Balenced or rca?

Discussion in 'AV Receivers' started by Bobby T, Jun 3, 2005.

  1. Bobby T

    Bobby T Supporting Actor

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    What's the difference between using balenced connections or rca from pre/pro to amp?
     
  2. TimRP

    TimRP Stunt Coordinator

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    Taken from Rane.com and the reference section there:

    "balanced line: The IEEE dictionary defines a balanced circuit as "a circuit in which two branches are electrically alike and symmetrical with respect to a common reference point, usually ground." This is the essence of a balanced interconnect. Namely, that two lines are driven equally and oppositely with respect to ground. Normally this also implies that the receiving circuits have matching impedances. Exactly matching impedances is preferred for it provides the best common mode rejection. Balances lines are the preferred method (for hum free) interconnecting of sound systems using a shielded twisted-pair. Because of its superior noise immunity, balanced lines also find use in interconnecting data signals, e.g., RS-422, and digital audio, e.g., AES/EBU. The principal behind balanced lines is that the signal is transmitted over one wire and received back on another wire. The shield does not carry any information, thus it is free to function as a true shield, but must be earth grounded at each end to be successful. (For a detailed tutorial on proper grounding practices, see RaneNote: Sound System Interconnection) [Long Answer: To understand why balanced lines are so successful, first examine a balanced, or differential (equivalent term) output stage, and then an input stage: A differential output stage simultaneously drives two lines, one positive and one negative. The voltage difference between these two wires is the audio signal. The two signals form an envelope that rides the wires to the balanced input stage. Note that the audio signal exists uniquely between these two lines -- not between them and ground. The complete circuit path travels down on the positive line and back on the negative line. Ground is not needed to transmit the signal -- this is the essence and power of balanced lines. Ground is used only for shielding and safety purposes. Conversely, an unbalanced line is one that transmits the audio signal between one wire and ground. The circuit path is down the wire and back through the shield cable connected to ground. Ground is the return path; the circuit does not work without it. A balanced (or differential) input stage extracts the difference between the two input lines, and that, of course, is the desired audio signal. It receives the envelope sent down the cable by the differential output. This circuit's shining virtue is its great noise rejection ability. It has what is called great common-mode rejection. The concept here relies on induced noise showing up equally (or common) on each wire. It is mainly due to EMI (electromagnetic interference: passing through or near magnetic fields), RFI (radio frequency interference: strong broadcast signals), noisy ground references, or a combination of all three. The best balanced line designs have exactly equal impedance from each line relative to ground, guaranteeing equal noise susceptibility. Since the balanced input stage amplifies only the difference between the lines, it rejects everything else (noise) that is common to the lines.] See: Analog Signal Connection in the Real World by Bruce Hofer, one of the founders of Audio Precision."
     
  3. Kenneth Harden

    Kenneth Harden Screenwriter

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    I heard that balanced connectors actually give you slightly WORSE sound than unbalanced, but they are better over long runs and noise rejection.

    True or not?
     
  4. EvanW

    EvanW Stunt Coordinator

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    i hear no difference in pro audio but this could be because of the speaker quality, however u get less signal loss over longer runs, we ran a mic with 150 foot of balance XLR interconnect and it sounded no worse than it did with 25 feet .
     
  5. SteveMetcalf

    SteveMetcalf Agent

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    The thing you need to be careful of is source and load impedance. A balanced circuit (xlr)has a 600ohm impedance. An rca jack is rated 75 ohms. If you have a 75ohm source and a 600 ohm load, watch out! The signal level will be seriously degraded. As for overall sound quality, if you were to look at the patch bay of any professional recording studio, you would see a mixture of connection types, with engineer preference toward balanced.
    The only exception here is a servo-balanced connection which changes the signal to adapt for impedance variances. Check the input and output impedances of anything you hook up to ensure that they match. If you have to you can drive a low impedance load using a high impedance source, just not the other way around.
     

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