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Need Help/Advice about Sound System

Discussion in 'Electronic Basics' started by JonM, Feb 22, 2006.

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  1. JonM

    JonM Guest

    Hi,

    I have a question for anyone with experience with sound systems for
    meeting halls, churches, PA systems, etc.

    Recently I was asked to help with repairing a sound system in a meeting
    hall. My job is to solder connections for cables etc.

    Originally the system was set up as:

    -About 80 speakers wired in parallel. Each one has a small
    transformer mounted on it. I was told that this is set up as a 70 Volt
    Speaker System.
    -The speakers were powered by a TOA Amplifier that had a 70 Volt
    speaker output.

    Here is were my question comes in. The person responsible for
    installing new equipment is using the original speaker system but
    hooked it up to a ART SLA 2 Amplifier (see:
    http://www.artroch.com/downloads/specsheet/ART_SpecSheet_SLA2.pdf). As
    far as I can tell this amplifier does not output a 70 Volt signal to
    the speakers. The sound does come through, however my question is: Is
    it alright to use this amplifier with this speaker system? If not, how
    can I present evidence to the person in charge in a convincing way?

    Thank you all for your help.
     
  2. Lord Garth

    Lord Garth Guest

    Check to see if he installed a step-up transformer at the power amp output.
    I can't see it operating if not.
     
  3. JonM

    JonM Guest

    Check to see if he installed a step-up transformer at the power amp output.
    No, I can't see that he did.
     

  4. How many watts is the new amplifier?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  5. JonM

    JonM Guest

    200
     

  6. At 5000 ohms per watt (70 volt constant voltage system) that would be
    5000 ohms /200 watts for a 25 ohm load. It will work, but it would be
    better if properly matched with a line transformer.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  7. Chris

    Chris Guest

    Hi, Jon. The funny thing is, it works. Hmnnn.

    I would guess the intrepid person who initially wired it up set the
    outputs as bridged mono. Your tear-off sheet on your amp shows it can
    pump up to 560 watts into 8 ohms in that configuration. That's pretty
    close to 70 volts. And remember, the amp is primarily a voltage output
    device, as long as there's not excessive current.

    The thing is, if all 80 of your small PA 70.7 volt matching
    transformers are set to a tap below 7 watts, there will be a total of
    less than 560 total watts. Which means your amp is within safety
    range.

    Your setup is a little bizzare, but it might work well enough,
    considering you've got PA speakers. If you don't trust your
    installation person, you should call up the manufacturer in Rochester
    to check for sure. Get specifics on the number of PA speakers, and
    their tap settings (first guess, they're all the same, but you should
    check).

    Good luck
    Chris
     
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