Damage if accidentally used AC supply instead of DC?

Discussion in 'Effects, Pedals, Strings & Things' started by minty901, Feb 21, 2015.

  1. minty901

    minty901 Member

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    I used this...

    7.5VAC/400mA AC adapter for the Hum Debugger

    ...to power a standard 9VDC pedal accidentally (it looks very similar to one of my 500mA 9VDC adapters). I'm not sure which pedal it was (but all the pedals are 9VDC) as it was among a bunch on a power strip and I only noticed when I rearranged my board and unplugged the wall warts. Could I have done damage to one of the pedals? I've started to notice an annoying squeeking noise happening with my ISP Decimator G-string II noise gate whenever it closes the gate, but only really when using distortion -- I'm worried maybe this pedal got damaged or something as it is my most expensive pedal.

    Thoughts? I think all my pedals still appear to work, although I haven't actively tested all of them.
     
  2. sanfi4u

    sanfi4u Silver Supporting Member

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    Most of the pedals (Boss, Ibanez, Maxon, EHX, BYOC etc.) have a diode right after the power socket protecting a pedal from the reverse polarity and a filtering cap. So when 7.5 AC power is connected a pedal gets 7.5VDC with the right polarity and nothing bad happens. Just a ripple will be higher.
    Hopefully all of your pedals are designed this way. Otherwise there's a chance to fry a pedal.
     
  3. augur

    augur Member

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    I did personnaly fried a pedal this way.
    hopefully it had a security diode so could be repaired immediatly!
    but it might not be the case of all pedals...
     
  4. CodeMonk

    CodeMonk Member

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    Thats not really how it works.
    In a "normal" pedal...
    The diode is for reverse polarity protection.
    The capacitor is to smooth out the ripples.
    That doesn't change AC into DC.

    For that you need:

    1. **Bridge Rectifier (4 diodes connected to form a square or diamond pattern: http://en.wikipedia.org/wiki/Diode_bridge)
    2. Electrolytic cap to smooth out the AC.
    3. Zener Diode
    4. Resistor
    5. Voltage regulator to smooth out the DC. Being that you want to go from 7.5Vac to 7.5Vdc, a filter cap may suffice. But a regulator is the better option.

    There are other methods, but this one is pretty common.
    You can google it to see the various ways to go from AC to DC.


    Plugging AC into a DC device can mean death for that device, even if the voltage level is the same.
    Digital pedals can be more sensitive to damage.

    ** Or you can get one of these, much easier and more compact:
    [​IMG]
     
    Last edited: Feb 22, 2015
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  5. minty901

    minty901 Member

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    thanks for the replies guys. as an update, i havent tried all my pedals but most seem to be working fine (ill try the rest later). but one thing i have found out is that he reason the isp decimator was making a squeeking noise is cause i was using it on a 120mA outlet on my harley benton jr power supply. when i moved it to its own wart it worked fine. this is odd because the manual states that the decimator only requires 35 mA. maybe that is an underestimate.
     
  6. gibs5000

    gibs5000 Member

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    the one time I made this mistake was with a digitech AC power supply, and it actually fried the power supply rather than the pedal, not sure why, but its definately cheaper/easier to replace a $20 wall wart, than a $150 pedal.
     
  7. sanfi4u

    sanfi4u Silver Supporting Member

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    The protecting diode along with a filtering cap works as a simple rectifier and converts AC to DC. No doubt about it. And the fact that schematic bridge rectifier -> filter -> stabilizer -> filter is more commonly used and works better doesn't change it. As you wrote there are various ways of converting AC to DC.
    But protecting diode circuit is not mandatory thus there's no guarantee that plugging AC PSU (as well as reverse polarity psu) won't fry any particular pedal. So it's more safe to stay away of such experiments.
     
  8. stinkfoot

    stinkfoot Member

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    Over the years, I have repaired quite a few pedals that has been damaged by 9vAC supplies accidentally being plugged in. The protection diode had blown, shorting the power out (which thankfully protected the rest of the circuit). In some cases, the filter capacitor was also shorted out. I would not trust the protection diode to do any sort of usable rectification. You got lucky this time, probably because of the lower voltage (7.5vAC instead of 9vAC), but it is a good idea to clearly mark all plugs (at the pedal end) that aren't carrying regular center negative 9vDC, to avoid any future tears :)
     
  9. CodeMonk

    CodeMonk Member

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    You got me there.
    It becomes a half wave rectifier very briefly.
    Then it does its fuse imitation (in that it "sacrifices" itself to try to protect the rest of the circuit).
    I should have said "That doesn't change AC into USEFUL DC".
    Used as a rectifier circuit, its crap.
    Not useful for our purposes anyway.

    I just felt that that statement may give some people the impression that they can plug AC power into a DC powered pedal (given proper polarity and voltage) and everything will be just dandy as long as that protection diode and filter cap is in there.
    And I would classify a diode getting fried as "something bad happened".
    Though not as bad as things would be without it.
     
  10. sanfi4u

    sanfi4u Silver Supporting Member

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    Yes, you are right. Due to the high current through the open diode it won't last long and the diode will be fried quite soon. Agree!
     
  11. jordanky

    jordanky Member

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    I'm wih stinkfoot here. Of all the pedals I've repaired that have been attacked with AC power, nearly every one luckily only had a polarity protection diode fried, which is a simple fix. I can think of maybe two or three that were not in this group. If your pedal doesn't have a polarity protection diode, or you've replaced a fried one and the pedal still doesn't work, time to replace every IC and electrolytic cap on the board. Possibly transistors and other components as well. Hopefully it's not full of SMD components. Good luck!
     
  12. Floydsound

    Floydsound Member

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    Hello, everyone. First post here.
    I'm sorry to ressurrect such an old topic, but it's exactly what I wanted to talk about.

    Long story short:
    - I'm a noob about pedals, so, when my Mooer Eleclady arrived yesterday, I plugged a 9V AC power supply into it (which is a 9V DC pedal).
    - It made a loud and constant humming noise, and the flanger effect was messed up, with some kind of fast vibrating sound in each note.
    - I spent about less than 10 minutes like this, trying to figure out what was wrong.
    - When I realized what was wrong, I plugged in a 9V DC power supply, and the pedal was absolutely NORMAL.

    My question is: if the pedal is functioning normally, can I chill about this? Or, even though it seems fine, I may have damaged something important in there, decreasing its life span?

    Thanks in advance!
     
  13. stinkfoot

    stinkfoot Member

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    Usually, when the protection diode blows, it will short the power out (leaving the pedal dead). It is meant to do that, to protect the rest of the circuit. So if it works as normal, and has no burnt smell coming from it (sniff near the jacks), it should be fine.
     
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  14. amz-fx

    amz-fx Supporting Member

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    There are 2 main types of protection circuits used in pedals: a diode in series with the positive supply side, and a reverse connected diode across the power rails. They react differently to an AC input or even a reversed polarity power source.

    The series diode is probably going to be okay in either condition. The reverse connected diode will usually burn out, though in some pedals (like the Rat) a current limiting resistor is included and it is more likely to burn out and acts like a crude fuse.

    If the pedal is functioning normally, you can probably chill about it.

    regards, Jack
     
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  15. Floydsound

    Floydsound Member

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    Thanks a lot, guys!

    I have just sniffed near the jacks, and there's a weak odor of (what I think is) "not burned electrical things" (but I don't know if that's their natural odor or not). Do these electrical parts have a natural odor, and would the burning odor be easily recognizable?

    I really don't know which one is used on Mooer pedals, but I guess it's the series diode, based on your explanation :)

    I guess it was nothing serious then, thank God!
     
  16. stinkfoot

    stinkfoot Member

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    Burnt electronics have a very distinct smell, so it's not something you'd mistake for anything else. And like Jack said, this pedal could have a different type of polarity protection that isn't as likely to burn out. Either way, it seemed to have done its job, and if the pedal works as normal, it's ok.

    Clearly marking the plugs with the voltage and type is still a good idea, though :)
     
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  17. Floydsound

    Floydsound Member

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    I really appreciate your answers here, man! Thanks a lot for helping me chill about this :)
     

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