urgent: finding the i/p and o/p impedence using DRB.

Discussion in 'Homework Help' started by vishal60, Nov 30, 2009.

  1. vishal60

    Thread Starter New Member

    Nov 30, 2009
    3
    0
    1)why is the DRB connected in series to find the input impedence of an amplifier n why not in parallel with the input.??

    2)why is the o/p voltage reduced to half to find the i/p impedence??

    3)why are the DRB knobs increased from minimum position while finding the i/p impedence and why decreased from maximum for o/p impedence.??

    regards: vishal
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    What is a DRB?

    To measure the input impedance you add a resistance in series with the input of the amplifier and slowly increase the resistance when a fixed signal is feeding it. When the output of the amplifier becomes half then the resistance is the same as the input impedance of the amplifier because they make a voltage divider.

    It is difficult to measure the output impedance of a modern audio amplifier because its negative feedback makes the output impedance as low as 0.04 ohms or less.
     
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