What is the rationale for DC power adapter connections to be Center Negative?

#2
So I would guess because it makes the most sense from an electrical engineering perspective. But I think it was probably equally considered important that whatever standard got adopted - for whatever reason(s) - it was uniform across the industry to maximize compatibility and interoperability.

In the IT world we have a saying: Better some standard than none. Because any standard, even a flawed or less than ideal one, is a better alternative than having no standard at all. Look at MIDI.
 
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#5
History has not recorded why Boss and Maxon chose center negative as their standard; but they were the makers that had the most international success in the pedal market early on, so most manufacturers have gone along with that just to make things easier for themselves and their customers in the market. It's not a matter of practicality or ideal engineering, it's a matter of going along with the critical mass.
 
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#6
bongomania said:
History has not recorded why Boss and Maxon chose center negative as their standard; but they were the makers that had the most international success in the pedal market early on, so most manufacturers have gone along with that just to make things easier for themselves and their customers in the market. It's not a matter of practicality or ideal engineering, it's a matter of going along with the critical mass.
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We have often speculated that they wanted to make extra money off of selling power supplies. Outside of effect pedals, the world is center positive. This is only a guess. No facts to back it up.
 
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#7
When pedal manufacturers started using the barrel type power plugs they needed a way to ‘switch’ from internal battery to power adapter when a power plug was inserted. To have that ‘switch’ action in the power jack required the positive to be on the outside of the barrel, since the ground path was being used as an on-off power ‘switch’ at the signal jack.

-Frank
 
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#8
boomertech said:
When pedal manufacturers started using the barrel type power plugs they needed a way to ‘switch’ from internal battery to power adapter when a power plug was inserted. To have that ‘switch’ action in the power jack required the positive to be on the outside of the barrel, since the ground path was being used as an on-off power ‘switch’ at the signal jack.

-Frank
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I don't see why it matters which pole is on the switch circuit of the jack, break either leg and the current can't flow.
 
#9
CatSquare said:
I don't see why it matters which pole is on the switch circuit of the jack, break either leg and the current can't flow.
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Correct, either side can be used to break the flow. But, when you are working out a switching pathway for both the batt and power adapter AND the ground switching at the signal jack for pedal power when a batt is used, I believe that this method is the simplest.

-Frank
 
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#11
A quick google search found a more detailed way of explaining it than I have.

Pedal Power Basics

"A side note:


Most electronic devices and their power supplies have center-positive polarity, so why do pedals have center-negative polarity? Because many pedals work with either a battery or a power supply; and, to preserve the life of the battery, it is disconnected from the circuit when either (1) a power plug is inserted or (2) the input plug is removed. This is accomplished by connecting the battery's negative terminal to the input jack's ring contact and the battery's positive terminal to the sleeve shunt on the power jack. When the input plug is inserted, it completes the circuit for the negative battery terminal. When a power plug is inserted, it breaks the circuit to the positive terminal of the battery. Power jacks do not have a shunt for the center (pin) contact, so a center-positive power supply would not work in this type of circuit."

That's better!:thumbsup:
-Frank
 
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#12
boomertech said:
A quick google search found a more detailed way of explaining it than I have.

Pedal Power Basics

"A side note:


Most electronic devices and their power supplies have center-positive polarity, so why do pedals have center-negative polarity? Because many pedals work with either a battery or a power supply; and, to preserve the life of the battery, it is disconnected from the circuit when either (1) a power plug is inserted or (2) the input plug is removed. This is accomplished by connecting the battery's negative terminal to the input jack's ring contact and the battery's positive terminal to the sleeve shunt on the power jack. When the input plug is inserted, it completes the circuit for the negative battery terminal. When a power plug is inserted, it breaks the circuit to the positive terminal of the battery. Power jacks do not have a shunt for the center (pin) contact, so a center-positive power supply would not work in this type of circuit."

That's better!:thumbsup:
-Frank
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Oh I see, okay that makes sense. Thanks!
 
#13
boomertech said:
A quick google search found a more detailed way of explaining it than I have.

Pedal Power Basics

"A side note:


Most electronic devices and their power supplies have center-positive polarity, so why do pedals have center-negative polarity? Because many pedals work with either a battery or a power supply; and, to preserve the life of the battery, it is disconnected from the circuit when either (1) a power plug is inserted or (2) the input plug is removed. This is accomplished by connecting the battery's negative terminal to the input jack's ring contact and the battery's positive terminal to the sleeve shunt on the power jack. When the input plug is inserted, it completes the circuit for the negative battery terminal. When a power plug is inserted, it breaks the circuit to the positive terminal of the battery. Power jacks do not have a shunt for the center (pin) contact, so a center-positive power supply would not work in this type of circuit."

That's better!:thumbsup:
-Frank
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Excellent information! Never considered that aspect. Thank you!
 
#14
Dominic DeCosa said:
The overwhelming majority are center neg. The few that aren't have chosen to ignore the accepted standard.
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There were AC adapters with center positive many years before there were effect pedals - electronic devices not musical instrument related. I used AC adapters for ages before I ever saw one with a center negative and the first one I saw was when Roland started selling equipment in the USA (I'm sure they weren't the first - but the first time I needed a center Negative was when I bought a Roland device). In the early 70's I had many more center positive devices for musical instruments than I did center negative -- but I didn't have Japanese gear back then.

EDIT: I just read the link @boomertech posted - ah, makes perfect sense the switched connector to disconnect battery when using power supply. I think all of the center positive stuff I had was stuff that only ran on AC adapter and didn't take batteries at all. (I've got to start reading to the end of the thread before I respond :) )
 
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#15
There are a lot of devices that have center positive DC jacks and batteries (boomboxes, portable CD/tape players, etc), but unlike these other devices, pedals also have power switching on whether a plug is in the 1/4" input jack. The 1/4" input jack has to switch the ground because it works by connecting the sleeve and ring of the jack, and the sleeve is ground - signal ground, and frequently the chassis of the pedal. So that leaves only the non-ground voltage to be switched at the barrel of the DC power connector. The non-ground voltage is positive for nearly all modern pedals.

I don't know when switching power on the input jack was introduced, but the only part needed is a 1/4 stereo jack, and it must have been well before pedal manufacturers (Boss?) standardized on the 5.5mm barrel DC power jack.

The only time that I have managed to short pedal power is a pedal that has a PC board mounted power jack recessed behind the metal chassis, and I accidentally touched the plug barrel to chassis. Boss and many other pedals have the plastic jack flush with the chassis so this is less likely to happen (also, less likely if the pedal is painted).
 
#16
40Hz said:
So I would guess because it makes the most sense from an electrical engineering perspective. But I think it was probably equally considered important that whatever standard got adopted - for whatever reason(s) - it was uniform across the industry to maximize compatibility and interoperability.

In the IT world we have a saying: Better some standard than none. Because any standard, even a flawed or less than ideal one, is a better alternative than having no standard at all. Look at MIDI.
Click to expand...

or older phone USB connections. Or very old printer connections (I made a bunch of money custom soldering RS232 cables back in the day...)
 
#17
Agreed, it was BOSS who started all this in the 70s just to force you to have to buy their adapters too. While I do think that the barrel type of plugs are way better than any 3,5 mm or lesser "mini tele plug" there's a less risk of noise when plugging and unplugging with barrel types. The jack in the pedal was normally secured right to the box, which also dictated the wiring – as the box itself is ground, the sleeve of the jack/plug had to be negative. Because the metal neck and nut of the jack is connected to ground, you can sometimes see sparks when inserting the plug... ;) now is that a good thing?

But as for the center negative, I think it has to do with how all the pedal box are earthed grounded too. And the battery as already explained. The adapter jack also needs to switch out the battery positive wire (to disconnect the battery when you insert a plug in the jack), and since the DC/barrel type jack has the switch on the sleeve/barrel connection, that’s where Boss wired the positive. There are pedals where the jack is wired center positive – again, not ”positive tip” – and some of them need their own separate power source (because they are positive ground!).

Some manufacturers earths and grounds their chassis, but it is making the assumption that they're all made of some kind of steel. Plastic boxes must have different kinds of "schematics" to provide this, and it can both be connected to the power plug or not. I am not sure, but I think I've heard that with some pedals, while disconnecting, there's not as much hazard present, and if you change power plugs while the input and output are still active, no noise is heard, and if you have batteries in it, they will turn on active again. If you happen to not have plugged all the way in to the jack, there's less that can happen, in the hum/noise department. But I am not sure of this, since it is very dependent on the rest of the pedals construction anyway. It can be different for different pedals.

I do think, that from the start on, it had to do with disconnecting the onboard battery, and run it on power adaptors. I e that the battery became active when you plugged into input jack, and disconnected if there ever was a power adapter jacked in at the dc power jack. If you use both, it was better on having the center negative. On a pedal that can't be run on any batteries at all, it's kind of "doesn't matter".
 
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#18
But hey – why is the jack wired the way it is in the first place? It does seem a little odd to carry the positive on the sleeve of the plug, doesn’t it? Especially since it means that for a regular negative ground design, you can’t use a metal-sleeved jack (as it would send the positive straight to the chassis, and short the power out). Well, this is all Boss’ fault… before they started using the barrel type plug, almost all pedals had the 3.5mm (1/8″) mini plug instead. That plug is still used on some Electro-Harmonix pedals and the RAT, by the way. But Boss chose the 2.1mm barrel plug/jack for their compact pedal line, and others have since followed (for instance, Ibanez started using them in ’83, when the 9 series was released).

The 2.1mm barrel type jacks had a switch function, which was (and still is) used to switch the battery positive out when a plug is inserted in the jack. Since that switch was/is located on the sleeve connection, the positive voltage needed to go on the outside of the plug. Simple as that.

So that’s why the jacks on normal pedals are wired the way they are. But the plug polarity is not why some pedals short the power out if you try to daisy chain them. That has to do with the…

- - - - - - - -

Ground polarity
In normal guitar pedals, the battery/power negative is referenced to ground, with the positive sitting 9 volts above ground (hence the +9v term). But there are a few designs that are ”upside down”, where the battery/power positive is referenced to ground instead, with the negative sitting 9 volts below ground (-9v). These are called ”positive ground” (PNP), and they can not share its power with negative ground designs – that will short out the power supply. This is because the pedals share a common signal ground – through the patch cable – which in both pedals is connected to the chassis. The chassis is also connected to the power’s ground. In a ”regular” pedal the adapter/battery negative goes to this common ground, but in a PNP pedal the adapter positive is connected to the same ground. If you combine them, the result is of course a short-circuit in the power supply. The solution is to run the PNP pedal(s) from a separate supply, or to use batteries with them.

What bugs me is that the manufacturers don’t seem to realize that most people don’t know these things, and will inevitably get it wrong, without proper instructions.
 
#19
SanDiegoHarry said:
or older phone USB connections. Or very old printer connections (I made a bunch of money custom soldering RS232 cables back in the day...)
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Good man! Same here. Also sold a lot of serial adaptors, and wired up my share of "separators" to get around Apple's decision to use sync-on-green back in the not so good old days. Those were the days. Not. :laugh:
 
#20
ddnidd1 said:
The obvious choice would seem to be that the larger exposed outer surface of the plug, when unplugged, would be negative (ground) as in most other applications , rather than being the hot side.

The idea being to minimize an inadvertent short between the high side and ground.
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Power supply ground is not Earth or frame ground.
Walwart supplies "float" so accidentally or intentionally connectining one side to ground is not an issue.
I don't know how the terminal polarity is chosen, but it doesn't matter as long as the user doesn't mix it up.
For what it's worth--- in some old cars, the frame is +.
Jumping that vehicle with a typical - frame car will result in a serious explosion of one or both batteries.
 
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