mini amplifier oscillation, what can be done to correct this?

[neazoi]

Hello, I have made this circuit. https://www.electroschematics.com/263/miniature-audio-amplifier/
It works ok, but it has the tendency to oscillate and I hear a loud tone on the speaker.

Is there anything that I could do to prevent oscillation and achieve the full gain of the amplifier?

 

[Borber]

This amplifier can not oscillate. Check your signal source.

 

[amitjagtap]

It may not oscillating...you have to probe the output .. n check o/p frequency on oscilloscope.....It might amplifing input noise..

 

[godfreyl]

Is there anything that I could do to prevent oscillation and achieve the full gain of the amplifier?

First thing to do is increase C2 to 1000uF. If the power supply does not have a very low source impedance, it might help to increase C3 as well.

If there is any problem with High frequency (RF) stability, it may help to connect a small capacitor (47pF to 100pF) between the collector and base of T1.

C1 can be reduced to 1uF. That will set the low frequency rolloff to about 30Hz. If you're only interested in speech, or if you're using a small speaker with no low bass capability, then C1 could be reduced further to 100nF or 150nF.

 

[neazoi]

First thing to do is increase C2 to 1000uF. If the power supply does not have a very low source impedance, it might help to increase C3 as well.

If there is any problem with High frequency (RF) stability, it may help to connect a small capacitor (47pF to 100pF) between the collector and base of T1.

C1 can be reduced to 1uF. That will set the low frequency rolloff to about 30Hz. If you're only interested in speech, or if you're using a small speaker with no low bass capability, then C1 could be reduced further to 100nF or 150nF.

You got right into the heart of the problem!
reducing C1 to 100nF and increasing C3 to 1000uF made the "oscillation buzz" to almost disappear.
increasing C2 only decreased the frequency of the buzz. also the capacitor you suggested between the base and collector of T1, did not make any improvements in my case.

There is still a very small amount of buzz, which I need to figure out how to remove.

- - - Updated - - -

You got right into the heart of the problem!
reducing C1 to 100nF and increasing C3 to 1000uF made the "oscillation buzz" to almost disappear.
increasing C2 only decreased the frequency of the buzz. also the capacitor you suggested between the base and collector of T1, did not make any improvements in my case.

There is still a very small amount of buzz, which I need to figure out how to remove.

Update: I finally replaced the 4.7k input resistor with a 5.6k and the remaining buzz totally disappeared. It may had to do something with the gain, or interaction with the previous stages? who knows...