2 stage audio amplifier

Thread Starter

00edenn

Joined Nov 14, 2022
3
Hello,
im trying to assemble this circuit but its not working at all. i used 2n3904 transistor. i have checked the connection and its all good maybe i should add more resistors? please let me know how to modify it so it works. 62837F1B-5D3E-4472-AB8B-EAF09936DDB2.jpeg
 

WBahn

Joined Mar 31, 2012
27,903
I don't see any biasing network for the output transistor.

A quick look at the transistor specs leads me to think that the 3904 is probably okay to use, though the 3403 appears to have significantly higher gain at lower currents. That is possibly causing more base current in Q1 than the biasing network can support.
 

Thread Starter

00edenn

Joined Nov 14, 2022
3
I don't see any biasing network for the output transistor.

A quick look at the transistor specs leads me to think that the 3904 is probably okay to use, though the 3403 appears to have significantly higher gain at lower currents. That is possibly causing more base current in Q1 than the biasing network can support.
could you please tell me how to do that?
 

Audioguru again

Joined Oct 21, 2019
5,420
I properly biased the base of the output transistor at about half the supply voltage so that the transistor can pull up the output voltage and the 10k emitter resistor can pull down the output voltage.

Notice that I increased the output capacitor so that it passes audio. Your little 33uF passed only squeaks.
The 10k output resistor is severely overloaded by the 8 ohms speaker:
 

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