What happens when a tip-negative pedal contacts a tip-positive pedal?

Discussion in 'Effects, Pedals, Strings & Things' started by StompBoxBlues, Oct 7, 2006.

  1. StompBoxBlues

    StompBoxBlues Member

    Messages:
    18,618
    Joined:
    Sep 20, 2005
    Location:
    under the stars
    Ashamedly...I am actually an electronics techincian, but haven't thought enough about this and wondered if someone else know...I ought to know, but am a little unsure.

    Three scenarios...

    1) two battery driven fuzz pedals, one with PNP (and positive ground to pedal), the other NPN (with negative ground on the pedal)...the two pedals make contact...what, if anything happens?

    2) One battery driven positive ground, one powered (from "the brick" or another power supply) negative ground pedal make contact...what happens?

    3) Both running from ONE DC power supply, with one negative (normal) ground pedal, and the other adjusted cable for it being positive ground..the pedals make contact...what happens?

    I mean, voltage is the electrical potential between any two points. It is relative (usually ground, but also relative to other points)...but if you place two 1.5 batteries with positive going to negative on the next you make a larger voltage (3 volts), if you place them positive to positive and negative to negative, they sum to 0 volts...(but lotsa current and probably nasty things)...

    But I have not thought enough about pedals, their chassis grounds and relative to the signal that passes through them.

    So, can any knowledgeble person clarify for me a little of this...especially if they can damage the pedals if they end up touching each other?
     
  2. 908SSP

    908SSP Supporting Member

    Messages:
    5,801
    Joined:
    Jun 22, 2004
    Location:
    Michigan
    Electrically I don't know. I do know they work just fine together. Lots of guys probably never gave it any thought. But for example a Klone is tip positive which is the opposite of 90% of the pedals on the market. Have you heard of any problems? Except of course getting the polarity of the AC adapter right. ;)
     
  3. gaspedals.net

    gaspedals.net Member

    Messages:
    666
    Joined:
    May 13, 2006
    Location:
    Seattle, WA
    Depends on the circuits, best case you will loose power and get no signal, worst case you will blow a transistor etc. Some circuits have a polarity protection diode to protect it from reverse polarity. I never really considered the pedals making contact though, I would think the paint would generally shield contact - but why not just keep them apart?

    NO PEDAL SEX!
    [​IMG]
     
  4. StompBoxBlues

    StompBoxBlues Member

    Messages:
    18,618
    Joined:
    Sep 20, 2005
    Location:
    under the stars
    Thanks guys...um, on the "why not just keep them apart"...because it is easy to have them bump into each other on a pedalboard by accident?

    Mainly I wasn't worried or thinking about the "if you accidentally plug in a negative tip power to a positive tip pedal" at all....all cases were just different power sources, but still asking the main question if it caused a problem.

    Back in '74 a friend of mine and I, as kids, lit out for California from Chicago. My buddy had a '56 Chrysler New Yorker. The car was positive ground (really!). We installed a tape deck before leaving, to have some tunes, and hooked up according to the install manual, it went backwards. We had to reverse the power into it.

    I always wondered if anything happend if the car touched another car...now I only think the voltage would have been 24 volts available IF one connected car #1's positive battery to car number 2's negative.

    Otherwise, not a problem I think. It is probably the same deal here, but because there is a signal path between them as well, I was wondering if there was any danger then.

    I probably just should draw this out schematically and see what it looks like....
     
  5. BJF

    BJF Member

    Messages:
    981
    Joined:
    Mar 11, 2003
    Location:
    Stockholm
    Hi StompBoxBlues

    Scenario 1

    Nothing happens from cases contacting- ground is ground and circuit has voltage relative to ground

    Scenario 2
    Nothing happens for the same reason as above

    Scenario 3
    It depends on the powersupply construction
    A: if DC sources are galvanically isolated nothing happens

    B if DC sources share one pole,, like in a poleinverting cable, there will be a short which would if you have an EC approved DC supply, give only temporary loss of power until short is removed or proceed to nasty things or just breakdown of powersupply

    Originally posted by StompBoxBlues
    "I mean, voltage is the electrical potential between any two points. It is relative (usually ground, but also relative to other points)...but if you place two 1.5 batteries with positive going to negative on the next you make a larger voltage (3 volts), if you place them positive to positive and negative to negative, they sum to 0 volts...(but lotsa current and probably nasty things)..."

    Yes that gives a little granade

    Originally posted by StompBoxBlues
    "But I have not thought enough about pedals, their chassis grounds and relative to the signal that passes through them."

    Well, this would entirely be a DC concern

    Originally posted by StompBoxBlues
    "So, can any knowledgeble person clarify for me a little of this...especially if they can damage the pedals if they end up touching each other?"

    Your fuzzes won't be hurt by this but your powersupply can take harm.

    Oh when charging car batteries where poles actually have contact polairty is of course to be observed or just the sparks would ignite the battery fluid.

    Yes I know, just do the Kirschoff walk and it should be clear ;)



    BJ


    NO PEDAL SEX!
    [​IMG]
    :nono
     
  6. zachary vex

    zachary vex Member

    Messages:
    767
    Joined:
    Nov 17, 2002
    Location:
    minneapolis, minnesota
    1) two battery driven fuzz pedals, one with PNP (and positive ground to pedal), the other NPN (with negative ground on the pedal)...the two pedals make contact...what, if anything happens?

    nothing.

    2) One battery driven positive ground, one powered (from "the brick" or another power supply) negative ground pedal make contact...what happens?

    nothing

    3) Both running from ONE DC power supply, with one negative (normal) ground pedal, and the other adjusted cable for it being positive ground..the pedals make contact...what happens?

    can't happen. you can't connect them to the same power supply without shorting out that power supply, because the + and - are immediately shorted by the audio cable between the pedals connecting the chassis!
     
  7. Stressfest

    Stressfest Member

    Messages:
    3,494
    Joined:
    Mar 14, 2006
    Location:
    Perth, West Australia
    Hey Jay...so that's how you keep up with demand. They're making themselves now :D
     
  8. BJF

    BJF Member

    Messages:
    981
    Joined:
    Mar 11, 2003
    Location:
    Stockholm
    Thanks,
    sounds better than:
    B if DC sources share one pole, like in a poleinverting cable, there will be a short which would if you have an EC approved DC supply, give only temporary loss of power until short is removed or proceed to nasty things or just breakdown of powersupply.
    BJ
     
  9. StompBoxBlues

    StompBoxBlues Member

    Messages:
    18,618
    Joined:
    Sep 20, 2005
    Location:
    under the stars
    Many Thanks BJF and Zachary!

    I appreciate the help!
     
  10. gaspedals.net

    gaspedals.net Member

    Messages:
    666
    Joined:
    May 13, 2006
    Location:
    Seattle, WA
    :rotflmao

    I wish!
     
  11. guitarpkr67

    guitarpkr67 Supporting Member

    Messages:
    5,246
    Joined:
    Oct 24, 2005
    Location:
    Pineville, LA
  12. Bricks

    Bricks Member

    Messages:
    39
    Joined:
    Sep 19, 2006
    I need an adult!@!! I Need an adult!!@!!!!#!$!
     

Share This Page