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
    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
    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.