+/-15V DC from 9v ac

[9 volts]

Hey there, does anyone have a schematic for getting  +/-15V DC  from a 9v ac adapter using 7815 and  7915? I know how to get it from a higher voltage transformer but know it's possible to get it from 9ac. Thanks

[Auke Haarsma]

depends on the current draw you expect.

If it stays under ~30 mA you could try the voltage double at GEO (uses max1044) to get to 18V. Then put that 18V into the 7915 7815. You need to feed to 7815/7915 2-3V above what the voltage regulator puts output.

gl

[9 volts]

Wow what a rig! Thanks for the link I've had a quick look through and with have a better look tomorrow.   

[9 volts]

Hey I'm continuing this one as it may help someone out in the future. (less experienced like myself). From my research GGG has a dual power supply pcb layout and if I've got it right, I can put a bridge voltage doubler in before it. Then a 9v ac adapter can be used.

[km-r]

since its AC, you may use cascaded voltage doublers...

[9 volts]

Right on! thanks for that. Bridge creates dc. Thanks again.

[km-r]

you might also wanna try this very elegant circuit:
http://web.telia.com/~u85920178/power/vconv_01.htm

[George Giblet]

If you are starting with main AC then rectifier based voltage doubler is fairly straight forward.

This site is clearer:

http://www.radio-electronics.com/info/circuits/diode_voltage_multiplier/diode_volt_mult.php

You would the circuit as is to generate the positive rail.  You build another one with all the *caps and diodes* reversed to generate the negative rail. 

You connect both circuits to the transformer terminals.  You do this in such a way that the first cap of each circuit connects together (ie. - terminal of cap of first circuit to + of cap of second circuit then both the transformer).   The 0V output is common to both circuits, this is the lower terminal in the picture shown on the above site.

You will end-up with about +/- 25VDC at the output, depending on the transformer.   The cap size depends on current but 470uF to 1000uF should do.

[9 volts]

Hey there, thanks for the links. I think this stuff can be really handy with effects eg neutron, maestro sample hold etc. So much of the old synth effects use the dual power supplies. I'm intrigued as to how some of Craig Andertons effects with a higher voltage as alot of those use dual supplies. Thanks again, I'm doing something similar to Geoges link but I love that schem from km-r. Could be very handy in the future. Thanks again

[9 volts]

Hey I built this today, I put a cascade voltage doubler infront of tge ggg bipolar ps. No luck so far. I used 4700uf instead on 1000uf caps in the ggg part and 1000uf caps on the cvd. A voltage reading shows that at junction of the diodes in the cvd straight after the first cap a drop down to 2v........which is weird, I've checked the layout and it seems ok.(using 9v wallwart/powerpack)

[km-r]

i might try a lil complicated design... SMPS! 

[9 volts]

I looked up voltage doubler in an electronic dictionary, the schematic was different to the one above (same piece count- two diodes, two caps) but it also converted to dc.(maybe this one does also). For the time being I'm feeding the bipolar with a proper 240v to 22v transformer and it's working. I'd like to get it sussed out though as a 9v ac adapter is pretty common.Thanks again

[Paul Perry (Frostwave)]

There are a couple of different voltage doubler circuits.
For this application - a bipolar supply - you need the one that has a common ground for the input & output, as George Giblet shows. And you need to have a think about what peak ratings you need for the caps 
I sure wish I had done this years ago when I started making my +-15V pedals - because it sure is easier to get  9v AC plugpacks, than the 14 to 18v AC plugpacks that I need!