shielding a pedal

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mmorse, May 2, 2008.

  1. mmorse

    mmorse Member

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    Recently I bought a pedal board for the few pedals I have. I have an old (70s) King Vox wah that I use. A couple years ago I put in a DPDT switch so it is now true bypass when off because it did suck a good bit a tone until I did that.

    Now I have a new issue. Being on a board now, the pedal is much closer to the power strip I use to power the other pedals. When the wah is switched on, it picks up a nasty 60 cycle hum from the power strip. Moving it away from the strip eliminates the hum but is not a practical solution as it needs to be a good 5-6 feet away.

    Any ideas how to keep the pedal on the board and not have the hum? Going all battery is not possible because 2 of the pedals are external power only.
     
  2. HipKitty

    HipKitty Silver Supporting Member

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    start by shielding the input and output jacks...however, only ground (the shield part of the wire) to the ground of the jacks....the other side of the wires should not have any shield connection at all...just the center wire. Cut back the shield and shrink wrap that area of the wire so only the center wire is exposed. Do not "double ground" these wires by using the shield (to ground) on both sides of these wires.

    also, make sure that you have good cables....worn or poor quality cables can cause interference.
     
  3. mmorse

    mmorse Member

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    Sorry, you lost me. :confused:
     
  4. HipKitty

    HipKitty Silver Supporting Member

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    Use shielded wire (or cable to some). We use RG-174.

    From the input jack to the switch (or component board), you strip the wire so you have the braided (shield) wire and the (center) wire still wrapped in it's cover. Unbraid the shield wire, wrap it into a single wire..away from the "center" wire. Strip some of the "center" wire so you can solder it to the "tip" leg of the jack. The (no longer braided) shield is soldered to the ground leg of the jack.

    On the other side of the wire, going to the switch or board, strip the wire approximately 1" or so back from the tip so no shielded braid is exposed...just the covered "center" wire. Shrink wrap around that area to prevent any possible shield from getting exposed and shorting anything out. Just strip this "center" wire enough to solder it where it should go.

    Do the same at the output jack...keep the braided shield grounded at the jack,

    In short, the braided shield should only be exposed and soldered on one end, the jack side.

    Does this help?
     
  5. alltone

    alltone Member

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    If the wah cabinet , bottom plate and foot pedal are all metal you have a 99% shield already. The inductor http://www.robertkeeley.com/images/other/fasel.jpg is prone to picking up hum from proximity to power supply transformers etc.
    I would suggest covering the inductor http://www.harmony-central.com/ProductImages/Large/000000764.jpg with a thin layer of (insulating) plastic and over that a piece of copper foil to completely shield the inductor. Take care that the foil DOES NOT touch any other components on the circuit board.
    The foil could be held in place with a drop of silicone sealant or a piece of foam sandwiched between the inductor and bottom plate. A small wire soldered from the foil covering to a ground point in the pedal should eliminate any further hum.
     
  6. Axekisser

    Axekisser Member

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    I shielded the wires on an old EH Cryin' Tone wah that hummed and it got stupid quiet! I also used copper shielding on some passive equipment on my board and that worked great also. Try 'em both and you should be fine!
     
  7. mmorse

    mmorse Member

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    The pedal has a metal case and a metal bottom plate. Here's a gut shot. If the inductor is the reddish block on the board, that appears to be metal also. Maybe it's not a shielding issue.

    [​IMG]
     
  8. mmorse

    mmorse Member

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    Well, I traced the problem to the PSU of my new Blackstar HT Dual pedal. Apparently, there's an issue with this pedal and wah pedals. They don't get along. Many players have had the same problem. Short of finding another PSU, I don't know how I'm going to fix it. The PSU for the HT puts out 16v at 800ma. Guess I need to find another adapter or stop using my wah. Kinda sucks...
     
  9. Randy

    Randy Member

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  10. mmorse

    mmorse Member

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    It may not be the PSU per se. Moving it further away didn't help. However, moving the wah further away from the Blackstar pedal itself did. Moving the wah about 5 ft. from the Blackstar cut the hum way down. The hum only happens with the wah engaged and the High gain channel 2 of the Blackstar engaged.
     
  11. JasonG

    JasonG Member

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    Been trying to find out where I can purchase a kit to shield the inductor in my Teese Picture Wah. Any leads? Haven't gotten a response from Gene who originally provided these. Thanks. Jason
     
  12. Mike9

    Mike9 Supporting Member

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    You can get battery caps w/leads at radio hack and solder that to a boss type 9v plug and voila - a 9v external battery source. Some pedals just sound better on battery and some of the older ones really like carbon zinc. I get Panasonic carbon zinc 9v's at a dollar store - 2 for a buck.
     
  13. JasonG

    JasonG Member

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    The Teese has a dc jack and with the vintage power adjustment on the Voodoo labs Pedal Power 2, I get it to sound just like it does with a battery. I sat there with my favorite zinc battery and plugged and unplugged the dc jack comparing until I got the same tone. Only problem is the hum from the PP2. I can live with it but I'd rather not, especially since the latest Teese Karmaflux Inductor is virtually immune to EMI. Geoffrey Teese quickly responded to my email about this and offered to upgrade the inductor, pot and switch for a VERY reasonable price. Great guy! Great pedal!
     
  14. dick wiewy

    dick wiewy Member

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    Try slipping some ferrite beads over the offending wire. It's been my experience that the lead from the wah's pot to the output jack tip can act like an antenna. I used ferrite beads of approximately 3/16" inch diameter over bare wire. If you leave the insulation on the beads effectiveness is reduced. Besides it's a very short connection so 10 beads ought to just fit.

    DW.
     
  15. Phospheros

    Phospheros Member

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    I think your problems might amazingly disappear if you use something like this: http://www.voodoolab.com/pedalpower_2.htm

    I know its not the question you asked, but its probably the solution that works. :) 80% of the time its a power issue with pedal boards, especially for the guys that have to have 10+ of them.
     
  16. zombiwoof

    zombiwoof Supporting Member

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    The square red component is indeed the inductor, but it is encased in plastic, not metal. I think that's the TDK inductor, if I'm not mistaken. Nice wah, by the way.

    Al
     

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