Im currently trying to desing a class AB amp. I have currently got so far as bellow. I have the base voltages set at around 0.7V to just allow forward conducting of the BE diodes, and reduce crossover distortion.

My question is how come for my design I do not have any voltage gain? Or is this stage purely for current gain? Also, in most designs I see for a class AB there is another transistor on the input to the pushpull pair. Is this for the voltage gain? Like in AB class amp, design considerations. If so how could I implement this stage into my design. I will finally add a differential pair on the input after I complete this stage.

enter image description here


You have no voltage gain because Q1 and Q2 are emitter followers, a circuit configuration with a nominal gain of 1. You do have current gain, however, due to the current gain of Q1 and Q2 so the overall effect is power gain. If you need voltage gain, you can add a voltage amplifier at the input. This could be a differential pair but you could also use an operational amplifier. You should arrange to take overall feedback from the output,however, to reduce the distortion of the power stage.

| improve this answer | |
  • \$\begingroup\$ Ok thanks, in the schematic thats attached in the link, is Q3 a buffer so that the input to the Q1Q2 do not draw current from the differential pair then? \$\endgroup\$ – JS60 Mar 31 '15 at 2:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.