[sdiy] Wallwarts and ground?

[Scott Gravenhorst]

"James R. Coplin" <james at ticalun.net> wrote:
>So, I’m helping a friend finish up his MFOS Sound Lab project 
>and I want to run it off of a 9v wall wart instead of batteries. 
>The power supply delivers +/-9v but no dedicated ground. I guess 
>I never thought about it as I always just use the power supply 
>for my modular so voltage and ground paths are always there. What 
>do I do to provide a ground with the wallwart supply? 
>

Hi James,

I am assuming you're referring to a signal ground?  In all of the
wallwart powered circuits I've used, one side of the DC power supply is
picked as ground.  If it's a dual supply made with 2 halfwave
rectifiers, then the zero volt point is ground.  If it's a single
supply, the "appliance" should have a signal ground that is called out
in the schematic.  This signal ground will almost always be connected
to one side of the supply.  The only exception I can think of is a
circuit which uses a single supply, but provides a signal ground by
implementing a virtual ground.  In that case, the virtual ground is the
signal ground.  Regardless of whether it's a virtual ground or a power
supply zero volts point or simply one rail of a single supply, the
signal ground can be the earth ground too because we're talking about a
system that is isolated with a transformer.  I suppose that it's always
possible to have a wallwart with a 3 pin mains side where the ground
pin is connected to one side of the secondary, but that is easy to
discover with an ohm meter.

Of course, if I'm full of kaka, someone here will educate me (c:



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