enter image description hereI'm trying to build a class AB amplifier with push-pull pair of power transistors for audio amplifier. the circuit works fine with low voltage(~0.2V) but the input peak voltage varies between 0.2 - 2V. at 2 volts the circuit starts fine but the voltage decays so quickly and signal distortion happens. when i insert h.p.filter, smaller capacitors bottleneck the signal.
the pair is DC biased with 1.4V difference between npn base and pnp base. There're two stages(common emitter amplifier and common collector) before this stage. Graph A is the circuit after one minute. Graph B is the circuit at the initialization.

  • \$\begingroup\$ You are using two Darlingtons, which you claim have their bases separated by 1.4 V. And placing them in an overly-simplified circuit arrangement of other parts that cannot be made to work well, anyway. I've no interest at all in helping you tinker with a bad circuit. The only good for it is to find out all the ways in which you should not design such a circuit. So what's your actual goal? Because helping you with that hot mess isn't very interesting. But maybe if I knew what you wanted to do, there may be something interesting then. \$\endgroup\$
    – jonk
    Jan 8 at 2:53
  • \$\begingroup\$ Seems to be missing a transistor for the bias cct. \$\endgroup\$ Jan 8 at 5:01
  • \$\begingroup\$ The only easy way to use complementary emitter followers is with gain and feedback to eliminate crossover distortion. why not use an Op Amp? otherwise you have thermal drift and no bias thermal matching \$\endgroup\$ Jan 8 at 6:07
  • \$\begingroup\$ What is R5 bringing to the party? \$\endgroup\$
    – Andy aka
    Jan 8 at 10:30
  • \$\begingroup\$ I`m trying to build a simple audio amplifier using transistors, R5 is for limiting Ic. \$\endgroup\$
    – Ahmed Emad
    Jan 8 at 11:11

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