Guys,
I have a question on the "diode pop & crackle suppressor" circuit that i have attached. Can you please answer what the purpose of capacitor is ? If diode is directing the current, why do we need the capacitor ?

Thanks.

 

The capacitor blocks DC. The diode is clamping signal to the speaker to prevent "pops and crackles". Can't tell if it will have an adverse effect on speaker performance.

 

It removes any DC voltage from the signal, which reduces the speakers signal swing.

 

That is a bogus circuit and would never be used in a real amplifier.
It will clip any signal above a positive 0.6V, limiting the undistorted sound to an 8Ω speaker at about 20mW.