240v to 12v transformer. [Archive]

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Devil

3rd July 2007, 09:00

Hopefully some of you electrically types could help me out.

I've got a boxed 12" sub with 300w amp that I used to run in my car. Don't have a car anymore so I thought i'd hook it up to the home theatre system.

What would a suitable transformer be so I can plug it into the mains? Found a heavy duty one, that can supply @ 25A, but that's a bit excessive. I'd just want to run the one amplifier off it.

Help?

tri boy

3rd July 2007, 09:15

Try talking to a model train enthusiast
They have to step power down, and vary amperage.
Some of there set ups are quite large, but run on low voltage.

skelstar

3rd July 2007, 09:43

I'd just want to run the one amp off it.
Hee hee, I thought you meant you only wanted to run 1A off it, so I was going to say: "ummm a 12v 1A transformer?".

Technically 300W/12V = 25A ... *shrugs*

Thats a big transformer.

Devil

3rd July 2007, 09:45

Hee hee, I thought you meant you only wanted to run 1A off it, so I was going to say: "ummm a 12v 1A transformer?".

Technically 300W/12V = 25A ... *shrugs*

Thats a big transformer.

:( Surely it cant require that kind of current??
DSE has one for $350 that deals with up to 25A.

For that kind of money i'd probably be better off buying a 240v power amp instead and removing the existing amp!

ManDownUnder

3rd July 2007, 09:47

yeah... big tranny.

You might be better off to sell the AMP on tardeme and replace it with it's 240V equivalent...

Devil

3rd July 2007, 09:57

Not that I doubt your knowledge, but then how does the car deal with running it? Very high current charging system?

Bah @ money!

pzkpfw

3rd July 2007, 10:00

Technically 300W/12V = 25A ... *shrugs*

Thats a big transformer.

300W PMPO, RMS, or...

Devil

3rd July 2007, 10:01

300W PMPO, RMS, or...

It's RMS....

...I dont think and Amp pumping out a whopping 300W PMPO will be pushing a 12" earthquake sub too far! heh

Laava

3rd July 2007, 10:03

Try Jaycar electronics[www.jaycar.co.nz] You need a power supply that is clean enough to power an amp, not just any old 12vDC will do it so I've been told.

Devil

3rd July 2007, 10:08

Ok, let me think about this. I have a pair of Denon AV amps at home. The main one is powering all speakers, 80w per channel. On the assumption that it has an internal crossover (fair assumption), I could run the sub pre-out from that one, into my second denon amp (55w per channel output). Then bypass the amp built into my sub, and run it using the speaker outputs, bridged.

Does that sound like it'd work?

edit: Hrm, I wonder if the second denon has a Slave-in.

Pixie

3rd July 2007, 10:55

WasPhantom

3rd July 2007, 11:23

I would also look at getting a second hand deep cycle battery ( you could get it new, but damn, they're not cheap ) and run that in parallel with your power supply - this is just to allow the amp to always get the current it requires, and will reduce the "clipping" you would likely otherwise get.

Devil

3rd July 2007, 11:30

If only I still had my 1.5kw power amp still lying around!

Cheers for the responses people.

avgas

3rd July 2007, 11:41

Ok for a start.....the 230 is AC and your amp is DC so you gonna have to do more than step down. regulate and rectify the preacher yells.
Cheapest option is if your only going to run low power is get a cheap battery charger and hook that up. High power your fucked.
But you will prob find that power ratings when it comes to amps is all bullshit.
WasPhantom has it sorted

avgas

3rd July 2007, 11:45

On the assumption that it has an internal crossover (fair assumption)
Does that sound like it'd work?

Your channels and reference channels (front back) aren't split between the amps?
Also watch out for internal phase crossing and one amp burning out the other.

cheese

3rd July 2007, 11:59

I just did the same thing and I went to surplistronics and got a 150w 230 plate amp. It was the easiest and cheapest way.

Can find it here

http://www.surplustronics.co.nz/shop/product-170.992.html

I think that it goes quite well. I've got a Alpine Bass ZR on it and it shakes my house pretty well.

Car audio amps do pull big current as the voltage is low. P =V x I so you need bigger I to get big P. You will dick around a fair bit getting a grunty enough power supply

the other option is to get one in from partsexpress.

http://www.partsexpress.com/

US dollar is kick ass right now. They have a 1000w version!!!!

imdying

3rd July 2007, 13:22

The cheapest way would be to run it of a 12v SLA battery that is continuously maintain by a cheap battery charger.
You could do this for under $100

If you have the 300VA transformer you could build a power supply for under $50.
You will need some filter caps and a rectifier.

A mate of mine who was into big car audio did this for his garage. I was skeptical, thought the battery would have a fairly short life span... but no, it worked well! As he already had a spare battery, it even cost him nothing to do, can't do better than that!

Devil

3rd July 2007, 13:46