Biasing techniques

Discussion in 'General Electronics Chat' started by mnada, Jan 19, 2013.

  1. mnada

    Thread Starter New Member

    Apr 5, 2012
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    • Hello, the following quote from the topic confuses me!

    It will make sense if the red highlighted text refer to the second case when the load resistance is high? Is that true?
    What confuses me is that the red highlighted text should not be related to "the old, lower-value load resistor in the circuit"


    • Also I have problem understanding the following quote from the same topic
    is this true? I thought the load line should fall on the horizontal portion and avoid to fall on the non horizontal portion


    • And finally what is the purpose of R1 in the following figure?

    [​IMG]
    Thanks
     
    Last edited: Jan 19, 2013
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    That is a HORRIBLE class-A audio amplifier. NOBODY makes that circuit. It even uses resistor values that are not sold.
    Almost ALL amplifiers for the last 50 years use a complementary push-pull class AB output stage with a coupling capacitor that does not force DC on the speaker.

    I simulated it. It is NOT an amplifier because its output level is LESS than its input level.
    The transistor is not biased properly (its base current is much too low) so it clips the signal.
     
  3. mnada

    Thread Starter New Member

    Apr 5, 2012
    26
    0
    It was mentioned in the topic that this design has a flaw that is related to the divider loading and was solved by adjusting the values of the divider resistors.


    • What is the simulation software you are using ?
    • any help with the other 2 points?
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    I am using the free LTspiceIV software from Linear Technology.

    I removed the 1k series base resistor but then the input capacitor value was much too low so I increased it 100 times.
    There is voltage gain now so decreased the input level 75 times.
    The transistor is still with its base current much too low so it is almost cutoff.

    The transistor circuit has no negative feedback so it is severely distorted.
     
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