How Does a Volume Control (Potentiometer/Variable Resistor) Work?

Описание: How does a potentiometer work? How does a variable resistor work? How does a volume control work? Antique radio restoration. The volume control is called a variable resistor, because it’s a resistor, with variable resistance. Nowadays, variable resistors are commonly known as potentiometers. Let’s take a closer look at one to see how they work.

The shaft projects outside the cabinet, and is turned using the volume knob. Removing the back cover, reveals the resistor. It’s connected at both ends to the two outer terminals, which connect to the audio signal.

As the signal comes into the resistor, it passes through a long, fine wire that’s wrapped around the curved track. The wire is made of a material that resists electrical current. At the beginning of the wire, there is less resistance, but as it gets longer, resistance increases, and less signal can pass. When the signal leaves the outer terminal, its strength has been significantly reduced.

If we wanted just one, very low volume, this reduced signal could be sent on to the detector grid. But of course, we really want to be able to vary our radio volume from low to high. And any point in-between.

Thanks to the wiper, we can do just that. The center terminal is attached to the wiper’s contact point. When the knob is turned fully counterclockwise, it rotates the wiper to contact the part of the resistor with the most resistance and weakest signal.

When the signal flows into the resistor, it’s picked up by the wiper, sent out of the middle terminal, and to the tube grid.

As the knob is turned clockwise, the wiper moves to a point with less resistance, and the circuit strength increases. As a result, the volume from the speaker also increases.

When the knob is turned fully clockwise, resistance is lowest, circuit strength increases, and volume is at maximum.

Sometimes the resistive track on a potentiometer isn’t a wire, but instead carbon film. Over time, the film and wiper can corrode causing the volume and tone controls to sound scratchy when operated.

Special cleaners are designed to remove this corrosion, and usually, a squirt or two, and a few turns of the knob, remove scratchiness from potentiometers. Sometimes though, the track becomes so damaged that replacing a potentiometer is necessary.

Fortunately, the volume control in our radio was in good shape and just needed a squirt of control cleaner.

Notice too, that the on/off switch for the radio is piggybacked to the volume control, so one knob, can serve both functions.

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