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I am design a 1W audio amplifier and i want to have 8V peak to peak output signal but if i increased the R4 resistor then the output signal would be clipped. My input is 0.3V max sinewave. Here is my schematic. Can anyone help me increased my voltage output. And can anyone tell me how to graph the current through the load.enter image description here

this is my recent voltage output enter image description here

EDIT Here is the output signal after i tried some of the recommend, both the current and the voltage output signal got clipped, although the current has got better enter image description here but if i connect the R4 back to the output of the op amp, the signals are not clipping anymore. Can someone explain it to me, and i can still use some helps in increased both the current and voltage output without clipping. Thank you all for your help. enter image description here

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  • \$\begingroup\$ I can't help you with that lousy class-AB topology. It's got to change. \$\endgroup\$ Commented Jun 9, 2024 at 23:57
  • \$\begingroup\$ Can you tell me what i could change because i got the original schematic from here: deeptronic.com/electronic-circuit-design/… and i think that it show 2 separate stage which is the voltage amplifier (the op amp) and the power amplifier (2 transistor) which fit my professor requirement. \$\endgroup\$ Commented Jun 10, 2024 at 0:33
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    \$\begingroup\$ The NFB is tied to the wrong place for one thing. But there really is much more I very much dislike. Fabio and others here know which end is up. I'll let them handle it. \$\endgroup\$ Commented Jun 10, 2024 at 2:54

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All the base current for the output stage has to flow through R5 for the positive cycle and R6 for the negative cycle.

With an 8 ohm load and 4V peak there is 500mA flowing in the load. You need at least 20mA or so base current available for Q1 and Q2. When R5 and R6 are 1k there is not enough base drive.

Q1 and Q2 should be made into darlington pairs and the base resistors bootstrapped with capacitors from the output to give adequate drive.

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  • \$\begingroup\$ Are there any ways that i can increased the base current for Q1 and Q2 without adding any extra transistors? \$\endgroup\$ Commented Jun 10, 2024 at 4:40
  • \$\begingroup\$ Just reducing the value of the resistors would help. But the amount of current you need would probably be beyond the capability of the opamp. Bootstrapping them would also help. Also as another poster said the feedback should come from the output, not the opamp directly. \$\endgroup\$ Commented Jun 11, 2024 at 0:14
  • \$\begingroup\$ I have tried to make the Q1 and Q2 into Darlington pairs but the output current is still around 350mA, should i changed the transistor to have more gain or did i made any mistake ? \$\endgroup\$ Commented Jun 11, 2024 at 2:59
  • \$\begingroup\$ @PhongTô - 2N3904/6 are not really suitable for the currents you need. You need higher power ones for the final transistors. What supply voltage are you using? \$\endgroup\$ Commented Jun 11, 2024 at 22:57
  • \$\begingroup\$ I am using 24V. Can you suggest me some transistors that more suitable for my amplifier. \$\endgroup\$ Commented Jun 12, 2024 at 1:36
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The schematic posted is not an exact copy of the circuit referenced by the OP in the comments; the differences mean the circuit posted by the OP will not perform as well as the referenced circuit.

Hint: compare how the op-amp negative input is connected in both circuits, you will see a difference.

The circuit in the reference is sort-of OK as an amplifier, but you can do much better. Some of the issues you will need to consider have been addressed here:
https://electronics.stackexchange.com/a/688822/341959

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  • \$\begingroup\$ Thank you for your comment! \$\endgroup\$ Commented Jun 10, 2024 at 4:36
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One thing you’ll probably want to do is connect the feedback resistor R4 to the output of the amplifier instead of the output of the opamp. This will bring the output stage into the feedback loop, reducing distortion.

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  • \$\begingroup\$ Thank you for your comment, i will try it! \$\endgroup\$ Commented Jun 10, 2024 at 4:41

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