Ground Planes

[saxtim]

Hi,

I've been designing a few of my own layouts recently and I've started to incorporate large ground planes on them, generally where these is space on the board that'd normally be open (for example the outside edges of the boards, where there is space for screws etc.  I've done this primarily because I'm using negative photo resist board, so having large ground planes turns into saved toner when i'm printing my designs before developing.

I have noticed that most layouts for Stompboxes I've seen don't have ground planes - is there any reason not to have them?  Is there any good reason to have them other than the one I've got?  I've read about reducing noise and stuff, but I don't imagine this is a problem normally if people don't use them.

thanks

tim

[Paul Perry (Frostwave)]

There is (as you might imagine) a lot of science to ground plane use, just slapping some in might not necessarily improve thngs. And yes, the average guitar effect is not operating at such a low noise situation that layout is critical. (things that might cause layout problems: BBD clocks, LFO swiching spikes, power supply returns, feedbackto input of high gain stages. Yes, the RG book is full of good stuff.
The fact that so many guitar fx boxes are working great with no attention whatever to layout, shows it is usually not an issue. Don't try to build a computer like that, though.

[R.G.]

Exactly correct Paul.

The real skinny on grounding in the general sense is that at low (like audio) frequency, you want isolated ground returns to have direct control of *where* the return current flows.

As frequency rises, you gradually move into needing "ground* to be a plane where you have low inductance over a whole surface so that RF effects get distributed, not isolated.

With even faster frequencies and especially with fast, sharp edged logic signals, you're into needing transmission lines per signal, and "ground" can no longer be considered something which can both keep signals clean and distribute power as it does for audio and lower-rf range signals.

Grounding is an art. I got several ugly and memorable lessons in grounding early in my career; later I found some good references and sucked them into memory to keep those lessons from recurring.