VOX WAH

molitovv · November 21, 2006, 05:20:56 PM

hello again all

why is it when you add a power adaptor to a WAH pedal it starts humming like a mother whatsit???

can anything be done to help?

cheers
matt

jonathan perez · November 21, 2006, 06:07:10 PM

MANY discussions on this, i suggest you use the SEARCH button.

in a nutshell, power supplys will produce noise in wahs if the wah is near to, say, the power strip, or supply itself. wall warts included.

molitovv · November 21, 2006, 06:48:42 PM

i had a quick look at the circuit, seems like any interference on the powersupply in injected straight into the transistor, tried putting a vreg to clean it up, but no luck. what about a choke?

RedHouse · November 21, 2006, 07:17:04 PM

You've got other issues if the voltage regulator didn't clean it up, maybe you have a ground loop situation?

molitovv · November 22, 2006, 05:59:37 PM

What sort of issues do you think???

Paul Marossy · November 22, 2006, 06:25:25 PM

It's called EMI - ElectroMagnetic Interference. The inductor in a wah pedal will pick up hum by magnetic coupling. Assuming you have a newer Vox wah with a built-in DC jack and power filter cap, the only real effective way to get rid of it is to increase the distance between the wah and the inductor (wah pedal) - like 3 or 4 feet away.

molitovv · November 22, 2006, 06:59:49 PM

no i have a older one that i have added the jack to.

tried a filter cap. tried a vreg.

Paul Marossy · November 22, 2006, 09:09:51 PM

Try putting the wall wart farther away from the way pedal. What size filter cap did you use? Usually, a 220uF cap across the power supply will do it. And, don't forget to add a 100 ohm resistor in series with the positive leg of the jack to the PCB.

darron · November 23, 2006, 05:43:38 AM

i added a power jack to my vox v847 wah. too noisy to use... then i realised i was using an unregulated power supply.

using a well regulated power supply it works as though it has a battery in it now (for all practical purposes except recording anyway). i can run the power supply right beside it without problems. don't use unregulated power supplies with your gear! they sound like poo... there's the solution anyway.

alderbody · November 23, 2006, 06:27:40 AM

Did you try to shield the inductor?

One of the best ways to do this is with mu-metal.

Copper tape (connected to ground?) should work, too.

But i think that it somehow made my wah a bit "blunt" (not too much treble), so i removed the shield.

Mine didn't hum anyway, although i never use batteries.

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VOX WAH