Well, if you must use a switcher, then:

Make a completely solid and seperate ground plane for the analog.  Connect to
the PSU ground at one point only.  Bring +V in through a PI filter, which is a
cap, inductor, and cap.  Place a linear regulator there to drop +v to 6V.  It
will take out frequencies that the PI filter did not.  Hopefully, assuming the
low pass regions overlap.

So you also need a negative voltage.  You can use one of those 7660 style chips,
but many folks find that they have terrible noise.  The other possible solution
is to use an isolated DC/DC converter, either off the shelf or built around a
transformer from PICO or Premier Magnetics.  You can generate both + and - with
one part.  You still have switcher noise, which you try to take out as mentioned
above, but at least you have an isolated ground.

Audio design is a lot harder than many people think.  Good luck.

Chris Eddy

Tobie Horswill wrote:

> Hi,
>
>     I've just started working on an audio project involving an 16F877 and an
> Analog Devices SSM2160 (requiring a  -6V,+6V supply). Any hints on how the
> two supply voltages should be generated and routed on the PCB in order to
> minimise digital leakage in the audio ? I know this isn't a great idea but
> if possible I would be using using a small +5V, +12V laptop computer style
> switching supply. How can I best isolate the circuit from the switching
> noise ? I'm a programmer kind of guy, not an power-supply engineer so please
> forgive my electronics shortcomings... _-.\
>
> Tobie