Forums Music Sound Engineering muting relay – best practice?

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  • #1056333
    General Lighting
    Moderator

    this might be one for cheeseweasel or Pat TBH as its getting down to component level stuff but I’ve offered to build a auto mute circuit for Totem (Biotech) so he doesn’t have to keep turning down his monitor amp when presenting his show using a microphone to avoid howling the stream.

    I’m also getting a whole crate of lamp indicators with wall opals and other bits and pieces off the old nurse call system at work as its being replaced, and stacked pyramid opals (they currently have incandescant lamps with room numbers but easily could be relamped with LEDs) – there are way more than I can use so can build him a multicolour light stack to put outside his studio, that way the wife and kids know when he is on air and not to bother Dad too much unless its an emergency!

    I’ve actually put a reed switch and a couple of magnets aside for this but this time I’m going to be using discrete components for the design rather than an Arduino (which TBH was a bit overkill except it was easier to use it to send the IR MUTE command to my amp).

    so instead the circuit will be same as a closed loop burglar alarm (as the reed is closed when the mic fader is at the bottom then opens as the mic is faded up) – and balanced audio will be switched via a small signal DPDT relay like most broadcast mixers operate. when the relay is in MUTE position, is is best to just put a 600R resistor across the two legs of the audio for each channel (rather than a dead short) or any other value?

    #1275266
    cheeseweasel
    Participant

    I only have a fairly basic understanding of electronics, but I’ve certainly heard of others making simple muting circuits by just shorting the two legs together. What is the advantage of using a resistor?

    #1275265
    BioTech
    Participant

    Sweet, I’d forgotten you’d offered to do that mate, nice one. I’m assuming the idea would be to have this in line with the monitor aux out from the desk?

    If you will enjoy building this then be my guest, I’ll be more than happy to use it. It’s not 100% necessary though as I do not need to feed the mic to the monitor. The “on air” light would be awesome though.

    #1275262
    General Lighting
    Moderator

    @cheeseweasel 554534 wrote:

    I only have a fairly basic understanding of electronics, but I’ve certainly heard of others making simple muting circuits by just shorting the two legs together. What is the advantage of using a resistor?

    depends on what is at the distant end (i.e the op amp driving the mixer control room output) – especially there is already an existing series resistor on the output, or any DC offset. Op amps do not like being driven into a dead short, it knackers them. similarly with valve stuff. DC offsets cause thumps/bangs. Most Japanese amps use a bipolar transistor as a switch for muting but downstream of the series resistor.

    That said most new kit does have these resistors but its hard to get the circuit diagrams, plus I was taught a lot my my electronics by old boys the BBC and British Telecom who always liked to do things the proper way (shorting an Openreach circuit (or any similar copper circuit) with DC signalling will cause it to flag as defective and the automatic testing will dis it at the exchange end to stop excessive loop current, which isn’t ideal if you are using it to send programme material down!)

    #1275263
    General Lighting
    Moderator

    @BioTech 554612 wrote:

    Sweet, I’d forgotten you’d offered to do that mate, nice one. I’m assuming the idea would be to have this in line with the monitor aux out from the desk?

    If you will enjoy building this then be my guest, I’ll be more than happy to use it. It’s not 100% necessary though as I do not need to feed the mic to the monitor. The “on air” light would be awesome though.

    I’d forgot your soundcraft desk has a separate monitor matrix – but TBH building a basic LED indicator makes everything even simpler and you would not need to have the reed switch stuck below your fader (which doesn’t look pretty but worked well)

    I’m still waiting for the rest of the maintenance staff at my work to haul out the old nurse call system but at least I’ve found the super bright LED’s again – CPC and CREE changed the part numbers for some bizzare reason. I can get any of red, green, amber or blue – but even with a single one you definitely want an opal (diffuser) as they are too bright to look at directly…

    #1275264
    General Lighting
    Moderator

    an update : I got a load of lamp units / opals including 6 way triangle ones. some of these are now used for showing MIC LIVE or other faders active on the main mixer (via a different control circuit), but as I had a spare alarm reed switch I put it on the door and updated the arduino circuit to mute the speakers if the door is open, unless an override button is pressed.

    it can also turn the amp volume up or down via two other buttons, force a speaker mute condition by a red button and also has a watchdog indicator (to show the arduino sketch has not locked up) and a command received indicator that also repeats the telephone alert strobe (the PVR/VFR number 00 44 1449 797553 will flash this but is otherwise silent, voicemails and robocalled texts also make ths strobe flash so I shouild always notice this)

    http://www.youtube.com/watch?v=LC6eaBC2g6k

    http://www.youtube.com/watch?v=m3B6lIEkUb4

    http://www.youtube.com/watch?v=WWZ2sIwC67U

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Forums Music Sound Engineering muting relay – best practice?