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Transformer Substitutions

Using 70.7 Volt Transformers on 50 Volt & 100 Volt Systems

Loudspeakers which incorporate 70.7 volt line matching transformers can be utilized on 50 volt and 100 volt systems by following two simple rules:

  1. For 50 volt Systems the power consumed from the line will be one half of what is shown on the transformer.
    Example: The 2 watt tap on a 70.7 volt transformer will consume only one watt when connected to a 50 volt line.
  2. For 100 volt Systems the power consumed from the line will be two times what is shown on the transformer.
    Example: The 2 watt tap on a 70.7 volt transformer will consume 4 watts when connected to a 100 volt line.

Remember, there will be a corresponding increase or decrease of 3dB in the output level of the loudspeaker when the power is doubled or halved.

Caution: Do not exceed the maximum wattage rating of the transformer. The maximum wattage rating can be determined by noting the highest power tap on the transformer.

  1. Common Transformer Voltages

    1. 25 Volt Transformer
      1. Electrical Codes classify 25 volt as low Voltage, doesn't require conduit
      2. Lower impedance than a 70 volt system
      3. More line loss than a 70 volt system
        1. Fewer speakers per circuit
        2. Shorter cable lengths
        3. Larger gauge cable is typically required
    2. 70 Volt Transformer
      1. Electrical Codes typically classify 70 volt as high voltage, and may require conduit
      2. Higher impedance than a 25 volt system
      3. Loss line loss than a 25 volt system
        1. More speakers per circuit
        2. Longer cable lengths
        3. Smaller gauge cable is typically required
    3. 50 Volt Transformer
      1. Typically used overseas
      2. Lower impedance than a 100 volt system
      3. More line loss than a 100 volt system
        1. Less speakers per circuit
        2. Shorter cable lengths
        3. Larger gauge cable is typically required
    4. 100 Volt Transformer
      1. Typically used overseas
      2. Higher Impedance than a 50 volt system
      3. Less line loss than a 50 volt system
        1. More speakers per circuit
        2. Longer cable lengths
        3. Smaller gauge cable is typically required
    equation01

    equation03
    		 equation02

    equation04

  2. Using 25 volt Transformers

    1. On a 70 volt system
      The transformer will draw 8 times the marked wattage on the transformer
    2. On a 50 volt system
      The transformer will draw 4 times the marked wattage on the transformer
    3. On a 100 volt system
      The transformer will draw 16 times the marked wattage on the transformer
    equation05 equation06 equation07


  3. Using 70 volt Transformers

    1. On a 25 volt system
      The transformer will draw 1/8 the marked wattage on the transformer
    2. On a 50 volt system
      The transformer will draw 1/2 the marked wattage on the transformer
    3. On a 100 volt system
      The transformer will draw 2 times the marked wattage on the transformer
    equation08 equation09 equation10


  4. Using 50 volt Transformers

    1. On a 25 volt system
      The transformer will draw 1/4 the marked wattage on the transformer
    2. On a 70 volt system
      The transformer will draw 2 times the marked wattage on the transformer
    3. On a 100 volt system
      The transformer will draw 4 times the marked wattage on the transformer
    equation11 equation12 equation13


  5. Using 100 Volt Transformers

    1. On a 25 volt system
      The transformer will draw 1/16 the marked wattage on the transformer
    2. On a 70 volt system
      The transformer will draw 1/2 the marked wattage on the transformer
    3. On a 50 volt system
      The transformer will draw 1/4 the marked wattage on the transformer
    equation14 equation15 equation16


  6. Speaker Load Substitution
    The power provided to a speaker can be varied by reconfiguring the speaker load and utilizing alternate secondary impedance connections
    1. Using a 4 Ohm Transformer Secondary
      1. Connecting an 8 ohm speaker load will draw 1/2 the marked wattage on the transformer
      2. Connecting a 16 ohm speaker load will draw 1/4 the marked wattage on the transformer

      equation17
      equation18 equation19


    2. Using an 8 Ohm Transformer Secondary
      1. Connecting a 4 ohm speaker load will draw 2 times the marked wattage on the transformer
      2. Connecting a 16 ohm speaker load will draw 1/2 the marked wattage on the transformer

      equation20
      equation21 equation22


    3. Using a 16 Ohm Transformer Secondary
      1. Connecting a 4 ohm speaker load will draw 4 times the marked wattage on the transformer
      2. Connecting an 8 ohm speaker load will draw 2 times the marked wattage on the transformer

      equation23
      equation24 equation25




  7. Cautions

    1. The total wattage draw from all of the transformers cannot exceed the power output of the amplifier

    2. The total impedance load should not be less than the minimum output impedance of the amplifier

    3. The wattage draw through the transformer should not exceed the highest wattage marked on the transformer