what are Diodes for in Audio Amplfiers?

[Leghrand DeJesus]

Hi! Im a newbie here with regard to amplifiers. Now, I very curious what are those sets of diodes for in the circuit? Can anyone satisfy my curiosity please?

 

[FvM]

They are used to bias complementary class AB stages. It should be mentioned that this is a badly designed amplifier, it's hardly possible to explain all implemented flaws in a few words.

If you are interested to learn about audio amplifiers, please start with reasonable designs.

 

[Audioguru]

The 8 ohm speaker is driven through a series 180k resistor!

 

[FvM]

The 8 ohm speaker is driven through a series 180k resistor!

It might be that some schematic's junction points did disappear.

 

[Audioguru]

It might be that some schematic's junction points did disappear.

Why does the circuit have TWO output stages? The one with the 2N3904, 2N3906 and 2 diodes and the other one with more transistors and 3 diodes.

 

[FvM]

Why does the circuit have TWO output stages?

Looks like a electronics newbie tried to invent a square wheel.

 

[Leghrand DeJesus]

And how would you define reasonable designs sir?

 

[Audioguru]

And how would you define reasonable designs sir?

There are hundreds of class-AB audio amplifier circuits shown in Google. Most are excellent but some are very poor like the one you showed.

 

[iimagine]

Here is a good page about Discrete Low power AF experiments
**broken link removed**