[sdiy] getting +/- 12V from a 9V source

[harry]

MPJA.com had some linear line-wart supplies with +5, +12, -12...

for like $8 you could be finished.  Buy TWO for when the first one fails...
in twenty years....

H^) harry

Philip Olsson wrote:

> > Hi list,
> >
> > Just wondering. I'm still puzzeling about a preamp thing I want to built for
> > a friend (RIAA, maybe someone remembers my last post).
> >
> > Now there is a problem with the power supply. I want to drive a +/- 12V
> > circuit from a 9V wallpart (because they are so cheap and common). I don't
> > feel like building a full blown +/- 12V supply just for a preamp.
> >
> > Can't I just up-transform the 9V again? It shouldn't be a big deal to throw
> > together a wien-bridge sine oscillator, a fat tranny as a driver and the
> > output through two little transformers. Then add a rectifier, some caps and
> > a 7912/7812 pair.
> >
> > My idea would be to use these 1:3 audio-transformers, which where used to
> > match the impendance of amplifier stages in early (tube and germanium)
> > amplifier designs. These are cheap and small. I have little experience with
> > them. Will they stand the current? I only need some mA to drive the 7812 and
> > a dual opamp.
> >
> > Also a different option would be to use a diode+cap step-up circuit. I've
> > seen these as ready to use chips, but never dealed with them. Anyone used
> > them for audio?
> >
> >
> > Enlight me with your wisdom  :)
> >
> >   Nils Pipenbrinck
>
> Can´t you drive the circut whit +9v?
> If its just the opamp that are going to be powerd check the datasheet for the opamp...
> Its probly just a matter of changing resistors.
> Could you show us the circut?
> / Olsson

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