Power transformer and amplifier Rating

Discussion in 'Homework Help' started by bonjing, Aug 4, 2009.

  1. bonjing

    Thread Starter Member

    Dec 7, 2008
    12
    0
    hi,

    Q: What should be the correct power transformer rating for 100watt 4 ohm amplifier? FORMULA.

    Q: 2x18" 1000watt loudspeaker, what should be the correct power amplifier in order to drive those speakers. FORMULA.


    thanks:confused:
     
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  3. mellowmon

    Member

    Jan 24, 2009
    17
    0
    you can use OHM's LAW and POWER LAW.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Also use some common sense.
    Nobody plays an amplifier at full blast all the time. If the amplifier has its volume control turned up so that the peaks are barely clipped then the average output power is 1/10th to 1/5th of the power at clipping.

    You need to know the efficiency of the amplifier to be able to calculate how much more power is needed from the transformer to heat it.

    There is no correct amplifier. A 20W amplifier, a 200W amplifier or a 2000W amplifier will power the two 1000W speakers very well. A 10W, 100W or 1000W amplifier will also work well. It depends on how loud you want it to play.
     
  5. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
    As audioguru mentioned, consider the efficiency.

    up to 50% of your power rating will be lost in biasing if it is a class A amplifier.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    No.
    A class-A amplifier wastes 500% of its output power at clipping.
    A class-AB amplifier wastes 50% of its output power at clipping.

    A class-A amplifier wastes 500% of its max output power when it is idle.
    A class-AB amplifier wastes a small amount of power when it is idle.
     
  7. daviddeakin

    Active Member

    Aug 6, 2009
    207
    27
    Are you sure?
    A class A amplifier dissipating 100W at idle should ideally deliver 50W to the speaker at full volume, which is only 100% 'wastage'.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I use an old Southwest Technical class A headphone amp. It dissipates 45 watts a side for less than 2 watts out. They sound great, but are very inefficient.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    Elliot Sound Products have a class-A amplifier project that dissipates 5 times as much power as its output power.
     
  10. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
  11. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
    Could it be that valve amps are ridiculously inefficient? I've only been thinking of transistor types.
     
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