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Topic: Why Do Single-Coil Pickups Hum? |
Lee Baucum
From:
McAllen, Texas (Extreme South) The Final Frontier
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Posted 24 May 2005 12:07 pm |
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I know. I know. It's because they don't know the words. (Hah! Beat ya to it!)
But seriously. Where is the hum coming from? Through the air? Through the power cord? Both?
Usually it's 60 cycle hum from the power source, so it's pretty close to a B natural (I think). But is that hum coming up the power cord and through all the equipment that is hooked up between the guitar and the amp?
Inquiring minds want to know.
Lee, from South Texas |
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 24 May 2005 12:33 pm
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Lee, the 60hz (hum) is coming through the air. The pickup coil actually acts as the secondary winding of a transformer. The AC line, or device connected to the line, is the primary winding.
When you hear the hum, pick up your guitar and rotate it. You will find that the hum level varies. The location of the guitar is critical if you have this type of hum. |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 24 May 2005 1:25 pm
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Correct. To elaborate a bit, when you have a changing electric current through a wire, it sets up a changing electromagnetic field around the wire. If you do the math (solve Maxwell's equations), you'll see that this alternating field radiates through the air, or even in a vacuum. Your pickup coil is just there to act as the transformer secondary.
The standard humbucking pickup is set up as two single coils in series. The magnet(s) around each coil are magnetically reversed from each other. Electrically, the coils are wound in reverse orientation. Thus, a signal picked up magnetically (e.g., string vibrations which perturb the magnetic field around the pickup and induce a current in the coils) are at first out-of-phase in each coil, but then when they go through the reversed coils, get put back in-phase, giving roughly double the output. But signals which are picked up directly through the reversed coils (e.g., stray electromagnetic fields picked up by the coils directly) add together out-of-phase and are approximately cancelled. |
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