Why negative center on DC jacks connections?

[Labaris]

Hi everyone.

This is how most of pedals are wired:



I've always wonder why?
It would be more logical to me to wire it the other way, with positive center.

Any idea of why is it done this way by almost everybody? Is it because of the switching-system that popular DC jacks have?

Thanks in advance

[R.G.]

I've always wonder why?
It would be more logical to me to wire it the other way, with positive center.
Any idea of why is it done this way by almost everybody? Is it because of the switching-system that popular DC jacks have?

It's pretty much because Boss decided to do it that way, put it in all their pedals that way, and shipped adapters that did it that way. So anyone who wanted to sell a pedal that would work with a Boss power adapter had to put in that style jack, and anyone who wanted to sell a power adapter that fit the zillions of Boss pedals had to make their power adapters work that.

Him that gets there fustest with the mostest - to torture a Stonewall Jackson quotation - sets the standard.

[zombiwoof]

When they started putting power jacks on pedals, it seems that all of the U.S. pedal manufacturers (DOD, Whirlwind, EH, MXR, etc.) used the 1/8" mini phone plug jacks, and most of them were wired positive center, and the Japanese manufacturers used the Boss-style neg-center barrel jacks.  I don't know exactly why, but over time the Boss-style won out, and the U.S. manufacturers changed over to the Boss style jack wiring.  I guess the industry wanted to have a standard, and that's the way it turned out.   There were also those Performer series pedals by DOD that were 18-volt powered, they used a large 1/4" phone plug on those.  I find it interesting that the negative center barrel jacks became the standard, but when guys started having large pedalboards it was easier to have all of the pedals wired the same way, to use with the power supplies that have multiple outputs.

Al

[Labaris]

I've always wonder why?
It would be more logical to me to wire it the other way, with positive center.
Any idea of why is it done this way by almost everybody? Is it because of the switching-system that popular DC jacks have?

It's pretty much because Boss decided to do it that way, put it in all their pedals that way, and shipped adapters that did it that way. So anyone who wanted to sell a pedal that would work with a Boss power adapter had to put in that style jack, and anyone who wanted to sell a power adapter that fit the zillions of Boss pedals had to make their power adapters work that.

Him that gets there fustest with the mostest - to torture a Stonewall Jackson quotation - sets the standard.

Ok, thanks for the info!
And I really don't like that standard... It's a problem when you have metallic jacks, in metallic boxes...

Does shielding work properly with this "positive-reference" in the box?

[jasperoosthoek]

And I really don't like that standard... It's a problem when you have metallic jacks, in metallic boxes...

Me neither but we're stuck with it... I found out the hard way: the first box I built with a metallic power jack and signal jack sockets shorted out because of that reason. It does work however on positive ground effects.

Does shielding work properly with this "positive-reference" in the box?

I've put a metallic power jack socket in a friends cheap Russian big muff clone. This effectively connected the enclosure to 9 volts. I did not hear any difference. As long as your power supply is stable enough with a nice cap the 9 volts is just as much a ground for noise as the 'normal' ground.

[Thomeeque]

I've always wonder why?

My theory always was that it's for battery switching (battery must be switched off when {A} INPUT jack is unplugged and {B} DC jack is plugged) - as INPUT jack switching can be done only for the negative pole of battery (as it allows connect only to the ground and ground = negative pole mostly), DC jack may switch only positive pole of battery and usual DC jack construction allows switching only for the outer contact not for the central pin.

I still believe it

T.

[deadastronaut]

i thought it would be to stop the box from being positive..and shorting on other stuff?...

[Rob Strand]

@Thomeeque

That's always been my feeling too.  It come down to the best economics and practicalities for the sockets.

(My late 70's active Ibanez bass (no DC jacks obviously) had a special socket which switched the battery positive rail.    The socket was deeper, and flimsy, and it failed.)

[Boner]

Bumping a dead thread instead of starting a new one! Since my question in related...

So if you have a pedal that is only powered by a DC jack and there is no battery, would it be beneficial to switch to a center positive instead of boss style center negative? You could more easily ground the box at that one point I figured.

[Ice-9]

I've always wonder why?

My theory always was that it's for battery switching (battery must be switched off when {A} INPUT jack is unplugged and {B} DC jack is plugged) - as INPUT jack switching can be done only for the negative pole of battery (as it allows connect only to the ground and ground = negative pole mostly), DC jack may switch only positive pole of battery and usual DC jack construction allows switching only for the outer contact not for the central pin.

I still believe it



T.

Exactly this ^

[thermionix]

Meh, just as easy to do either way.  (Neg from battery snap to switching DC jack, then to input jack ring)

[Rob Strand]

So if you have a pedal that is only powered by a DC jack and there is no battery, would it be beneficial to switch to a center positive instead of boss style center negative? You could more easily ground the box at that one point I figured.

It's easier to mount with a centre positive.  However if the external supply had a lot of ripple and the circuit had on on-board PSU cap, the current pulses would flow through ill-defined paths in the circuit and could cause an annoying and allusive hum problem.    The isolated sockets force (or allow) you to connect the external PSU to the "best" point in the circuit.

A lot of network equipment products use the centre-positive adaptors.  However it usually connects to the PCB and is then routed to the "best" point in the circuit; together with any RF filters that are required.   They don't tend to wire the outside of the power connector to the metal box and, more often than not, the box is plastic anyway.

[Mark Hammer]

Why are 2.1mm plugs/jacks the standard, now, after so many years of 1/8" phone plugs?  Simple.  Because you can tell end-users to insert the plug BEFORE plugging in the wallwart to apply power as many times as you want, and they are still going to plug a live power source into the pedal and  short out the supply, yielding a big spark.  Barrel plugs sidestep that.

Though not likely a major factor in more universal adoption of barrel plugs, they are AC-friendly, since no polarity is assumed with an external AC supply.

Just note that, when a pedal can be powered by an internal battery, such that inserting a power-plug disables that battery, 95-97 times out of 100, the standard observed will be outside-pos/inside-neg, because the outside shaft is used to nudge the default contact with the internal battery out of the way.  HOWEVER, where it is assumed the pedal can only be used with an external supply, and does not have any internal source, it can be the manufacturer's perogative to go with outside-neg, possibly for safety reasons. And some have, although the more common presence of power bricks these days, as opposed to individual device-specific wallwarts, has nudged pedal-makers to just do what everyone else does.

[amptramp]

The original stompboxes, the Fuzz Face and the Wah pedal, were implemented with PNP transistors so the positive was the ground.  Since the signal was AC-coupled into and out of the unit, there is no problem connecting to other pedals regardless of their internal polarity.  Once external power supplies were built to supplant the battery, the positive shell had already been established and since power supplies were being built that way, everyone had to adapt to that.

[thermionix]

Fuzz Face, Rangemaster, other Ge fuzzes.  But off the top of my head I'm not aware of any PNP wahs.

[Mark Hammer]

Which is why I said 95-97 out of 100.

[Rob Strand]

Why are 2.1mm plugs/jacks the standard, now, after so many years of 1/8" phone plugs?

There's the safety aspect that 1/8" plugs can short quite easily but 2.1mm (etc) are a lot harder to short
Then there's the dumb-user aspect of plugging the wall-wart into the headphone or mic jack.