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Pub. Address volume & wiring?

Discussion in 'Electronic Basics' started by DaveC, Jan 14, 2004.

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  1. DaveC

    DaveC Guest

    I think I understand the purpose of PA wiring: increase impedance and voltage
    over the speaker runs to minimize the loss percentages. I'm unsure, however,
    how to adjust relative volume at each speaker due to difference distances
    from the amplifier.

    I have seen that PA audio transformers have several secondary winding taps.
    This is to match the impedance of the speaker, correct?

    How do you adjust for relative volume for each speaker?

    Also, since voltage is high (~100v, I seem to remember...), does PA require
    code-compliant wiring? What type is this?

  2. The taps are on the primary. you select the tap to give the required
    level at each speaker. the total should be close to the amplifier's
    rated output power, in watts. The wiring requirements depend on the
    voltage, and your local codes.
    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)

    Michael A. Terrell
    Central Florida
  3. "DaveC" wrote ...
    Assume you are talking about "70-volt" (or similar)
    wiring systems also known as "constant voltage".

    *NOT ALL* "PA wiring" is of this "constant voltage" variety.
    If you don't use the accepted terms, you will get faulty responses.
    Or differences in: room size, noise, desired levels, speaker
    efficiency, etc. etc. etc.
    If they are "constant voltage" transformers, they will typically
    have serveral PRIMARY taps to adjust how much power/volume
    you feed to that particular speaker. If you are using "70v"
    transformers on a 70v line, the taps are typically labeled directly
    in "watts" (how convienent!)

    SOME constant voltage transformers ALSO have SECONDARY
    TAPS. But most of them that I have ever seen are "hard-wired"
    for 8 ohms output/secondary. Typically labled "4 ohm", "8 ohm",
    "16 ohm" etc.
    With the PRIMARY taps.
    Depends on your local jurisdiction. I believe the National
    Electrical Code (widely used across the USA) allows 70v
    to use "class 2" wiring. 100v may have to use the same
    wiring as power circuits.
  4. DaveC

    DaveC Guest

    Indeed, I've refreshed my memory and it says "70 volt" on the amp's output
    I'll ask the local building inspectors about 70 volt audio wiring.

  5. DaveC

    DaveC Guest

    If I have an amplifier that doesn't have 70-volt output, can I use a
    constant-voltage transformer in reverse, putting the 8-ohm winding to the
    amp? Then I could connect the 70-volt winding to the wires to carry the
    current to the speaker where there would be a traditionally-connected c.v.

    Accepting the absolute of loss in the transformers, this should work OK,
    shouldn't it?

  6. How do you think they get a 70 volt output in the first place? They
    install the same transformer on the chassis to convert the low impedance
    to 70 volts.
    MCM carries three transformers for this:

    555-6450 50 Watt
    555-6452 100 Watt
    555-6452 200 Watt

    4 or 8 Ohm primary, and a single 70.7 volt secondary. All three are
    on sale till Feb. 20, 2004 at:

    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)

    Michael A. Terrell
    Central Florida
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