I have a 9v circuit board in a metal case (that adds a sound effect to an audio signal, but that's beside the point). The proper way my diagram says to hook up the 9v DC power is to have the -ve output from the DC converter hooked up to "gnd" which I presume is the ground. Consequently, the positive end is hooked up to "9v IN(+)" which is clearly marked with a + sign. So here's my dilema. My audio jack has an audio signal ring(basically a contact that the audio plug touches when plugged in) and a ground ring, also the jack is meant to be set up with the ground ring sitting against my metal case. I have attached my ground ring wire to the ground on the circuit board too!! . But now that means that my metal case is "hot" and I feel that the two grounds have different meanings and shouldn't be connected. Are the two grounds (for the cicuit board and the audio jack) too different in their function to be hooked up to each other? (let's assume I wired the circuit board correctly 'cause it works and reversing the polarity just makes it start smoking LOL)

 

A stereo audio connection consists of three conductors and a corresponding stereo plug (and jack) has three conducting surfaces, which are normally called the tip, the ring, and the sleeve. In a standard stereo setup, the left channel is on the tip, the right channel is on the ring, and the ground is the on the sleeve.

Although there are circuits which have more than one "ground," most simple audio systems share a common ground. In those systems, the ground from the DC power supply and the ground from the audio line are common.

 

That is very helpful and it sounds like you know what you're talking about! So you say I have it hooked up correctly, but since the sleeve of my audio jack is connected to the ground is connected to the DC power supply is connected to my metal case... theoretically if I had two of my encased devices, plugged in device#1 and made the cases for device#1 and device#2 touch each other, I could power device#2(if I stuck the positive wire of device#2 into the soil outside my place to give the electrons somewhere to go). Which does not seem like the right way to use electricity :S. Do people generally insulate their metal cases with a coat of paint or something? That would fix my mental anguish, but is that normal?

 

Ground on the metal case does not make it "hot". It makes it a normal system. A stereo, LCD TV, DVR, Satellite Tuner, Cable Tuner all have their chassis at GROUND POTENTIAL.

If you hooked your box into your audio system correctly (and you did, if you wired it like you said), you will be fine.