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Old 1st September 2002, 12:38 PM   #1
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Exclamation i have a problam.... i have a car amp and i want...

i have a problam.... i have a car amp and i want to us in my home... i want to buy transformer 12V but i dont know how match amper (- A -) i need for this amplifier...
someone can help ?

my amp is 800W RMS total
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Old 1st September 2002, 01:01 PM   #2
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Hi

If the amp is rated at 800W, allowing for inefficiencies in its switch mode converter, you need roughly a 1kW power supply. This works out at a massive 83A at 12V! You would be better off buying a lead acid car battery (and charger) to run the amp off, than building such a huge 83A supply.

IMHO, it is in fact probably more worthwile to just buy a mains amp for use inside. Unless you buy a very large (and expensive!) battery, the car amp will drain it quickly at full power; a 100Ah type could cost over $200US, and will only last just over an hour. Remember, this cost does not include a charger. If you already have a battery you can use, then go for it, but in the long run I should just buy a good quality PA amp - this will be far more reliable for DJ use anyway. Yamaha do some good value entry level units, or you could get a more prestigious brand second hand.

Hope this helps,
Tim.
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Old 1st September 2002, 01:19 PM   #3
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soo what u say that i need to the amp a car battery 12VAh ( i have one) and connect charger to the battery.... all in once...
and is work good?
i have a charger of 15.5 A 13.8V is good?
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Old 1st September 2002, 02:33 PM   #4
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my hebrew is a little rusty but from the specs on the unit
it is 4 channels @ 200 watts per channel into 1 ohm @ 2%thd.
which is 100 watts per channel into 2 ohms, 50 watts
per channel into 4 ohms, and 25 watts per channel into
8 ohms.

The switching power supply in the unit is 80% efficient absolute
maximum. The amplifiers are either A/B or B which means
that they are 50% efficient max which results in an amplifier
that is 40% efficient.

So 800 watts turns into 2000 watts, which at the nominal
battery voltage of 13.2 volts is 151 amperes!

But it is not designed to be used at home and would be
horrible for any home use. Speakers for home use are either
4 or 8 ohms resulting in far less power than you would
expect.

Even the cheapest of japanese receivers would be better.
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Old 1st September 2002, 02:54 PM   #5
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My AMP is :

800W RMS TOTAL

4x 400W RMS in 2 Ohm
4x 200W RMS in 4 Ohm
2x 400W RMS in 4 Ohm
2x 200W RMS in 8 Ohm

12V A (dont know)
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Old 1st September 2002, 04:16 PM   #6
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I do this for a living.... I am MECP. An 800w 4ch amp would be much bigger than the one shown in the photo. This amp is crap. I say this because only low-end amp manufactures claim such outragous specs. This amp just might produce 800w--with a 16v power suplly on a test bench at 1000Hz with 25%THD. Like I said, cheap. Another example would be the Rockford 700s 2ch amp. its twice as large as the amp in the photo. and it will produce 700w at 14v @2 ohms mono all channels driiven. RF test each amp and includes a test report of the amp in the box. You may get 20w with this thing off a 13.8v regulated power supply..but it will be very distorted.

At the retail location I work at we use a very large 12v ps and a 1F cap and we still dont get half of what this amp will do in a car...

Have fun playing around with it though.. just dont expect a whole lot...
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Old 1st September 2002, 04:19 PM   #7
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Kevin's scientific analysis proceeds with validity; however, from a marketing standpoint: on these amplifiers the 800W is used as a marketing tool. The absolute maximum power the power supply can deliver instantaneously for brief instances is 800W. The amplifier is really only about 100-175W total. The power supply can be constructed from a 10VAC RMS (500VA) secondary transformer, some beefy discrete diode packages, and some huge filter caps. However, it would be cheaper and more effective to build or buy an amplifier designed for the indoor use intended...

BeanZ
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Old 1st September 2002, 04:42 PM   #8
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I did try to be nice without directly calling the amp
"cheap" which it certainly is
and "crap" which it is too.

If you notice from the picture you can see the 12 volt
power input connectors. Do you think that this can handle
100+ amp peaks???

No free lunch here. Power in * efficiency === power out.

Very few automobiles have alternators of sufficient strength
to power such a device if it actually met spec.

If you actually ran this thing at even half power all channels
driven it would go into thermal meltdown in less than 10
minutes.

In reality this amp is at most 25 watts per channel all
channels driven into 8 ohms. And likely at really lousy
thd numbers too.

This is part of the reason the Federal Trade Commission has
specs on how things like this have to be measured.

I'll post a picture on tuesday of an Oxford Instrument
Magnet power supply. It is 0 to 20 volts @ 0 to 125 amperes.
It takes two people to move it. The output cables are
.75 inch diameter fine strand pure copper.
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Old 1st September 2002, 05:05 PM   #9
trwh is offline trwh  United Kingdom
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"soo what u say that i need to the amp a car battery 12VAh ( i have one) and connect charger to the battery.... all in once...
and is work good?
i have a charger of 15.5 A 13.8V is good?"

No, you need a 12V lead acid battery with a high Ah rating, say 50Ah or more. You charge the battery and then connect it to the amp.

You will by now have read the negative comments posted about your amp - Kevin et al are quite right, take the power rating of this amp with a pinch of salt. Don't expect HI-FI sound quality, and don't expect the reliability of a real PA amp (I assume you're thinking of using the amp in a live situation given your handle "DJ").

See ya,
Tim.
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Old 1st September 2002, 07:11 PM   #10
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The easy way to determine the needed power supply: Look at the rating of the fuse that the amplifier uses. Add oh- about 10-25% to that, depends the size of filter caps in the PS. That is the size of power supply you need.

OR.....

DJ,

Aren't you the guy that wanted to put a home amp in your car? Just swap the fish out of water with the the cat in a lake. (insert sly grin here...)

Aud_Mot
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