Help with Positive v Negative ground wiring for DC jacks.

[carboncomp]

With lots of help from the forum, I have been working on a PCB with 3pdt Switch + Jacks + DC

And I think I have it right now for Negative ground NPN version, for centre negative 2.1mm DC jack?



BUT having a little bit of a problem with Positive ground PNP version. I would like to power a PNP circuits with a centre positive 2.1mm DC jack.

I have flipped the polarity of the battery, and changed all +9v connections to -9v, but do I have to switch anything on the DC socket connections, as I'm already changing from centre negative to centre positive on the PSU?    

[carboncomp]

And do I have to flip the LED round for the PNP version? 

[antonis]

LED flipping is the easiest part...
(current conventionallly flows from high to low voltage points, so from GND to -9V)

For DC jack:
If you'll try to power a centre positive jack from a centre  negative one, you'll get a short-circuit..

It doesn't realy matter the actual jack connection as long as you feed it with the right power polarity - meaning that you MUST power it with a 0V and -9V power supply...

[carboncomp]

meaning that you MUST power it with a 0V and -9V power supply...

Sorry, I am very confused now with you saying I have to use a -9v power supply?

Seem like other PNP pedals use a normal 9v Positive Center PSU (like all the Fulltone pedals)....so don't understand what you mean by the power supply needing to be -9v?

[antonis]

As long as your pedal is powered from battery ONLY, you'll have not any problem (with reverse battery polarity of course..)

For external power connection it's not enough to just reverse jack's polarity because your circuit needs a 0V(GND) to -9V supply, which - if you don't "create" it inside the pedal (with a voltage inverter or so..) - you have to take it from an already "reversed" one...


edit: links are gone...
(retry)

http://www.diystompboxes.com/smfforum/index.php?topic=76974.0
http://www.diystompboxes.com/smfforum/index.php?topic=101852.0
http://www.diystompboxes.com/smfforum/index.php?topic=73354.0
http://www.diystompboxes.com/smfforum/index.php?topic=92919.0

[carboncomp]

For external power connection it's not enough to just reverse jack's polarity because your circuit needs a 0V(GND) to -9V supply, which - if you don't "create" it inside the pedal (with a voltage inverter or so..)

I don't think you are right.

Surely you only need a voltage inverter if you want to daisy chain the positive ground pedal with negative ground pedals, its like saying you need a -9v battery!

Here is a link for 3PDT, True Bypass with LED, DC Jack/Battery power, Grounded Input, For PNP Positive Voltage Ground Wiring Diagram, no mention of a -9v supply needed.
http://www.generalguitargadgets.com/pdf/ggg_sw_3pdt_tb_pnp_dcj_gi.pdf

[GGBB]

This is correct except you need to flip the LED.

[Thecomedian]

I don't think there's any issue regarding how you wire the DC jack up, unless it makes an electrical connection to your enclosure, which is at ground potential to the rest of the circuit. Lets say you put this circuit on a breadboard instead, and had two wires going from your DC jack. If you plugged a center positive power supply into the DC jack, you'd want to run the wire that goes from the center to your circuit's ground. If you plugged in a center negative power supply, you'd want to run the DC jack's sleeve, which has the positive side, to your circuit's ground.

[karbomusic]

I'm already changing from centre negative to centre positive on the PSU

If you flip the polarity of the PSU that is the same as -9V for our purposes (such as reversing the wires on the PSU plug. Yes, that will work IF I read your post correctly and it is likely I did not. I did it that way for my PNP pedals but I cannot use that same PSU at the same time for a negative ground pedal because it will short via ground leg of the audio patch cable that connects the two. You'd need isolation to deal with that or, again like I do, 1 PSU for NPN, 1 for PNP, which in itself is isolation, done.

[carboncomp]

So this layout will work with PNP pedals as long as I'm using a plastic DC jack, positive centre DC PSU, and will still disconnect the battery when the input jack is removed?

(Flipped LED, and added input diode)


Or I could just use a standard centre negative PSU if I remove the battery connection from the input ring tab, and don't daisy-chain with NPN pedals? (maybe the better option for pedals I don plan on having a battery inside?)

[antonis]

For external power connection it's not enough to just reverse jack's polarity because your circuit needs a 0V(GND) to -9V supply, which - if you don't "create" it inside the pedal (with a voltage inverter or so..)

I don't think you are right.

As you wish...

But if you intend to externaly power your positive ground pedal from a negative ground PS, you'll have some problems - despite of your DC jack wiring...


edit: Maybe I didn't understand your query - if your problem is just to disconnect battery when powering externally from an "indepented" PS, then you're OK..

[carboncomp]

For external power connection it's not enough to just reverse jack's polarity because your circuit needs a 0V(GND) to -9V supply, which - if you don't "create" it inside the pedal (with a voltage inverter or so..)

I don't think you are right.

As you wish...

But if you intend to externaly power your positive ground pedal from a negative ground PS, you'll have some problems - despite of your DC jack wiring...

Can anyone else clarify this?

As I don't have any problems powering my Fulltone 69 PNP pedal with a CENTER Positive(+) 9 volts DC PSU 

[induction]

For external power connection it's not enough to just reverse jack's polarity because your circuit needs a 0V(GND) to -9V supply, which - if you don't "create" it inside the pedal (with a voltage inverter or so..)

I don't think you are right.

As you wish...

But if you intend to externaly power your positive ground pedal from a negative ground PS, you'll have some problems - despite of your DC jack wiring...

This is still wrong. The voltage that comes out of DC adapters is isolated from the mains. It has no ground reference until you give it one. A circuit can be positive or negative ground, but an adapter is not. Adapters, like batteries, supply a voltage difference between the two leads, but no absolute voltage until you attach one of those leads to a reference voltage. If you attach the positive lead of a 9V adapter to ground, the other lead instantaneously becomes -9V. Alternately, if you attach the negative lead to ground the other lead becomes +9V. There is no need to find an elusive 'positive ground adapter' (I'm not sure such a thing exists). As long as you don't daisy chain positive and negative ground circuits together, any 9V wall wart will do.

Edit: Although any wall wart will work, I recommend a regulated and filtered psu, especially for anything in the fuzz face family.

[antonis]

I edited my previous answer...

(you haven't info about "isolated" GND e.t.c.)


@ carboncomp: As long as you don't mix grounds (with other negative GND circuits) you are just fine...!!!

@ induction: I completely agree - except from the titles "positive" & "negative" for adaptor leads..
(I don't think that there is an actual polarity - is more than in term of voltage difference between the two of them..)

P.S. On a second thought I think that we are talking about exactly the same case..

[induction]

@ carboncomp: As long as you don't mix grounds (with other negative GND circuits) you are just fine...!!!

Sorry to nitpick, but this is still wrong. Ground is ground. All ground points in the pedal chain are attached to each other already via the cable sleeve that connects to the 'true' ground via the amplifier. You don't want to touch points together that have different voltages, like ground and +9V or -9V, but your ground points can and will all be connected.

Maybe the confusion comes from the misleading terms 'positive ground' and 'negative ground'. These would be more accurately described as 'negative supply voltage' and 'positive supply voltage'. Ground is zero volts in both cases, which is more positive than -9V and more negative than +9V, which I assume is where the name comes from.

Or maybe this is just a language barrier issue. In which case, I hope I haven't been a jerk about it.

[antonis]

Now I've totally missed you...  

As you said, adaptor leads are not grounded so you can name them as we like..

So if we want to create TWO voltage differences (+9V to GND and GND to -9V) we have to use GND as a common voltage reference but NOT with two identical pairs of adaptor leads with just reversing one of them...!!!

[induction]

Now I've totally missed you... 

As you said, adaptor leads are not grounded so you can name them as we like..

This is true until we attach either of them to a voltage reference. At that point both leads have absolute voltages associated with them.

So if we want to create TWO voltage differences (+9V to GND and GND to -9V) we have to use GND as a common voltage reference but NOT with two identical pairs of adaptor leads with just reversing one of them...!!!

You can certainly create a bipolar psu out of two isolated 9V adapters by tying the positive lead of one to the negative lead of the other. If you attach that combined lead to ground, then you have 0V, +9V, and -9V. I don't see the problem.

If by 'two identical pairs of adaptor leads with just reversing one of them' you mean a daisy chain, then I agree, don't do that. Otherwise, I'm not sure what you're getting at. The fact remains that the ground points of a positive ground circuit and a negative ground circuit in the same signal chain are the same voltage, and if you decide for some reason to run a wire from one ground point to the other, there will not be a short circuit. At worst there will be a ground loop, since these points are already connected. Do you disagree?

[antonis]

If by 'two identical pairs of adaptor leads with just reversing one of them' you mean a daisy chain, then I agree, don't do that.

That's exactly what I meant..

I completely agree with
<You can certainly create a bipolar psu out of two isolated 9V adapters by tying the positive lead of one to the negative lead of the other. If you attach that combined lead to ground, then you have 0V, +9V, and -9V.>
because I agree that it's a matter of "reference point"
(with this combination we can also have a +18V, +9V and 0V or 0V, -9V and -18V - depending on the point that we place as GND)

[induction]

Ok. I think we all agree then. Any 9V adapter can be used for either positive ground or negative ground 9V circuits, but not both at the same time (unless a charge pump is involved). And no inverter is necessary to get 0 and -9V out of a standard 9V DC (non-daisy chained) adapter.

[antonis]

Ok. I think we all agree then.

I think that it's (local) time for a beer...!!