the car amp ... and it'll take up a lot less room, weight a lot less, not look so ugly, not involve battery acid in the living room, be more efficient and you won't have to worry about how to get rid of all that hum from the battery charger -- which, by the way, may not be able to handle your current requirements at 100% duty cycle.<p>Dean<hr></blockquote><p>Though will sound like trash, assuming the word "wal-mart" isn't a typo..<p>The car amp would sound much better and would most likely be worth the higher price.<p>Whats wrong with the 25A switching supply I linked to? Too expensive?

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Re: auto amp

Post by Dean Huster » Sun Jan 30, 2005 12:10 pm

Well, depending on the kind of speakers that are being driven, I doubt that the Wal-Mart amp would sound any worse. That is a supposition based on the fact that everything electronic is coming down in price and getting better in specifications in the process because of integration. I figure that stereo amps probably fall into line just like televisions, VCRs, telephones, DVD and CD players, etc. At least Wal-Mart is pretty good about giving you your money back if not satisfied without having to deal with the equipment manufacturer.<p>Is the switching supply too expensive? As a test bench tool for fixing automotive equipment, probably not. As a single-purpose box sitting there hidden away powering a stereo amp? In MY opinion, yes, but that's me. Everyone has their own worth on something like that and there's no reason that my preference should be felt by all!<p>However, two points. First, in my book, "Radio Shack" is just as dirty a term as is "Wal-Mart". All you have to do is talk to the idiots that manage and sell at either store to figure that one out. Second, RS is out of stock on that item everywhere, another typical RS scenario.<p>I didn't ever bad-mouth RS when I was writing the "Q & A" column even if they did refuse to supply a few parts here and there in trade for free advertising. They deserved it then, too. Why did I change?<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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jwax
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Re: auto amp

Post by jwax » Mon Jan 31, 2005 8:12 am

400 watts? Would that be RMS power, pk, or pk-pk?
Maybe average.
Must be a big house.
:)

paulrevelcet
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Re: auto amp

Post by paulrevelcet » Mon Jan 31, 2005 10:34 am

4 channel 100 watts per channel, not sure but I think it is rms, it is a fairly new amp that was in a car I bought but had a new system put in it. I build arcade games for people and thought it would be nice to use in one, I like the way it looks and with a window mod in the game it would give it that look that car audio enthusiasts go for.<p>All I can find at walmart is the surround sound systems, not sure if that is what you were talking about or not but they dont sell just an audio amp.<p>Thanks everyone for the help

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haklesup
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Re: auto amp

Post by haklesup » Tue Feb 01, 2005 3:18 pm

Dean's point is sound (pun). A typical household Amp (and there are few pure amplifiers that are not part of a radio or something) could be had for less money than a car amp plus a high current 12V supply. A linear supply needs a heavy expensive transformer and a switching supply of that current could cost $400.<p>Converting 120V AC (low current) down to 12V DC (with all that expensive high current) then back up to 80V DC (mid current) is the long way around the block when you can just go from 120V AC to 80V DC in one step without any heavy duty conductors required.

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Re: auto amp

Post by Mike » Fri Feb 11, 2005 6:07 pm

I wonder, can switching power supplies be ran in parallel?<p>If so, you could get 2 or 3 of these:
https://www.brigarelectronics.com/Merch ... ry_Code=PS<p>They each put out 13A 12VDC and are only 20 bucks.

upsmaster
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Re: auto amp

Post by upsmaster » Fri Feb 11, 2005 6:20 pm

Hi
400 watts mostly peak ratings
yes there is dc to dc converter in the power supply to raise the voltage to 40 or so volts. Any battery charger you use with a cap across the buss may not work because of cap charging inrush depends on cap charger amp combo and a dc/dc converter draws a large slug of curren when it starts with or with out a load . I use two hp 40 volt 40 amp and 40 volt 60 amp power supplys.<p> joe

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