Power source

[Martin Czech]

> > I agree, I really need a good power source and making one would be good
> experience.  I realized that this power source (from other members on the
> list and the display on my "new" scope, an RCA last calibrated on 1974) is
> simply fulwave rectified and no smoothing -probably because its just used
> to push little cars across a track. The cap I used worked well but now I
> have a problem.  I used two identical resistors to divide voltage and get
> a ground out, Problem is once I connect a circuit the voltages go crazy
> and ground moves to about two volts from the positive rail. 
> 
>  How can I buffer the power source so that other resistances in the
> circuit dont change the scale of the power source?
> 

I think the basic scheme to get bipolar power from a single coil
wall wart is to use half way rectifying.
Use one trafo output as gnd. The other will feed two caps (to gnd) 
via two diodes, one for the positive and one for the negative
cycle. This way you get a stable gnd, but now the power rails
are only half way rectified. Should be ok for experiments.

Of course, you have to get the voltages right at the trafo,
not behind the full wave bridge.

If you downlad all lepers effect schematics (in one file)
there are a couple of such circuits, to feed those effects
that need bipolar power.

m.c.