Question about Relay Switches

Discussion in 'Homework Help' started by raycrause, Apr 12, 2016.

  1. raycrause

    Thread Starter New Member

    Apr 12, 2016
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    Hi, I got this question for homework at my sound engineering college. I researched for relay switches but couldn't find any helpful info. The question is: "You need to create a remote on/off switch for the amplifiers on stage while doing an installation of a sound system at the local club. The amplifiers must be switched on and off from the mixer position, without running thick power cables next to the audio cables between the stage and Front Of House. Explain the specifications for the relay switch to be used, the connections to this relay switch and the PSU to control the relay. Remember that we do not want to add any additional EMI noise to the sound."
     
  2. Marley

    Member

    Apr 4, 2016
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    40
    I presume you mean switching the power to the amplifiers from a remote position? Not something that is normally done - but still..

    To switch the amplifier power you will need a relay. This allows a low voltage, low power signal to switch a much larger voltage and current. The relay can be magnetic/mechanical with contacts or could be solid-state (look up SSR). In both cases it needs to be rated to handle the expected current (which for an amplifier could be much higher than its normal running current). To reduce EMI, especially if the control wires are close to the audio connections, it will be better if the control voltage is quite low and DC. In fact, it is not the voltage that matters, but the "rate of change of the voltage and current" that induces voltages into nearby wiring. So slowing the step change in voltage and current is a good thing. Also screening, twisted pairs, etc. also useful.
     
  3. raycrause

    Thread Starter New Member

    Apr 12, 2016
    2
    0
    Thanks Marley, this helped me a bit to understand it more. But how should I wire the relay switch (using the magnetic relay) to the amplifiers to switch them on?
     
  4. Marley

    Member

    Apr 4, 2016
    142
    40
    Here is a simplified circuit diagram:
    relay.png
     
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