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Snake Cable

November 26th, 2009 Leave a comment Go to comments

Snake Cable
PLEASE HELP. What is the difference between a "Balanced" and an "Unbalance" snake cable?

I am in search of a Male TRS to Male RCA audio cable for my audio system. When I Googled the request, it resulted in terms such as "SNAKE, BALANCED, AND UNBALANCED." Can any of you tell me what these terms mean?

Balanced audio connections are extremely important in sound recording and production because they allow for the use of very long cables with reduced introduction of outside noise. The most common balanced connector is the 3-pin XLR, which is used with microphones because of its durable construction. Many microphones have low impedance (low-Z), which makes long microphone cables susceptible to some forms of outside noise, and a perfect application for a balanced line, which cancels out most of this outside noise.

A balanced audio connection has three wires. Two of these are used for the signal, with one of inverted polarity to the other. (For instance, in an XLR connector, pin 2 carries the signal with normal polarity, and pin 3 carries an upside-down version of the same signal.) The third wire is a ground and is used to shield the other two. The received signal is the difference between the two signal lines. This signal recombination can be implemented with a differential amplifier where the negated signal is tied to the negative terminal of the operational amplifier. A balun may also be used instead of an active differential amplifier device. Much of the noise induced in the cable is induced equally in both signal lines, so this noise can be easily rejected - the noise received in the second, negated line is applied against the first, upright signal, and cancelled out when the two signals are added together.

The separate shield of a balanced audio connection also yields a noise rejection advantage over a typical two-conductor arrangement such as used on domestic hi-fi where the shield is actually one of the two signal wires and is not really a shield at all, but relies on its low, but in practice not zero, impedance to signal ground. Any noise currents induced into a balanced audio shield will not therefore be directly modulated onto the signal, whereas in a two-conductor system they will be. This also prevents ground loops.

If the power amplifiers of a public address system are located at any distance from the mixing console, it is also normal to use balanced lines for the signal paths from the mixer to these amplifiers. Many other components, such as graphic equalizers and effects units, have balanced inputs and outputs to allow this. In recording and for short cable runs in general, a compromise is necessary between the noise reduction given by balanced lines and the noise and distortion introduced by the extra circuitry they require.

While XLR connectors are the most common balanced connector, quarter-inch (¼" or 6.5mm) TRS connectors (tip-ring-sleeve) are also commonly used. Many hybrid jacks are now designed to take either XLR or TRS.

On TRS plugs, the tip is "hot" (positive), the ring is "cold" (negative), and the sleeve is ground (earthed or chassis). If a stereophonic or other binaural signal is plugged into such a jack, one channel (usually the right) will be subtracted from the other (usually the left), leaving an unlistenable L − R (left minus right) signal instead of normal monophonic L + R. Reversing the polarity at any other point in a balanced audio system will also result in this effect at some point when it is later mixed-down with its other channel.

Telephone lines also carry balanced audio, though this is generally now limited to the local loop. It is called this because the two wires form a balanced loop through which both sides of the conversation travel.

Data lines, including digital audio, are also frequently balanced, normally using AES/EBU (AES3) with XLR connectors for pro audio. Eight-channel analog balanced audio connectors like ADAT use DB25 connectors, which can also carry up to 16 digital channels.

If balanced audio must be fed into an unbalanced connection, the negative wire should be tied to ground.

Zebra and Snake @ Cable Factory

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