[sdiy] "backwards" connected positive regulator (was: Problem with 723 PSU)

[Synthusiast]

Hi list,

I'm still working on my Tiracon 6V synth and I've noticed that it uses the
method of a "backwards" connected positive voltage regulator (LM317) for
the -15V rail. I was and still am a little puzzled about how this method
exactly works. Is there a site on the web that explains the theory behind
this way of designing negative rails?

TIA,
Martijn

> Thanks a lot, all of you who have offered advice on this problem!
> I looked at it some more last night.
> It seems the theory with the long cable causing the problems was a false
assumtion.
> I was fooled by the fact that when I connected the transformer direcly, I
also disconnected the other PSU unit.
> What most likely causes the problem is that I run two units from the same
transformer winding.
> This works fine for the positive regulator, but evidently not for the
negative. This isn't really surprising, considering how the regulator is
designed (positive regulator connected "backwards").
> I'm almost certain that if I get another small transformer to run one of
the two regulators used for -15V, everything will be fine.
> Connecting resitsors, caps, ferrite beads etc to the AC inputs did not
help, by the way.
>
> /Jorgen
>