Balanced Line Technology

Balanced inputs and outputs have been used for many years in professional audio, but profound misconceptions about their operation and effectiveness still survive. Conventional wisdom about them is sometimes wrong. Balanced Line Technology web page gives you a good look at the balanced line technology in audio applications. The balanced line technology is also applicable to many other fields as well. Here is one piece of information picked from the Balanced Line Technology web page.

Ground voltages coupled in through the common ground impedance; often called “common-impedance coupling” in the literature. This is the root of most ground loop problems. the equipment safety grounds cause a loop ABCD; the mere existence of a loop in itself does no harm, but it is invariably immersed in a 50 Hz magnetic field that will induce mains-frequency current plus odd harmonics into it. This current produces a voltage drop down the non-negligible ground-wire resistance, and this once again effectively appears as a voltage source in each of the two signal lines. Since the CMRR is finite a proportion of this voltage will appear to be differential signal, and will be reproduced as such. The most common cause of ground-loop current is the connection of a system to two different “grounds” that are not actually at the same AC potential


  1. Twisted pair RCA cables again « Tomi Engdahl’s ePanorama blog says:

    [...] get rid of the noise that is coupled as common mode noise to the twisted pair. In systems that use Balanced Line Technology the twisted pair cable construction combined with differential receivers and signal sources make [...]

  2. Value Trendsetter 30 says:

    Speaking of reviewing the content numerous will like this because it’s real and it’s good reading from an author that’s writing it for us to read

  3. Tomi Engdahl says:

    Differential Signaling: Designing for Long, Fast, or Noisy Applications

    This video is your intro to Differential Signaling: Go faster, further.

    Bil Herd has covered single-ended topics like TTL, and CMOS, but when increase the speed or distance a signal needs to travel, Differential Signaling is key. This is why it is used in many modern standards like LVDS, CML, and LVPECL

  4. Tomi Engdahl says:

    Cable shields

    Of the different choices that are available for grounding a shield braid that encloses a differential pair of signal wires, please consider that the shield braid be grounded only at the signal source, at the input end, and not at the output end.

    As a first thought, and as something that is often advocated, grounding a shield at both ends may result in severe ground loop currents which could adversely impact EMI and isolation properties.

    As a second thought, with the shield grounded only at the output end
    the interground interference signal, Enoise, can induce a differential noise signal between the two outputs E1 and E2 that feed the differential amplifier

    As a third thought, grounding the shield only at the input end averts both the ground loop problem and the time constant mismatch problem.

    Enoise as a common mode signal so that no differential voltage is created between E1 and E2. The A2 differential amplifier is thereby protected from Enoise.


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