Power supply polarity with multiple effects

[MikeH]

I couldn't find anything this specific in my search, and I'm pretty sure the answer is "no", but can you house a positive ground and a negative ground circuit in the same enclosure?  I suppose that since ground is still at 0V in a positive ground circuit (right?) you could do it with 2 different power supplies, but something tells me that the whole damn thing will simply short out and not work.  Anyone done this with success?

[mdh]

You could easily do it with a bipolar power supply.  Take a look at R.G.'s "power supply basics" at GEO. The key is that the positive and negative supplies have to be referenced to the same ground.  There are even three-terminal regulators for negative supplies (positive ground), the 79xx series or the LM337T, counterpart to the LM317T positive regulator.

[rubix cube]

I asked a similar question a while ago but I think I posted it in the wrong place.  Is it possible to use a dual power supply (9V, Gnd, -9V), and power positive ground effects with Gnd and -9V, and negative ground effects with 9V and Gnd?  Could you then use Gnd both circuits and the chassis all together?  (Sorry if I merely rephrased your question!)

[R.G.]

Is it possible to use a dual power supply (9V, Gnd, -9V), and power positive ground effects with Gnd and -9V, and negative ground effects with 9V and Gnd?  Could you then use Gnd both circuits and the chassis all together?

Yes, it is possible.

I couldn't find anything this specific in my search, and I'm pretty sure the answer is "no", but can you house a positive ground and a negative ground circuit in the same enclosure?  I suppose that since ground is still at 0V in a positive ground circuit (right?) you could do it with 2 different power supplies, but something tells me that the whole damn thing will simply short out and not work.  Anyone done this with success?

Let me be specific - yes. Ground can be shared with positive and negative ground effects. It has to be, as a matter of fact. Think about if you have two effects, one positive ground and one negative ground, both powered by batteries. You plug them together in series.

The cable braid forces the signal ground on both effects to be at the same voltage, which we'll call zero volts. If we then connect a voltmeter (-) lead to the shield braid and measure the terminals of the battery in the positive ground pedal, we find that the (+) one is connected to signal ground (because, after all, it's a positive ground pedal!) and the other terminal, the battery (-) one measures -9V.  All is well.

When we go measure the battery terminal voltages in the negative ground box, we find that the (-) one is at 0V and the (+) one is at +9V.

Notice that it does not matter whether they are in the same physical box or not. The connection of signal ground between the boxes forces the signal ground to be the same voltage whether they are in one box or two boxes.

Now let's think. This is the painful part. We have two batteries. The (-) terminal of one is connected to the (+) terminal of the other by the signal ground shield braid. The power supplies we have left over are then one +9V and one -9V. We can replace the batteries with two power supplies which do the same thing and it will all work fine. No sparks. We have to supply the two effects with THREE different voltages: +9V, ground, and -9V.

What we can't do is make ONE battery or ONE single (not bipolar) power supply be both batteries. That is the connection that shorts out. This is because a single battery or power supply has only two different terminals. If we try to force two terminals to match three voltages, something unpleasant happens. Mother Nature is displeased and shows this by heating up the single battery until smoke comes out.

Did that help?

[rubix cube]

So, if I understand you correctly, I could use a bipolar supply in a metal enclosure (I'd be using one I made from variable regulators to give me from +5V, 0V and -5V up to +15V, 0V and -15V). I could then power my PNP Fuzz Face with the 0V to -9V from the power supply, and a microamp (or any neg gnd effect) to the +9V and 0V of the supply?  And also an effect like the Neutron (thanks by the way!)? If I can, it seems logical to me.  What I don't understand is why I've never come across it: I assumed that meant I was missing something.

Thanks for lots of great info!