10 linear power supplies on one board: shared ground? or isolated ground planes?

[xefned]

I'm still debating the idea of making a small batch of PCBs for the Weber stompbox transformer with 9 secondary windings.

If I were smart, would I share the ground plane among all 10 PSUs, or give each PSU a separate plane?



I found a debate where both methods were criticized, at least hypothetically, with no real conclusion.
My hunch is that fully floating grounds will eliminate the possibility of hum through shared grounds. This is how I've always run mine. Any other thoughts out there?

RG Keen's Spyder design seems to imply floating is better. Scott Swartz seems to do it this way too at his GGG project. Same situation with the layout at Geofex. Still, I can't help but worry that this is somehow problematic. I don't own a commercial unit to open and see how the pros do it.

 

[xefned]

OK, ISOLATED it is! I read a bunch of posts by R.G. Keen over at DIYSB and the answer seems to be obvious: "Of course you isolate the grounds, you just isolated everything else along the way, why share ground hum between channels now?" I will now let this thread sink to the bottom of the ocean floor.

FWIW, I've been using this design with floating grounds for almost 10 years with no problems so I'm gonna fret over one dude's concern.

This project is the opposite of economical. Each channel has an adjustable regulator, 3 smoothing electrolytics: 1000µF, 100µF, 10µF, and of course, separate bridge rectifiers and transformer windings (thanks to the Weber) for every channel. It's really the gonzo way to do it.

Sensible people will just buy the Walrus Aetos; it has separate transformer secondaries for each channel. And at $170, it's less than the cost of a boutique pedal. No brainer. Incidentally, I contacted Walrus Audio support and they confirmed each 9v output has a dedicated secondary. I believe Voodoo Labs does it this way too. Some other brands appear to use the word "isolated" even when they're just regulating the same AC source. I guess "isolated" can mean whatever you want.

But I already have one of these Weber transformers laying around. They've been selling them since 2004 so a few other people out there could probably use this. Years later, they will find this thread thanks to search keywords like: WPDLXFMR-1 Transformer, DIY stompbox power supply.

 

[Stickman393]

I believe you came to the correct conclusion.

The thing that comes to mind for me here is that, regardless of if the power supplies are floating or not, many guitar pedal circuits will share one element: they will bond the negative end of the power supply to instrument ground.

So, once the power supply is connected to the FX, and then to the instrument, they're no longer floating independently. They all share a common ground point: that is, instrument ground.

It would seem to me that good practice would be to keep these grounds isolated from each other until they reach the circuit in which power is being used. If one was to, say, bond all those grounds together at the PS, and then have all the pedals that are being powered share a common ground via the instrument cable, you would have created a circular path in which electrons could flow with little resistance.

I think I read about as far as "ground dirt" and then my eyes glazed over a bit. I suppose maybe this dude is referring to noise inherent in the mains power supply? Though that's got nothing to do with ground. Ground is ground, ground is dirt, ground is simply what we tend to use in the states as a center reference for 230v single phase utility power. We bond our neutral wire's potential to ground, making 115v difference between ground (or neutral) and L1 or L2.

We choose ground cause...well...why not. It's a large reservoir of atoms and electrons and its not real easy to push those electrons around. It provides consistency, and with circuit breakers it keeps us safe if conductors break loose and energize something that has low resistance to ground. Current follows that path and the circuit breaker trips, instead of a floating setup where...ah...you might touch something and just happen to present yourself as a path.

Granted...I'm relatively uneducated in electrical theory. They taught us the bare minimum in the apprenticeship, a lot of what I've put together has been independent study. So I can, and often do, get things wrong.

 

[fig]

We choose ground cause...well...why not.

I've always thought the electrons did the choosing...interesting stuff! That is part of the whole electron hole in my edyoukashun.

 

[Stickman393]

Electrons...they just wanna hop to the next atom with an inviting, empty spot in it's orbit. But for current to continually flow through a conductor...instead of just hopping from one spot to another, something has to continually maintain potential on either side of that conductor.

Tie one end of that voltage generator to ground, and you essentially force that line to SIT DOWN, STOP MOVING, jeezus, kids these days...

While line 2 continues acting a fool, jumping back and forth around the other kid. Who is also line 1, but he's grounded.

Eh? Eh?

 

[fig]

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