Car audio guru/hack needed.

[The Buddha]

OK so I got this mother of a subwoofer. It had a 300 watt amp that died and the speaker can actually handle 500 rms and 800 peak or some such power, it was insane when I ran it via off my friends car amp. It also is a 4 ohm, and a 4 ohm plate amp is near impossible to find.

So here is my thought/idea/problem/solution/geniousity.

300-500 watt house amps are $$$$$$$ ... and 300-500 watt car amps are dirt cheap, matter of fact a few of em turned up @ my door cold, wet and shivering a few weeks ago ...

I know a car amp has to turn DC 12v into AC and back to DC for ~30-36v rail voltage cos all the mosfets need that ... for a 30-36V rail you need to land somewhere near 24-28v AC.
So I find a 110v to 28V transformer ... and as luck would have it several of those have also turned up cold wet and shivering in the last few months in several dead receivers.

So, what is the Q ... fine. And has anyone tried it. And can I see pics ... and how did it work ...

Cool.
Buddha.

[Firstoni]

O_o okay I think I got most of that, why go to the trouble of a 110v - 28v transformer, when you could just get a 110ac - 12dc transformer and run the car amp directly instead of breaking into its guts?

[noworries]

Hi B, some folk recommend using a PC power supply to run car sound equipment at home. Easy to source used or new, have a bit of wattage grunt, and provide a neat installation.

See http://www.youtube.com/watch?v=c3tlFxO1stU.

He may have been smoking something at the time he put the vid together, though. Some other vid leads at that YT page. Good luck with the project.

[Paulcet]

I don't know, and this advice may be worth as much as it cost you... But I don't think a PC power supply will give you as much 12VDC power as you would want.  There are several sections in a PC power supply, and only one (or 2 depending) 12 volt section(s).  And the 450 watts in a 450W power supply is the total capacity of all the separate sections.

[noworries]

Yeh Paul, u cld well be right re power availability on the PC unit, haven't tried the bodge myself. Some of the available hobby power units can push out the watts but then B wld be spending out a bit. Reckon he's onto a good idea here tho with the cheapness of the car audio gear X by power output.

[The Buddha]

Thanks for all the ideas ... keep em comming.

Yes ac to dc and then back to AC has a lot of loss. Also the 6-700 watts I need in a DC 12V power supply, I dont think I can use a PC power supply ... one other thing - I want to fit it all in that sub's cabinet. The weight and bulk are no issue, there is tons of room, but PC supplies have fans that get rather loud. A transformer into the voltage rail is my best bet, however the car amp uses a high speed switching mechanism I am yet to really understand, and my transformer will at best be very very low speed ... dunno if it would make a diff.

Cool.
Buddha.

[The Buddha]

OK someone on an audio forum sorted me out.
DC is convereted to ac in a car amp. However that is done via a switching some or other which operated @ 40-120 K hz ... house current is 60 hz ... so unless I can get it 1000 times faster I am out of luck ... its that high speed that will allow it to handle the transient surges inherent in a car sub. If I design it just right ... or just wrong depending on your point of view, its easily possible to blow up a 800 watt PC type power supply with a 200 watt car amp wihtout even driving the thing hard.
So I need a cheap 12-14V DC power supply that is capable of ~800-1000 watts.
Simpler quest I'd say ...
Cool.
Buddha.

[noworries]

Yeh, with a 12v supply running out to a 300 and up watt auto amplifier, it's the amperage thats going to be the killer in regard to cheap/cobbled up power supplies.  EG 12 volts x 25 amps gives ya 300 watts of power. And, I know it's only a couple of volts, but the amplifier is probably looking for 13.8v at source (which the auto would happily have supplied on charge) ....mightn't make that much difference but at 12v pure could allow audio distortion to emerge lower on the volume level. So do we know what circuitry the amplifier uses to transform it's orginal auto 12 volt input up to the 28-30 volt  level?

[noworries]

woops, B, posts. crossing.

[The Buddha]

Auto amp uses something called a PSV - switching something.
Anyway a 12V PC supply with a single rail capable of the amerage/wattage will work if I feed it 12V ... I dont think that 13.6 is the problem, for example, JL 500/1 amps which is my target amp for this cos it also was the cleanest sounding, it only use 12, not 13.6. However ... PC rails will not supply the 3-400 watts from 1 rail, in fact they rarely supply 3-400 watts worth in the 12V unless its a huge power supply.
The trick is to get a big 12V DC source cheap.
Cool.
Buddha.

[Firstoni]

http://www.trcelectronics.com/12-volt-power-supply.shtml   hope this helps....

[The Buddha]

I've seen that, the trick is to find what else that type of Powersupply went into, find out where they are junking it, get there, cut it open and buy it. I aint spending 300 bones on a power supply, cos 300 bones can get me a bridgeable mono amp capable of pushing 4-500 watts straight up. Like a rotel 1080 or a nad 2400 ... though both of those would be too cool looking to be stuffed inside my sub cabinet I'd sit it on top of the sub and admire them everytime the sub made a bump.

Or do what my friend did and wire up the C channel of his 1980 into a pair of cerwin vega 18" subs. Sadly a 1980 isn't a dolby machine and for hometheater it is rather like using a sledgehammer to pick your teeth. However it does sound very good and crisp if run by itself. Yea 260 watts will do that for ya ...

Heck for all the pain this is causing I can get a 2-300 watt mono bridged 3886 based amp off fleabay. Though I ahve heard that they are rather fragile and die often ... chinass crap ... typical.

Cool.
Buddha.

[The Buddha]

http://www.shine7.com/audio/bpa300_3.htm

That was what I was thinking ... That also maye have to sit outside, a sub cabinet wall fitting, could shake that to bits.

Cool.
Buddha.

[noworries]

This little 1500w sucker, with less than a day to go, currently (ho-ho) bid at $61.00

http://cgi.ebay.com/Silverstone-ST1500-Strider-Series-1500W-Power-Supply-/260687369698?pt=PCA_UPS&hash=item3cb22d95e2

[The Buddha]

That guy ended @ 150+, I actually need a single 12v outlet, not that mess of wires in a PC power suppply.
I may be just better off getting a 9V 200 amp transformer, stuffing a rectification circuit after that and getting 13 or so ...
Cool.
Buddha.