Small shock from pos earth pedal

Frequently asked questions regarding powering your pedal.
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Post by stupidsignup »

Ok I have A level physics (an exam at age 18 in the UK) so have smattering of theory.

But why do I get a shock from my wah wah when I'm powering it from a mains 9v PSU?
The PSU is in one wall socket, I'm sat holding my guitar which goes into an amp, plugged in to another wall socket.
Obviously this is a low 9 volt shock but I'm surprised I can feel it quite strongly, like an ant bite.
I suppose I'm just making a circuit between the +9v outer case of the wah to guitar based earth via the strings.
But I don't see other people complain of this?

(I have a healthy fear of electric shocks having nearly killed myself age 7)

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Post by Liquitone »

A Wah is a negative earth pedal and its v-, not its v+ should not be in contact with the casing. In a positive ground pedal it's the v+ that's connected to the case but the 9v+ ground being a reference point you should not be getting a shock when you touch a positive ground case and your guitar. You are basically touching the same reference point because the voltages of both the positive ground and negative ground pedals are not directly touching your guitars hardware or pedal's enclosures.
I don't have a degree so there are maybe others who understand and can explain it better than me.
That said, I have had mild but annoying electrical shocks when touching my pedals when I ran a Pedalboard with a combination of 9v,12v,18v and 24v negative ground and 9v positive ground pedals on it.
I made very sure everything was in good shape, especially the amps and power-supplies and it was, but I was still getting these mild shocks, that felt a bit like static discharge.

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Post by Govmnt_Lacky »

DO you run active pickups?

If not... Do you have your guitar's bridge grounded?

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Post by boblob »

That doesn't sound too encouraging.

You generally shouldn't feel 9V as it's not enough to break down your skin's resistance. IIRC, you won't feel anything under ~ 18V, so I would think there's something else going on here. If I were you I'd get everything properly checked out.

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Post by DrNomis »

It could be that the 9V plugpack you're using is a Switchmode type, they do tend to cause earth shocks...... :thumbsup
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Post by Lucifer »

My wife gets a big shock every time I bring home a new pedal :twisted:
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