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June 2017 Giveaway

Center Tap

In coils and transformers a center tap is a tap (see WFTD Tap) at the center of the winding of wire, which puts it at the halfway point of the overall impedance and voltage of the coil. Center taps are often used to provide a zero reference (kind of like ground, but different) for the two sides of a differential or balanced circuit. For example, if a center tap was taken from a transformer that supplied 220 volts you would end up with two “legs” that each provide 110 volts (as is often the case in common household electrical service in the U.S.). The AC signal provided between the center tap (which is common to each leg) and each end of the coil will be at the opposite polarity, Balanced AC supply devices commonly found in recording studios operate by tapping the center of a transformer running at 120 volts, which provides two 60 volt legs in a differential configuration. In audio circuits center tapped transformers and coils can be used to create balanced circuits. The coil tap function of a guitar’s electronics also provides a similar function. But in many of those cases when the coil is “tapped” (see WFTD Coil Tap) the user is really just turning off one half of a differential system that always has a center tap. This is common for guitarists because it allows a humbucking pickup to also be able to work as a single coil pickup.

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