Ground planes

[sfr]

Sorry to go sort of OT again - I'll get back to building the stompboxes soon enough, and then I'll be asking of plenty of stupid on-topic questions!

I'm looking to build the firefly amp, and want to try my hand at turret-board construction.   I have an awfull lot of copper-clad laying around, so I was wondering about the possibility of just etching out the spaces around where the turrets would go, and leaving the copper on the rest of the board - shouldn't effect anything if I leave it like that, but what if I make the whole thing a ground plane?  I can't seem to find any information searching Google and various forums as to whether this would be good or bad - I can see a few amps makers use a similar approach, but I'm not sure if there are other factors that need to be taken into consideration.  When I get home I'll paw through my books, but I thought I'd ask here as well - is this liable to effect an amplifier circuit in a positive or negative way, or have no real effect if the amp is already in a proper enclosure?

How about effects pedals?  Do the use of ground planes (which I guess would be most effectively implemented in a multi-layer pre-fab boards?) have any benefits or drawbacks there? I can't find the thread now, but I seem to remember reading one a while back where it was noted that it did help avoid noise from LFO circuitry or something of that sort bleeding into the signal lines (I don't think I'm thinking the exactly right thing, I have more of vague "idea" of what I'm talking about)

So basically, I'm curious about ground planes and if anyone can point me towards some references either online or in dead-tree form, that'd be great.  I'm trying to make a more consciencous effort to learn principles and not just construction technique.


thanks!

.j

[Peter Snowberg]

In a nutshell noise is transported in two ways. It's either conducted, or it's radiated. You can add RC filtering to a signal or power rail to attenuate the conducted noise, but that doesn't address the radiated noise at all. That's where ground planes come in.

When laying out a plane, you either want almost total coverage, or you want a bunch of subsections with a single path of conduction back to your main grounding point. You don't want to end up with multiple ground paths, because they will start to make your boards act like transformer windings and they will pick up noise radiated from other sources.

When you make a plane with traces or components next to it, it's like making every wire into part of a very small capacitor. The values are so small that they will only affect radio frequency stuff. Audio is quite safe from those effects, except for extreme cases. I think your firefly will probably benefit overall. Tube amps are funny things; the radiated energy is so much higher at high voltages. If you try a really high gain circuit like a TrainWreck, where constructive and destructive capacitive coupling are essential ingredients, the tone will probably fall apart (than again.... I don't know.... I've never tried that ).

Sorry, no links, but I hope that helps.

Take care,
-Peter

[Paul Perry (Frostwave)]

Yeah, make it a plane. It can't (at audio) be any differen than just having a turret construction close to the inside of a metal box! Only connect the plane to the ground once, though.