Making a Art installation safe whilst printing with resistive paint).

Discussion in 'The Projects Forum' started by Tony Elliott, Aug 3, 2015.

  1. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    Connected to a mains supplied amplifier are some oscillators running on 12v batteries. I am printing with paint that is connected to these oscillators, that resists the voltage (approx 0.2 - 6v) and I am worried that there is a potential for electrocution if a in-house amp isn't earthed properly. I have read that I can put a DI box in-between the amp and my battery powered electronics in a book: Hand Made Electronic Music by Nicholas Collins. Has anyone got any in-depth solutions advice for this please?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    It is not at all clear what you are trying to do. Are the oscillators in the audio frequency range? Do you want sounds to change as you draw? It would be very dificult to market commercially an audio amplifier that did not have a fully isolated power supply. That being said, you should be able to measure the resistance from the input connector shield to tha AC earth ground (assuming a 3-wire AC plug). If the amp has a 2-wire AC plug, we'll need to get into more detail.

    Amp make/model?

    ak
     
  3. #12

    Expert

    Nov 30, 2010
    16,283
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    What AK is saying here is that it is very unlikely that you can even purchase a, "killer" amplifier. Still, the safety check can be done with a $4 meter from Harbor Freight.

    The way I say it is, you've been reading books, haven't you? ;)
    A good book will cover the safety hazards, even the most unusual safety hazards, because the author assumes you are reading it because you don't already know. You are asking about a most unusual problem in the modern world. I would be wary of this kind of problem in the Pantages Theater because the place is 85 years old. It might have modern electronics, but a good sound and light man will check for these remote possibilities.
     
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The risk is very small since your electronics are battery powered and, I assume, only connect to the audio inputs of the mains powered amplifier.

    If you're really concerned, you could add another layer of isolation by connecting little 1:1 audio transformers between the output of your electronics and the input to the amplifier.
     
  5. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Attached is the article that I read from the book: Hand Made Electronic Music by Nicholas Collins.

    When I read this I thought that it might be wise to build or buy something to go between my battery powered oscillators and a mains powered amp. you see it could be any amp if I'm showing my work in a place that has a PA.
     
  6. #12

    Expert

    Nov 30, 2010
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    I would think any place where you plug into the PA, it will be powered by the wall outlet in the equipment room. That doesn't necessarily mean the PA system was, "hacked". If it was, public orators and musicians would be dropping like flies.

    You can:
    Buy an audio isolation box,
    check for dead performers,
    and/or measure for voltage from the input jacks to an Earth ground.

    Earth ground is usually the round hole in a wall outlet, the larger of the two slots in a wall outlet, or some metal plumbing pipes. If you can't prove that a valid Earth ground is available, you are free to use the audio isolation box.
     
    Tony Elliott likes this.
  7. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Thank you, I'll look into two options: DI box and 1:1 audio transformer.
     
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