Originally Posted by vixr
here is an example of a signal generator I wanted to build... the first uses a large ground "buss"
Actually, this isn't what I was referring to as a ground/power bus. Here's the PPA v2 layout:
The pink bits are where the red and blue traces overlap.
The power busses I was referring to are up at the top, where we have massive V+ and V- busses, because the space was there. Since it lowers the power supply's ESR, we did it.
Now, down at the bottom, you see the input signal traces going underneath a true ground plane, between the rear input pads and the pot. Here, the ground plane does the same thing that the ground shield does in a nice cable. The alternative would be either to have 6-ish inches of unshielded cable between the rear panel and the pot, or "encourage" builders to use shielded cable. Because we could do the right thing for the builder on the board, we did.
Now, to my real point about ground planes vs. power/ground busses: imagine trying to snake a ground plane anywhere into the middle of that board. We tried. It falls apart like rotten lace. When the amount of top-and-bottom signal traces gets this dense, you see the value of 4+ layer boards.
As for your board, the one with the ground plane — yes, that's what I'd call it — is better. The point we're all trying to make is that putting it on the other side of the board would be even better.
But, beware: with a true ground plane, you often want to cut holes in it around sensitive parts of the circuit, where you don't want coupling to ground. Op-amp input pins are a biggie.
Speaking of, what is U1, and why does it have 10 pins, two of which seem to be duplicates? And why are there no bypass caps?