Guard Ring vs. "U" Shaped PCB Ground

[Myriad Society]

Given a standard 4 sided PCB... I was wondering if anyone had any input as to whether it was better to use the regular "U" shaped ground around 3 sides of the board that is fairly typical of layouts found on this forum and in R.G.'s book or are there any advantages/disadvantages to laying out a guard ring around all 4 sides of the board.

I suppose that using a guard ring may be an un-needed EMI/RFI protection redundancy if the effect would already be chassis grounded to an aluminum enclosure through the jacks. Concerns are that I wondered if it's possible to accidentally create a loop antenna doing this or some sort of Faraday cage that may keep external interference out but not allow internally generated interference an escape path so to speak. This gets into things I know very little about and has caused me layout issues in the past.

Perhaps none of this makes any sense and I'm just way over thinking it....

[Joe Hart]

I don't believe there are any advantages.  My thought is that if you use a "U" shape, then you always know which side is "down" and which is "up."  But maybe that's just me.
-Joe Hart

[R.G.]

Well, at least you are thinking! 

The "U" isn't perfect by any means. It's just a solution that works in the highly-restricted domain of small effects boards for audio. A ring is OK in many instances, but any time you have conductive rings, you have the potential (did I really say that!?  ) to get circulating currents and create loop antennas, as you are thinking about. Circulating currents can be a disaster if you have a source of intense magnetic fields nearby that cut the loop and cause high currents - but you can't get an M-field that intense into a shielded stopbox. Loop antennas can cause problems, but again, a shielded stompbox is generally proof against that, and in any case, the size of a loop you could put into a stompbox is going to be pretty high frequency.

One real reason for using the U is more prosaic: it makes layout easier by giving you a local source of ground, and also leaves one edge of the card open for sticking wiring pads into.

I don't think Ring versus U is actually a huge consideration in audio effects. I would not hesitate to use a ring if I didn't need to put pads on one side.

[Myriad Society]

Guys, thanks for the input. Your comments are much appreciated as always 

I think, in retrospect, this is about what I expected to hear but wanted to bring this up as I'm working on a booster which is hung up in layout (typical for me) but wouldn't be too difficult to move a few things around & connect the ground trace "U" accross the top to create the guard ring and place offboard connections just inside of it.

I think I'll stick to the "U" design then if there's nothing to really benefit from changing.