[sdiy] wall wart confusion

[amokan]

I didn't pay attention back in high school electronics when it came to power
supplies so please forgive me if this is a newbie question...

I've built bipolar supply kits for modular use but never really understood
_how_ they work. Negative supplies are a mystery to me. I know there is a
difference between ground and the negative rail, but I don't know what the
difference is. A 9v battery is in-fact bipolar, yes?

Long story short, I'm working on modules that will run in a stomp box format
and I'm trying to figure out the cheapest & easiest way to power them. I
know I could use the dual 9v battery solution to power them (assuming the
circuits could run at 9v) but I'd really like to just use a standard 9v or
12v dc wallwart that I have laying around the house. How do I get a negative
voltage off of a standard 12v wall wart? Is it already there normally, or
just a positive and a ground?

Sorry for rambling. If there is a web resource explaining this, please let
me know.

Thanks!
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