Raptorman

iTrader: (1)

I have a xtrons double din unit I removed from my bugeye
as it wasn't working properly and drained the car battery and
have managed to power it up in the house using a old pc psu.

I know it requires 12v input and I have a old scalextric power
unit and was wondering if I could use it for the head unit
instead of the PC psu with all its extra messy wires.

The scalextric power supply states on the top that the output
is 12v=11va? Does that mean it would do the job?

john banks

The output of a car stereo can be in the region of 50W RMS. An 11VA (=W) isn't going to cut it.

Raptorman

iTrader: (1)

Cool, just wondered really, does the 12=11va mean it varies then
as I am no expert in electronics.

Oh I see now, the 11va means its only 11 watts output is that what
you mean?

neil-h

Think you'll find that most headunits are 50W peak, so more like 35WRMS (at some given frequency).

As for the OP and his power supply, best bet is to check the fuse rating and multiply that by 14V. That will give you an idea of output power you'll need from your supply (it VA or W, its the same for DC).

ALi-B

iTrader: (1)

Ignoring the lack of watts: The other thing about generic power supplies is the rectification.

In english(ish) the conversion of AC to DC

With a basic power supply, like a scalextric, no smoothing is done. You just get teh raw output from the diodes. If you are lucky it may have a smoothing capacitor or two, but under heavy load it won't do much to give you a smooth power supply

What will happen is the negative will be like this: ______
and the postive will pulse at 50hz (50 times a second), like this - - - - - (the logo on the supply's casing will often show this)

So what you are getting isn't pure DC. That pulsing will very likely make the headunit give out a background buzz to the speakers.


You need a switched mode power supply designed to power sensitive devices (anything with a microprocessor). PC and laptop supplies are switched mode. As are some of the powerbricks for A/V eqipment (like Virgin Tivo boxes).

When I was a teenager (uh oh ) and sold my car, I took out all my car audio gear and decided to use it in my bedroom, I ran my old car stereo and seperate power amplifier off a few computer PSUs..they were rated at a few hundred watts. But even then if I cranked up the volume they'd trip the overload on the PSUs

PS...The art of good HiFi is the power supply...until more recent years mains power was quite restrictive in getting big watts (i.e 300w+ RMS per channel) out of the wall socket without it either sounding poor or being very expensive

JDM_Stig

iTrader: (3)

also dont forget not to try those big house speakers on it as the chances are they are 8 ohm impedance

ALi-B

iTrader: (1)

Higher Impedance won't matter too much: It'll just mean the amp won't give out its full rated watts (rule of thumb is the output at 8ohms is roughly half that at 4ohms)

Going to lower rated impedance is what cuases harm/damage, as the amp is driving a lower resistance and the extra current flow can make it overheat (amp and power supply).

I ran an old Sony amp at 2ohms for a while...it didn't last long

domino46

Just hook it up to a battery charger works fine for me ,,,,or you could just buy a stereo for your house with a 240v Input lol

wrx5343

PC power supply should be more than enough really

Raptorman

iTrader: (1)

I am keeping it on the PC psu, just added 2 more speakers to
it and its working fine.

The intent was to use it as a outdoor sound system during the
summer(if we have one) so just need to figure out a box design
to hold it all.

Cheers for the tech info chaps.

wrx5343

http://www.ikeahackers.net/2013/04/b...ar-stereo.html

Qwertyco

iTrader: (2)

I run mine on an old laptop power supply.
I have a big old Wharfedale floorstanding speaker with a single din head unit mounted in it, a couple of cheap car tweeters sunk into it and it sit's in my garage and BELTS the top tunes out!
Something like this:
http://www.ebay.co.uk/itm/65W-Notebo...item20dd8facdc

wrx5343

Headunits are only rated to run on 12v-14v not up on 19v, would be better off with this on 15v

http://www.ebay.co.uk/itm/Universal-...item565cfa77d4

Qwertyco

iTrader: (2)

Oops yes! Ebay search failed me. I think I got a 14v one, or you can get a bigger one and feed it through a cheap ebay voltage regulator.

http://www.ebay.co.uk/itm/Voltage-St...item417c758661

I tried my 'Frankenstein Speaker' with some small amps as well, and there are a couple that will not run on 12v,
they need a minimum of 13 before they fire up.
I did a lot of trial and error before I got it to work properly.
Mk1 has an old AT computer supply in it, so it has an on/off switch, and a 2002 Alpine radio cassette head unit, sounds excellent. I gave this one away to a mate.
Mk2 has the laptop charger, and takes various head units, and a small amp.
There is space for a double din, so I might give it a go.
The main problem with these 'Frankies' is that they lose the radio stations when you power them down.
I have a battery backup planned to fix this.

Raptorman

iTrader: (1)

Do you have any photos of the finished setup?

john banks

I was actually thinking about 12.5WRMS x 4 channels! Certainly my 50Wx4 claimed Kenwood head unit wasn't on the same planet for volume through the same speakers as a Kenwood 35WRMS x 4 amp that about 4 times the size and weight.

ALi-B

iTrader: (1)

True John...My head unit is 45watts x4...but its peak watts, its actually 20watts DIN@14.4 volts, and the spec doesn't clarify if that's all channels driven (probably not). Either way I had a old 4x100 watt amp which is rated at roughly 4x25watt RMS and power-wise it would easily blow the head unit out the water (I now run a 4x150watt RMS Alpine PDX F6 Class D amp)

What limits car radio amplifier power is the power supply...or to be precisethe DC to DC conversion of it (12volts single polarity to a -30 and +30volts split rail supply). Thats what makes traditional amps so heavy. Class D amps though are a world apart in terms of power to weight ratio (as well as size and efficiency).

Qwertyco

iTrader: (2)

Not at the moment, I'm working overseas, I'll put some up in a couple of weeks.

Basically I got an old pair of eBay Wharfedale Valdus 400 http://www.minhembio.com/bilder/bild/?pic_id=85437.jpg floorstanders for 12 quid (both tweeters were dead), an eBay Alpine head unit for a fiver, gutted an old PC, stuck in a spare pair of tweeters, turned the speaker upside down, cut a hole for the head unit cage, removed the speaker crosover, wired the 2 bass speakers to the rear channel, tweeters to the front channel, a bit of wiring, and there you go.
It absolutely ROCKS!


Mk2 is similar, but a bit more refined, and still work in progress.