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Question about pickups


dvkerner96

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Hello, I am wondering if it is possible to burn out a pickup on an electric guitar by touching a source of electricity (a speaker plug, for example) and then touching one of the guitar strings (completing the flow of electricity). This happened to me and I don't know if it could have damaged my pickup, or if I am just being paranoid. Please let me know what you think!

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Plugging a guitar into a speaker jack might blow one but even there you'd need someone else playing through the amp making sound to generate a signal. Its an unlikely scenario at best.

 

A pickup is a long coil of wire. You need to apply enough current to both ends of the coil to blow one. When you touch your strings you're only touching the grounded side and the electricity will always take the path of least resistance to ground. Touching the strings is the same as touching your amps chassis or an AC outlet ground. You may feel a shock if you touch something else that creates a ground loop, but the pickup isn't going to pass that voltage through the coil You would need access to the hot wire on the other end of the coil which is unlikely to happen just playing the guitar.

 

If you have a dead coil it would more likely be caused by a physical shock vs an electrical one. Bumping a pole magnet is a common way of damaging a coil inside, especially with Strat type magnets which are simply glued in place. Sometimes a bad solder contact can do it. Solder rosin left behind is corrosive and can eat away at the copper then some vibration or hitting the pickup with a pick can finish the job. Sometimes the coil is wound too tight and the small hair like wires under stress inside just break.

 

Pickups that have tape winding around the coils can have problems too. The tape may be tight when its first put on. Temp and humidity can allow the tape to expand or give which can pull on the outside winds and eventually snap a wire. Allot of humbuckers have this bobbin tape exposed too.

 

These are all defects and not the norm however. Pickups can and usually do take allot of abuse and still function.

 

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. ..

You need to apply enough current to both ends of the coil to blow one...

 

... You may feel a shock if you touch something else that creates a ground loop, but the pickup isn't going to pass that voltage through the coil…

 

I don't have "two degrees in electronics" but I always thought that Voltage gets applied to both ends of a circuit (across a load) and Current goes through the circuit. That's the only way Ohm's Law makes any sense to me - and I base everything I do in electronics on Ohm's Law.

 

Please correct me if I am wrong.

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onelife:

I asked because that happened to me, but my pickup is still working, I just thought that it sounded a little quieter than before it happened, but it is likely that it is in my head. I just wanted to make sure! It has happened more than once, and there were times when I felt a small shock, and times when I didn't. This particular time, I don't think I did, or if I did, then it was very small. Thank you for your reply!

 

WRGKMC:

Okay, thank you for your reply and for the explanation! I appreciate it! I don't know much about the way electronics work, so that is valuable information that I will remember! I do have another question on the same subject, if a pickup were to be damaged by electrical or physical shock, or anything, would it just shut off completely, or would it be possible for it to just lose volume or tone, but still turn on?

 

DeepEnd:

Thanks for the reply!

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. . .

I do have another question on the same subject, if a pickup were to be damaged by electrical or physical shock, or anything, would it just shut off completely, or would it be possible for it to just lose volume or tone, but still turn on?

 

The coil in a pickup is essentially a long insulated wire that is wound many times around a magnet. It is possible, although not very likely, than an electrical (or perhaps even a physical) shock could damage some of the insulation. If this occurs then some of the windings may become connected together creating a short circuit.

 

The short circuit would shorten the effective length of the wire and reduce the number of windings that are contributing to the electrical output of the pickup. If this were to occur then the pickup would still work but the output level would be lower. It would, however, be a very unusual occurrence - it is more likely that the pickup would stop working altogether.

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First of all...the voltage at the speaker end is still pretty low. Something like 5 volts?

A rough value for the internal resistance of the human body is 300-1,000 Ohms...lets assume 500 ohms.

V=IR so we are talking about 10 mA current

P=IV so power would be .05 watts (remember that the speaker had a resistance of just 8 ohms so wattage is different there.

 

 

10ma would rate as something between "threshold of sensation" to "mild sensation"

 

https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

 

This is assuming the entire current of the speaker output passes through your body with NONE of the current passing through the guitar as well.

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My guess is that the pickup is damaged for some other reason...or possibly the magnet has become demagnetized.

 

Back to Ohm's law.

 

5v=IR

 

The typical resistance across a pickup is in the kilo-ohm range...lets assume 5K?

 

5 divided by 5K is 1 mA...I seriously doubt that's going to burn through pickup wire.

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Current is constant in a series circuit. If the body and the guitar are in series, then all of the current passes through both.

 

5 Volts across 8 Ohms is just a little over 3 Watts. A typical 40 Watt amp will produce approximately 18 Volts across 8 Ohms at full power which would push 2 Amps (and a bit) of Current through the speaker.

 

Let's assume 600 Ohms for human body resistance just to make the math easier. The additional 600 Ohm load is insignificant compared to the 8 Ohm speaker so the 18 Volts won't change which means that even a 40 Watt amp running at full power would only push 30 mA through our hypothetical 600 Ohm human body.

 

That current level will go way down if it has to pass through the pickup as well. 18 Volts across 6K Ohms is a mere 3 mA.

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Okay, thank you! What kinds of things should I not plug into? I never plug into anything but amps and some pedals, and an occasional PA (I don't like that, though). Thank you for your reply!

 

AC outlets etc.

but seariously, improperly grounded equipment can be a lethal hazard.

 

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The biggest danger are old guitar amps that aren't properly grounded...or worse, don't even use a power transformer and instead simply rectify the 120V coming out of your wall outlet directly.

 

Back in the 1950's, wall outlets didn't have that third grounding wire at the outlet. All the electricity went to the amp with no way of shunting it away if there was a short in the circuit.

 

What's worse...these problems could sometimes go all the way to the guitar and the player.

 

Fortunately all modern equipment is grounded and you don't need to check for stuff like this.

But when playing very old equipment that has sat in a garage for 50 years without ever being serviced....you might run across something dangerous. Best to have an amp tech check it out and add the proper circuitry to make it up to code.

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