Bipolar +12v / -12v power supply from 9v? is this possible?

[loki]

Hi guys,
I'm thinking about building an effect that requires a +12v / -12v supply, but i would like to obtain it from the 9v wall wart that powers my other pedals, so i was thinking about this:

1st. using the charge pump from GEO http://www.geofex.com/circuits/+9_to_33.htm to get +17v

and then

2nd. putting that 17v into the bipolar power supply from GGG http://www.generalguitargadgets.com/index.php?option=content&task=view&id=191&Itemid=216
with 7812 and 7912 regulators to get +12v and -12v

I'm not sure this will work though... the project at GGG uses a transformer to get the 15-18v needed to obtain the +12 / -12v and i don't know if the nature of the power from the transformer secondary is the same i can obtain from the charge pump (i still don't understand well the difference between  AC/DC and regulated/unregulated)

hope you can help me
Thanks

[Mark Hammer]

Far easier and simpler to get a wallwart that starts with 12vac (they are a dime a dozen), rectify (to just under 17v), smooth and regulate, to make your +/-12v bipolar supply and down-regulate to 9v.  That will probably give you a higher quality 9v supply too since you'll have two cascaded steps of regulation involved.

[JimRayden]

(i still don't understand well the difference between  AC/DC and regulated/unregulated)

Well then you have missed a very important part of electronics.

Electronics for dummies:

DC - one voltage all the time
AC - voltage changes from positive to negative periodically. In USA, that happens 60 times per second. Bzzzz.
Regulating - using a special chip that makes the DC super stable.

-------------
Jimbo

[Nasse]

geofex thing gives DC
ggg thing wants AC

so no good

[Dave Eason]

I've used the 1044 charge pump converter in a simple buffer, to actually see how good it was.  I was pleased with the results.  I used it to get -9V and +9V out of one battery, so I didn't need any biased circuits, and coupling caps weren't toally necassary (well, a good measure, to stop a DC ofset "coming in" from another source).  The MAX1044 has the boost feature, so the internal oscillation of the charging/discharging of the reservoir caps is pushed out of the audio freqency range - I disconnected tho boost and there was a nasty whistling at about 7/8 k.

So Yes, You can get bi polar DC supplies from one battery and a DC-DC converter (they can go pretty high too), but not AC voltages like the 50Hz mains.

You could take this: http://www.geofex.com/circuits/+9_to_-9.htm

then modify using the method like: http://www.geofex.com/circuits/+9_to_33.htm which is just utilising simple diode clamp circuits

to push the voltages up to 17, then regulate and smooth.  Im sure that would work

[cx_deluxe]

Definitely get a 12vAC wallwart and build the Bipolar Power Supply from GGG:
http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf
Way less futzing around.
First power supply I ever built.  It was easy, it works well.  Go for it.  You'll have it together in minutes.  Using mine to power my spring reverb drive/return.

Oh.  make sure you pay attention to the pinouts on the 7912.  They are different than the 7812.  I didn't get it wrong but I had to look twice.

[loki]

thanks for your replies guys... we i think i'll def go for the GGG one then... with 12vac wall wart, or a suitable transformer if i can find one

cheers

[Paul Perry (Frostwave)]

That ggg bipolar is how I do it in my Frostwave pedals, hundreds out there with no problems. I use a 14V ac wart and 15v regs, the old analog synth stuff that some of my gear is based on, mostly used +-15v rails.

[Sir H C]

To do this you would really need to use switching regulators with inductors.  These are not very plug and play to get working right without noise and other issues.  Best to just use a 12 volt AC.