Newbie: Dumb question on tip polarity

[Dr Yes]

Hi all,

I am pretty much a luddite where electronics is concerned but I wanted to ask a few basic questions on positive/negative tip polarity and how this affects effects.

In essence my rig is a simple Warwick powered pedalboard (Warwick FX Pedal Flight Case RC23120B) with the following connections:

- 1 x DC cable, mini jack / 9 V battery clip
- 6 x 9/12V DC cables with changeable polarity, mini jack / coaxial
- 3 x 9/12V DC cables, mini jack / mini jack

However, it seems to me that it only wants to accept positive tip connections and swithcing any connector to a negative tip justs sends the board ape and it overloads (a light helpfully comes on).

I'd like to buy a cheap noise gate to put at the end (I guess?) of the chain and the Artec Noise Gate seems to fit the bill - true bypass etc - but is this a stoopid move. I also like the sound of another Artec pedal the Fuzz Town, but again, if it's negative tip I fear I may have problems.

What's the issue here please?

Dave.

PS Sorry for being a dunce - I am a humanities major not a scientist/engineer!

[Mark Hammer]

When a pedal has the option to use battery or wall power, the power jack has the task of enabling battery power when no plug is inserted, and disabling the battery when a power plug is inserted. Normally, this is accomplished by having the inserting of the plug push something out of the way so that the default connection with the battery is interrupted/broken, leaving the battery out of circuit.

Because of their design, phone-type plugs MUST push the contact using the tip of the plug, and barrel-type plugs MUST push the contact using the outside shaft. Because chassis-mount mini-phone jacks are generally metal and thus grounded to the chassis, the tip is always positive and the shaft always negative.

In the case of barrel jacks, they come in two flavours: plastic body or metal body. The latter is, again, necessarily grounded to the chassis while the plastic one can be whatever you like. This has led to some problematic non-standardization.

If there is no battery to switch off, then a barrel-plug-equipped wallwart can actually make use of a metal-body outside-grounded barrel jack. This is the opposite of what you'd find on most stompbox-oriented power supplies. Because this concept is so bloody hard to explain to novices, companies like Boss, et al simply say "Use our supply and only our supply". They don't really make money off the supplies, but they do manage to keep their pedals working longer, and field far fewer repairs, when they can be confident that no one is plugging in an outside-neg supply to their pedal.

In a nutshell, the two styles of plugs (phone, barrel) can be summarized as follows:
- mini phone plugs have the advantage of standardization - tip is always positive - but the disadvantage of requiring the user to insert the plug before engaging the power supply itself...if they want to avoid shorts and sparks (wasn't that a Joni Mitchell album "Short and Sparks"? );
- barrel plugs have the advantage of never producing shorts on insertion, and making it hard to touch both pos and neg at once with your fingers, but the disadvantage of not being universally standardized with respect to polarity.

[Dr Yes]

Hey Mark,

Thanks for such an informative answer.

I think I've got it from this. So, and I could be missing the point, if my stomp box says it's negative tip, then it won''t be an issue if, and only if, I plan to always leave it plugged in and never risk shorting it out?

In other words, you're saying the issue is more to do with shorting than anything else?

[Steve Conner]

I did major in engineering, and design industrial electronics for a living, but I didn't really understand Mark's post.

Maybe he can correct me, but I think that irrespective of the details of the power jack, the negative power connection should end up connected to the metal casing of the pedal, and also the sleeves of the audio jacks, which we call "ground".

The polarity of the jack tip doesn't matter, it's the polarity of the internal circuitry that does, and for any modern pedal it should be positive.

Unless, that is, you have some funky old pedal with PNP transistors that runs off a negative supply. In which case, the positive power connection will end up hooked to ground. And because the grounds of all the pedals are necessarily connected together by the patch leads that carry the audio signals, the positive gets connected to the negative. Ie, your power supply gets shorted out.

Or, you accidentally "convert" one of your pedals to positive ground by plugging the power in backwards.


It wasn't clear from your original post whether you were asking for help with a problem. If you do have a problem, it must be one of the following:

You have a positive ground pedal somewhere in your setup, in which case you need a separate supply for it.

You have the power to one of your pedals connected up backwards, this should be obvious because it won't work and may even be damaged. (You didn't try reversing one of them to "see if negative tip would work", did you? Think about it.)

[Dr Yes]

Originally Posted by Steve Conner

I did major in engineering, and design industrial electronics for a living, but I didn't really understand Mark's post.

Maybe he can correct me, but I think that irrespective of the details of the power jack, the negative power connection should end up connected to the metal casing of the pedal, and also the sleeves of the audio jacks, which we call "ground".

The polarity of the jack tip doesn't matter, it's the polarity of the internal circuitry that does, and for any modern pedal it should be positive.

Unless, that is, you have some funky old pedal with PNP transistors that runs off a negative supply. In which case, the positive power connection will end up hooked to ground. And because the grounds of all the pedals are necessarily connected together by the patch leads that carry the audio signals, the positive gets connected to the negative. Ie, your power supply gets shorted out.

Or, you accidentally "convert" one of your pedals to positive ground by plugging the power in backwards.


It wasn't clear from your original post whether you were asking for help with a problem. If you do have a problem, it must be one of the following:

You have a positive ground pedal somewhere in your setup, in which case you need a separate supply for it.

You have the power to one of your pedals connected up backwards, this should be obvious because it won't work and may even be damaged. (You didn't try reversing one of them to "see if negative tip would work", did you? Think about it.)

Hi Steve,

I have a Cub Scout's science badge - and even that was a bit dodgy on my part - so I am none the wiser in much of this!!

Thankfully, I've had a reply from the company that's selling it which says it's positive - so it shouldn't be a problem. I know Behringer pedals are different and my problem was I didn't want to have to a) run a noise gate off a battery (as it would drain quickly) and b) I didn't want to have to buy a separate power supply. Seems I won't have to as they say:

"Hello, thanks for your message. I just checked the pedals and the symbol is DC9V + -. The pedals work with all regular 9v power supplies just like Boss or other pedals."

But thanks guys.

[Steve Conner]

Oh well, all I'm trying to say is that it should work fine irrespective of whether your new pedals are negative or positive tip.

And that you can't test whether it would work by changing the polarity on one of your DC cables and plugging it into one of your existing pedals. This will just apply power to the pedal backwards and short your supply out.

[Dr Yes]

Originally Posted by Steve Conner

Oh well, all I'm trying to say is that it should work fine irrespective of whether your new pedals are negative or positive tip.

And that you can't test whether it would work by changing the polarity on one of your DC cables and plugging it into one of your existing pedals. This will just apply power to the pedal backwards and short your supply out.

And it's appreciated Steve. All I meant was I am a dunce and it all goes over my head. But I get it now - thanks.

[Mark Hammer]

Steve, perhaps the missing element is the term "mini-jack", which I took to be a mini phone jack (1/8"). While there are some exotic phone jacks that use complex mechanisms to switch things via the shaft pushing contacts out of the way. Closed circuit phone jacks, whether of the 1/4" or 1/8" variety, use the tip to disconnect V+ from the battery source (or rather disconnect the battery from the circuit's V+ connection). I suppose if the chassis/box was plastic, or if the jack itself had a plastic body (like those "Marshall" jacks), one might conceivably use the tip to make/break a ground connection, but that seems highly unlikely. In the case of metal-chassis stompboxes using mini phone-jacks to connect wallwarts, the shaft of the plug WILL be negative/ground, and the tip will be positive, because it HAS to be.

All the power cables in the good doctor's pedalboard will share the same ground, which means that all pedals being powered by that system will have to be negative ground, and have a tip-positive connection internally, or else they will inadvertently shunt pos and neg together.

Does that make sense?

[Steve Conner]

Yes, but I don't even think you need the tip-positive condition, just the negative ground one. As long as all the pedals are negative ground, you can swap the polarities of the DC cables and find some configuration that works. Preferably not by trial and error, as that risks blowing up your stomp box collection...

[Mark Hammer]

Okay, I think I see where you're going.

If the pedal jack was wired in opposite fashion, and the power cable had some sort of polarity flip-around, AND the jack was insulated from the chassis, yes you possibly could use it without things blowing up.

But as has been noted, mini phone-jacks are generally shaft-to-ground (or at least those or the ones I tend to see used).