Dear Mr. Guru, I am sorry for being absent for a long time. I am not using a low passfilter and it is still ok. If i connect an audio power amplifier with a pre-amplifier i can hear a clear noise. Actually i m using a pre-amplifier circuit and would like to know what is the purpose of capacitor C2 in the circuit. You gave the explanation but i am sorry i didnt understand it. As you have said it block the dc but it is not at the input of the circuit so i was wondering. Well i will be grateful to you for the kind reply, Thanking you, Yours Faithfully, Mughal.