Negative vs. Positive ground

[trumpus]

Hey,

I was browsing GGG and noticed there were 2 different schematics for the rangemaster - a negative and a positive ground.  What is the difference between the two, and what are the ramifications (i figure this has something to do with power supply, but i'm a total newb, so i need a bit of clarification...

Thanks,
Brian

[chokeyou]

not having built a rangemaster, I'm not the authority on the subject. I think the original rangemaster was positive ground, which allowed it to use the NPN transistors it did. The problem with that is, you cant have it on the same power supply as your other pedals (if you run one). The negative ground version uses PNP transistors and is compatible with the other pedals on your power supply. If you're running a battery, you can go either way. I think you can actually use it with any power supply you may have, just as long as any other pedals sharing that supply use the same polarity ground. I'm sure somebody else will chime in here soon to correct me and go into detail a little farther.

[trumpus]

How does this (or does this even) affect the beginner project, which i believe uses an NPN?  Can i still use a dc jack?

Brian

[brett]

Hi.
In the old days, the best transistors were PNP (positive, negative, positive), which worked best with positive ground power supplies.  These days, most people build negative ground circuits, except for a couple that sound really good with old-fashioned PNP transistors.  Two common circuits like this are the Fuzzface and the rangemaster. 
It's not too dificult to buy some old germanium PNP transistors, but for a first project you might find fewer hassles with modern NPN devices and neg ground.
good luck

[trumpus]

....ok....but i still don't understand the meat and potatoes of this, and how this would affect which power supply i can use?  With an NPN, can i stil use my Godlyke, which powers my other pedals, or do i need to use a 9V only?

Brian

[R.G.]

 - There are several kinds of transistors. The rangemaster circuits use bipolar (literally, two polarities) transistors, which come in NPN and PNP versions.
- PNP transistors were the first commercially successful transistors because they were easier to make with germanium.
- NPN germanium transistors do exist, but they are rarer than PNP types because they are harder to make operate well.
- Silicon transistors were originally NPN types because NPN is easier to make in silicon. PNP silicon came later, and only recently  (1980's) improved to nearly as good as silicon NPN
- PNP transistor circuits tend to work best with positive ground power supplies; that means that the positive side of the battery is connected to signal ground and the negative side is connected to power the circuit.
- NPN transistor circuits tend to work best with negative ground power supplies; that means that the negative side of the battery is connected to signal ground and the positive side is connected to power the circuit.
- Both kinds of transistors *can* be powered from either polarity of power supply, with some difficulty. Powering PNP on negative ground or NPN on positive ground requires special techniques to ensure that the circuit does not have strange problems. (to the more educated readers: I'm simplifying for the newbies.) It is highly recommended that unless you're quite skilled and know a good deal about layout and circuit parasitics, you do not use opposite polarity power supplies, no matter who recommends them to you.
- You cannot successfully power both a positive ground circuit and a negative ground circuit at the same time from a single battery (or single-voltage power supply) and also connect them with a signal cable because the signal cable ground is connected to the positive end of the battery in the positive ground circuit and also the negative end of the battery at the negative ground circuit, effectively shorting out the battery.
-  I don't know what your Godlyke power supply puts out. If it's the only one I've seen, it puts out a single 9V supply. If it's like that, then you cannot power both positive ground and negative ground at the same time successfully.
- If you must power both positive ground and negative ground circuits at the same time, you need to supply *both* +9V to ground *and* -9V to ground. This is what makes people want to diddle with inverse power setups; they want to avoid providing a second power supply voltage.

[trumpus]

Thanks for all the info R.G.!

I've realized i just don't know enough yet, or have enough experience (having never built a circut with a transistor yet!) to really, truly understand this!

A follow up question...so how does this impact the "type" of power supply i can use.  FOr the beginner progject, which uses an NPN capacitor, can i use a standard Boss bower supply?  If not, what power supply can i use?  I want to put an LED and a DC jack in the beginner project, bu ti don't want to oscrew it up.

Brian