Nearly damaged my new pedal!!

[feddozz]

Yesterday I got a new looper/overdub pedal from ebay and I wanted to test it. I plugged my new PP3 to 2.1 DC connector to power the pedal with a battery (I do not have a power supply unit yet and the pedal do not have room for a battery).

The pedal would not work. I disconnected after a few seconds. I started fearing the pedal was faulty. I got into debugging mode. Started measuring voltage from the battery, etc. It turned out that the connector (PP3 to 2.1 DC socket) was giving me +9V in the center lug and 0V in the outer ring!!

Fortunately the pedal did not get damaged but I think I got close. Was I right in thinking this cable should have given me negtive center lug? I do not want to link the specific product, I already contacted the vendor about this. Their description page does not specify polarity.

I just wanted to warn people to test our own assumption when debugging.

Have a nice day.

[M.A.P]

Hi Vince,

was that an already complete connector or something you built by yourself? I searched for such a connector and ended up building one by my own. I made the same mistake because the connectors of the plug weren't labeled with tip and ring.
If it's not a DIY pedal you bought there should be a diode that shorts the input when polarity of the battery is wrong. Your pedal will be safe but the battery will get very hot, believe me 

Greetings from Germany,
Marcus

[GibsonGM]

Good catch, Fed...not all adapters have the same polarity!  As you found out

When I get spare wall warts, sometimes I put masking tape right on them with a big pic of the barrel - the "C" and center circle  - and mark out which is positive so I can tell at a glance.   

Glad it didn't fry your looper!

[Frank_NH]

I almost got stung by this too.  I saw that someone was giving away an old iHome iPod boom box at work, and it came with a 12V wall wart.  Cool - 12V supply!  I was going to try it out when I checked the label on the supply, and sure enough it was center positive!  Yikes.

[GibsonGM]

It gets even more interesting when you cut the cord and reverse the wires so it IS center negative, LOL!

Almost all the time, if it's not one of my 'go to for DIY' wall warts, made for pedals, I'll grab the meter and make sure...

[Jdansti]

All of my "in use" wall warts are marked with their voltage and polarity. I've got a couple of boxes of miscellaneous wall warts that I might use some day.  If I decide to put one into service, I always check the voltage and polarity and reverse the polarity if necessary. Following that, I mark the unit with the output voltage and polarity.

[vigilante397]

This one has almost fried me as well, especially since my first few builds I decided to go center positive so I could use the metal DC jacks, so for a while half my wall warts were center positive and half were center negative Glad you were able to stop before it killed something!

[feddozz]

Thanks everybody. I contacted the seller and they told me that centre negative is uncommon, apart from stomp boxes. I can't judge but I think the description of the item should include this detail.

[induction]

Thanks everybody. I contacted the seller and they told me that centre negative is uncommon, apart from stomp boxes. I can't judge but I think the description of the item should include this detail.

At the very least it should be marked on the adapter itself:


But now that you've been through this, I'm sure you'll double-check polarity every time you use an adapter in the future. Once bitten, twice shy, etc.

[Jdansti]

Thanks everybody. I contacted the seller and they told me that centre negative is uncommon, apart from stomp boxes. I can't judge but I think the description of the item should include this detail.

I disagree with the seller.  There are a lot of non-Stompbox manufacturers who use center negative. I got chewed out by my EE-boss years ago for assuming a piece of equipment was center positive just because I thought that anyone who made center negative equipment would be crazy to do such a thing. I've learned not to assume anything about equipment specs.

[thermionix]

Thanks everybody. I contacted the seller and they told me that centre negative is uncommon, apart from stomp boxes. I can't judge but I think the description of the item should include this detail.

Seems like center-positive used to be pretty standard, from what I recall.  I don't know when it started going the other way with pedals, but was probably started by Boss or another major manufacturer, and everyone else started following suit.  It's a bit counterintuitive to me.  If you think of a coax guitar cable, there really is no positive or negative, but you kind of think of it as center being hot/positive, and shield being ground/negative.  Maybe that's just me.

[ElectricDruid]

Yeah, agree. The centre-negative thing is a bit unhelpful really, and if it was Boss that started it (like everyone thinks) then I wish they'd done it the other way around. Roland are usually pretty good at engineering! (understatement of the week)

But that's how it is now, so we live with it, like the QWERTY keyboard.

Tom

[Jamdog]

So...  When building your own pedal,  is it best to go center negative?

[deadastronaut]

yes...

OP what pedal is it?

[feddozz]

It's a Rowin looper. 28GBP from China. Seems it works all right

[Jamdog]

yes...

I am still new to the guitar,  so I wasn't aware of the wall warts and their negative centers,  thanks to this thread I "corrected"  my two pedals today. 

Now I just need to get wall warts and stop wasting batteries...

Thanks.

I got into thinking,  what would be the proper way to prevent damage from putting an inverted wall warts to a homemade pedal?

Can we add some protective circuits?

[Jdansti]

yes...

I am still new to the guitar,  so I wasn't aware of the wall warts and their negative centers,  thanks to this thread I "corrected"  my two pedals today. 

Now I just need to get wall warts and stop wasting batteries...

Thanks.

I got into thinking,  what would be the proper way to prevent damage from putting an inverted wall warts to a homemade pedal?

Can we add some protective circuits?

Yes. Google "reverse polarity protection" and you'll see several ways of doing it. RG at geofex has an elegant way of doing it which eliminates some of the drawbacks of other methods: http://www.geofex.com/article_folders/cheapgoodprot.htm

[Jamdog]

yes...

I am still new to the guitar,  so I wasn't aware of the wall warts and their negative centers,  thanks to this thread I "corrected"  my two pedals today. 

Now I just need to get wall warts and stop wasting batteries...

Thanks.

I got into thinking,  what would be the proper way to prevent damage from putting an inverted wall warts to a homemade pedal?

Can we add some protective circuits?

Yes. Google "reverse polarity protection" and you'll see several ways of doing it. RG at geofex has an elegant way of doing it which eliminates some of the drawbacks of other methods: http://www.geofex.com/article_folders/cheapgoodprot.htm

I kinda like the simple diode approach.  Just putting it between the + and -  at the power jack,  unless you leave the wrong power supply for a quite long period,  seems suitable.  I mean...  Connect,  doesn't work,  oh,  yeah,  wrong power: shouldn't cook the diode that fast? Or would it?


I think I'll add some to my pedals tomorrow.

[dbp512]

Yeah, agree. The centre-negative thing is a bit unhelpful really, and if it was Boss that started it (like everyone thinks) then I wish they'd done it the other way around. Roland are usually pretty good at engineering! (understatement of the week)

But that's how it is now, so we live with it, like the QWERTY keyboard.

Tom

From what I remember reading Boss wanted to include a DC jack with a switch so you could use a battery if desired, but didn't want it to drain when the pedal is plugged into a supply. Apparently the easiest/only way to do it was to use a switching jack, and the lug that switched was on the sleeve, so they needed to put power on the outside. Or I could have that backwards, but necessity dictated center-negative pedals. I guess other companies decided to do the same and eventually it became the standard

[Jamdog]

Yeah, agree. The centre-negative thing is a bit unhelpful really, and if it was Boss that started it (like everyone thinks) then I wish they'd done it the other way around. Roland are usually pretty good at engineering! (understatement of the week)

But that's how it is now, so we live with it, like the QWERTY keyboard.

Tom

From what I remember reading Boss wanted to include a DC jack with a switch so you could use a battery if desired, but didn't want it to drain when the pedal is plugged into a supply. Apparently the easiest/only way to do it was to use a switching jack, and the lug that switched was on the sleeve, so they needed to put power on the outside. Or I could have that backwards, but necessity dictated center-negative pedals. I guess other companies decided to do the same and eventually it became the standard

You could as well switch on the outer sleeve with negative,  I do not think it was a nessecity rather than a design choice.