12v to 6v... speaker power

[david656]

...for these computer speakers i have they need 6v DC to be powered, is there a simple way to cut 12v down to 6 from the pc molex?

thanks

 

[HaRuMaN]

You could try using the 5V that the PC molex already puts out.

[rovingmind]

zener diode voltage regulator.........

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

if you don't need much current. don't want to mess with an adjustable voltage regulator, and the 5 volt line won't power it.

[richms]

Zener regulators are horribly inefficiant tho.

I have had no luck with a shared power supply on cheap computer speakers before, as the ground on the audio input was not common to the -ve of the supply to the speakers, there was a virtual ground in the circuit. Made speakers go pop and not work anymore. No big loss with the ones I tried tho

[Blanka]

The power brick for these speakers is gone?
Simplest is a 7806 voltage regulator, but from 12V, half the power will be converted to heat. So if it is 1 amp, it should have a heatsink capable of dissapating 6 W.
http://nl.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5166177

With more efficiency, you can use a DC-DC regulator:
http://nl.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0389356

[rovingmind]

i agree an adjustable voltage regulator chip driving a transistor on a decent heatsink being fed by the 12 volt line would be better than a zener,  but usually those computer speakers dont require much current.  I usually dont bother building power supplies for projects.  I have a box of various sized ones scrapped from other equipment along with the inevitable box'o wallwarts

[richms]

If you want a switching regulator then a nokia car charger will do the job, they are about $2 and output about 6.5v at a few 100mA.

[Popcorrin]

You can easily get 7v by using a 12v and 5v line, and  I'm sure the speakers will work fine off 7v. 
Actually, chances are they will work fine off of 5v.

[rovingmind]

You can easily get 7v by using a 12v and 5v line,

 ok i'll bite.  HOW

[Popcorrin]

You can easily get 7v by using a 12v and 5v line,

 ok i'll bite.  HOW

Just hook up the 12v line to the positive line and 5v to the negative line and you will have 7v(12v-5v=7v).

[richms]

And if you do that and the ground is shared between the power and audio (which most things do) then you will potentially smoke your audio cable, your soundcard, your motherboard etc if you connect it because you are then shorting yout 5v rail thru the ground of the speakers and the soundcard.

IME things that come with a isolated plugpack generally work best on an isolated power supply and strange things happen when you start to common up power supplies to things like that with them having no protection against the resultant groundloops.

[rovingmind]

well said rich

I've seen that work before, but not with switching supply circuits..  plus audio wants a common ground between sound source and amplifier, keeps hum down. (can't remember the proper terms at the moment- been a long day)

[Popcorrin]

And if you do that and the ground is shared between the power and audio (which most things do)

I've used a number of pc computer speaker hacks and this definitely isn't always the case and if there is an instance where the ground is shared between the two the fix is as easy as adding a diode to the 5v line.

[david656]

Hi,

Thanks to all who have added a comment it is greatly appreciated.

From the comments above it seems there is no simple fool proof way with out adding a certain amount of resistance and a certain diode. I've given it some thought and remembered that the computer power supplies with the in and out 3 pin kettle sockets work like a power strip in what ever come out of it turns on when the pc does...

would it be possible to just split out the cable to my monitor and to a small 6v transformer like N93CC at maplins 'Chassis Tx 6V/6VA' ... is this a straight forward 230/240vac to 6vdc ?

cheers 

[richms]

No, the output of powersupplies doesnt come on with the PC, its just a passthru and seldom found on current power supplies.

I would connect the 5v up to the speaker and try it off a different source - isolated like an ipod or one of those old things that spins CDs and plays, that way you can decide if they work well enough on the reduced voltage.

Then to see if its ok to plug into the computer you want to check for voltage between the 3.5 mm plug's sleeve and the chassis of the computer - there should be zero volts or close enough to it, if there is zero volte - plug it in - if you get 2.5v or so then you have a virtual ground in the speaker and its a lot of work to get it to work and not worth it.

Then see if you end up with any noise as a result of a ground loop - if none, then well done, your finished