Unbalanced signal lines are characterized by the fact that the cable and connectors use only two conductors, a center conductor surrounded by a shield.
Examples of unbalanced wiring are found in tip/sleeve 1/4-in guitar cords or the cables used with many CD players and tape decks which terminate with RCA phono type connectors.
In an unbalanced configuration, the shield surrounds a single center conductor.
The shield stays at a constant ground potential (as it is connected to ground when plugged into equipment) while the signal voltage in the center conductor varies in a positive and negative manner relative to it.
Because the shield completely surrounds the center or “hot” conductor and is connected to ground, it intercepts most of the electrical interference encountered by the cable and passes it away harmlessly to ground.
Very little or no interference will be able to reach the center conductor where it would interact with desired signal.
Because the shield is one of the two conductors required to complete the circuit, it must always be connected at both ends of the cable.
This may set up a condition called a “ground loop” that sometimes produces hum when the grounds of different pieces of electrical equipment are connected to each other.
Unbalanced: A single center conductor is surrounded by a shield.
Note: A shield that consists of wire that is braided instead of just spun around the center in a spiral will provide superior coverage. Spiral shield is less expensive but can spread apart when the cable is flexed, exposing the center conductor to unwanted hum and buzz.
If outside electrical interference does manage to penetrate the shield, it will mix with the desired signal that is present in the center conductor and be amplified right along with it as noise, buzz, etc.
This might not be a huge problem with electric guitars, tape decks and unbalanced microphones when the cable is only a few feet long.
But in environments containing a lot of interference or when an unbalanced signal is sent long distances, such as down a snake, it will become more and more susceptible to unwanted interference.
This problem can be alleviated with the use of balanced lines.