Wiring 9V DC Jack on a Vox Wah

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mgarrison99, Mar 5, 2008.

  1. mgarrison99

    mgarrison99 Silver Supporting Member

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    Hey folks. I just picked up a Vox 847 and decided to install a 9V jack in lieu of the battery-only option for the unit. What I thought was a simple job has now frustrated me. I wired negative to the tip and am using my DC Brick to power it. However, it appears to be "pulsing" through my amp as if an alternating current is still coming through it. I've used 9V battery jacks to hard wire my pedals before, but thought this might be a cleaner option. I also tried to power this with my OneSpot adapter, and althought I can get a clean sound through it, I can not get the pedal to activate. I am using a standard 5.5mm (OD)/2.1mm (ID) jack from Radio Shack, and the DC Brick using the same size cables according to their specs (plus it's a tight fit).

    Any suggestions as to what my two left thumbs have done? Thanks!!!:jo
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  2. mcdes

    mcdes Member of no importance

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    might also be that its metal and the ground from the power is also touching the audio ground. on some it can be done this way but i have built a few which didnt like it at all.

    so trial and error, try a all plastic plug to isolate from the casing, as the audio jacks a re grounded to the casing aswell, prob help to use marshall type there too, to isolate it from the casing and getting interference.

    at least its an inexpensive place to start.

    next thing to do is to install an led indicator on as well, ha.
     
  3. VacuumVoodoo

    VacuumVoodoo Member

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    Just a speculation based on the photo:
    Is that 9V jack isolated from the box?
    IF yes then: the red wire and solder lug on the jack seem to sit damn close to the screw holding PCB to the metal box. Could be a short causing DC Bricks foldback current limiter to kick in resulting in pulsating sound, the other power source you tried has possibly just a short circuit current limit so no pulsing and no juice to the circuit either.
    IF Not isolated then: (+) on the outside barrel gets shorted to ground as soon you plug the guitar cable in as it connects the (-) to ground when it activates battery
    You're getting clean sound through because this thing has a true bypass.
     
  4. mgarrison99

    mgarrison99 Silver Supporting Member

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    Thanks for the insight, guys. I might try some rubber washers in an attempt to isolate it. I'll also rotate it a bit to keep the positive lug away from the board.
     
  5. mgarrison99

    mgarrison99 Silver Supporting Member

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    Picked up a rubber grommet at Lowe's and installed it. Problem solved! Thanks, guys/gals!
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  6. VacuumVoodoo

    VacuumVoodoo Member

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    Glad we were able to help. Appreciate your reporting back.
     

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