Pnp/npn how do I know?

[Chris mudd]

Hey all,
I am still working on getting better at wiring and layout. I am not clear on something.
When I am looking at layouts everywhere on this site, how do I know whether a layout uses center negative or center positive power?

Thanks!

[cjonesplay]

This can get confusing. If you're talking about PNP Germanium circuits (usually older designs like Fuzz Face and Rangemaster), you're looking at center positive power. 95% of other circuits are center negative. If you see PNP germanium in a circuit, it's going to be powered by -9 volt and you will see that on the vero instead of +9.

There are two ways to deal with this. You can add a chip called the 7660s (and the 1044 and a couple of others) that will invert the 9v from - to + and only then you can daisy chain a circuit. This is well-documented on the main site. Many of the veros include a version with this already.

Second, you can convert a PNP germanium circuit to NPN by switching the polarity (literally flipping them 180 degrees) of all electrolytic/tantalum polarized capacitors. That's it. This has been explained ad naseum but I still have to look it up every once in a while just to remind myself:)

[nocentelli]

PNP/NPN and centre negative/positive are separate, although related issues.

None of the layouts here will specify centre negative (BOSS style) OR center positive (old EHX, DOD and others with 1/8" mini jack adaptor plugs) because it is a descriptor of how the DC power jackplug is wired, and is irrelevant to the way the circuit works: The only concern you need to have is if you use a centre negative jack socket (most likely, because it is pretty standard) you need to use a plastic one, because with a metal socket the positive side of the supply will short with the grounded case.

NPN/PNP is to do with whether the circuit needs ground to be the more positive or more negative of the two sides of the power supply. This is easy to understand if you first think of using a battery to power the circuit. For the NPN fuzzface, you will need to connect the - ve from the battery (i..e. black wire from the battery snap) to the emitters, and the red to the collectors. I prefer to call this "positive power" but it is known as "negative ground": Ground for this circuit is by convention called 0v (one pole of the supply), and the power rail is +9v relative to ground.

In a PNP fuzzface, you have to connect the black wire to the collectors, and red goes the the emitters: Essentially the battery has been flipped in it's connections to the circuit.

The problem comes when these two separate situations interact. If you want the PNP fuzzface, it is fine to run off a battery: You just need to make sure the black wire from the battery snap goes to collectors, not emitters. However, if you try to wire your pedal with a DC jack socket, when you hook up the socket to the circuit board, you will find that you cannot wire the DC adaptor power correctly to the circuit without shorting the power supply. It is better to think of NPN circuits using 0v and +9v, whereas PNP need 0v and - 9v: The latter situation can be easily accommodated by using a battery and just flipping the connections. A DC supply cannot do this unless you add a voltage inverter to your fuzz circuit (e.g. 7660S) to give you the - 9v

[Chris mudd]

THANKS FOR THE REAPONSE!

So, if I look at a vero board diagram and it has -9v at the point where the non-ground wire mount to the board, it is not center negative?

Am I making it moe complicated than I need to?

[nocentelli]

This is a really good explanation written quite a while ago by a fx power supply guy:

http://stinkfoot.se/archives/532

... but a slightly shorter version = IF you have a pnp fuzz, and if you want a DC power socket, you must also install a voltage inverter if you want to daisy chain that pedal ever. It does not matter whether centre negative or centre positive socket is used.