[sdiy] Isolating a +-15v/+5v PSU?

[Jeff Farr]

>That depends entirely on the load. For a few CMOS chips,

Ahh, I misread that.. I get it now.  I've got 15 logic IC's in the
design, so I would think an additional smoothing cap before the 7805
would be a good idea, 100nF should be enough, no?  And then another
100nF on the output of the regulator to help with those downward
spikes?

With that in place the layout becomes the next important part for
creating isolation.  I plan on placing the analog PSU and digital PSU
on their respective ground planes with the AC input in between the two
and then placing the smoothing caps in such a way that the returning
ripple current doesn't flow through the common terminal of the
regulators.  Any other tips?

And now, a question about Star grounding VS using a ground plane:
Most of what I've read about star grounding pertains to tube amps and
the like where there can be substantial differences in the amount of
current flowing through the circuits, hence providing direct lines
back to 0v on the transformer so that they don't influence smaller
current areas.  However, most synth circuits that I've seen (or
understand) don't have large differences in current, and furthermore
I've been told that Op-Amps have very good supply rejection at audio
frequencies.. So, how much do I stand to gain by creating a grounding
tree in the analog section?