help with 9v power supply

[nopainkiller]

I'm biulding a little bridged op-amp ghetto blaster and want to make it battery powered, but it also NEEDs to be outlet powered too. I don't know how to do this. I ripped apart something that had one in it, and tried to use it in my breaboard, but when I get it to work, there's a hum kinda bumpy noise. There are three prongs on it, I dunno wut for.

How do I hook these up??? i have no experience with this stuff. The ac adapter turns it to direct current, correct? I feel stupied, but I've been searching for days on how to do this and can't find anything so I post here.

[sean k]

There should be some articles on how power supply units work. If I were you and had the knowledge you say you have then I'd buy a 9VDC regulated supply and wire the input for it, one of those little 2.5mm DC inputs, so it switches off the battery when the DC is plugged in. There are three pins on the DC inputs and I always wire mine with the centre prong positive then switch the negative.

See how you go with that.

[nopainkiller]

thnxs, I figured out how to use it, that the third pin is for the live battery wire.