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

[Scott Gravenhorst]

My $0.02: I would try a bipolar supply made with a 9 vac
transformer, dual halfwave, sorta heavy filter.  For one OpAmp,
as a preamp...  Not much demand from the supply.  I think it would
work well with no regulation.

Just seconding whoever else said that before...

I will say this in addition, these are the kinds of projects
that make me glad that I am an electro-packrat.  I save ALL
wallwarts I find that are destined for the trash.  They are also
physically quite small, so they  don't consume much space to 
collect.


>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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