Ground loops and TTL supply from PSU questions

Hello,

I have two questions.

First, do I need to be concerned with ground loops for computer circuits? I
am planning on taking 5V and Ground from a molex off of the PSU to power a
small circuit that I am building inside of the computer case. The circuit
will use that ground as a reference for a voltage (2V or so) coming off of
the video card adaptor (AGP port).

Am I going to be okay referencing the voltage from the video card to the
ground wire from the PSU, or should I reference it to something on the video
card itself? If I do need to reference it to something on the card itself,
would it be okay to tie the ground on the video card to the ground on the
molex from the PSU?

My second question concerns using the 5V output from the PSU as the Vcc for
a TTL chip. Should I use a voltage regulator to ensure that the supply is at
5V (and not too far over), or is it generally okay to just use the 5V as it
comes off of the molex?

Thanks for any insights into these concerns,

Jon

.

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