I have never used a TDA2822M amplifier so I look at its spec's on the datasheet.Hi, i am just testing my power amp which connecting the output of pre-amp(include mic) to a volume control ( before it have 1 CR network) and then connect it to input of power amp which have a earphone connect at the output of power-amp, and i found out that there have alot of noise ( very noisy) can be hear by earphone with the minimum volume, when adjust to maximum, it will be very loud noisy sound come out from earphone.. may i know what is the problem?
With no input its input noise is rated at 2.5uV when its input has a 10k resistor. It might be 3uV with your volume control turned down to zero.
Its voltage gain is about 95 so its output noise is 285uV.
Earphones produce 90dB when the power is 1mW which is a voltage of 179mV into 32 ohms. 179mV/285uV is 628 times which is about 56dB so the noise level in the earphones is about 90 - 56= 34dB which is a very low sound level.
Maybe you built the circuit on a breadboard and its high stray capacitance is causing the amplifier to oscillate and produce noise.