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reducing ac adaptor voltage

Discussion in 'General Electronics Discussion' started by matrix, May 19, 2011.

  1. matrix

    matrix

    1
    0
    May 19, 2011
    Hello -

    I have a guitar effects pedal that requires a 9VDC 300mA power supply. I have several AC adaptors I kept from other devices, but none are exactly those numbers.
    I have for instance, a 13VDC 300mA AC adaptor from HP (I assume it was for a laptop). The mA are correct but the voltage isn't. From what I have found out so far, the voltage must be correct or it will damage the pedal. Apparently I could use an adaptor that had a higher mA value (500mA vs 300mA), but not a lower value, and as long as the voltage was correct it would work OK. Am I correct so far?

    If so, then my question is how could I reduce the adaptor I have to 9VDC?

    Thanks!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    You are correct. The voltage should be close (+/- 1 volt probably won't matter in this case) and the current rating must be greater or equal to the original. The polarity of the connector must also e the same (typically centre or tip is positive).

    You can reduce the voltage with a voltage regulator. In this case, reducing it from 13 to 8 at a couple of hundred mA is relatively easy. You can build a voltage regulator from an LM317, some resistors and capacitors, or you can buy already made up units from ebay. You probably need to place it inside some sort of case too.
     
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