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Parallel Balanced LINE Connections

Discussion in 'Amps and Cabs [BG]' started by bgavin, Apr 18, 2003.


  1. Does anybody (Bob Lee) know the impact of using a Y cable or other parallel wiring scheme with regard to balanced LINE levels?

    I want to parallel the line from my mixer LINE OUT to both my PLX 1202 and into another LINE device (headphone distribution).
     
  2. BTTT
     
  3. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Active electronic outputs generally have fairly low impedances, and they are meant to drive bridging--or high-impedance--loads.

    For example, if a device's output Z is n ohms and the input impedance of the device it's driving is 10n ohms or higher, then you'll get a suitable transfer of the signal voltage, with less than 1 dB of loss. This is because the output Z and input Z form a voltage divider, and the higher the ratio of the input Z to the output Z, the less the voltage is reduced.

    In practice, most interconnections of pro gear have an output/input Z ratio of much higher than 10:1.

    Connecting a second device in parallel will cause a reduction in the signal voltage, but if the total load impedance is many times greater than the output Z, the change will be negligible, like maybe a couple tenths of a dB. Parallel-connected devices, naturally, get the same voltage.

    It's similar to when you have one lamp turned on in a room and then you turn on a second one; you might've had 120.0 VAC before and 119.8 VAC after you turn on the second lamp--for all practical purposes, it's the same line voltage.

    If you connect an unbalanced input in parallel with a balanced interconnection, the whole interconnection becomes unbalanced unless you used an isolation transformer.
     
  4. So, in short terms, no problem?

    I'm considering using a balanced OUT parallel'ed into two balanced INs.

    The entire system will remain balanced.
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Yup, shouldn't be a problem.