[sdiy] Dual DC-Power from a single AC-supply

[np]

Hey!

I recently had the problem to get a dual DC voltage from a single AC 
transformer winding. I've asked around on the net and a old tube-guy 
showed me a circuit that I haven't seen anywhere before.

http://torus.untergrund.net/tubes/double_rectifier.png

It's voltage doubling with two cascaded bridge rectifiers. I have built 
the circuit and use it to power a OpAmp circuit. The power I get from 
this rectification is of better quality than what I get with DC voltage 
doublers/inverters (less hiss), and it has advantages over simple diode 
voltage doubling:  I get less and higher frequency ripple. It's easier 
for the transformer as both half-waves are used and you need less filtering.

For the AC coupling-capacitors I use 470µF.  These work fine even if I 
draw 50mA from each rail

Since it works so well and only need three additional cheap parts  I 
thought I'd post it here. Maybe the one or another can now put salvaged 
12V single supply trannies or AC wall-warts into better use..

Cheers,
  Nils